{"id":600,"date":"2021-12-17T21:49:13","date_gmt":"2021-12-17T21:49:13","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/8-earth-history\/"},"modified":"2025-01-21T01:03:29","modified_gmt":"2025-01-21T01:03:29","slug":"8-earth-history","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/8-earth-history\/","title":{"raw":"8 Earth History","rendered":"8 Earth History"},"content":{"raw":"[caption id=\"attachment_3273\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/CdC1-scaled.jpg\"><img class=\"wp-image-3273 size-large\" title=\"By Matt Affolter\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/CdC1-scaled-1.jpg\" alt=\"The rock is a 750' spire.\" width=\"1024\" height=\"683\"><\/a> Spider Rock, within Canyon de Chelly National Monument, not only has a long human history with the Din\u00e9 tribe, but also has a long geologic history. The rocks are Permian in age, and formed in the desert conditions that dominated North America toward the end of the Paleozoic through the middle Mesozoic. Erosion of the canyon occurred in the Cenozoic.[\/caption]\n\n<strong>KEY CONCEPTS<\/strong>\n\n<strong>By the end of this chapter, students should be able to:<\/strong>\n<ul>\n \t<li>Explain the big-bang [pb_glossary id=\"2655\"]theory[\/pb_glossary] and origin of the [pb_glossary id=\"2700\"]elements[\/pb_glossary]<\/li>\n \t<li>Explain the [pb_glossary id=\"2201\"]solar system[\/pb_glossary]\u2019s origin and the consequences for Earth.<\/li>\n \t<li>Describe the turbulent beginning of Earth during the [pb_glossary id=\"2203\"]Hadean[\/pb_glossary] and [pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eons[\/pb_glossary]<\/li>\n \t<li>Identify the transition to modern [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary], and evolution that occurred in the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]<\/li>\n \t<li>Describe the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] evolution and [pb_glossary id=\"1708\"]extinction[\/pb_glossary] of invertebrates with hard parts, fish, amphibians, reptiles, tetrapods, and land plants; and [pb_glossary id=\"2576\"]tectonics[\/pb_glossary] and sedimentation associated with the [pb_glossary id=\"2623\"]supercontinent[\/pb_glossary] [pb_glossary id=\"3366\"]Pangea[\/pb_glossary]<\/li>\n \t<li>Describe the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] evolution and [pb_glossary id=\"1708\"]extinction[\/pb_glossary] of birds, dinosaurs, and mammmals; and [pb_glossary id=\"2576\"]tectonics[\/pb_glossary] and sedimentation associated with the breakup of [pb_glossary id=\"3366\"]Pangea[\/pb_glossary]<\/li>\n \t<li>Describe the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] evolution of mammals and birds, paleoclimate, and [pb_glossary id=\"2576\"]tectonics[\/pb_glossary] that shaped the modern world<\/li>\n<\/ul>\n&nbsp;\n\n[caption id=\"attachment_2486\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/GeologicClock.png\"><img class=\"wp-image-52 size-medium\" title=\"By WoudloperDerivative work: Hardwigg (File:Geologic_clock.jpg) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AGeologic_Clock_with_events_and_periods.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/GeologicClock-300x288.png\" alt=\"The circle starts at 4.6 billion years ago, then loops around to zero.\" width=\"300\" height=\"288\"><\/a> Geologic time on Earth, represented circularly, to show the individual time divisions and important events. Ga=billion years ago, Ma=million years ago.[\/caption]Entire courses and careers have been based on the wide-ranging topics covering Earth\u2019s history. Throughout the long history of Earth, change has been the norm. Looking back in time, an untrained eye would see many unfamiliar life forms and terrains. The main topics studied in Earth history are paleogeography, paleontology, and paleoecology and paleoclimatology\u2014respectively, past landscapes, past organisms, past ecosystems, and past environments. This chapter will cover briefly the origin of the universe and the 4.6 billion year history of Earth. This Earth history will [pb_glossary id=\"3080\"]focus[\/pb_glossary] on the major physical and biological events in each [pb_glossary id=\"2190\"]Eons[\/pb_glossary] and [pb_glossary id=\"2191\"]Era[\/pb_glossary].\n<h2><strong>8.1 Origin of the Universe<\/strong><\/h2>\n[caption id=\"attachment_3275\" align=\"alignright\" width=\"349\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/HubbleDeepField.jpg\"><img class=\"wp-image-518\" title=\"NASA, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-300x294.jpg\" alt=\"The picture has over 1500 galaxies.\" width=\"349\" height=\"342\"><\/a> The Hubble Deep Field. This image, released in 1996, is a composite long-exposure picture of one of the darkest parts of the night sky. Every light on this image that does not have diffraction spikes is believed to be an entire galaxy, with hundreds of billions of stars, demonstrating the immense size and scope of the universe.[\/caption]\n\nThe universe appears to have an infinite number of galaxies and solar systems and our [pb_glossary id=\"2201\"]solar system[\/pb_glossary] occupies a small section of this vast entirety. The origins of the universe and [pb_glossary id=\"2201\"]solar system[\/pb_glossary] set the context for conceptualizing the Earth\u2019s origin and early history.\n<h3><b>8.1.1 Big-Bang Theory<\/b><\/h3>\n[caption id=\"attachment_3276\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/UniverseTimeline.jpg\"><img class=\"wp-image-519 size-medium\" title=\"By NASA\/WMAP Science Team (Original version: NASA; modified by Ryan Kaldari) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ACMB_Timeline300_no_WMAP.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/UniverseTimeline-300x195.jpg\" alt=\"It starts small, then explodes outward\" width=\"300\" height=\"195\"><\/a> Timeline of expansion of the Universe[\/caption]<span style=\"font-weight: 400\">The mysterious details of events prior to and during the origin of the universe are subject to great scientific debate. The prevailing idea about how the universe was created is called the <strong>big-bang [pb_glossary id=\"2655\"]theory[\/pb_glossary]<\/strong>. Although the ideas behind the big-bang [pb_glossary id=\"2655\"]theory[\/pb_glossary] feel almost mystical, they are supported by Einstein\u2019s [pb_glossary id=\"2655\"]theory[\/pb_glossary] of general relativity. Other scientific evidence, grounded in empirical observations, supports the big-bang [pb_glossary id=\"2655\"]theory[\/pb_glossary].<\/span>\n\n<span style=\"font-weight: 400\">The big-bang [pb_glossary id=\"2655\"]theory[\/pb_glossary] proposes the universe was formed from an infinitely dense and hot [pb_glossary id=\"2589\"]core[\/pb_glossary] of material. The bang in the title suggests there was an explosive, outward expansion of all matter and space that created atoms. [pb_glossary id=\"2641\"]Spectroscopy[\/pb_glossary] confirms that hydrogen makes up about 74% of all matter in the universe. Since its creation, the universe has been expanding for 13.8 billion years and recent observations suggest the rate of this expansion is increasing<\/span><span style=\"font-weight: 400\">.\u00a0<\/span>\n<h4><span style=\"font-weight: 400\">Spectroscopy<\/span><\/h4>\n[caption id=\"attachment_3277\" align=\"alignright\" width=\"383\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/EM_Spectrum_Properties_edit.svg_.png\"><img class=\"wp-image-520\" title=\"By Inductiveload, NASA [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEM_Spectrum_Properties_edit.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/EM_Spectrum_Properties_edit.svg_-300x178.png\" alt=\"The figure shows the various wavelengths of electromagnetic light, the scale of the wavelength, the frequency, and the temperature of objects that produces waves.\" width=\"383\" height=\"227\"><\/a> The electromagnetic spectrum and properties of light across the spectrum.[\/caption]<span style=\"font-weight: 400\"><strong>[pb_glossary id=\"2641\"]Spectroscopy[\/pb_glossary]<\/strong> is the investigation and measurement of spectra produced when materials interacts with or emits electromagnetic radiation. <em>Spectra<\/em> is the plural for <em>spectrum<\/em> which is a particular [pb_glossary id=\"3186\"]wavelength[\/pb_glossary] from the <strong>[pb_glossary id=\"2642\"]electromagnetic spectrum[\/pb_glossary]<\/strong>. Common spectra include the different colors of visible light, X-rays, ultraviolet waves, microwaves, and radio waves. Each beam of light is a unique mixture of wavelengths that combine across the spectrum to make the color we see. The light wavelengths are created or absorbed inside atoms, and each [pb_glossary id=\"3186\"]wavelength[\/pb_glossary] signature matches a specific [pb_glossary id=\"2700\"]element[\/pb_glossary]. Even white light from the Sun, which seems like an uninterrupted continuum of wavelengths, has gaps in some wavelengths. The gaps correspond to [pb_glossary id=\"2700\"]elements[\/pb_glossary] present in the Earth\u2019s [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] that act as filters for specific wavelengths. These missing wavelengths were famously observed by Joseph von Fraunhofer (1787\u20131826) in the early 1800s<\/span><span style=\"font-weight: 400\">, but it took decades before scientists were able to relate the missing wavelengths to atmospheric filtering<\/span><span style=\"font-weight: 400\">. <\/span>[pb_glossary id=\"2641\"]Spectroscopy[\/pb_glossary] shows that the Sun is mostly made of hydrogen and helium. Applying this process to light from distant stars, scientists can calculate the abundance of [pb_glossary id=\"2700\"]elements[\/pb_glossary] in a specific star and visible universe as a whole. Also, this spectroscopic information can be used as an interstellar speedometer.\n<h4><span style=\"font-weight: 400\">Redshift<\/span><\/h4>\n[caption id=\"attachment_3278\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Dopplerfrequenz.gif\"><img class=\"wp-image-521 size-medium\" title=\"By Charly Whisky 18:20, 27 January 2007 (yyy) (Own work) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>, <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5-2.0-1.0&quot;>CC BY-SA 2.5-2.0-1.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ADopplerfrequenz.gif&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Dopplerfrequenz-300x75.gif\" alt=\"In this animated image, the car moves, and the waves are pushed in the front, and stretched behind it.\" width=\"300\" height=\"75\"><\/a> The Doppler effect is heard as a car moves. The waves in front of the car are compressed together, making the pitch higher. The waves in the back of the car are stretched, and and the pitch gets lower.[\/caption]<span style=\"font-weight: 400\">The <strong>[pb_glossary id=\"2643\"]Doppler effect[\/pb_glossary]<\/strong> is the same process that changes the pitch of the sound of an approaching car or ambulance from high to low as it passes. When an object emits waves, such as light or sound, while moving toward an observer, the wavelengths get compressed. In sound, this results in a shift to a higher pitch. When an object moves away from an observer, the wavelengths are extended, producing a lower pitched sound. The [pb_glossary id=\"2643\"]Doppler effect[\/pb_glossary] is used on light emitted from stars and galaxies to determine their speed and direction of travel<\/span><span style=\"font-weight: 400\">. Scientists, including Vesto Slipher (1875\u20131969)<\/span><span style=\"font-weight: 400\"> and Edwin Hubble (1889\u20131953)<\/span><span style=\"font-weight: 400\">, examined galaxies both near and far and found that almost all galaxies outside of our galaxy are moving away from each other, and us. Because the light wavelengths of receding objects are extended, visible light is shifted toward the red end of the spectrum, called a <strong>[pb_glossary id=\"2195\"]redshift[\/pb_glossary]<\/strong>. In addition, Hubble noticed that galaxies that were farther away from Earth also had the greater amount of [pb_glossary id=\"2195\"]redshift[\/pb_glossary], and thus, the faster they are traveling away from us. The only way to reconcile this information is to deduce the universe is still expanding. Hubble\u2019s [pb_glossary id=\"2651\"]observation[\/pb_glossary] forms the basis of big-bang [pb_glossary id=\"2655\"]theory[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_4252\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Example-of-Doppler-Shift-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-522\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/a3RfULw7aAY[\/embed]\n<h4><span style=\"font-weight: 400\">Cosmic Microwave Background Radiation<\/span><\/h4>\n[caption id=\"attachment_3279\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/CosmicBackground.png\"><img class=\"wp-image-523 size-medium\" title=\"By NASA \/ WMAP Science Team [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AIlc_9yr_moll4096.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/CosmicBackground-300x150.png\" alt=\"The map is blue with slight bright spots of green\/yellow\" width=\"300\" height=\"150\"><\/a> Heat map, showing slight variations in background heat, which is related to cosmic background radiation.[\/caption]<span style=\"font-weight: 400\">Another strong indication of the big-bang is <strong>[pb_glossary id=\"2196\"]cosmic microwave background radiation[\/pb_glossary]<\/strong>. Cosmic radiation was accidentally discovered by Arno Penzias (1933\u2013) and Robert Woodrow Wilson (1936\u2013) <\/span>when they were trying to eliminate background noise from a communication satellite. They discovered very faint traces of energy or heat that are omnipresent across the universe. This energy was left behind from the [pb_glossary id=\"2194\"]big bang[\/pb_glossary], like an echo.\n<h3><b>8.1.2 Stellar Evolution<\/b><\/h3>\n[caption id=\"attachment_3280\" align=\"alignleft\" width=\"400\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Nucleosynthesis_periodic_table.svg_-1.png\"><img class=\"wp-image-524\" title=\"By Cmglee (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a> or <a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ANucleosynthesis_periodic_table.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Nucleosynthesis_periodic_table.svg_-1-300x150.png\" alt=\"This shows the period table. Some elements are made in the big bang, some are made in stellar processes.\" width=\"400\" height=\"200\"><\/a> Origin of the elements on the periodic table, showing the important role the star life cycle plays.[\/caption]Astronomers think the [pb_glossary id=\"2194\"]big bang[\/pb_glossary] created lighter [pb_glossary id=\"2700\"]elements[\/pb_glossary], mostly hydrogen and smaller amounts of [pb_glossary id=\"2700\"]elements[\/pb_glossary] helium, lithium, and beryllium. Another process must be responsible for creating the other 90 heavier [pb_glossary id=\"2700\"]elements[\/pb_glossary]. The current model of stellar evolution explains the origins of these heavier [pb_glossary id=\"2700\"]elements[\/pb_glossary].\n<h4><span style=\"font-weight: 400\">Birth of a star<\/span><\/h4>\n[caption id=\"attachment_3281\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Eagle_nebula_pillars.jpg\"><img class=\"wp-image-525 size-medium\" title=\"By Credit: NASA, Jeff Hester, and Paul Scowen (Arizona State University) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEagle_nebula_pillars.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Eagle_nebula_pillars-300x296.jpg\" alt=\"It is several large column of gas\" width=\"300\" height=\"296\"><\/a> Section of the Eagle Nebula known as \"The Pillars of Creation.\"[\/caption]Stars start their lives as [pb_glossary id=\"2700\"]elements[\/pb_glossary] floating in cold, spinning clouds of gas and dust known as <strong>[pb_glossary id=\"2197\"]nebulas[\/pb_glossary]<\/strong>. Gravitational attraction or perhaps a nearby stellar explosion causes the [pb_glossary id=\"2700\"]elements[\/pb_glossary] to condense and spin into disk shape. In the center of this disk shape a new star is born under the force of gravity. The spinning whirlpool concentrates material in the center, and the increasing gravitational forces collect even more mass. Eventually, the immensely [pb_glossary id=\"3333\"]concentrated[\/pb_glossary] mass of material reaches a critical point of such intense heat and pressure it initiates [pb_glossary id=\"2198\"]fusion[\/pb_glossary].\n<h4><span style=\"font-weight: 400\">Fusion<\/span><\/h4>\n[caption id=\"attachment_3282\" align=\"alignleft\" width=\"211\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/FusionintheSun.svg_.png\"><img class=\"wp-image-526 size-medium\" title=\"<a href=&quot;Borb&quot; title=&quot;User:Borb&quot;>Borb<\/a> [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFusionintheSun.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/FusionintheSun.svg_-211x300.png\" alt=\"There are 3 steps\" width=\"211\" height=\"300\"><\/a> General diagram showing the series of fusion steps that occur in the sun.[\/caption][pb_glossary id=\"2198\"]Fusion[\/pb_glossary] is not a chemical reaction. <strong>[pb_glossary id=\"2198\"]Fusion[\/pb_glossary]<\/strong> is a nuclear reaction in which two or more nuclei, the centers of atoms, are forced together and combine creating a new larger atom. This reaction gives off a tremendous amount of energy, usually as light and solar radiation. An [pb_glossary id=\"2700\"]element[\/pb_glossary] such as hydrogen combines or fuses with other hydrogen atoms in the [pb_glossary id=\"2589\"]core[\/pb_glossary] of a star to become a new [pb_glossary id=\"2700\"]element[\/pb_glossary], in this case, helium. Another product of this process is energy, such as solar radiation that leaves the Sun and comes to the Earth as light and heat. [pb_glossary id=\"2198\"]Fusion[\/pb_glossary] is a steady and predictable process, which is why we call this the main phase of a star\u2019s life. During its main phase, a star turns hydrogen into helium. Since most stars contain plentiful amounts of hydrogen, the main phase may last billions of years, during which their size and energy output remains relatively steady.\n\n[caption id=\"attachment_3283\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Star_life_cycles_red_dwarf_en.svg_.png\"><img class=\"wp-image-527 size-medium\" title=\"By cmglee, NASA Goddard Space Flight Center (File:star_life_cycles_red_dwarf.jpg) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStar_life_cycles_red_dwarf_en.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Star_life_cycles_red_dwarf_en.svg_-300x200.png\" alt=\"It shows many steps\" width=\"300\" height=\"200\"><\/a> Two main paths of a star's life cycle, depending on mass.[\/caption]The giant phase in a star\u2019s life occurs when the star runs out of hydrogen for [pb_glossary id=\"2198\"]fusion[\/pb_glossary]. If a star is large enough, it has sufficient heat and pressure to start fusing helium into heavier [pb_glossary id=\"2700\"]elements[\/pb_glossary]. This style of [pb_glossary id=\"2198\"]fusion[\/pb_glossary] is more energetic and the higher energy and [pb_glossary id=\"2689\"]temperature[\/pb_glossary] expand the star to a larger size and brightness. This giant phase is predicted to happen to our Sun in another few billion years, growing the radius of the Sun to Earth\u2019s orbit, which will render life impossible. The mass of a star during its main phase is the primary factor in determining how it will evolve. If the star has enough mass and reaches a point at which the primary [pb_glossary id=\"2198\"]fusion[\/pb_glossary] [pb_glossary id=\"2700\"]element[\/pb_glossary], such as helium, is exhausted, [pb_glossary id=\"2198\"]fusion[\/pb_glossary] continues using new, heavier [pb_glossary id=\"2700\"]elements[\/pb_glossary]. This occurs over and over in very large stars, forming progressively heavier [pb_glossary id=\"2700\"]elements[\/pb_glossary] like carbon and oxygen. Eventually, [pb_glossary id=\"2198\"]fusion[\/pb_glossary] reaches its limit as it forms iron and nickel. This progression explains the abundance of iron and nickel in rocky objects, like Earth, within the [pb_glossary id=\"2201\"]solar system[\/pb_glossary]. At this point, any further [pb_glossary id=\"2198\"]fusion[\/pb_glossary] absorbs energy instead of giving it off, which is the beginning of the end of the star\u2019s life<span style=\"font-weight: 400\">.<\/span>\n<h4><span style=\"font-weight: 400\">Death of a Star<\/span><\/h4>\n[caption id=\"attachment_3284\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Crab_Nebula.jpg\"><img class=\"wp-image-528 size-medium\" title=\"NASA and ESA image, public domain.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-300x300.jpg\" alt=\"The picture is of dust and gas.\" width=\"300\" height=\"300\"><\/a> Hubble space telescope image of the Crab Nebula, the remnants of a supernova that occurred in 1054 C.E.[\/caption]\n\n<span style=\"font-weight: 400\">The death of a star can range from spectacular to other-worldly (see figure). Stars like the Sun form a planetary [pb_glossary id=\"2197\"]nebula[\/pb_glossary], which comes from the collapse of the star\u2019s outer layers in an event like the implosion of a building. In the tug-of-war between gravity\u2019s inward pull and [pb_glossary id=\"2198\"]fusion\u2019s[\/pb_glossary] outward push, gravity instantly takes over when [pb_glossary id=\"2198\"]fusion[\/pb_glossary] ends, with the outer gasses puffing away to form a [pb_glossary id=\"2197\"]nebula[\/pb_glossary]. More [pb_glossary id=\"1933\"]massive[\/pb_glossary] stars do this as well but with a more energetic collapse, which starts another type of energy release mixed with [pb_glossary id=\"2700\"]element[\/pb_glossary] creation known as a [pb_glossary id=\"2199\"]supernova[\/pb_glossary]. In a <strong>[pb_glossary id=\"2199\"]supernova[\/pb_glossary]<\/strong>, the collapse of the [pb_glossary id=\"2589\"]core[\/pb_glossary] suddenly halts, creating a [pb_glossary id=\"1933\"]massive[\/pb_glossary] outward-propagating shock wave. A [pb_glossary id=\"2199\"]supernova[\/pb_glossary] is the most energetic explosion in the universe short of the [pb_glossary id=\"2194\"]big bang[\/pb_glossary]. The energy release is so significant the ensuing [pb_glossary id=\"2198\"]fusion[\/pb_glossary] can make every [pb_glossary id=\"2700\"]element[\/pb_glossary] up through uranium<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3285\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/08.1_blackhole_NASA_2019.png\"><img class=\"wp-image-529 size-medium\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-300x175.png\" alt=\"Blurry telescope photo of a fuzzy red halo around an entirely black center. The black center represents the first photograph of an actual black hole captured in 2019.\" width=\"300\" height=\"175\"><\/a> A black hole and its shadow have been captured in an image for the first time in 2019, a historic feat by an international network of radio telescopes called the Event Horizon Telescope (Source: NASA)[\/caption]\n\n<span style=\"font-weight: 400\">The death of the star can result in the creation of white dwarfs, neutron stars, or black holes. Following their deaths, stars like the Sun turn into white dwarfs<\/span><span style=\"font-weight: 400\">.<\/span>\n\nWhite dwarfs are hot star embers, formed by packing most of a dying star\u2019s mass into a small and dense object about the size of Earth. Larger stars may explode in a [pb_glossary id=\"2199\"]supernova[\/pb_glossary] that packs their mass even tighter to become neutron stars. Neutron stars are so dense that protons combine with electrons to form neutrons. The largest stars collapse their mass even further, becoming objects so dense that light cannot escape their gravitational grasp. These are the infamous black holes and the details of the physics of what occurs in them are still up for debate.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"48\"]\n\n[caption id=\"attachment_4240\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.1-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-530\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.1 via this QR Code.[\/caption]\n<h2><strong>8.2 Origin of the Solar System: The Nebular Hypothesis<\/strong><\/h2>\n[caption id=\"attachment_3286\" align=\"alignleft\" width=\"252\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/M42proplyds.jpg\"><img class=\"wp-image-531\" title=\"By C.R. O'Dell\/Rice University; NASA [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AM42proplyds.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/M42proplyds-300x224.jpg\" alt=\"It is a small cloud\" width=\"252\" height=\"188\"><\/a> Small protoplanetary discs in the Orion Nebula[\/caption]<span style=\"font-weight: 400\">Our [pb_glossary id=\"2201\"]solar system[\/pb_glossary] formed at the same time as our Sun as described in the [pb_glossary id=\"2200\"]nebular hypothesis[\/pb_glossary]. The <strong>[pb_glossary id=\"2200\"]nebular hypothesis[\/pb_glossary]<\/strong> is the idea that a spinning cloud of dust made of mostly light [pb_glossary id=\"2700\"]elements[\/pb_glossary], called a [pb_glossary id=\"2197\"]nebula[\/pb_glossary], flattened into a protoplanetary disk, and became a [pb_glossary id=\"2201\"]solar system[\/pb_glossary] consisting of a star with orbiting planets<\/span><span style=\"font-weight: 400\">. <\/span>The spinning [pb_glossary id=\"2197\"]nebula[\/pb_glossary] collected the vast majority of material in its center, which is why the sun Accounts for over 99% of the mass in our [pb_glossary id=\"2201\"]solar system[\/pb_glossary].\n\n&nbsp;\n<h3><b>8.2.1 Planet Arrangement and Segregation<\/b><\/h3>\n[caption id=\"attachment_3287\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fomalhaut_Circumstellar_Disk.jpg\"><img class=\"wp-image-532 size-medium\" title=\"By NASA\/JPL-Caltech\/K. Stapelfeldt (JPL), James Clerk Maxwell Telescope [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFomalhaut_Circumstellar_Disk.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fomalhaut_Circumstellar_Disk-300x240.jpg\" alt=\"The disc is lop sided\" width=\"300\" height=\"240\"><\/a> This disk is asymmetric, possibly because of a large gas giant planet orbiting relatively far from the star.[\/caption]<span style=\"font-weight: 400\">As our [pb_glossary id=\"2201\"]solar system[\/pb_glossary] formed, the nebular cloud of dispersed particles developed distinct [pb_glossary id=\"2689\"]temperature[\/pb_glossary] zones. Temperatures were very high close to the center, only allowing condensation of metals and [pb_glossary id=\"2709\"]silicate[\/pb_glossary] [pb_glossary id=\"2687\"]minerals[\/pb_glossary] with high melting points. Farther from the Sun, the temperatures were lower, allowing the condensation of lighter gaseous molecules such as methane, ammonia, carbon dioxide, and water<\/span><span style=\"font-weight: 400\">. This [pb_glossary id=\"2689\"]temperature[\/pb_glossary] differentiation resulted in the inner four planets of the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] becoming rocky, and the outer four planets becoming gas giants.<\/span>\n\n[caption id=\"attachment_3288\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/HL_Tau_protoplanetary_disk.jpg\"><img class=\"wp-image-533 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-300x300.jpg\" alt=\"The orange disk has zones that are darker, indicating the planets are growing by using that material in the disk.\" width=\"300\" height=\"300\"><\/a> Image by the ALMA telescope of HL Tauri and its protoplanetary disk, showing grooves formed as planets absorb material in the disk.[\/caption]\n\nBoth rocky and gaseous planets have a similar growth model. Particles of dust, floating in the disc were attracted to each other by static charges and eventually, gravity. As the clumps of dust became bigger, they interacted with each other\u2014colliding, sticking, and forming proto-planets. The planets continued to grow over the course of many thousands or millions of years, as material from the protoplanetary disc was added. Both rocky and gaseous planets started with a solid [pb_glossary id=\"2589\"]core[\/pb_glossary]. Rocky planets built more rock on that [pb_glossary id=\"2589\"]core[\/pb_glossary], while gas planets added gas and ice. Ice giants formed later and on the furthest edges of the disc, accumulating less gas and more ice. That is why the gas-giant planets Jupiter and Saturn are [pb_glossary id=\"2831\"]composed[\/pb_glossary] of mostly hydrogen and helium gas, more than 90%. The ice giants Uranus and Neptune are [pb_glossary id=\"2831\"]composed[\/pb_glossary] of mostly methane ices and only about 20% hydrogen and helium gases.\n\n[caption id=\"attachment_4330\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis.jpg\"><img class=\"wp-image-534 size-medium\" title=\"A. Angelich (NRAO\/AUI\/NSF)\/ALMA (ESO\/NAOJ\/NRAO)\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-300x255.jpg\" alt=\"It shows a ring of ice around the star\" width=\"300\" height=\"255\"><\/a> This artist\u2019s impression of the water snowline around the young star V883 Orionis, as detected with ALMA.[\/caption]\n\n&nbsp;\n\nThe planetary [pb_glossary id=\"2831\"]composition[\/pb_glossary] of the gas giants is clearly different from the rocky planets. Their size is also dramatically different for two reasons: First, the original planetary [pb_glossary id=\"2197\"]nebula[\/pb_glossary] contained more gases and ices than metals and rocks. There was abundant hydrogen, carbon, oxygen, nitrogen, and less silicon and iron, giving the outer planets more building material. Second, the stronger gravitational pull of these giant planets allowed them to collect large quantities of hydrogen and helium, which could not be collected by weaker gravity of the smaller planets.\n\n[caption id=\"attachment_2515\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/02.2_TolucaMeteorite.jpg\"><img class=\"wp-image-83 size-medium\" title=\"By H. Raab (User:Vesta) (Own work) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ATolucaMeteorite.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/02.2_TolucaMeteorite-300x225.jpg\" alt=\"The meteorite is polished showing the Widmanst\u00e4tten Pattern.\" width=\"300\" height=\"225\"><\/a> A polished fragment of the iron-rich Toluca Meteorite, with octahedral Widmanst\u00e4tten Pattern.[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">Jupiter\u2019s [pb_glossary id=\"1933\"]massive[\/pb_glossary] gravity further shaped the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] and growth of the inner rocky planets. As the [pb_glossary id=\"2197\"]nebula[\/pb_glossary] started to coalesce into planets, Jupiter\u2019s gravity accelerated the movement of nearby materials, generating destructive collisions rather than constructively gluing material together<\/span><span style=\"font-weight: 400\">. <\/span>These collisions created the asteroid belt, an unfinished planet, located between Mars and Jupiter. This asteroid belt is the source of most <strong>[pb_glossary id=\"2202\"]meteorites[\/pb_glossary]<\/strong> that currently impact the Earth. Study of asteroids and [pb_glossary id=\"2202\"]meteorites[\/pb_glossary] help geologist to determine the age of Earth and the [pb_glossary id=\"2831\"]composition[\/pb_glossary] of its [pb_glossary id=\"2589\"]core[\/pb_glossary], [pb_glossary id=\"2586\"]mantle[\/pb_glossary], and [pb_glossary id=\"2580\"]crust[\/pb_glossary]. Jupiter\u2019s gravity may also explain Mars\u2019 smaller mass, with the larger planet consuming material as it migrated from the inner to outer edge of the [pb_glossary id=\"2201\"]solar system[\/pb_glossary]<span style=\"font-weight: 400\">.\u00a0<\/span>\n<h4><span style=\"font-weight: 400\">Pluto and planet definition<\/span><\/h4>\n[caption id=\"attachment_3290\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/EightTNOs.png\"><img class=\"wp-image-535 size-medium\" title=\"By Lexicon [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>, <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5-2.0-1.0&quot;>CC BY-SA 2.5-2.0-1.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEightTNOs.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/EightTNOs-300x218.png\" alt=\"It shows many objects\" width=\"300\" height=\"218\"><\/a> Eight largest objects discovered past Neptune.[\/caption]<span style=\"font-weight: 400\">The outermost part of the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] is known as the Kuiper belt, which is a scattering of rocky and icy bodies. Beyond that is the Oort cloud, a zone filled with small and dispersed ice traces. These two locations are where most comets form and continue to orbit, and objects found here have relatively irregular orbits compared to the rest of the [pb_glossary id=\"2201\"]solar system[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>Pluto, formerly the ninth planet, is located in this region of space. The XXVIth General Assembly of the International Astronomical Union (IAU) stripped Pluto of planetary status in 2006 because scientists discovered an object more [pb_glossary id=\"1933\"]massive[\/pb_glossary] than Pluto, which they named Eris. The IAU decided against including Eris as a planet, and therefore, excluded Pluto as well. The IAU narrowed the definition of a planet to three criteria: 1) enough mass to have gravitational forces that force it to be rounded, 2) not [pb_glossary id=\"1933\"]massive[\/pb_glossary] enough to create [pb_glossary id=\"2198\"]fusion[\/pb_glossary], and 3) large enough to be in a cleared orbit, free of other planetesimals that should have been incorporated at the time the planet formed. Pluto passed the first two parts of the definition, but not the third. Pluto and Eris are currently classified as dwarf planets.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"49\"]\n\n[caption id=\"attachment_4241\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.2-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-536\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.2 via this QR Code.[\/caption]\n<h2><span style=\"font-size: 28px\">8.3 Hadean Eon<\/span><\/h2>\n[caption id=\"attachment_3270\" align=\"alignleft\" width=\"232\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/17.18_Geologic_Time_Scale_with_years-1.jpg\"><img class=\"wp-image-3270 size-medium\" title=\"Image by Belinda Madsen\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/17.18_Geologic_Time_Scale_with_years-1-1.jpg\" alt=\"The Geologic Time Scale with an age of each unit shown by a scale\" width=\"232\" height=\"300\"><\/a> Geologic Time Scale with ages shown[\/caption]\n\nGeoscientists use the geological time scale to assign relative age names to events and rocks, separating major events in Earth\u2019s history based on significant changes as recorded in rocks and [pb_glossary id=\"2176\"]fossils[\/pb_glossary]. This section summarizes the most notable events of each major time interval. For a breakdown on how these time intervals are chosen and organized, see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/7-geologic-time\/\">chapter 7<\/a>.\n\n<span style=\"font-weight: 400\">The [pb_glossary id=\"2203\"]Hadean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary], named after the Greek god and ruler of the underworld Hades, is the oldest [pb_glossary id=\"2190\"]eon[\/pb_glossary] and dates from 4.5\u20134.0 billion years ago<\/span><span style=\"font-weight: 400\">. \u00a0<\/span>\n\n[caption id=\"attachment_3244\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Hadean.png\"><img class=\"wp-image-491 size-medium\" title=\"By Tim Bertelink (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHadean.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Hadean-300x161.png\" alt=\"The surface of Earth is full of volcanoes.\" width=\"300\" height=\"161\"><\/a> Artist's impression of the Earth in the Hadean.[\/caption]<span style=\"font-weight: 400\">This time represents Earth\u2019s earliest history, during which the planet was characterized by a partially molten surface, [pb_glossary id=\"1181\"]volcanism[\/pb_glossary], and asteroid impacts. Several mechanisms made the newly forming Earth incredibly hot: gravitational [pb_glossary id=\"1446\"]compression[\/pb_glossary], [pb_glossary id=\"2966\"]radioactive[\/pb_glossary] decay, and asteroid impacts. Most of this initial heat still exists inside the Earth. The [pb_glossary id=\"2203\"]Hadean[\/pb_glossary] was originally defined as the birth of the planet occurring 4.0 billion years ago and preceding the existence of many rocks and life forms. However, geologists have dated [pb_glossary id=\"2687\"]minerals[\/pb_glossary] at 4.4 billion years, with evidence that liquid water was present<\/span><span style=\"font-weight: 400\">. <\/span><span style=\"font-weight: 400\"> There is possibly even evidence of life existing over 4.0 billion years ago<\/span><span style=\"font-weight: 400\">. However, the most reliable record for early life, the microfossil record, starts at 3.5 billion years ago<\/span><span style=\"font-weight: 400\">. <\/span>\n<h3><b>8.3.1 Origin of Earth's Crust<\/b><\/h3>\n[caption id=\"attachment_3291\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MohoDepth.png\"><img class=\"wp-image-538 size-medium\" title=\"By AllenMcC. (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMohomap.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MohoDepth-300x167.png\" alt=\"Places with mountain building have a deeper moho.\" width=\"300\" height=\"167\"><\/a> The global map of the depth of the moho, or thickness of the crust.[\/caption]<span style=\"font-weight: 400\">As Earth cooled from its molten state, [pb_glossary id=\"2687\"]minerals[\/pb_glossary] started to crystallize and settle resulting in a separation of [pb_glossary id=\"2687\"]minerals[\/pb_glossary] based on density and the creation of the [pb_glossary id=\"2580\"]crust[\/pb_glossary], [pb_glossary id=\"2586\"]mantle[\/pb_glossary], and [pb_glossary id=\"2589\"]core[\/pb_glossary]. The earliest Earth was chiefly molten material and would have been rounded by gravitational forces so it resembled a ball of [pb_glossary id=\"2673\"]lava[\/pb_glossary] floating in space. As the outer part of the Earth slowly cooled, the high melting-point [pb_glossary id=\"2687\"]minerals[\/pb_glossary] (see [pb_glossary id=\"1174\"]Bowen\u2019s Reaction Series[\/pb_glossary] in <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>) formed solid slabs of early [pb_glossary id=\"2580\"]crust[\/pb_glossary]. These slabs were probably unstable and easily reabsorbed into the liquid [pb_glossary id=\"2672\"]magma[\/pb_glossary] until the Earth cooled enough to allow numerous larger fragments to form a thin primitive [pb_glossary id=\"2580\"]crust[\/pb_glossary]. Scientists generally assume this [pb_glossary id=\"2580\"]crust[\/pb_glossary] was [pb_glossary id=\"2581\"]oceanic[\/pb_glossary] and [pb_glossary id=\"1956\"]mafic[\/pb_glossary] in [pb_glossary id=\"2831\"]composition[\/pb_glossary], and littered with impacts, much like the Moon\u2019s current [pb_glossary id=\"2580\"]crust[\/pb_glossary]. There is still some debate over when [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary] started, which would have led to the [pb_glossary id=\"2960\"]formation[\/pb_glossary] of [pb_glossary id=\"2575\"]continental[\/pb_glossary] and [pb_glossary id=\"1954\"]felsic[\/pb_glossary] [pb_glossary id=\"2580\"]crust[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Regardless of this, as Earth cooled and solidified, less dense [pb_glossary id=\"1954\"]felsic[\/pb_glossary] [pb_glossary id=\"2687\"]minerals[\/pb_glossary] floated to the surface of the Earth to form the [pb_glossary id=\"2580\"]crust[\/pb_glossary], while the denser [pb_glossary id=\"1956\"]mafic[\/pb_glossary] and [pb_glossary id=\"1957\"]ultramafic[\/pb_glossary] materials sank to form the [pb_glossary id=\"2586\"]mantle[\/pb_glossary] and the highest-density iron and nickel sank into the [pb_glossary id=\"2589\"]core[\/pb_glossary]. This differentiated the Earth from a homogenous planet into a heterogeneous one with layers of [pb_glossary id=\"1954\"]felsic[\/pb_glossary] [pb_glossary id=\"2580\"]crust[\/pb_glossary], [pb_glossary id=\"1956\"]mafic[\/pb_glossary] [pb_glossary id=\"2580\"]crust[\/pb_glossary], [pb_glossary id=\"1957\"]ultramafic[\/pb_glossary] [pb_glossary id=\"2586\"]mantle[\/pb_glossary], and iron and nickel [pb_glossary id=\"2589\"]core[\/pb_glossary].<\/span>\n<h3><b>8.3.2 Origin of the Moon<\/b><\/h3>\n[caption id=\"attachment_3292\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Back_side_of_the_Moon_AS16-3021.jpg\"><img class=\"wp-image-539 size-medium\" title=\"By Apollo 16 astronauts [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABack_side_of_the_Moon_AS16-3021.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Back_side_of_the_Moon_AS16-3021-300x298.jpg\" alt=\"It looks different then the side we don't normally see.\" width=\"300\" height=\"298\"><\/a> Dark side of the Moon[\/caption]<span style=\"font-weight: 400\">Several unique features of Earth\u2019s Moon have prompted scientists to develop the current [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] about its [pb_glossary id=\"2960\"]formation[\/pb_glossary]. The Earth and Moon are tidally locked, meaning that as the Moon orbits, one side always faces the Earth and the opposite side is not visible to us. Also and most importantly, the chemical compositions of the Earth and Moon show nearly identical [pb_glossary id=\"2701\"]isotope[\/pb_glossary] ratios<\/span><span style=\"font-weight: 400\"> and volatile content<\/span><span style=\"font-weight: 400\">. <\/span>Apollo missions returned from the Moon with rocks that allowed scientists to conduct very precise comparisons between Moon and Earth rocks. Other bodies in the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] and [pb_glossary id=\"2202\"]meteorites[\/pb_glossary] do not share the same degree of similarity and show much higher variability. If the Moon and Earth formed together, this would explain why they are so chemically similar.\n\n[caption id=\"attachment_3293\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/ArtistsConceptMoonFormation.jpg\"><img class=\"wp-image-540 size-medium\" title=\"By NASA\/JPL-Caltech [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File:Artist%27s_concept_of_collision_at_HD_172555.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/ArtistsConceptMoonFormation-300x240.jpg\" alt=\"The Earth and this object are colliding in a giant explosion.\" width=\"300\" height=\"240\"><\/a> Artist's concept of the giant impact from a Mars-sized object that could have formed the moon.[\/caption]Many ideas have been proposed for the origin of the Moon: The Moon could have been captured from another part of the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] and formed in place together with the Earth, or the Moon could have been ripped out of the early Earth. None of proposed explanations can account for all the evidence. The currently prevailing [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] is the <strong>giant-impact [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary]<\/strong><span style=\"font-weight: 400\">. <\/span>It proposes a body about half of Earth\u2019s size must have shared at least parts of Earth\u2019s orbit and collided with it, resulting in a violent mixing and scattering of material from both objects. Both bodies would be [pb_glossary id=\"2831\"]composed[\/pb_glossary] of a combination of materials, with more of the lower density splatter coalescing into the Moon. This may explain why the Earth has a higher density and thicker [pb_glossary id=\"2589\"]core[\/pb_glossary] than the Moon.\n\n[caption id=\"attachment_4254\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-541\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/UIKmSQqp8wY[\/embed]\n\n<em><span style=\"font-weight: 400\">Computer simulation of the evolution of the Moon (2 minutes).<\/span><\/em>\n<h3><b>8.3.3 Origin of Earth\u2019s Water<\/b><\/h3>\n[caption id=\"attachment_3294\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Comet_on_7_July_2015_NavCam.jpg\"><img class=\"wp-image-542 size-medium\" title=\"&quot;ESA\/Rosetta\/NAVCAM,\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-300x300.jpg\" alt=\"Jets are seen coming off of the comet.\" width=\"300\" height=\"300\"><\/a> Water vapor leaves comet 67P\/Churyumov\u2013Gerasimenko.[\/caption]\n\n<span style=\"font-weight: 400\">Explanations for the origin of Earth\u2019s water include [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] outgassing, comets, and [pb_glossary id=\"2202\"]meteorites[\/pb_glossary]. The [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] outgassing [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] for the origin of Earth\u2019s water is that it originated from inside the planet, and emerged via [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] processes as vapor associated with [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] eruptions<\/span><span style=\"font-weight: 400\">.\u00a0 Since all [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] eruptions contain some water vapor, at times more than 1% of the volume, these alone could have created Earth\u2019s surface water. Another likely source of water was from space. Comets are a mixture of dust and ice, with some or most of that ice being frozen water. Seemingly dry meteors can contain small but measurable amounts of water, usually trapped in their [pb_glossary id=\"2687\"]mineral[\/pb_glossary] structures<\/span><span style=\"font-weight: 400\">. During heavy bombardment [pb_glossary id=\"2192\"]periods[\/pb_glossary] later in Earth\u2019s history, its cooled surface was pummeled by comets and [pb_glossary id=\"2202\"]meteorites[\/pb_glossary], which could be why so much water exists above ground. There isn\u2019t a definitive answer for what process is the source of ocean water. Earth\u2019s water isotopically matches water found in [pb_glossary id=\"2202\"]meteorites[\/pb_glossary] much better than that of comets<\/span><span style=\"font-weight: 400\">. However, it is hard to know if Earth processes could have changed the water\u2019s isotopic signature over the last 4-plus billion years<\/span><span style=\"font-weight: 400\">. <\/span>It is possible that all three sources contributed to the origin of Earth\u2019s water.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"50\"]\n\n[caption id=\"attachment_4242\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.3-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-543\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.3 via this QR Code.[\/caption]\n<h2><strong>8.4 Archean Eon<\/strong><\/h2>\n[caption id=\"attachment_3295\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Archean.png\"><img class=\"wp-image-544 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-300x134.png\" alt=\"It shows volcanoes, impacts, and stromatolites.\" width=\"300\" height=\"134\"><\/a> Artist's impression of the Archean.[\/caption]\n\n<span style=\"font-weight: 400\">The <strong>[pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]<\/strong>, which lasted from 4.0\u20132.5 billion years ago, is named after the Greek word for beginning. This [pb_glossary id=\"2190\"]eon[\/pb_glossary] represents the beginning of the rock record. Although there is current evidence that rocks and [pb_glossary id=\"2687\"]minerals[\/pb_glossary] existed during the [pb_glossary id=\"2203\"]Hadean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]<\/span><span style=\"font-weight: 400\">, <\/span>the [pb_glossary id=\"2205\"]Archean[\/pb_glossary] has a much more robust rock and [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record.\n\n&nbsp;\n\n&nbsp;\n<h3><b><\/b><span style=\"font-weight: 400\">8.4.1 Late Heavy Bombardment<\/span><\/h3>\n[caption id=\"attachment_3296\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Pluto-in-true-color_2x_JPEG-edit-frame.jpg\"><img class=\"wp-image-545 size-medium\" title=\"NASA, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-300x300.jpg\" alt=\"The smooth plain is different than the cratered surrounding surface.\" width=\"300\" height=\"300\"><\/a> 2015 image from NASA's New Horizons probe of Pluto. The lack of impacts found on the Tombaugh Regio (the heart-shaped plain, lower right) has been inferred as being younger than the Late Heavy Bombardment and the surrounding surface due to its lack of impacts.[\/caption]\n\nObjects were chaotically flying around at the start of the [pb_glossary id=\"2201\"]solar system[\/pb_glossary], building the planets and moons. There is evidence that after the planets formed, about 4.1\u20133.8 billion years ago, a second large spike of asteroid and comet impacted the Earth and Moon in an event called <strong>[pb_glossary id=\"2206\"]late heavy bombardment[\/pb_glossary]<\/strong><span style=\"font-weight: 400\">. <\/span>[pb_glossary id=\"2202\"]Meteorites[\/pb_glossary] and comets in stable or semi-stable orbits became unstable and started impacting objects throughout the [pb_glossary id=\"2201\"]solar system[\/pb_glossary]. In addition, this event is called the lunar cataclysm because most of the Moons craters are from this event. During [pb_glossary id=\"2206\"]late heavy bombardment[\/pb_glossary], the Earth, Moon, and all planets in the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] were pummeled by material from the asteroid and Kuiper belts. Evidence of this bombardment was found within samples collected from the Moon.\n\n[caption id=\"attachment_3297\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Lhborbits.png\"><img class=\"wp-image-546 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-300x100.png\" alt=\"It shows 3 pictures.\" width=\"300\" height=\"100\"><\/a> Simulation of before, during, and after the late heavy bombardment.[\/caption]\n\n<span style=\"font-weight: 400\">It is universally accepted that the [pb_glossary id=\"2201\"]solar system[\/pb_glossary] experienced extensive asteroid and comet bombardment at its start; however, some other process must have caused the second increase in impacts hundreds of millions of years later. A leading [pb_glossary id=\"2655\"]theory[\/pb_glossary] blames gravitational [pb_glossary id=\"3103\"]resonance[\/pb_glossary] between Jupiter and Saturn for disturbing orbits within the asteroid and Kuiper belts <\/span>based on a similar process observed in the Eta Corvi star [pb_glossary id=\"2664\"]system[\/pb_glossary]<span style=\"font-weight: 400\">.<\/span>\n<h3><b>8.4.2 Origin of the Continents<\/b><\/h3>\n[caption id=\"attachment_2512\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Earth-cutaway-schematic-english.svg_-1.png\"><img class=\"size-medium wp-image-51\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1-300x211.png\" alt=\"The crust and lithosphere are on the outside of the Earth and are thin. Below the crust is the mantle and core. Below the lithosphere is the asthenosphere.\" width=\"300\" height=\"211\"><\/a> The layers of the Earth. Physical layers include lithosphere and asthenosphere; chemical layers are crust, mantle, and core.[\/caption]\n\n&nbsp;\n\n<span style=\"font-weight: 400\">In order for [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary] to work as it does currently, it necessarily must have continents. However, the easiest way to create [pb_glossary id=\"2575\"]continental[\/pb_glossary] material is via [pb_glossary id=\"1178\"]assimilation[\/pb_glossary] and differentiation of existing continents (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>). This chicken-and-egg quandary over how continents were made in the first place is not easily answered because of the great age of [pb_glossary id=\"2575\"]continental[\/pb_glossary] material and how much evidence has been lost during [pb_glossary id=\"2576\"]tectonics[\/pb_glossary] and [pb_glossary id=\"2677\"]erosion[\/pb_glossary]. While the timing and specific processes are still debated, [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] action must have brought the first [pb_glossary id=\"2575\"]continental[\/pb_glossary] material to the Earth\u2019s surface during the [pb_glossary id=\"2203\"]Hadean[\/pb_glossary], 4.4 billion years ago<\/span><span style=\"font-weight: 400\">. <\/span>This model does not solve the problem of [pb_glossary id=\"2575\"]continent[\/pb_glossary] [pb_glossary id=\"2960\"]formation[\/pb_glossary], since [pb_glossary id=\"1179\"]magmatic differentiation[\/pb_glossary] seems to need thicker [pb_glossary id=\"2580\"]crust[\/pb_glossary]. Nevertheless, the continents formed by some incremental process during the early history of Earth<span style=\"font-weight: 400\">. The best idea is that density differences allowed lighter [pb_glossary id=\"1954\"]felsic[\/pb_glossary] materials to float upward and heavier [pb_glossary id=\"1957\"]ultramafic[\/pb_glossary] materials and [pb_glossary id=\"3345\"]metallic[\/pb_glossary] iron to sink. These density differences led to the layering of the Earth, the layers that are now detected by [pb_glossary id=\"3087\"]seismic[\/pb_glossary] studies. Early protocontinents accumulated [pb_glossary id=\"1954\"]felsic[\/pb_glossary] materials as developing [pb_glossary id=\"2591\"]plate[\/pb_glossary]-[pb_glossary id=\"2576\"]tectonic[\/pb_glossary] processes brought lighter material from the [pb_glossary id=\"2586\"]mantle[\/pb_glossary] to the surface<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3299\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fig21oceanocean.gif\"><img class=\"wp-image-3299 size-medium\" title=\"USGS, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig21oceanocean-1.gif\" alt=\"The ocean plate subducts beneath a different ocean plate.\" width=\"300\" height=\"173\"><\/a> Subduction of an oceanic plate beneath another oceanic plate, forming a trench and an island arc. Several island arcs might combine and eventually evolve into a continent.[\/caption]\n\n<span style=\"font-weight: 400\">The first solid evidence of modern [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary] is found at the end of the [pb_glossary id=\"2205\"]Archean[\/pb_glossary], indicating at least some [pb_glossary id=\"2575\"]continental[\/pb_glossary] [pb_glossary id=\"2590\"]lithosphere[\/pb_glossary] must have been in place. This evidence does not necessarily mark the starting point of [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary]; remnants of earlier [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] activity could have been erased by the [pb_glossary id=\"2671\"]rock cycle[\/pb_glossary]<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_2523\" align=\"alignright\" width=\"419\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/CratonGeolProv.jpg\"><img class=\"wp-image-92\" title=\"By USGS (http:\/\/earthquake.usgs.gov\/data\/crust\/maps.php) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AWorld_geologic_provinces.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/CratonGeolProv-300x159.jpg\" alt=\"The legend shows shields, platforms, orogens, basins, large igneous provinces, and extended crust.\" width=\"419\" height=\"222\"><\/a> Geologic provinces of Earth. Cratons are pink and orange.[\/caption]The stable interiors of the current continents are called <strong>[pb_glossary id=\"2640\"]cratons[\/pb_glossary]<\/strong> and were mostly formed in the [pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]. A [pb_glossary id=\"2640\"]craton[\/pb_glossary] has two main parts: the <strong>[pb_glossary id=\"2207\"]shield[\/pb_glossary]<\/strong>, which is crystalline [pb_glossary id=\"1971\"]basement[\/pb_glossary] rock near the surface, and the <strong>[pb_glossary id=\"2208\"]platform[\/pb_glossary]<\/strong> made of sedimentary rocks covering the [pb_glossary id=\"2207\"]shield[\/pb_glossary]. Most [pb_glossary id=\"2640\"]cratons[\/pb_glossary] have remained relatively unchanged with most [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] activity having occurred around [pb_glossary id=\"2640\"]cratons[\/pb_glossary] instead of within them. Whether they were created by [pb_glossary id=\"2576\"]plate tectonics[\/pb_glossary] or another process, [pb_glossary id=\"2205\"]Archean[\/pb_glossary] continents gave rise to the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] continents that now dominate our planet.\n\n[caption id=\"attachment_3300\" align=\"alignleft\" width=\"258\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Zealandia_topography.jpg\"><img class=\"wp-image-548 size-medium\" title=\"By World Data Center for Geophysics &amp;amp; Marine Geology (Boulder, CO), National Geophysical Data Center, NOAA [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AZealandia_topography.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Zealandia_topography-258x300.jpg\" alt=\"It shows Zealandia\" width=\"258\" height=\"300\"><\/a> The continent of Zealandia[\/caption]<span style=\"font-weight: 400\">The general guideline as to what constitutes a [pb_glossary id=\"2575\"]continent[\/pb_glossary] and differentiates [pb_glossary id=\"2581\"]oceanic[\/pb_glossary] from [pb_glossary id=\"2575\"]continental crust[\/pb_glossary] is under some debate. At passive margins, [pb_glossary id=\"2575\"]continental crust[\/pb_glossary] grades into [pb_glossary id=\"2581\"]oceanic crust[\/pb_glossary] at passive margins, making a distinction difficult<\/span><span style=\"font-weight: 400\">. Even island-[pb_glossary id=\"2609\"]arc[\/pb_glossary] and hot-spot material can seem more closely related to [pb_glossary id=\"2575\"]continental crust[\/pb_glossary] than [pb_glossary id=\"2581\"]oceanic[\/pb_glossary]. Continents usually have a [pb_glossary id=\"2640\"]craton[\/pb_glossary] in the middle with [pb_glossary id=\"1954\"]felsic[\/pb_glossary] [pb_glossary id=\"2675\"]igneous[\/pb_glossary] rocks. There is evidence that submerged masses like Zealandia, that includes present-day New Zealand, would be considered a [pb_glossary id=\"2575\"]continent[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. [pb_glossary id=\"2575\"]Continental crust[\/pb_glossary] that does not contain a [pb_glossary id=\"2640\"]craton[\/pb_glossary] is called a [pb_glossary id=\"2575\"]continental[\/pb_glossary] fragment, such as the island of Madagascar off the east [pb_glossary id=\"2890\"]coast[\/pb_glossary] of Africa<\/span><span style=\"font-weight: 400\">.<\/span>\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n<h3><b>8.4.3 First Life on Earth<\/b><\/h3>\n[caption id=\"attachment_3301\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MicrobialMats.jpg\"><img class=\"wp-image-549 size-medium\" title=\"By Smith609 (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ARunzelmarken.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MicrobialMats-300x167.jpg\" alt=\"Rocks with a wrinkled texture, formed by microbial mats\" width=\"300\" height=\"167\"><\/a> Fossils of microbial mats from Sweden[\/caption]Life most likely started during the late [pb_glossary id=\"2203\"]Hadean[\/pb_glossary] or early [pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eons[\/pb_glossary]. The earliest evidence of life are chemical signatures, microscopic filaments, and microbial mats. Carbon found in 4.1 billion year old [pb_glossary id=\"2175\"]zircon[\/pb_glossary] grains have a chemical signature suggesting an organic origin. Other evidence of early life are 3.8\u20134.3 billion-year-old microscopic filaments from a [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] [pb_glossary id=\"1187\"]vent[\/pb_glossary] deposit in Quebec, Canada. While the chemical and microscopic filaments evidence is not as robust as [pb_glossary id=\"2176\"]fossils[\/pb_glossary], there is significant [pb_glossary id=\"2176\"]fossil[\/pb_glossary] evidence for life at 3.5 billion years ago. These first well-preserved [pb_glossary id=\"2176\"]fossils[\/pb_glossary] are photosynthetic microbial mats, called [pb_glossary id=\"2213\"]stromatolites[\/pb_glossary], found in Australia.\n\n[caption id=\"attachment_3302\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/15.2_greenhouse-gas-molecules.jpg\"><img class=\"wp-image-550 size-medium\" title=\"https:\/\/climate.nasa.gov\/system\/internal_resources\/details\/original\/249_Causes-greenhouse-gas-molecules-cropped-more-55.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-300x192.jpg\" alt=\"Illustration of the molecular shape of greenhouse gases.\" width=\"300\" height=\"192\"><\/a> Greenhouse gases were more common in Earth\u2019s early atmosphere.[\/caption]\n\nAlthough the origin of life on Earth is unknown, [pb_glossary id=\"2652\"]hypotheses[\/pb_glossary] include a chemical origin in the early [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] and ocean, deep-sea [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] vents, and delivery to Earth by comets or other objects. One [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] is that life arose from the chemical environment of the Earth\u2019s early [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] and oceans, which was very different than today. The oxygen-free [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] produced a reducing environment with abundant methane, carbon dioxide, sulfur, and nitrogen compounds. This is what the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] is like on other bodies in the [pb_glossary id=\"2201\"]solar system[\/pb_glossary]. In the famous Miller-Urey [pb_glossary id=\"2653\"]experiment[\/pb_glossary], researchers simulated early Earth\u2019s [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] and lightning within a sealed vessel. After igniting sparks within the vessel, they discovered the [pb_glossary id=\"2960\"]formation[\/pb_glossary] of amino acids, the fundamental building blocks of proteins.\u00a0 In 1977, when scientists discovered an isolated ecosystem around [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] vents on a deep-sea [pb_glossary id=\"2630\"]mid-ocean ridge[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>), it opened the door for another explanation of the origin of life. The [pb_glossary id=\"2921\"]hydrothermal[\/pb_glossary] vents have a unique ecosystem of critters with [pb_glossary id=\"1184\"]chemosynthesis[\/pb_glossary] as the foundation of the food chain instead of photosynthesis. The ecosystem is deriving its energy from hot chemical-rich waters pouring out of underground towers. This suggests that life could have started on the deep [pb_glossary id=\"2885\"]ocean floor[\/pb_glossary] and derived energy from the heat from the Earth\u2019s interior via [pb_glossary id=\"1184\"]chemosynthesis[\/pb_glossary]. Scientists have since expanded the search for life to more unconventional places, like Jupiter\u2019s icy moon Europa.\n\n[caption id=\"attachment_4244\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.4.3-Animation-QR-Code.png\"><img class=\"size-thumbnail wp-image-551\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this animation via this QR Code.[\/caption]\n\n[video width=\"854\" height=\"480\" webm=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Miller-Urey_experiment_-_Work_by_the_C3BC_consortium_licensed_under_CC-BY-3.0.webm.480p.webm\"][\/video]\n\n<em>Animation of the original Miller-Urey 1959 [pb_glossary id=\"2653\"]<em>experiment<\/em>[\/pb_glossary] that simulated the early [pb_glossary id=\"2667\"]<em>atmosphere<\/em>[\/pb_glossary] and created amino acids from simple [pb_glossary id=\"2700\"]<em>elements<\/em>[\/pb_glossary] and compounds. <\/em>\n\nAnother possibility is that life or its building blocks came to Earth from space, carried aboard comets or other objects. Amino acids, for example, have been found within comets and [pb_glossary id=\"2202\"]meteorites[\/pb_glossary]. This intriguing possibility also implies a high likelihood of life existing elsewhere in the cosmos.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"51\"]\n\n[caption id=\"attachment_4243\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.4-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-552\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.4 via this QR Code.[\/caption]\n<h2><strong><span style=\"font-size: 28px\">8.5 Proterozoic Eon<\/span><\/strong><\/h2>\n[caption id=\"attachment_3303\" align=\"alignleft\" width=\"216\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Photosynthesis.gif\"><img class=\"wp-image-553 size-medium\" title=\"By At09kg (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APhotosynthesis.gif&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Photosynthesis-216x300.gif\" alt=\"Water and carbon dioxide go into plants, making sugar and oxygen.\" width=\"216\" height=\"300\"><\/a> Diagram showing the main products and reactants in photosynthesis. The one product that is not shown is sugar, which is the chemical energy that goes into constructing the plant, and the energy that is stored in the plant which is used later by the plant or by animals that consume the plant.[\/caption]The <strong>[pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]<\/strong>, meaning \u201cearlier life,\u201d comes after the [pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary] and ranges from 2.5 billion to 541 million years old. During this time, most of the central parts of the continents had formed and [pb_glossary id=\"2591\"]plate[\/pb_glossary] [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] processes had started. Photosynthesis by microbial organisms, such as single-celled cyanobacteria, had been slowly adding oxygen to the oceans. As cyanobacteria evolved into multicellular organisms, they completely transformed the oceans and later the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] by adding [pb_glossary id=\"1933\"]massive[\/pb_glossary] amounts of free oxygen gas (O<sub>2<\/sub>) and initiated what is called the <strong>[pb_glossary id=\"2210\"]Great Oxygenation Event[\/pb_glossary] (GOE<\/strong>). This drastic environmental change decimated the anaerobic bacteria, which could not survive in the presence of free oxygen. On the other hand, aerobic organisms could thrive in ways they could not earlier<span style=\"font-weight: 400\">. <\/span>\n\nAn oxygenated world also changed the chemistry of the planet in significant ways. For example, iron remained in [pb_glossary id=\"2705\"]solution[\/pb_glossary] in the non-oxygenated environment of the earlier [pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]. In chemistry, this is known as a reducing environment. Once the environment was oxygenated, iron combined with free oxygen to form solid precipitates of iron [pb_glossary id=\"1919\"]oxide[\/pb_glossary], such as the [pb_glossary id=\"2687\"]mineral[\/pb_glossary] hematite or magnetite. These precipitates accumulated into large [pb_glossary id=\"2687\"]mineral[\/pb_glossary] deposits with red [pb_glossary id=\"2849\"]chert[\/pb_glossary] known as [pb_glossary id=\"2931\"]banded[\/pb_glossary]-iron [pb_glossary id=\"2960\"]formations[\/pb_glossary], which are dated at about 2 billion years<span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3304\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MichiganBIF-1.jpg\"><img class=\"wp-image-371 size-medium\" title=\"By Wilson44691 (Own work) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMichiganBIF.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MichiganBIF-1-300x206.jpg\" alt=\"The rock shows red and brown layering.\" width=\"300\" height=\"206\"><\/a> Alternating bands of iron-rich and silica-rich mud, formed as oxygen combined with dissolved iron.[\/caption]&nbsp;\n\nThe [pb_glossary id=\"2960\"]formation[\/pb_glossary] of iron [pb_glossary id=\"1919\"]oxide[\/pb_glossary] [pb_glossary id=\"2687\"]minerals[\/pb_glossary] and red [pb_glossary id=\"2849\"]chert[\/pb_glossary] (see figure) in the oceans lasted a long time and prevented oxygen levels from increasing significantly, since [pb_glossary id=\"2707\"]precipitation[\/pb_glossary] took the oxygen out of the water and deposited it into the rock [pb_glossary id=\"2857\"]strata[\/pb_glossary]. As oxygen continued to be produced and [pb_glossary id=\"2687\"]mineral[\/pb_glossary] [pb_glossary id=\"2707\"]precipitation[\/pb_glossary] leveled off, [pb_glossary id=\"2815\"]dissolved[\/pb_glossary] oxygen gas eventually [pb_glossary id=\"2706\"]saturated[\/pb_glossary] the oceans and started bubbling out into the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. Oxygenation of the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] is the single biggest event that distinguishes the [pb_glossary id=\"2205\"]Archean[\/pb_glossary] and [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] environments. In addition to changing [pb_glossary id=\"2687\"]mineral[\/pb_glossary] and ocean chemistry, the GOE is also tabbed as triggering Earth\u2019s first [pb_glossary id=\"1700\"]glaciation[\/pb_glossary] event around 2.1 billion years ago, the Huron [pb_glossary id=\"1700\"]Glaciation[\/pb_glossary]. Free oxygen reacted with methane in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] to produce carbon dioxide. Carbon dioxide and methane are called greenhouse gases because they [pb_glossary id=\"3342\"]trap[\/pb_glossary] heat within the Earth\u2019s [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], like the insulated glass of a greenhouse. Methane is a more effective insulator than carbon dioxide, so as the proportion of carbon dioxide in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] increased, the [pb_glossary id=\"1715\"]greenhouse effect[\/pb_glossary] decreased, and the planet cooled.\n<h3><b>8.5.1 Rodinia<\/b><\/h3>\n[caption id=\"attachment_3305\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Rodinia_reconstruction.jpg\"><img class=\"wp-image-554 size-medium\" title=\"By John Goodge [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ARodinia_reconstruction.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Rodinia_reconstruction-300x267.jpg\" alt=\"The image shows the continents arrange in a possible orientation of Rodinia.\" width=\"300\" height=\"267\"><\/a> One possible reconstruction of Rodinia 1.1 billion years ago. Source: John Goodge, modified from (Dalziel 1997).[\/caption]<span style=\"font-weight: 400\">By the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary], lithospheric plates had formed and were moving according to [pb_glossary id=\"2591\"]plate[\/pb_glossary] [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] forces that were similar to current times. As the moving [pb_glossary id=\"2591\"]plates[\/pb_glossary] collided, the ocean basins closed to form a <strong>[pb_glossary id=\"2623\"]supercontinent[\/pb_glossary]<\/strong> called <strong>[pb_glossary id=\"2211\"]Rodinia[\/pb_glossary]<\/strong>. The [pb_glossary id=\"2623\"]supercontinent[\/pb_glossary] formed about 1 billion years ago and broke up about 750 to 600 million years ago, at the end of the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>One of the resulting fragments was a [pb_glossary id=\"2575\"]continental[\/pb_glossary] mass called <strong>[pb_glossary id=\"2212\"]Laurentia[\/pb_glossary]<\/strong> that would later become North America. Geologists have reconstructed [pb_glossary id=\"2211\"]Rodinia[\/pb_glossary] by matching and aligning ancient mountain chains, assembling the pieces like a jigsaw puzzle, and using paleomagnetics to orient to magnetic north.\n\n<span style=\"font-weight: 400\">The disagreements over these complex reconstructions is exemplified by geologists proposing at least six different models for the breakup of [pb_glossary id=\"2211\"]Rodinia[\/pb_glossary] to create Australia<\/span><span style=\"font-weight: 400\">, Antarctica<\/span><span style=\"font-weight: 400\">, parts of China<\/span><span style=\"font-weight: 400\">, the Tarim [pb_glossary id=\"2640\"]craton[\/pb_glossary] north of the Himalaya<\/span><span style=\"font-weight: 400\">, Siberia<\/span><span style=\"font-weight: 400\">, or the Kalahari [pb_glossary id=\"2640\"]craton[\/pb_glossary] of eastern Africa<\/span><span style=\"font-weight: 400\">. <\/span>This breakup created lots of shallow-water, biologically favorable environments that fostered the evolutionary breakthroughs marking the start of the next [pb_glossary id=\"2190\"]eon[\/pb_glossary], the [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary].\n\n&nbsp;\n<h3><b>8.5.2 Life Evolves<\/b><\/h3>\n[caption id=\"attachment_3306\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Stromatolites_in_Sharkbay.jpg\"><img class=\"wp-image-555 size-medium\" title=\"By Paul Harrison [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStromatolites_in_Sharkbay.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Stromatolites_in_Sharkbay-300x223.jpg\" alt=\"Picture of modern cyanobacteria (as stromatolites) in Shark Bay, Australia. The brown, blobby stromatolites are slightly sticking out of the shallow water of the ocean.\" width=\"300\" height=\"223\"><\/a> Modern cyanobacteria (as stromatolites) in Shark Bay, Australia.[\/caption]Early life in the [pb_glossary id=\"2205\"]Archean[\/pb_glossary] and earlier is poorly documented in the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record. Based on chemical evidence and evolutionary [pb_glossary id=\"2655\"]theory[\/pb_glossary], scientists propose this life would have been single-celled photosynthetic organisms, such as the cyanobacteria that created <strong>[pb_glossary id=\"2213\"]stromatolites[\/pb_glossary]<\/strong>. Cyanobacteria produced free oxygen in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] through photosynthesis. Cyanobacteria, archaea, and bacteria are <strong>[pb_glossary id=\"2214\"]prokaryotes[\/pb_glossary]<\/strong>\u2014primitive organisms made of single cells that lack cell nuclei and other organelles.\n\n[caption id=\"attachment_3307\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Stromatolites_hoyt.jpg\"><img class=\"wp-image-556 size-medium\" title=\"By Rygel, M.C. (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStromatolites_hoyt_mcr1.JPG&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Stromatolites_hoyt-300x200.jpg\" alt=\"Round structures of grey limestone are remnants of the blobby nature of the living stromatolites, fossilized in rock.\" width=\"300\" height=\"200\"><\/a> Fossil stromatolites in Saratoga Springs, New York.[\/caption]A large evolutionary step occurred during the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary] with the appearance of <strong>[pb_glossary id=\"2215\"]eukaryotes[\/pb_glossary]<\/strong> around 2.1 to 1.6 billion years ago. [pb_glossary id=\"2215\"]Eukaryotic[\/pb_glossary] cells are more complex, having nuclei and organelles. The nuclear DNA is capable of more complex replication and regulation than that of [pb_glossary id=\"2214\"]prokaryotic[\/pb_glossary] cells. The organelles include mitochondria for producing energy and chloroplasts for photosynthesis. The [pb_glossary id=\"2215\"]eukaryote[\/pb_glossary] branch in the tree of life gave rise to fungi, plants, and animals.\n\nAnother important event in Earth\u2019s biological history occurred about 1.2 billion years ago when [pb_glossary id=\"2215\"]eukaryotes[\/pb_glossary] invented sexual reproduction. Sharing genetic material from two reproducing individuals, male and female, greatly increased genetic variability in their offspring. This genetic mixing accelerated evolutionary change, contributing to more complexity among individual organisms and within ecosystems (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/7-geologic-time\/\">Chapter 7<\/a>).\n\n[pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] land surfaces were barren of plants and animals and geologic processes actively shaped the environment differently because land surfaces were not protected by leafy and woody vegetation. For example, rain and [pb_glossary id=\"3134\"]rivers[\/pb_glossary] would have caused [pb_glossary id=\"2677\"]erosion[\/pb_glossary] at much higher rates on land surfaces devoid of plants. This resulted in thick accumulations of pure [pb_glossary id=\"1915\"]quartz[\/pb_glossary] [pb_glossary id=\"2834\"]sandstone[\/pb_glossary] from the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary] such as the extensive [pb_glossary id=\"2935\"]quartzite[\/pb_glossary] [pb_glossary id=\"2960\"]formations[\/pb_glossary] in the [pb_glossary id=\"2589\"]core[\/pb_glossary] of the Uinta Mountains in Utah.\n\n[caption id=\"attachment_3308\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/DickinsoniaCostata.jpg\"><img class=\"wp-image-557 size-medium\" title=\"<a href=&quot;https:\/\/en.wikipedia.org\/wiki\/User:Verisimilus&quot; class=&quot;extiw&quot; title=&quot;wikipedia:User:Verisimilus&quot;>Verisimilus<\/a> at <a href=&quot;https:\/\/en.wikipedia.org\/wiki\/&quot; class=&quot;extiw&quot; title=&quot;wikipedia:&quot;>English Wikipedia<\/a> [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>, <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/2.5&quot;>CC BY 2.5<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ADickinsoniaCostata.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/DickinsoniaCostata-300x225.jpg\" alt=\"The fossil is a flat, leaf-shaped\" width=\"300\" height=\"225\"><\/a> Dickinsonia, a typical Ediacaran fossil.[\/caption]Fauna during the [pb_glossary id=\"2216\"]Ediacaran[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary], 635.5 to 541 million years ago are known as the <strong>[pb_glossary id=\"2216\"]Ediacaran fauna[\/pb_glossary]<\/strong>, and offer a first glimpse at the diversity of ecosystems that evolved near the end of the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary]. These soft-bodied organisms were among the first multicellular life forms and probably were similar to jellyfish or worm-like. [pb_glossary id=\"2216\"]Ediacaran fauna[\/pb_glossary] did not have hard parts like shells and were not well preserved in the rock records. However, studies suggest they were widespread in the Earth\u2019s oceans. Scientists still debate how many species were evolutionary dead-ends that became [pb_glossary id=\"1708\"]extinct[\/pb_glossary] and how many were ancestors of modern groupings. The transition of soft-bodied [pb_glossary id=\"2216\"]Ediacaran[\/pb_glossary] life to life forms with hard body parts occurred at the end of the [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] and beginning of the [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary] [pb_glossary id=\"2190\"]Eons[\/pb_glossary]. This evolutionary explosion of biological diversity made a dramatic difference in scientists\u2019 ability to understand the history of life on Earth.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"52\"]\n\n[caption id=\"attachment_4245\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.5-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-558\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.5 via this QR Code.[\/caption]\n<h2><strong>8.6 Phanerozoic Eon: Paleozoic Era<\/strong><\/h2>\n[caption id=\"attachment_3249\" align=\"alignleft\" width=\"243\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/ElrathiakingiUtahWheelerCambrian.jpg\"><img class=\"wp-image-497 size-medium\" title=\"By Wilson44691 (Own work) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AElrathiakingiUtahWheelerCambrian.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/ElrathiakingiUtahWheelerCambrian-243x300.jpg\" alt=\"It has three lobes\" width=\"243\" height=\"300\"><\/a> The trilobites had a hard exoskeleton, and is an early arthropod, the same group that includes modern insects, crustaceans, and arachnids.[\/caption]<span style=\"font-weight: 400\">The <strong>[pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary]<\/strong> [pb_glossary id=\"2190\"]Eon[\/pb_glossary] is the most recent, 541 million years ago to today, <\/span>and means \u201cvisible life\u201d because the [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary] rock record is marked by an abundance of [pb_glossary id=\"2176\"]fossils[\/pb_glossary]. [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary] organisms had hard body parts like claws, scales, shells, and bones that were more easily preserved as [pb_glossary id=\"2176\"]fossils[\/pb_glossary]. Rocks from the older [pb_glossary id=\"2218\"]Precambrian[\/pb_glossary] time are less commonly found and rarely include [pb_glossary id=\"2176\"]fossils[\/pb_glossary] because these organisms had soft body parts. [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary] rocks are younger, more common, and contain the majority of extant [pb_glossary id=\"2176\"]fossils[\/pb_glossary]. The study of rocks from this [pb_glossary id=\"2190\"]eon[\/pb_glossary] yields much greater detail. The [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary] is subdivided into three [pb_glossary id=\"2191\"]eras[\/pb_glossary], from oldest to youngest they are [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] (\u201cancient life\u201d), [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] (\u201cmiddle life\u201d), and [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] (\u201crecent life\u201d) and the remaining three chapter headings are on these three important [pb_glossary id=\"2191\"]eras[\/pb_glossary].\n\n[caption id=\"attachment_3309\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Trilobite_Heinrich_Harder.jpg\"><img class=\"wp-image-559 size-medium\" title=\"Trilobites, by Heinrich Harder, 1916.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder-300x186.jpg\" alt=\"The trilobites are crawling over the sea floor\" width=\"300\" height=\"186\"><\/a> Trilobites, by Heinrich Harder, 1916.[\/caption]\n\n<span style=\"font-weight: 400\">Life in the early <strong>[pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary]<\/strong> was dominated by [pb_glossary id=\"2883\"]marine[\/pb_glossary] organisms but by the middle of the [pb_glossary id=\"2191\"]era[\/pb_glossary] plants and animals evolved to live and reproduce on land. Fish evolved jaws and fins evolved into jointed limbs. The development of lungs allowed animals to emerge from the sea and become the first air-breathing tetrapods (four-legged animals) such as amphibians. From amphibians evolved reptiles with the amniotic egg. From reptiles evolved an early ancestor to birds and mammals <\/span><span style=\"font-weight: 400\">and their scales became feathers and fur. Near the end of the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], the [pb_glossary id=\"1429\"]Carboniferous[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary] had some of the most extensive forests in Earth\u2019s history. Their fossilized remains became the [pb_glossary id=\"2856\"]coal[\/pb_glossary] that powered the industrial revolution<\/span>\n<h3><strong>8.6.1 Paleozoic Tectonics and Paleogeography<\/strong><\/h3>\n[caption id=\"attachment_3310\" align=\"alignleft\" width=\"256\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/North_america_craton_nps.gif\"><img class=\"wp-image-560 size-medium\" title=\"USGS, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/North_america_craton_nps-256x300.gif\" alt=\"It is a map of North America\" width=\"256\" height=\"300\"><\/a> Laurentia, which makes up the North American craton.[\/caption]\n\nDuring the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], sea-levels rose and fell four times. With each sea-level rise, the majority of North America was covered by a shallow tropical ocean. Evidence of these submersions are the abundant [pb_glossary id=\"2883\"]marine[\/pb_glossary] sedimentary rocks such as [pb_glossary id=\"2851\"]limestone[\/pb_glossary] with [pb_glossary id=\"2176\"]fossils[\/pb_glossary] corals and [pb_glossary id=\"2845\"]ooids[\/pb_glossary]. Extensive sea-level [pb_glossary id=\"3119\"]falls[\/pb_glossary] are documented by widespread [pb_glossary id=\"2961\"]unconformities[\/pb_glossary]. Today, the midcontinent has extensive [pb_glossary id=\"2883\"]marine[\/pb_glossary] sedimentary rocks from the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] and western North America has thick layers of [pb_glossary id=\"2883\"]marine[\/pb_glossary] [pb_glossary id=\"2851\"]limestone[\/pb_glossary] on block faulted mountain ranges such as Mt. Timpanogos near Provo, Utah<span style=\"font-weight: 400\">.\u00a0<\/span>\n\n[caption id=\"attachment_3311\" align=\"alignright\" width=\"267\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Pangaea_continents.png\"><img class=\"wp-image-3311 size-medium\" title=\"By en:User:Kieff (File:Pangaea continents.png) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APangaea_continents.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pangaea_continents-1.png\" alt=\"Pangaea has a crescent shape.\" width=\"267\" height=\"300\"><\/a> A reconstruction of Pangaea, showing approximate positions of modern continents.[\/caption]<span style=\"font-weight: 400\">The assembly of [pb_glossary id=\"2623\"]supercontinent[\/pb_glossary] <strong>[pb_glossary id=\"3366\"]Pangea[\/pb_glossary]<\/strong>, sometimes spelled [pb_glossary id=\"3366\"]Pangaea[\/pb_glossary], was completed by the late [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary]. The name [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] was originally coined by Alfred Wegener and means \u201call land.\u201d [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] is the when all of the major continents were grouped together as one by a series of [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] events including [pb_glossary id=\"2602\"]subduction[\/pb_glossary] island-[pb_glossary id=\"2609\"]arc[\/pb_glossary] accretion, and [pb_glossary id=\"2575\"]continental[\/pb_glossary] collisions, and ocean-[pb_glossary id=\"1461\"]basin[\/pb_glossary] closures. In North America, these [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] events occurred on the east [pb_glossary id=\"2890\"]coast[\/pb_glossary] and are known as the Taconic, Acadian, Caledonian, and Alleghanian orogenies<\/span><span style=\"font-weight: 400\">.<\/span><span style=\"font-weight: 400\"> The Appalachian Mountains are the erosional remnants of these mountain building events in North America. Surrounding [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] was a global ocean [pb_glossary id=\"1461\"]basin[\/pb_glossary] known as the Panthalassa. Continued [pb_glossary id=\"2591\"]plate[\/pb_glossary] movement extended the ocean into [pb_glossary id=\"3366\"]Pangea[\/pb_glossary], forming a large bay called the Tethys Sea that eventually divided the land mass into two smaller [pb_glossary id=\"2623\"]supercontinents[\/pb_glossary], Laurasia and Gondwana. Laurasia consisted of [pb_glossary id=\"2212\"]Laurentia[\/pb_glossary] and Eurasia, and Gondwana consisted of the remaining continents of South America, Africa, India, Australia, and Antarctica. <\/span>\n\n[caption id=\"attachment_4254\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-541\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/ovT90wYrVk4[\/embed]\n\n<em>Animation of [pb_glossary id=\"2591\"]<em>plate<\/em>[\/pb_glossary] movement the last 3.3 billion years. [pb_glossary id=\"3366\"]<em>Pangea<\/em>[\/pb_glossary] occurs at the 4:40 mark.<\/em>\n\nWhile the east [pb_glossary id=\"2890\"]coast[\/pb_glossary] of North America was tectonically active during the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], the west [pb_glossary id=\"2890\"]coast[\/pb_glossary] remained mostly inactive as a [pb_glossary id=\"2598\"]passive margin[\/pb_glossary] during the early [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary]. The western edge of North American [pb_glossary id=\"2575\"]continent[\/pb_glossary] was near the present-day Nevada-Utah border and was an expansive shallow [pb_glossary id=\"2891\"]continental shelf[\/pb_glossary] near the paleoequator. However, by the [pb_glossary id=\"2227\"]Devonian[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary], the Antler [pb_glossary id=\"2585\"]orogeny[\/pb_glossary] started on the west [pb_glossary id=\"2890\"]coast[\/pb_glossary] and lasted until the Pennsylvanian [pb_glossary id=\"2192\"]Period[\/pb_glossary]. The Antler [pb_glossary id=\"2585\"]orogeny[\/pb_glossary] was a [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] [pb_glossary id=\"2619\"]island arc[\/pb_glossary] that was accreted onto western North America with the [pb_glossary id=\"2602\"]subduction[\/pb_glossary] direction away from North America. This created a mountain range on the west [pb_glossary id=\"2890\"]coast[\/pb_glossary] of North American called the Antler highlands and was the first part of building the land in the west that would eventually make most of California, Oregon, and Washington states. By the late [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary], the Sonoma [pb_glossary id=\"2585\"]orogeny[\/pb_glossary] began on the west [pb_glossary id=\"2890\"]coast[\/pb_glossary] and was another [pb_glossary id=\"2620\"]collision[\/pb_glossary] of an [pb_glossary id=\"2619\"]island arc[\/pb_glossary]. The Sonoma [pb_glossary id=\"2585\"]orogeny[\/pb_glossary] marks the change in [pb_glossary id=\"2602\"]subduction[\/pb_glossary] direction to be toward North America with a [pb_glossary id=\"2617\"]volcanic arc[\/pb_glossary] along the entire west [pb_glossary id=\"2890\"]coast[\/pb_glossary] of North America by late [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] to early [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Eras[\/pb_glossary]<span style=\"font-weight: 400\">.<\/span>\n\nBy the end of the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], the east [pb_glossary id=\"2890\"]coast[\/pb_glossary] of North America had a very high mountain range due to [pb_glossary id=\"2575\"]continental[\/pb_glossary] [pb_glossary id=\"2620\"]collision[\/pb_glossary] and the creation of [pb_glossary id=\"3366\"]Pangea[\/pb_glossary]. The west [pb_glossary id=\"2890\"]coast[\/pb_glossary] of North America had smaller and isolated [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] highlands associated with [pb_glossary id=\"2619\"]island arc[\/pb_glossary] accretion. During the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], the size of the mountains on either side of North America would flip, with the west [pb_glossary id=\"2890\"]coast[\/pb_glossary] being a more tectonically active [pb_glossary id=\"2592\"]plate boundary[\/pb_glossary] and the east [pb_glossary id=\"2890\"]coast[\/pb_glossary] changing into a [pb_glossary id=\"2598\"]passive margin[\/pb_glossary] after the breakup of [pb_glossary id=\"3366\"]Pangea[\/pb_glossary].\n<h3><strong>8.6.2 Paleozoic Evolution<\/strong><\/h3>\n[caption id=\"attachment_3312\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Anomalocaris.jpg\"><img class=\"wp-image-562 size-medium\" title=\"See page for author [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAnomalocaris_canadensis_-_reconstruction_-_MUSE.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Anomalocaris-300x200.jpg\" alt=\"The animal has two arms and large eyes.\" width=\"300\" height=\"200\"><\/a> Anomalocaris reconstruction by the MUSE science museum in Italy.[\/caption]<span style=\"font-weight: 400\">The beginning of the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary] is marked by the first appearance of hard body parts like shells, spikes, teeth, and scales; and the appearance in the rock record of most animal phyla known today. That is, most basic animal body plans appeared in the rock record during the [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary]. This sudden appearance of biological diversity is called the <strong>[pb_glossary id=\"2220\"]Cambrian Explosion[\/pb_glossary]. <\/strong>Scientists debate whether this sudden appearance is more from a rapid evolutionary diversification as a result of a warmer [pb_glossary id=\"1710\"]climate[\/pb_glossary] following the late [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2910\"]glacial[\/pb_glossary] environments, better preservation and fossilization of hard parts, or artifacts of a more complete and recent rock record. For example, fauna may have been diverse during the [pb_glossary id=\"2216\"]Ediacaran[\/pb_glossary]\u00a0[pb_glossary id=\"2192\"]Period[\/pb_glossary], setting the state for the [pb_glossary id=\"2220\"]Cambrian Explosion[\/pb_glossary], but they lacked hard body parts and would have left few [pb_glossary id=\"2176\"]fossils[\/pb_glossary] behind<\/span><span style=\"font-weight: 400\">. Regardless, during the [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary] 541\u2013485 million years ago marked the appearance of most animal phyla<\/span><span style=\"font-weight: 400\">. <\/span>\n\n[caption id=\"attachment_3313\" align=\"alignleft\" width=\"112\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Opabinia.jpg\"><img class=\"wp-image-563 size-medium\" title=\"&quot;Charles\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-112x300.jpg\" alt=\"The animal has a long trunk with claws at the end.\" width=\"112\" height=\"300\"><\/a> Original plate from Walcott's 1912 description of Opabinia, with labels: fp = frontal appendage, e = eye, ths = thoracic somites, i = intestine, ab = abdominal segment.[\/caption]\n\n<span style=\"font-weight: 400\">One of the best [pb_glossary id=\"2176\"]fossil[\/pb_glossary] sites for the [pb_glossary id=\"2220\"]Cambrian Explosion[\/pb_glossary] was discovered in 1909 by <a href=\"http:\/\/www.nasonline.org\/member-directory\/deceased-members\/20000936.html\">Charles Walcott (1850\u20131927)<\/a> in the <strong>Burgess [pb_glossary id=\"2839\"]Shale[\/pb_glossary]<\/strong> in western Canada. The Burgess [pb_glossary id=\"2839\"]Shale[\/pb_glossary] is a <strong>[pb_glossary id=\"2221\"]Lagerst\u00e4tte[\/pb_glossary]<\/strong>, a site of exceptional [pb_glossary id=\"2176\"]fossil[\/pb_glossary] preservation that includes impressions of soft body parts. This discovery allowed scientists to study [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary] animals in immense detail because soft body parts are not normally preserved and fossilized. Other [pb_glossary id=\"2221\"]Lagerst\u00e4tte[\/pb_glossary] sites of similar age in China and Utah have allowed scientist to form a detailed picture of [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary] biodiversity. The biggest mystery surrounds animals that do not fit existing lineages and are unique to that time. This includes many famous fossilized creatures: the first compound-eyed trilobites; <em>Wiwaxia<\/em>, a creature covered in spiny [pb_glossary id=\"2591\"]plates[\/pb_glossary];<em> Hallucigenia<\/em>, a walking worm with spikes;<em> Opabinia<\/em>, a five-eyed arthropod with a grappling claw; and <em>Anomalocaris<\/em>, the alpha predator of its time, complete with grasping appendages and circular [pb_glossary id=\"2698\"]mouth[\/pb_glossary] with sharp [pb_glossary id=\"2591\"]plates[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>Most notably appearing during the [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary] is an important ancestor to humans. A segmented worm called <em>Pikaia<\/em> is thought to be the earliest ancestor of the <strong>[pb_glossary id=\"2222\"]Chordata[\/pb_glossary]<\/strong> phylum that includes [pb_glossary id=\"2222\"]vertebrates[\/pb_glossary], animals with backbones<span style=\"font-weight: 400\">.\u00a0<\/span>\n\n[caption id=\"attachment_3314\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Coral_Outcrop_Flynn_Reef-1.jpg\"><img class=\"size-medium wp-image-564\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1-300x225.jpg\" alt=\"The reef has many intricacies.\" width=\"300\" height=\"225\"><\/a> A modern coral reef.[\/caption]\n\n&nbsp;\n\nBy the end of the [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary], mollusks, brachiopods, nautiloids, gastropods, graptolites, echinoderms, and trilobites covered the sea floor. Although most animal phyla appeared by the [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary], the biodiversity at the family, genus, and species level was low until the [pb_glossary id=\"2225\"]Ordovician[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary]. During the <strong>Great [pb_glossary id=\"2225\"]Ordovician[\/pb_glossary] Biodiversification Event<\/strong>, [pb_glossary id=\"2222\"]vertebrates[\/pb_glossary] and invertebrates (animals without backbone) became more diverse and complex at family, genus, and species level. The cause of the rapid speciation event is still debated but some likely causes are a combination of warm temperatures, expansive [pb_glossary id=\"2575\"]continental[\/pb_glossary] shelves near the equator, and more [pb_glossary id=\"1181\"]volcanism[\/pb_glossary] along the [pb_glossary id=\"2630\"]mid-ocean ridges[\/pb_glossary]. Some have shown evidence that an asteroid breakup event and consequent heavy [pb_glossary id=\"2202\"]meteorite[\/pb_glossary] impacts correlate with this diversification event. The additional [pb_glossary id=\"1181\"]volcanism[\/pb_glossary] added nutrients to ocean water helping support a robust ecosystem. Many life forms and ecosystems that would be recognizable in current times appeared at this time. Mollusks, corals, and arthropods in particular multiplied to dominate the oceans<span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3315\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Guadalupe_Nima2.jpg\"><img class=\"wp-image-565 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-300x206.jpg\" alt=\"The entire mountain is one big fossil.\" width=\"300\" height=\"206\"><\/a> Guadalupe National Park is made of a giant fossil reef.[\/caption]\n\nOne important evolutionary advancement during the [pb_glossary id=\"2225\"]Ordovician[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary] was [pb_glossary id=\"2898\"]reef[\/pb_glossary]-building organisms, mostly colonial coral. Corals took advantage of the ocean chemistry, using [pb_glossary id=\"1918\"]calcite[\/pb_glossary] to build large structures that resembled modern [pb_glossary id=\"2898\"]reefs[\/pb_glossary] like the Great Barrier [pb_glossary id=\"2898\"]Reef[\/pb_glossary] off the coast of Australia. These reefs housed thriving ecosystems of organisms that swam around, hid in, and crawled over them. Reefs are important to paleontologists because of their preservation potential, [pb_glossary id=\"1933\"]massive[\/pb_glossary] size, and in-place ecosystems. Few other [pb_glossary id=\"2176\"]fossils[\/pb_glossary] offer more diversity and complexity than [pb_glossary id=\"2898\"]reef[\/pb_glossary] assemblages<span style=\"font-weight: 400\">.<\/span>\n\n<span style=\"font-weight: 400\">According to evidence from [pb_glossary id=\"2910\"]glacial[\/pb_glossary] deposits,\u00a0 a small [pb_glossary id=\"1700\"]ice age[\/pb_glossary] caused sea-levels to drop and led to a major [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary] by the end of the [pb_glossary id=\"2225\"]Ordovician[\/pb_glossary]. This is the earliest of five <strong>[pb_glossary id=\"2223\"]mass extinction[\/pb_glossary]<\/strong> events documented in the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record. During this [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary], an unusually large number of species abruptly disappear in the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record (see video).\u00a0<\/span>\n\n<span style=\"font-weight: 400\">Life bounced back during the [pb_glossary id=\"2226\"]Silurian[\/pb_glossary] [pb_glossary id=\"2192\"]period[\/pb_glossary]<\/span><span style=\"font-weight: 400\">.<\/span><span style=\"font-weight: 400\">\u00a0The major evolutionary event was the development of the forward pair of gill arches into jaws, allowing fish new feeding strategies and opening up new ecological niches.<\/span>\n\n[caption id=\"attachment_4253\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-566\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/aO9mOAKXvJs[\/embed]\n\n<em>3-minute video describing [pb_glossary id=\"2223\"]<em>mass extinctions<\/em>[\/pb_glossary] and how they are\u00a0defined.<\/em>\n\n[caption id=\"attachment_3316\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Placoderm.jpg\"><img class=\"wp-image-567 size-medium\" title=\"By User:Haplochromis (Self-photographed) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABothriolepis_panderi.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Placoderm-300x264.jpg\" alt=\"This fish is covered with armor.\" width=\"300\" height=\"264\"><\/a> The placoderm Bothriolepis panderi from the Devonian of Russia[\/caption]<span style=\"font-weight: 400\">Life bounced back during the [pb_glossary id=\"2226\"]Silurian[\/pb_glossary] [pb_glossary id=\"2192\"]period[\/pb_glossary]. The [pb_glossary id=\"2192\"]period[\/pb_glossary]\u2019s major evolutionary event was the development of jaws from the forward pair of gill arches in bony fishes and sharks. Hinged jaws allowed fish to exploit new food sources and ecological niches. This [pb_glossary id=\"2192\"]period[\/pb_glossary] also included the start of armored fishes, known as the placoderms. In addition to fish and jaws, [pb_glossary id=\"2226\"]Silurian[\/pb_glossary] rocks provide the first evidence of [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] or land-dwelling plants and animals<\/span><span style=\"font-weight: 400\">. The first vascular plant, <em>Cooksonia,<\/em> had woody tissues, [pb_glossary id=\"3116\"]pores[\/pb_glossary] for gas exchange, and veins for water and food transport<\/span><span style=\"font-weight: 400\">. Insects, spiders, scorpions, and crustaceans began to inhabit moist, freshwater [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] environments<\/span><span style=\"font-weight: 400\">. \u00a0<\/span>\n\n[caption id=\"attachment_3317\" align=\"alignleft\" width=\"392\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fishapods.png\"><img class=\"wp-image-568\" title=\"By Graphic by dave souza, incorporating images by others, as description (Own work by uploader using commons sources) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0-3.0-2.5-2.0-1.0&quot;>CC BY-SA 4.0-3.0-2.5-2.0-1.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFishapods.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fishapods-300x153.png\" alt=\"Six different fish\/amphibians are shown, with variation between totally swimming and fully walking.\" width=\"392\" height=\"200\"><\/a> Several different types of fish and amphibians that led to walking on land.[\/caption]<span style=\"font-weight: 400\">The [pb_glossary id=\"2227\"]Devonian[\/pb_glossary] [pb_glossary id=\"2192\"]Period[\/pb_glossary] is called the Age of Fishes due to the rise in plated, jawed, and lobe-finned fishes . The lobe-finned fishes, which were related to the modern lungfish and coelacanth, are important for their eventual evolution into tetrapods, four-limbed [pb_glossary id=\"2222\"]vertebrate[\/pb_glossary] animals that can walk on land. \u00a0The first lobe-finned land-walking fish, named <em>Tiktaalik<\/em>, appeared about 385 million years ago and serves as a transition [pb_glossary id=\"2176\"]fossil[\/pb_glossary] between fish and early tetrapods<\/span><span style=\"font-weight: 400\">. <\/span>Though Tiktaalik was clearly a fish, it had some tetrapod structures as well. Several [pb_glossary id=\"2176\"]fossils[\/pb_glossary] from the [pb_glossary id=\"2227\"]Devonian[\/pb_glossary] are more tetrapod like than fish like but these weren\u2019t fully [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary]. The first fully [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] tetrapod arrived in the Mississippian (early [pb_glossary id=\"1429\"]Carboniferous[\/pb_glossary]) [pb_glossary id=\"2192\"]period[\/pb_glossary]. By the Mississippian (early [pb_glossary id=\"1429\"]Carboniferous[\/pb_glossary]) [pb_glossary id=\"2192\"]period[\/pb_glossary], tetrapods had evolved into two main groups, amphibians and amniotes, from a common tetrapod ancestor. The amphibians were able to breathe air and live on land but still needed water to nurture their soft eggs. The first reptile (an amniote) could live and reproduce entirely on land with hard-shelled eggs that wouldn\u2019t dry out.\n\n<span style=\"font-weight: 400\">\u00a0Land plants had also evolved into the first trees and forests<\/span><span style=\"font-weight: 400\">. Toward the end of the [pb_glossary id=\"2227\"]Devonian[\/pb_glossary], another [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary] event occurred. This [pb_glossary id=\"1708\"]extinction[\/pb_glossary], while severe, is the least temporally defined, with wide variations in the timing of the event or events. [pb_glossary id=\"2898\"]Reef[\/pb_glossary] building organisms were the hardest hit, leading to dramatic changes in [pb_glossary id=\"2883\"]marine[\/pb_glossary] ecosystems<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3318\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Arthropleura.png\"><img class=\"wp-image-569 size-medium\" title=\"By Tim Bertelink (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArthropleura.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Arthropleura-300x156.png\" alt=\"The millipede is about 2 meters long.\" width=\"300\" height=\"156\"><\/a> A reconstruction of the giant arthropod (insects and their relatives) Arthropleura.[\/caption]<span style=\"font-weight: 400\">The next time [pb_glossary id=\"2192\"]period[\/pb_glossary], called the [pb_glossary id=\"1429\"]Carboniferous[\/pb_glossary] (North American geologists have subdivided this into the Mississippian and Pennsylvanian [pb_glossary id=\"2192\"]periods[\/pb_glossary]), saw the highest levels of oxygen ever known, with forests (e.g., ferns, club mosses) and swamps dominating the landscape <\/span><span style=\"font-weight: 400\">. This helped cause\u00a0the largest arthropods ever<\/span><span style=\"font-weight: 400\">, like the millipede <\/span><i><span style=\"font-weight: 400\">Arthropleura<\/span><\/i><span style=\"font-weight: 400\">, at 2.5 meters (6.4 feet) long! It also saw the rise of a new group of animals, the reptiles. The evolutionary advantage that reptiles have over amphibians is the amniote egg (egg with a protective shell), which allows them to rely on non-aquatic environments for reproduction. This widened the [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] reach of reptiles compared to amphibians. This booming life, especially plant life, created cooling temperatures as carbon dioxide<\/span><span style=\"font-weight: 400\">\u00a0was removed from the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. By the middle [pb_glossary id=\"1429\"]Carboniferous[\/pb_glossary], these cooler temperatures led to an [pb_glossary id=\"1700\"]ice age[\/pb_glossary] (called the Karoo [pb_glossary id=\"1700\"]Glaciation[\/pb_glossary]) and less-productive forests. The reptiles fared much better than the amphibians, leading to their diversification<\/span><span style=\"font-weight: 400\">. This [pb_glossary id=\"2910\"]glacial[\/pb_glossary] event lasted into the early [pb_glossary id=\"1428\"]Permian[\/pb_glossary]<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3319\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Dimetrodon_grandis.jpg\"><img class=\"wp-image-570 size-medium\" title=\"<a href=&quot;https:\/\/en.wikipedia.org\/wiki\/User:DiBgd&quot; class=&quot;extiw&quot; title=&quot;wikipedia:User:DiBgd&quot;>DiBgd<\/a> at <a href=&quot;https:\/\/en.wikipedia.org\/wiki\/&quot; class=&quot;extiw&quot; title=&quot;wikipedia:&quot;>English Wikipedia<\/a> [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>, <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/2.5&quot;>CC BY 2.5<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ADimetrodon_grandis.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Dimetrodon_grandis-300x169.jpg\" alt=\"The animal has a large mouth with sharp teeth and a large sail on its back.\" width=\"300\" height=\"169\"><\/a> Reconstruction of Dimetrodon.[\/caption]<span style=\"font-weight: 400\">By the [pb_glossary id=\"1428\"]Permian[\/pb_glossary], with [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] assembled, the [pb_glossary id=\"2623\"]supercontinent[\/pb_glossary] led to a dryer [pb_glossary id=\"1710\"]climate[\/pb_glossary], and even more diversification and domination by the reptiles<\/span><span style=\"font-weight: 400\">. The groups that developed in this warm [pb_glossary id=\"1710\"]climate[\/pb_glossary] eventually radiated into dinosaurs. Another group, known as the synapsids, eventually evolved into mammals<\/span><span style=\"font-weight: 400\">. Synapsids, including the famous sail-backed <\/span><i><span style=\"font-weight: 400\">Dimetrodon<\/span><\/i><span style=\"font-weight: 400\"> are commonly confused with dinosaurs.<\/span><span style=\"font-weight: 400\">\u00a0Pelycosaurs (of the Pennsylvanian to early [pb_glossary id=\"1428\"]Permian[\/pb_glossary] like <\/span><i><span style=\"font-weight: 400\">Dimetrodon) <\/span><\/i><span style=\"font-weight: 400\">are the first group of synapsids that exhibit the beginnings of mammalian characteristics such as well-differentiated dentition: incisors, highly developed canines in lower and upper jaws and cheek teeth, premolars and molars. Starting in the late [pb_glossary id=\"1428\"]Permian[\/pb_glossary], a second group of synapsids, called the therapsids (or mammal-like reptiles) evolve<\/span><span style=\"font-weight: 400\">, and become the ancestors to mammals.<\/span>\n<h4><span style=\"font-weight: 400\">Permian Mass Extinction<\/span><\/h4>\n[caption id=\"attachment_2911\" align=\"alignright\" width=\"399\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/World-map-or-flood-basalts.jpg\"><img class=\"wp-image-307\" title=\"By Williamborg [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFlood_Basalt_Map.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/World-map-or-flood-basalts-300x168.jpg\" alt=\"World map of flood basalts. Note the largest is the Siberian Traps\" width=\"399\" height=\"223\"><\/a> World map of flood basalts. Note the largest is the Siberian Traps[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">The end of the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]era[\/pb_glossary] is marked by the largest [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary] in earth history. The [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]era[\/pb_glossary] had two smaller [pb_glossary id=\"2223\"]mass extinctions[\/pb_glossary], \u00a0but these were not as large as the <\/span><b>[pb_glossary id=\"1430\"]Permian Mass Extinction[\/pb_glossary]<\/b><span style=\"font-weight: 400\">, also known as the <\/span>[pb_glossary id=\"1430\"]Permian-Triassic Extinction Event[\/pb_glossary]<span style=\"font-weight: 400\">. It is estimated that up to 96% of [pb_glossary id=\"2883\"]marine[\/pb_glossary] species and 70% of land-dwelling ([pb_glossary id=\"2902\"]terrestrial[\/pb_glossary]) [pb_glossary id=\"2222\"]vertebrates[\/pb_glossary] went extinct<\/span><span style=\"font-weight: 400\">. Many famous organisms, like sea scorpions and trilobites, were never seen again in the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record. <\/span><span style=\"font-weight: 400\">What caused such a widespread [pb_glossary id=\"1708\"]extinction[\/pb_glossary] event? The exact cause is still debated, though the leading idea relates to extensive [pb_glossary id=\"1181\"]volcanism[\/pb_glossary] associated with the <strong>Siberian [pb_glossary id=\"3342\"]Traps[\/pb_glossary]<\/strong>, which are one of the largest deposits of [pb_glossary id=\"1197\"]flood basalts[\/pb_glossary] known on Earth, dating to the time of the [pb_glossary id=\"1708\"]extinction[\/pb_glossary] event<\/span><span style=\"font-weight: 400\">. The eruption size is estimated at over 3 million cubic kilometers<\/span><span style=\"font-weight: 400\"> that is approximately 4,000,000 times larger than the famous 1980 Mt. St. Helens eruption in Washington. \u00a0The unusually large [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] eruption would have contributed a large amount of toxic gases, aerosols, and greenhouse gasses into the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. Further, some evidence suggests that the [pb_glossary id=\"1181\"]volcanism[\/pb_glossary] burned vast [pb_glossary id=\"2856\"]coal[\/pb_glossary] deposits releasing methane (a greenhouse gas) into the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. As discussed in <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/15-global-climate-change\/\">Chapter 15<\/a>, greenhouse gases cause the [pb_glossary id=\"1710\"]climate[\/pb_glossary] to warm. This extensive addition of greenhouse gases from the Siberian [pb_glossary id=\"3342\"]Traps[\/pb_glossary] may have caused a runaway [pb_glossary id=\"1715\"]greenhouse effect[\/pb_glossary] that rapidly changed the [pb_glossary id=\"1710\"]climate[\/pb_glossary], acidified the oceans, disrupted food chains, disrupted carbon cycling, and caused the largest [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary]<\/span><span style=\"font-weight: 400\">.<\/span>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"53\"]\n\n[caption id=\"attachment_4248\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Video-QR-Code.png\"><img class=\"size-thumbnail wp-image-571\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this interactive activity via this QR Code.[\/caption]\n<h2><b>8.7 Phanerozoic Eon: Mesozoic Era<\/b><\/h2>\n[caption id=\"attachment_3321\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fighting_dinosaurs.jpg\"><img class=\"wp-image-572 size-medium\" title=\"By Yuya Tamai from Gifu, Japan (2014-03-25 13.04.52) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/2.0&quot;>CC BY 2.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFighting_dinosaurs_(1).jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fighting_dinosaurs-300x173.jpg\" alt=\"The dinosaurs are fighting\" width=\"300\" height=\"173\"><\/a> Perhaps the greatest fossil ever found, a velociraptor attacked a protoceratops, and both were fossilized mid sequence.[\/caption]<span style=\"font-weight: 400\">Following the [pb_glossary id=\"1430\"]Permian Mass Extinction[\/pb_glossary], the <strong>[pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary]<\/strong> (\"middle life\") was from 252 million years ago to 66 million years ago. As [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] started to break apart, mammals, birds, and flowering plants developed. The [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] is probably best known as the age of reptiles, most notably, the dinosaurs.<\/span>\n<h3><span style=\"font-weight: 400\">8.7.1 Mesozoic Tectonics and Paleogeography<\/span><\/h3>\n[caption id=\"attachment_3322\" align=\"alignleft\" width=\"200\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Pangea_animation_03.gif\"><img class=\"size-full wp-image-573\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pangea_animation_03.gif\" alt=\"The continents separate into their current configuration.\" width=\"200\" height=\"160\"><\/a> Animation showing Pangea breaking up[\/caption]\n\n&nbsp;\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"3366\"]Pangea[\/pb_glossary] started breaking up (in a region that would become eastern Canada and United States) around 210 \u00a0million years ago in the Late [pb_glossary id=\"1438\"]Triassic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Clear evidence for this includes the age of the [pb_glossary id=\"2678\"]sediments[\/pb_glossary] in the Newark Supergroup [pb_glossary id=\"2624\"]rift[\/pb_glossary] basins and the Palisades [pb_glossary id=\"1970\"]sill[\/pb_glossary] of the eastern part of North America and the age of the Atlantic [pb_glossary id=\"2885\"]ocean floor[\/pb_glossary]. Due to sea-floor spreading, the oldest rocks on the Atlantic\u2019s floor are along the [pb_glossary id=\"2890\"]coast[\/pb_glossary] of northern Africa and the east coast of \u00a0North America, while the youngest are along the [pb_glossary id=\"2630\"]mid-ocean ridge[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3323\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/age_oceanic_lith.jpg\"><img class=\"wp-image-3323 size-medium\" title=\"Image via NOAA https:\/\/www.ngdc.noaa.gov\/mgg\/ocean_age\/data\/2008\/image\/age_oceanic_lith.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/age_oceanic_lith-1.jpg\" alt=\"The map shoes colors that represent different ages.\" width=\"300\" height=\"191\"><\/a> Age of oceanic lithosphere, in millions of years. Notice the differences in the Atlantic Ocean along the coasts of the continents.[\/caption]\n\n<span style=\"font-weight: 400\">This age pattern shows how the Atlantic Ocean opened as the young Mid-Atlantic Ridge began to create the seafloor. This means the Atlantic ocean started opening and was first formed here. The southern Atlantic opened next, with South America separating from central and southern Africa. Last (happening after the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] ended) was the northernmost Atlantic, with Greenland and Scandinavia parting ways.\u00a0<\/span><span style=\"font-weight: 400\">The breaking points of each [pb_glossary id=\"2624\"]rifted[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] margin eventually turned into the passive [pb_glossary id=\"2591\"]plate[\/pb_glossary] boundaries of the east [pb_glossary id=\"2890\"]coast[\/pb_glossary] of the Americas today.<\/span>\n\n[caption id=\"attachment_4248\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Video-QR-Code.png\"><img class=\"size-thumbnail wp-image-571\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this interactive activity via this QR Code.[\/caption]\n\n[video width=\"300\" height=\"200\" mp4=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2016\/07\/PangeaEADef.mp4\"][\/video]\n\n<em><a href=\"http:\/\/emvc.geol.ucsb.edu\/2_infopgs\/IP1GTect\/aPangeaAnim.html\">Video<\/a> of [pb_glossary id=\"3366\"]<em>Pangea<\/em>[\/pb_glossary] breaking apart and [pb_glossary id=\"2591\"]<em>plates<\/em>[\/pb_glossary] moving to their present locations. By Tanya Atwater.<\/em>\n\n[caption id=\"attachment_3324\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sevierorogeny.jpg\"><img class=\"wp-image-575 size-medium\" title=\"By Pinkcorundum (Own work) [<a href=&quot;http:\/\/creativecommons.org\/publicdomain\/zero\/1.0\/deed.en&quot;>CC0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASevierorogeny.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Sevierorogeny-300x113.jpg\" alt=\"It shows faulting and a volcanic arc\" width=\"300\" height=\"113\"><\/a> Sketch of the major features of the Sevier Orogeny.[\/caption]<span style=\"font-weight: 400\">In western North America, an active [pb_glossary id=\"2591\"]plate[\/pb_glossary] margin had started with [pb_glossary id=\"2602\"]subduction[\/pb_glossary], controlling most of the [pb_glossary id=\"2576\"]tectonics[\/pb_glossary] of that region in the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary]. Another possible island-[pb_glossary id=\"2609\"]arc[\/pb_glossary] [pb_glossary id=\"2620\"]collision[\/pb_glossary] created the Sonoman [pb_glossary id=\"2585\"]Orogeny[\/pb_glossary] in Nevada during the latest [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] to the [pb_glossary id=\"1438\"]Triassic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. In the [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary], another island-[pb_glossary id=\"2609\"]arc[\/pb_glossary] [pb_glossary id=\"2620\"]collision[\/pb_glossary] caused the Nevadan [pb_glossary id=\"2585\"]Orogeny[\/pb_glossary], a large Andean-style [pb_glossary id=\"2617\"]volcanic arc[\/pb_glossary] and thrust belt<\/span><span style=\"font-weight: 400\">. The Sevier Orogeny followed in the Cretaceous, which was mainly a volcanic arc to the west and a thin-skinned fold and thrust belt to the east<\/span><span style=\"font-weight: 400\">, meaning stacks of shallow [pb_glossary id=\"3065\"]faults[\/pb_glossary] and [pb_glossary id=\"1455\"]folds[\/pb_glossary] built up the topography. Many of the structures in the Rocky Mountains today date from this [pb_glossary id=\"2585\"]orogeny[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3325\" align=\"alignright\" width=\"250\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Cretaceous_seaway.png\"><img class=\"wp-image-576 size-full\" title=\"USGS, public domain.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Cretaceous_seaway.png\" alt=\"Water is covering the middle of North America.\" width=\"250\" height=\"301\"><\/a> The Cretaceous Interior Seaway in the mid-Cretaceous.[\/caption]\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"2576\"]Tectonics[\/pb_glossary] had an influence in one more important geographic feature in North America: the [pb_glossary id=\"1440\"]Cretaceous[\/pb_glossary] Western Interior Foreland [pb_glossary id=\"1461\"]Basin[\/pb_glossary], which flooded during high sea levels forming the <strong>[pb_glossary id=\"1433\"]Cretaceous\u00a0Interior Seaway[\/pb_glossary]<\/strong>. [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] from the west was the Farallon [pb_glossary id=\"2591\"]Plate[\/pb_glossary], an [pb_glossary id=\"2581\"]oceanic[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] connected to the Pacific [pb_glossary id=\"2591\"]Plate[\/pb_glossary] (seen today as remnants such as the Juan de Fuca [pb_glossary id=\"2591\"]Plate[\/pb_glossary], off the [pb_glossary id=\"2890\"]coast[\/pb_glossary] of the Pacific Northwest). [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] was shallow at this time because a very young, hot and less dense portion of the Farallon [pb_glossary id=\"2591\"]plate[\/pb_glossary] was [pb_glossary id=\"2602\"]subducted[\/pb_glossary]. This shallow [pb_glossary id=\"2602\"]subduction[\/pb_glossary] caused a downwarping in the central part of North America<\/span><span style=\"font-weight: 400\">. High sea levels due to shallow [pb_glossary id=\"2602\"]subduction[\/pb_glossary], and increasing rates of seafloor spreading and [pb_glossary id=\"2602\"]subduction[\/pb_glossary], high temperatures, and melted ice also contributed to the high sea levels<\/span><span style=\"font-weight: 400\">. These factors allowed a shallow epicontinental seaway that extended from the Gulf of Mexico to the Arctic Ocean to divide North America into two separate land masses<\/span><span style=\"font-weight: 400\">, Laramidia to the west and Appalachia to the east, for 25 million years<\/span><span style=\"font-weight: 400\">. Many of the [pb_glossary id=\"2856\"]coal[\/pb_glossary] deposits in Utah and Wyoming formed from swamps along the shores of this seaway<\/span><span style=\"font-weight: 400\">. By the end of the [pb_glossary id=\"1440\"]Cretaceous[\/pb_glossary], cooling temperatures caused the seaway to regress<\/span><span style=\"font-weight: 400\">.<\/span>\n<h3><span style=\"font-weight: 400\">8.7.2 Mesozoic Evolution<\/span><\/h3>\n[caption id=\"attachment_3326\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Mesozoic_Scene.jpg\"><img class=\"wp-image-577 size-medium\" title=\"By Gerhard Boeggemann (File was sent by Gerhard Boeggemann. Gallery) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5&quot;>CC BY-SA 2.5<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEuropasaurus_holgeri_Scene_2.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Mesozoic_Scene-300x225.jpg\" alt=\"Several dinosaurs and their relatives are in the scene.\" width=\"300\" height=\"225\"><\/a> A Mesozoic scene from the late Jurassic.[\/caption]<span style=\"font-weight: 400\">The [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] [pb_glossary id=\"2191\"]era[\/pb_glossary] is dominated by reptiles, and more specifically, the dinosaurs. The [pb_glossary id=\"1438\"]Triassic[\/pb_glossary] saw devastated ecosystems that took over 30 million years to fully re-emerge after the [pb_glossary id=\"1430\"]Permian Mass Extinction[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. \u00a0The first appearance of many modern groups of animals that would later flourish occurred at this time. \u00a0This includes frogs (amphibians), turtles (reptiles), [pb_glossary id=\"2883\"]marine[\/pb_glossary] ichthyosaurs and plesiosaurs ([pb_glossary id=\"2883\"]marine[\/pb_glossary] reptiles), mammals, and the archosaurs. \u00a0The archosaurs (\u201cruling reptiles\u201d) include ancestral groups that went [pb_glossary id=\"1708\"]extinct[\/pb_glossary] at the end of the [pb_glossary id=\"1438\"]Triassic[\/pb_glossary], as well as the flying pterosaurs, crocodilians, and the dinosaurs. \u00a0Archosaurs, like the placental mammals after them, occupied all major environments: [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] (dinosaurs), in the air (pterosaurs), aquatic (crocodilians) and even fully [pb_glossary id=\"2883\"]marine[\/pb_glossary] habitats ([pb_glossary id=\"2883\"]marine[\/pb_glossary] crocodiles). The pterosaurs, the first [pb_glossary id=\"2222\"]vertebrate[\/pb_glossary]\u00a0group to take flight, like the dinosaurs and mammals, start small in the [pb_glossary id=\"1438\"]Triassic[\/pb_glossary].<\/span>\n\n[caption id=\"attachment_3327\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Augustasaurus_BW.jpg\"><img class=\"wp-image-578 size-medium\" title=\"By Nobu Tamura (http:\/\/spinops.blogspot.com) (Own work) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/3.0&quot;>CC BY 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAugustasaurus_BW.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Augustasaurus_BW-300x189.jpg\" alt=\"It is a swimming reptile with a long neck\" width=\"300\" height=\"189\"><\/a> A drawing of the early plesiosaur Agustasaurus from the Triassic of Nevada.[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">At the end of the [pb_glossary id=\"1438\"]Triassic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">, another [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary] event occurred, the fourth major [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary] in the geologic record. This was perhaps caused by the Central Atlantic Magmatic Province [pb_glossary id=\"1197\"]flood basalt[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. The end-[pb_glossary id=\"1438\"]Triassic[\/pb_glossary] [pb_glossary id=\"1708\"]extinction[\/pb_glossary] made certain lineages go extinct and helped spur the evolution of survivors like mammals, pterosaurs (flying reptiles), ichthyosaurs\/plesiosaurs\/mosasaurs ([pb_glossary id=\"2883\"]marine[\/pb_glossary] reptiles), and dinosaurs<\/span><span style=\"font-weight: 400\">. <\/span>\n\n[caption id=\"attachment_3328\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Megazostrodon_sp._Natural_History_Museum_-_London.jpg\"><img class=\"wp-image-579 size-medium\" title=\"By Theklan (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMegazostrodon_sp._Natural_History_Museum_-_London.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Megazostrodon_sp._Natural_History_Museum_-_London-300x200.jpg\" alt=\"It is small, less than 5 inches, and looks like a shrew\" width=\"300\" height=\"200\"><\/a> Reconstruction of the small (&lt;5\") Megazostrodon, one of the first animals considered to be a true mammal.[\/caption]<span style=\"font-weight: 400\">Mammals, as previously mentioned, got their start from a reptilian synapsid ancestor possibly in the late [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Mammals stayed small, in mainly nocturnal niches, with insects being their largest prey. The development of warm-blooded circulation and fur may have been a response to this lifestyle<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3329\" align=\"alignright\" width=\"226\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Ornithischia.png\"><img class=\"wp-image-580\" title=\"By User:Fredrik (en:User:Fredrik) [<a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a> or <a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;>CC-BY-SA-3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AOrnithischia.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ornithischia-150x150.png\" alt=\"The bones of the pubis and ischium are close to each other.\" width=\"226\" height=\"186\"><\/a> Closed structure of a ornithischian hip, which is similar to a birds.[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">In the [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary], species that were previously common, flourished due to a warmer and more tropical [pb_glossary id=\"1710\"]climate[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. The dinosaurs were relatively small animals in the [pb_glossary id=\"1438\"]Triassic[\/pb_glossary] [pb_glossary id=\"2192\"]period[\/pb_glossary] of the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary], but became truly [pb_glossary id=\"1933\"]massive[\/pb_glossary] in the [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary]. \u00a0Dinosaurs are split into two groups based on their hip structure<\/span><span style=\"font-weight: 400\">, i.e. orientation of the pubis and ischium bones in relationship to each other. \u00a0This is referred to as the \u201creptile hipped\u201d saurischians and the \u201cbird hipped\u201d ornithischians. This has recently been brought into question by a new idea for dinosaur lineage.<\/span>\n\n[caption id=\"attachment_3330\" align=\"alignleft\" width=\"227\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Saurischia.png\"><img class=\"wp-image-581\" title=\"By Fred the Oyster [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASaurischia_pelvis_structure.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Saurischia.png\" alt=\"The bones of the pubis and ischium are away from each other.\" width=\"227\" height=\"214\"><\/a> Open structure of a saurischian hip, which is similar to a lizards.[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">Most of the dinosaurs of the [pb_glossary id=\"1438\"]Triassic[\/pb_glossary] were saurischians, but all of them were bipedal. The major adaptive advantage dinosaurs had was changes in the hip and ankle bones, tucking the legs under the body for improved locomotion as opposed to the semi-erect gait of crocodiles or the sprawling posture of reptiles. In the [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary], limbs (or a lack thereof) were also important to another group of reptiles, leading to the evolution of <\/span><i><span style=\"font-weight: 400\">Eophis<\/span><\/i><span style=\"font-weight: 400\">, the oldest snake<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3331\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Beipiao1mmartyniuk.png\"><img class=\"wp-image-582 size-medium\" title=\"By Matt Martyniuk (Dinoguy2) (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABeipiao1mmartyniuk.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Beipiao1mmartyniuk-300x158.png\" alt=\"It is a feathered dinosaur with large hand claws\" width=\"300\" height=\"158\"><\/a> Therizinosaurs, like Beipiaosaurus (shown in this restoration), are known for their enormous hand claws.[\/caption]<span style=\"font-weight: 400\">There is a paucity of dinosaur [pb_glossary id=\"2176\"]fossils[\/pb_glossary] from the Early and Middle [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">, but by the Late [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary] they were dominating the planet<\/span><span style=\"font-weight: 400\">. The saurischians diversified into the giant herbivorous (plant-eating) long-necked sauropods weighing up to 100 tons and bipedal carnivorous theropods, with the possible exception of the <\/span><i><span style=\"font-weight: 400\">Therizinosaurs<\/span><\/i><span style=\"font-weight: 400\">. All of the ornithischians (e.g <\/span><i><span style=\"font-weight: 400\">Stegosaurus, Iguanodon, Triceratops, Ankylosaurus,\u00a0<\/span><\/i><i>Pachycephhlosaurus<\/i>) were herbivorous with a strong tendency to have a \u201cturtle-like\u201d beak at the tips of their mouths.\n\n[caption id=\"attachment_2488\" align=\"alignleft\" width=\"222\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Archaeopteryx_lithographica_Berlin_specimen.jpg\"><img class=\"wp-image-54 size-medium\" title=\"By H. Raab (User: Vesta) (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;>CC BY-SA 3.0<\/a> or <a href=&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;>GFDL<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArchaeopteryx_lithographica_(Berlin_specimen).jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Archaeopteryx_lithographica_Berlin_specimen-222x300.jpg\" alt=\"The fossil has bird and dinosaur features.\" width=\"222\" height=\"300\"><\/a> Iconic \u201cBerlin specimen\u201d Archaeopteryx lithographica fossil from Germany.[\/caption]&nbsp;\n\n<span style=\"font-weight: 400\">The pterosaurs grew and diversified in the [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary], and another notable arial organism developed and thrived in the [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary]: birds. When <\/span><i><span style=\"font-weight: 400\">Archeopteryx<\/span><\/i><span style=\"font-weight: 400\"> was found in the Solnhofen [pb_glossary id=\"2221\"]Lagerst\u00e4tte[\/pb_glossary] of Germany<\/span><span style=\"font-weight: 400\">, a seeming dinosaur-bird hybrid, it started the conversation on the origin of birds. The idea that birds evolved from dinosaurs occurred very early in the history of research into evolution, only a few years after Darwin\u2019s <\/span><i><span style=\"font-weight: 400\">On the Origin of Species<\/span><\/i><span style=\"font-weight: 400\">. This study used a remarkable [pb_glossary id=\"2176\"]fossil[\/pb_glossary] of <\/span><i><span style=\"font-weight: 400\">Archeopteryx<\/span><\/i><span style=\"font-weight: 400\"> from a transitional animal between dinosaurs and birds. Small meat-eating theropod dinosaurs were likely the branch that became birds due to their similar features<\/span><span style=\"font-weight: 400\">. A significant debate still exists over how and when powered flight evolved. Some have stated a running-start model<\/span><span style=\"font-weight: 400\">, while others have favored a tree-leaping gliding model<\/span><span style=\"font-weight: 400\"> or even a semi-combination: flapping to aid in climbing<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3333\" align=\"alignright\" width=\"199\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Argentinosaurus_DSC_2943.jpg\"><img class=\"wp-image-583 size-medium\" title=\"By Eva K. (Eva K.) [<a href=&quot;http:\/\/www.gnu.org\/licenses\/old-licenses\/fdl-1.2.html&quot;>GFDL 1.2<\/a> or <a href=&quot;http:\/\/artlibre.org\/licence\/lal\/en&quot;>FAL<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArgentinosaurus_DSC_2943.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Argentinosaurus_DSC_2943-199x300.jpg\" alt=\"The dinosaur is huge! 130' long and 24' high.\" width=\"199\" height=\"300\"><\/a> Reconstructed skeleton of Argentinosaurus, from Naturmuseum Senckenberg in Germany.[\/caption]<span style=\"font-weight: 400\">The [pb_glossary id=\"1440\"]Cretaceous[\/pb_glossary] saw a further diversification, specialization, and domination of the dinosaurs and other fauna. One of the biggest changes on land was the transition to angiosperm-dominated flora. Angiosperms, which are plants with flowers and seeds, had originated in the [pb_glossary id=\"1440\"]Cretaceous[\/pb_glossary]<\/span><span style=\"font-weight: 400\">, switching many plains to grasslands by the end of the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. By the end of the [pb_glossary id=\"2192\"]period[\/pb_glossary], they had replaced gymnosperms (evergreen trees) and ferns as the dominant plant in the world\u2019s forests. Haplodiploid eusocial insects (bees and ants) are descendants from [pb_glossary id=\"1439\"]Jurassic[\/pb_glossary] wasp-like ancestors that co-evolved with the flowering plants during this time [pb_glossary id=\"2192\"]period[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. The breakup of [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] not only shaped our modern world\u2019s geography, but biodiversity at the time as well. Throughout the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary], animals on the isolated, now separated island continents (formerly parts of [pb_glossary id=\"3366\"]Pangea[\/pb_glossary]), took strange evolutionary turns. This includes giant titanosaurian sauropods (<\/span><i><span style=\"font-weight: 400\">Argentinosaurus<\/span><\/i><span style=\"font-weight: 400\">) and theropods (<\/span><i><span style=\"font-weight: 400\">Giganotosaurus<\/span><\/i><span style=\"font-weight: 400\">) from South America<\/span><span style=\"font-weight: 400\">.<\/span>\n<h4><span style=\"font-weight: 400\">K-T Extinction<\/span><\/h4>\n[caption id=\"attachment_3334\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Extinction_intensity.svg_.png\"><img class=\"wp-image-584 size-medium\" title=\"After: Raup, D. &amp; Sepkoski, J. (1982). &quot;Mass extinctions in the marine fossil record&quot;. Science 215: 1501\u20131503. DOI:10.1126\/science.215.4539.1501. Rohde, R.A. &amp; Muller, R.A. (2005). &quot;Cycles in fossil diversity&quot;. Nature 434: 209-210. DOI:10.1038\/nature03339. Sepkoski, J. (2002) A Compendium of Fossil Marine Animal Genera (eds. Jablonski, D. &amp; Foote, M.) Bull. Am. Paleontol. no. 363 (Paleontological Research Institution, Ithaca, NY). Signor, P. and J. Lipps (1982) &quot;Sampling bias, gradual extinction patterns and catastrophes in the fossil record&quot;, in Geologic Implications of Impacts of Large Asteroids and Comets on the Earth, I. Silver and P. Silver Eds, Geol. Soc. Amer. Special Paper 190, Boulder Colo. p. 291-296.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-300x183.png\" alt=\"There are many spikes, but the K\/T spike is second largest to the end Perlman.\" width=\"300\" height=\"183\"><\/a> Graph of the rate of extinctions. Note the large spike at the end of the Cretaceous (labeled as K).[\/caption]\n\n<span style=\"font-weight: 400\">Similar to the end of the [pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]era[\/pb_glossary], the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary] ended with the <\/span><b>K-Pg [pb_glossary id=\"2223\"]Mass Extinction[\/pb_glossary] <\/b><span style=\"font-weight: 400\">(previously known as the <\/span><b>[pb_glossary id=\"1434\"]K-T Extinction[\/pb_glossary]<\/b><span style=\"font-weight: 400\">) 66 million years ago<\/span><span style=\"font-weight: 400\">.<\/span><span style=\"font-weight: 400\"> This [pb_glossary id=\"1708\"]extinction[\/pb_glossary] event was likely caused by a large <\/span><b>[pb_glossary id=\"1435\"]bolide[\/pb_glossary] <\/b>(<span style=\"font-weight: 400\">an extraterrestrial impactor such as an asteroid, [pb_glossary id=\"2202\"]meteoroid[\/pb_glossary], or comet) that collided with earth<\/span><span style=\"font-weight: 400\">. Ninety percent of plankton species, 75% of plant species, and all the dinosaurs went [pb_glossary id=\"1708\"]extinct[\/pb_glossary] at this time.<\/span>\n\n[caption id=\"attachment_3335\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Impact_event.jpg\"><img class=\"wp-image-585 size-medium\" title=\"By The original uploader was Fredrik at English Wikipedia [Public domain, Public domain or Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AImpact_event.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Impact_event-300x209.jpg\" alt=\"The rock is slamming into the Earth\" width=\"300\" height=\"209\"><\/a> Artist's depiction of an impact event[\/caption]<span style=\"font-weight: 400\">One of the strongest pieces of evidence comes from the [pb_glossary id=\"2700\"]element[\/pb_glossary] iridium. Quite rare on Earth, and more common in [pb_glossary id=\"2202\"]meteorites[\/pb_glossary], it has been found all over the world in higher concentrations at a particular layer of rock that formed at the time of the K-T boundary. Soon other scientists started to find evidence to back up the claim. Melted rock spheres<\/span><span style=\"font-weight: 400\">, a special type of \u201cshocked\u201d [pb_glossary id=\"1915\"]quartz[\/pb_glossary] called stishovite, that only is found at impact sites, was found in many places around the world <\/span><span style=\"font-weight: 400\">. T<\/span><span style=\"font-weight: 400\">he huge impact created a strong thermal pulse that could be responsible for global forest fires<\/span><span style=\"font-weight: 400\">, strong acid rains<\/span><span style=\"font-weight: 400\">, a corresponding abundance of ferns, the first colonizing plants after a forest fire<\/span><span style=\"font-weight: 400\">, enough debris thrown into the air to significantly cool temperatures afterward<\/span><span style=\"font-weight: 400\">, and a 2-km high [pb_glossary id=\"3194\"]tsunami[\/pb_glossary] inferred from deposits found from Texas to Alabama<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3336\" align=\"alignleft\" width=\"268\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Chicxulub_radar_topography.jpg\"><img class=\"wp-image-586 size-medium\" title=\"By NASA\/JPL-Caltech [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AChicxulub_radar_topography.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Chicxulub_radar_topography-268x300.jpg\" alt=\"The crater is circular.\" width=\"268\" height=\"300\"><\/a> The land expression of the Chicxulub crater. The other side of the crater is within the Gulf of M\u00e9xico.[\/caption]<span style=\"font-weight: 400\">Still, with all this evidence, one large piece remained missing: the crater where the [pb_glossary id=\"1435\"]bolide[\/pb_glossary] impacted. It was not until 1991 <\/span><span style=\"font-weight: 400\">that the crater was confirmed using [pb_glossary id=\"3337\"]petroleum[\/pb_glossary] company geophysical data. Even though it is the third largest confirmed crater on Earth at roughly 180 km wide, the <\/span><b>[pb_glossary id=\"1437\"]Chicxulub Crater[\/pb_glossary]<\/b><span style=\"font-weight: 400\"> was hard to find due to being partially underwater and partially obscured by the dense forest canopy of the Yucatan Peninsula<\/span><span style=\"font-weight: 400\">. Coring of the center of the impact called the peak ring contained [pb_glossary id=\"1962\"]granite[\/pb_glossary], indicating the impact was so powerful that it lifted [pb_glossary id=\"1971\"]basement[\/pb_glossary] [pb_glossary id=\"2678\"]sediment[\/pb_glossary] from the [pb_glossary id=\"2580\"]crust[\/pb_glossary] several miles toward the surface<\/span><span style=\"font-weight: 400\">. In 2010, an international team of scientists reviewed 20 years of research and blamed the impact for the [pb_glossary id=\"1708\"]extinction[\/pb_glossary]<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_3337\" align=\"alignright\" width=\"298\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/India_Geology_Zones.jpg\"><img class=\"wp-image-587 size-medium\" title=\"By CamArchGrad (From: en:Image:India Geology Zones.jpg) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AIndia_Geology_Zones.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/India_Geology_Zones-298x300.jpg\" alt=\"It covers more than 200,000 square miles\" width=\"298\" height=\"300\"><\/a> Geology of India, showing purple as Deccan Traps-related rocks.[\/caption]<span style=\"font-weight: 400\">With all of this information, it seems like the case would be closed. However, there are other events at this time which could have partially aided the demise of so many organisms. For example, sea levels are known to be slowly decreasing at the time of the K-T event, which is tied to [pb_glossary id=\"2883\"]marine[\/pb_glossary] extinctions<\/span><span style=\"font-weight: 400\">, though any study on gradual vs. sudden changes in the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record is flawed due to the incomplete nature of the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record<\/span><span style=\"font-weight: 400\">. <\/span><span style=\"font-weight: 400\">Another big event at this time was the <\/span><b>Deccan [pb_glossary id=\"3342\"]Traps[\/pb_glossary]<\/b><span style=\"font-weight: 400\">\u00a0[pb_glossary id=\"1197\"]flood basalt[\/pb_glossary] [pb_glossary id=\"1181\"]volcanism[\/pb_glossary] in India. At over 1.3 million cubic kilometers of material, it was certainly a large source of material hazardous to ecosystems at the time, and it has been suggested as at least partially responsible for the [pb_glossary id=\"1708\"]extinction[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Some have found the impact and eruptions too much of a coincidence, and have even linked the two together<\/span><span style=\"font-weight: 400\">.<\/span>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"54\"]\n\n[caption id=\"attachment_4247\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-588\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.7 via this QR Code.[\/caption]\n<h2><strong>8.8 Phanerozoic Eon: Cenozoic Era<\/strong><\/h2>\n[caption id=\"attachment_3338\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Paracertherium.png\"><img class=\"wp-image-589 size-medium\" title=\"By Tim Bertelink (Own work) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0&quot;>CC BY-SA 4.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AIndricotherium.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Paracertherium-300x234.png\" alt=\"It is grey and tall.\" width=\"300\" height=\"234\"><\/a> Paraceratherium, seen in this reconstruction, was a massive (15-20 ton, 15 foot tall) ancestor of rhinos.[\/caption]<span style=\"font-weight: 400\">The <strong>[pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]<\/strong>, meaning \u201cnew life,\u201d is known as the age of mammals because it is in this [pb_glossary id=\"2191\"]era[\/pb_glossary] that mammals came to be a dominant and large life form, including human ancestors. Birds, as well, flourished in the open niches left by the dinosaur\u2019s demise. Most of the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] has been relatively warm, with the main exception being the [pb_glossary id=\"1700\"]ice age[\/pb_glossary] that started about 2.558 million years ago and (despite recent warming) continues today<\/span><span style=\"font-weight: 400\">. [pb_glossary id=\"2576\"]Tectonic[\/pb_glossary] shifts in the west caused [pb_glossary id=\"1181\"]volcanism[\/pb_glossary], but eventually changed the long-standing [pb_glossary id=\"2602\"]subduction[\/pb_glossary] zone into a [pb_glossary id=\"2601\"]transform[\/pb_glossary] boundary.<\/span>\n<h3><span style=\"font-weight: 400\">8.8.1 Cenozoic Tectonics and Paleogeography<\/span><\/h3>\n[caption id=\"attachment_4255\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Plate-Tectonics-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-4255\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Plate-Tectonics-Youtube-QR-Code-1.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/IDTBY5WDELg[\/embed]\n\n&nbsp;\n\n<em>Animation of the last 38 million years of movement in western North America. Note, that after the ridge is [pb_glossary id=\"2602\"]<em>subducted<\/em>[\/pb_glossary], [pb_glossary id=\"2600\"]<em>convergent<\/em>[\/pb_glossary] turns to [pb_glossary id=\"2601\"]<em>transform<\/em>[\/pb_glossary] (with [pb_glossary id=\"2599\"]<em>divergent<\/em>[\/pb_glossary] inland).<\/em>\n\n[caption id=\"attachment_3339\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Shallow_subduction_Laramide_orogeny.png\"><img class=\"wp-image-3339 size-medium\" title=\"By Melanie Moreno (Archived source link) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AShallow_subduction_Laramide_orogeny.png&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Shallow_subduction_Laramide_orogeny-1.png\" alt=\"The subducting plate goes right under the overriding plate\" width=\"300\" height=\"142\"><\/a> Shallow subduction during the Laramide Orogeny.[\/caption]<span style=\"font-weight: 400\">In the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary], the [pb_glossary id=\"2591\"]plates[\/pb_glossary] of the Earth moved into more familiar places, with the biggest change being the closing of the Tethys Sea with [pb_glossary id=\"2620\"]collisions[\/pb_glossary] such as the Alps, Zagros, and Himalaya, a [pb_glossary id=\"2620\"]collision[\/pb_glossary] that started about 57 million years ago, and continues today<\/span><span style=\"font-weight: 400\">. Maybe the most significant [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] feature that occurred in the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] of North America was the conversion of the west [pb_glossary id=\"2890\"]coast[\/pb_glossary] of California from a [pb_glossary id=\"2600\"]convergent[\/pb_glossary] boundary [pb_glossary id=\"2602\"]subduction[\/pb_glossary] zone to a [pb_glossary id=\"2601\"]transform[\/pb_glossary] boundary. [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] off the [pb_glossary id=\"2890\"]coast[\/pb_glossary] of the western United States, which had occurred throughout the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary], had continued in the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]. After the Sevier [pb_glossary id=\"2585\"]Orogeny[\/pb_glossary] in the late [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary], a subsequent [pb_glossary id=\"2585\"]orogeny[\/pb_glossary] called the Laramide [pb_glossary id=\"2585\"]Orogeny[\/pb_glossary], occurred in the early [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. The Laramide was [pb_glossary id=\"2612\"]thick-skinned[\/pb_glossary], different than the Sevier [pb_glossary id=\"2585\"]Orogeny[\/pb_glossary]. It involved deeper crustal rocks, and produced bulges that would become mountain ranges like the Rockies, Black Hills, Wind [pb_glossary id=\"3134\"]River[\/pb_glossary] Range, Uinta Mountains, and the San Rafael Swell. Instead of descending directly into the [pb_glossary id=\"2586\"]mantle[\/pb_glossary], the [pb_glossary id=\"2602\"]subducting[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] shallowed out and moved eastward beneath the [pb_glossary id=\"2575\"]continental[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] affecting the overlying [pb_glossary id=\"2575\"]continent[\/pb_glossary] hundreds of miles east of the [pb_glossary id=\"2575\"]continental[\/pb_glossary] margin and building high mountains.\u00a0 This occurred because the [pb_glossary id=\"2602\"]subducting[\/pb_glossary] [pb_glossary id=\"2591\"]plate[\/pb_glossary] was so young and near the [pb_glossary id=\"2630\"]spreading center[\/pb_glossary] and the density of the [pb_glossary id=\"2591\"]plate[\/pb_glossary] was therefore low and [pb_glossary id=\"2602\"]subduction[\/pb_glossary] was hindered.\u00a0<\/span>\n\n[caption id=\"attachment_3340\" align=\"alignright\" width=\"217\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sanandreas.jpg\"><img class=\"wp-image-3340 size-medium\" title=\"By Kate Barton, David Howell, and Joe Vigil [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASanandreas.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Sanandreas-1.jpg\" alt=\"The fault runs through California.\" width=\"217\" height=\"300\"><\/a> Map of the San Andreas fault, showing relative motion.[\/caption]<span style=\"font-weight: 400\">As the [pb_glossary id=\"2630\"]mid-ocean ridge[\/pb_glossary] itself started to subduct, the relative motion had changed. [pb_glossary id=\"2602\"]Subduction[\/pb_glossary] caused a relative convergence between the [pb_glossary id=\"2602\"]subducting[\/pb_glossary] Farallon [pb_glossary id=\"2591\"]plate[\/pb_glossary] and the North American [pb_glossary id=\"2591\"]plate[\/pb_glossary]. On the other side of the [pb_glossary id=\"2630\"]mid-ocean ridge[\/pb_glossary] from the Farallon [pb_glossary id=\"2591\"]plate[\/pb_glossary] was the Pacific [pb_glossary id=\"2591\"]plate[\/pb_glossary], which was moving away from the North American [pb_glossary id=\"2591\"]plate[\/pb_glossary]. Thus, as the [pb_glossary id=\"2602\"]subduction[\/pb_glossary] zone consumed the [pb_glossary id=\"2630\"]mid-ocean ridge[\/pb_glossary], the relative movement became [pb_glossary id=\"2601\"]transform[\/pb_glossary] instead of [pb_glossary id=\"2600\"]convergent[\/pb_glossary], which went on to become the San Andreas Fault System<\/span><span style=\"font-weight: 400\">. As the San Andreas grew, it caused east-west directed [pb_glossary id=\"1445\"]extensional[\/pb_glossary] forces to spread over the western United States, creating the [pb_glossary id=\"2462\"]Basin and Range[\/pb_glossary] province<\/span><span style=\"font-weight: 400\">. The [pb_glossary id=\"2601\"]transform[\/pb_glossary] [pb_glossary id=\"3065\"]fault[\/pb_glossary] switched position over the last 18 million years, twisting the mountains around Los Angeles<\/span><span style=\"font-weight: 400\">, and new [pb_glossary id=\"3065\"]faults[\/pb_glossary] in the southeastern California deserts may become a future San Andreas-style [pb_glossary id=\"3065\"]fault[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. During this switch from [pb_glossary id=\"2602\"]subduction[\/pb_glossary] to [pb_glossary id=\"2601\"]transform[\/pb_glossary], the nearly horizontal Farallon [pb_glossary id=\"2605\"]slab[\/pb_glossary] began to sink into the [pb_glossary id=\"2586\"]mantle[\/pb_glossary]. This caused magmatism as the [pb_glossary id=\"2602\"]subducting[\/pb_glossary] [pb_glossary id=\"2605\"]slab[\/pb_glossary] sank, allowing [pb_glossary id=\"2593\"]asthenosphere[\/pb_glossary] material to rise around it. This event is called the Oligocene ignimbrite flare-up, which was one of the most significant [pb_glossary id=\"2192\"]periods[\/pb_glossary] of [pb_glossary id=\"1181\"]volcanism[\/pb_glossary] ever<\/span><span style=\"font-weight: 400\">, including the largest single confirmed eruption, the 5000 cubic kilometer Fish Canyon [pb_glossary id=\"1953\"]Tuff[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. <\/span>\n<h3><span style=\"font-weight: 400\">8.8.2 Cenozoic Evolution<\/span><\/h3>\n[caption id=\"attachment_3341\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Hominidae_chart.svg_.png\"><img class=\"wp-image-593 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-300x101.png\" alt=\"Humans are most replated to Pan (chimpanzee)\" width=\"300\" height=\"101\"><\/a> Family tree of Hominids (Hominadae).[\/caption]\n\n<span style=\"font-weight: 400\">There are five groups of early mammals in the [pb_glossary id=\"2176\"]fossil[\/pb_glossary] record, based primarily on [pb_glossary id=\"2176\"]fossil[\/pb_glossary] teeth, the hardest bone in [pb_glossary id=\"2222\"]vertebrate[\/pb_glossary] skeletons<\/span><span style=\"font-weight: 400\">. For the purpose of this text, the most important group are the Eupantotheres, that diverge into the two main groups of mammals, the marsupials (like <\/span><i><span style=\"font-weight: 400\">Sinodelphys<\/span><\/i><span style=\"font-weight: 400\">) and placentals or eutherians (like <\/span><i><span style=\"font-weight: 400\">Eomaia<\/span><\/i><span style=\"font-weight: 400\">) in the [pb_glossary id=\"1440\"]Cretaceous[\/pb_glossary] and then diversified in the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]. \u00a0The marsupials dominated on the isolated island continents of South America and Australia, and many went [pb_glossary id=\"1708\"]extinct[\/pb_glossary] in South America with the introduction of placental mammals. Some well-known mammal groups have been highly studied with interesting evolutionary stories in the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]. For example, horses started small with four toes, ended up larger and having just one toe<\/span><span style=\"font-weight: 400\">. Cetaceans ([pb_glossary id=\"2883\"]marine[\/pb_glossary] mammals like whales and dolphins) started on land from small bear-like (mesonychids) creatures in the early [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] and gradually took to water<\/span><span style=\"font-weight: 400\">. However, no study of evolution has been more studied than human evolution. <\/span><b>Hominids<\/b><span style=\"font-weight: 400\">, the name for human-like primates, started in eastern Africa several\u00a0million years ago.<\/span>\n\n[caption id=\"attachment_3342\" align=\"alignright\" width=\"199\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Lucy_Skeleton.jpg\"><img class=\"wp-image-594 size-medium\" title=\"By Andrew from Cleveland, Ohio, USA (Lucy) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.0&quot;>CC BY-SA 2.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ALucy_Skeleton.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Lucy_Skeleton-199x300.jpg\" alt=\"The fossil is about 1\/2 complete\" width=\"199\" height=\"300\"><\/a> Lucy skeleton, showing real fossil (brown) and reconstructed skeleton (white).[\/caption]<span style=\"font-weight: 400\">The first critical event in this story is an environmental change from jungle to more of a savanna<\/span><span style=\"font-weight: 400\">, probably caused by changes in Indian Ocean circulation. While bipedalism is known to have evolved before this shift<\/span><span style=\"font-weight: 400\">, it is generally believed that our bipedal ancestors (like <\/span><i><span style=\"font-weight: 400\">Australopithecus<\/span><\/i><span style=\"font-weight: 400\">) had an advantage by covering ground more easily in a more open environment compared to their non-bipedal evolutionary cousins. There is also a growing body of evidence, including the famous \u201cLucy\u201d [pb_glossary id=\"2176\"]fossil[\/pb_glossary] of an Australopithecine, that our early ancestors lived in trees<\/span><span style=\"font-weight: 400\">. Arboreal animals usually demand a high intelligence to navigate through a three-dimensional world. It is from this lineage that humans evolved, using endurance running as a means to acquire more resources and possibly even hunt<\/span><span style=\"font-weight: 400\">. This can explain many uniquely human features, from our long legs, strong achilles, lack of lower gut protection, and our wide range of running efficiencies. <\/span>\n\n[caption id=\"attachment_3343\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Spreading_homo_sapiens.png\"><img class=\"wp-image-595 size-medium\" title=\"By NordNordWest (File:Spreading homo sapiens ru.svg by Urutseg) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASpreading_homo_sapiens_la.svg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Spreading_homo_sapiens-300x141.png\" alt=\"They started in Africa and migrated toward Asia and beyond.\" width=\"300\" height=\"141\"><\/a> The hypothesized movement of the homo genus. Years are marked as to the best guess of the timing of movement.[\/caption]<span style=\"font-weight: 400\">Now that the hands are freed up, the next big step is a large brain. There have been arguments from a switch to more meat eating<\/span><span style=\"font-weight: 400\">, cooking with fire<\/span><span style=\"font-weight: 400\">, tool use<\/span><span style=\"font-weight: 400\">, and even the construct of society itself<\/span><span style=\"font-weight: 400\"> to explain this increase in brain size. Regardless of how, it was this increased cognitive power that allowed humans to reign as their ancestors moved out of Africa and explored the world, ultimately entering the Americas through land bridges like the Bering Land Bridge<\/span><span style=\"font-weight: 400\">. The details of this worldwide migration and the different branches of the hominid evolutionary tree are very complex, and best reserved for its own\u00a0course.<\/span>\n<h4><span style=\"font-weight: 400\">Anthropocene and Extinction<\/span><\/h4>\n[caption id=\"attachment_3344\" align=\"alignright\" width=\"293\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/8.8_Extinctions_Africa_Austrailia_NAmerica_Madagascar.gif\"><img class=\"wp-image-596 size-medium\" title=\"By ElinWhitneySmith at English Wikipedia (Own work by the original uploader) [Public domain], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AExtinctions_Africa_Austrailia_NAmerica_Madagascar.gif&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8_Extinctions_Africa_Austrailia_NAmerica_Madagascar-293x300.gif\" alt=\"The mammals generally decrease after humans come.\" width=\"293\" height=\"300\"><\/a> Graph showing abundance of large mammals and the introduction of humans.[\/caption]<span style=\"font-weight: 400\">Humans have had an influence on the Earth, its ecosystems and [pb_glossary id=\"1710\"]climate[\/pb_glossary]. Yet, human activity can not explain all of the changes that have occurred in the recent past. The start of the [pb_glossary id=\"1443\"]Quaternary[\/pb_glossary] [pb_glossary id=\"2192\"]period[\/pb_glossary], the last and current [pb_glossary id=\"2192\"]period[\/pb_glossary] of the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary], is marked by the start of our current [pb_glossary id=\"1700\"]ice age[\/pb_glossary] 2.58 million years ago<\/span><span style=\"font-weight: 400\">. During this time [pb_glossary id=\"2192\"]period[\/pb_glossary], [pb_glossary id=\"2467\"]ice sheets[\/pb_glossary] advanced and retreated, most likely due to [pb_glossary id=\"1701\"]Milankovitch cycles[\/pb_glossary] (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/15-global-climate-change\/\">ch. 15<\/a>). Also at this time, various cold-adapted megafauna emerged (like giant sloths, saber-tooth cats, and woolly mammoths), and most of them went [pb_glossary id=\"1708\"]extinct[\/pb_glossary] as the Earth warmed from the most recent [pb_glossary id=\"2910\"]glacial[\/pb_glossary] maximum. A long-standing debate is over the cause of these and other extinctions. Is [pb_glossary id=\"1710\"]climate[\/pb_glossary] warming to blame, or were they caused by humans<\/span><span style=\"font-weight: 400\">? Certainly, we know of recent human extinctions of animals like the dodo or passenger pigeon. Can we connect modern extinctions to extinctions in the recent past? If so, there are several ideas as to how this happened. Possibly the most widely accepted and oldest is the hunting\/overkill [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. The idea behind this [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] is that humans hunted large herbivores for food, then carnivores could not find food, and human arrival times in locations has been shown to be tied to increased [pb_glossary id=\"1708\"]extinction[\/pb_glossary] rates in many cases.<\/span>\n\n[caption id=\"attachment_3345\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Bingham_Canyon_mine_2016.jpg\"><img class=\"wp-image-597 size-medium\" title=\"By Doc Searls from Santa Barbara, USA (2016_02_16_lga-ord-slc_156) [<a href=&quot;http:\/\/creativecommons.org\/licenses\/by\/2.0&quot;>CC BY 2.0<\/a>], <a href=&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABingham_Canyon_mine_2016.jpg&quot;>via Wikimedia Commons<\/a>\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Bingham_Canyon_mine_2016-300x180.jpg\" alt=\"The image is a large hole in a mountainside.\" width=\"300\" height=\"180\"><\/a> Bingham Canyon Mine, Utah. This open pit mine is the largest man-made removal of rock in the world.[\/caption]<span style=\"font-weight: 400\">Modern human impact on the environment and the Earth as a whole is unquestioned. In fact, many scientists are starting to suggest that the rise of human civilization ended and\/or replaced the [pb_glossary id=\"1444\"]Holocene[\/pb_glossary] [pb_glossary id=\"2193\"]epoch[\/pb_glossary] and defines a new geologic time interval: the <\/span><b>[pb_glossary id=\"1442\"]Anthropocene[\/pb_glossary]<\/b><span style=\"font-weight: 400\">. Evidence for this change includes extinctions, increased tritium (hydrogen with two neutrons) due to nuclear testing, rising pollutants like carbon dioxide, more than 200 never-before seen [pb_glossary id=\"2687\"]mineral[\/pb_glossary] species that have occurred only in this [pb_glossary id=\"2193\"]epoch[\/pb_glossary]<\/span><span style=\"font-weight: 400\">, materials such as plastic and metals which will be\u00a0long lasting \"[pb_glossary id=\"2176\"]fossils[\/pb_glossary]\" in the geologic record, and large amounts of earthen material moved<\/span><span style=\"font-weight: 400\">. The biggest scientific debate with this topic is the starting point. Some say that humans\u2019 invention of agriculture would be recognized in geologic [pb_glossary id=\"2857\"]strata[\/pb_glossary] and that should be the starting point, around 12,000 years ago<\/span><span style=\"font-weight: 400\">. Others link the start of the industrial revolution and the subsequent addition of vast amounts of carbon dioxide in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]<\/span><span style=\"font-weight: 400\">. Either way, the idea is that alien geologists visiting Earth in the distant future would easily recognize the impact of humans on the Earth as the beginning of a new geologic [pb_glossary id=\"2192\"]period[\/pb_glossary].<\/span>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"55\"]\n\n[caption id=\"attachment_4249\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.8-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-598\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 8.8 via this QR Code.[\/caption]\n<h2>Summary<\/h2>\nThe changes that have occurred since the inception of Earth are vast and significant. From the oxygenation of the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], the progression of life forms, the assembly and deconstruction of several [pb_glossary id=\"2623\"]supercontinents[\/pb_glossary], to the [pb_glossary id=\"1708\"]extinction[\/pb_glossary] of more life forms than exist today, having a general understanding of these changes can put present change into a more rounded perspective.\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n[h5p id=\"56\"]\n\n[caption id=\"attachment_4250\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Ch.8-Review-QR-Code.png\"><img class=\"size-thumbnail wp-image-599\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the review quiz for Chapter 8 via this QR Code.[\/caption]\n<h2><b>References<\/b><\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n \t<li class=\"csl-entry\">Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V., 1980, Extraterrestrial cause for the [pb_glossary id=\"1440\"]cretaceous[\/pb_glossary]-tertiary [pb_glossary id=\"1708\"]extinction[\/pb_glossary]: Science, v. 208, no. 4448, p. 1095\u20131108.<\/li>\n \t<li class=\"csl-entry\">Beerling, D., 2008, The emerald planet: how plants changed Earth\u2019s history: OUP Oxford.<\/li>\n \t<li class=\"csl-entry\">Boyce, J.W., Liu, Y., Rossman, G.R., Guan, Y., Eiler, J.M., Stolper, E.M., and Taylor, L.A., 2010, Lunar apatite with [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] volatile abundances: Nature, v. 466, no. 7305, p. 466\u2013469.<\/li>\n \t<li class=\"csl-entry\">Brueckner, H.K., and Snyder, W.S., 1985, Structure of the Havallah sequence, Golconda allochthon, Nevada: Evidence for prolonged evolution in an accretionary prism: Geol. Soc. Am. Bull., v. 96, no. 9, p. 1113\u20131130.<\/li>\n \t<li class=\"csl-entry\">Brusatte, S.L., Benton, M.J., Ruta, M., and Lloyd, G.T., 2008, The first 50 Myr of dinosaur evolution: macroevolutionary pattern and morphological disparity: Biol. Lett., v. 4, no. 6, p. 733\u2013736.<\/li>\n \t<li class=\"csl-entry\">Canup, R.M., and Asphaug, E., 2001, Origin of the Moon in a giant impact near the end of the Earth\u2019s [pb_glossary id=\"2960\"]formation[\/pb_glossary]: Nature, v. 412, no. 6848, p. 708\u2013712.<\/li>\n \t<li class=\"csl-entry\">Clack, J.A., 2009, The Fish\u2013Tetrapod Transition: New [pb_glossary id=\"2176\"]Fossils[\/pb_glossary] and Interpretations: Evolution: Education and Outreach, v. 2, no. 2, p. 213\u2013223., doi: <a href=\"https:\/\/doi.org\/10\/cz257q\">10\/cz257q<\/a>.<\/li>\n \t<li class=\"csl-entry\">Cohen, K.M., Finney, S.C., Gibbard, P.L., and Fan, J.-X., 2013, The ICS International Chronostratigraphic Chart: Episodes, v. 36, no. 3, p. 199\u2013204.<\/li>\n \t<li class=\"csl-entry\">Colbert, E.H., and Morales, M.A., 1991, History of the Backboned Animals Through Time: New York: Wiley.<\/li>\n \t<li class=\"csl-entry\">De Laubenfels, M.W., 1956, Dinosaur [pb_glossary id=\"1708\"]extinction[\/pb_glossary]: one more [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary]: J. Paleontol.<\/li>\n \t<li class=\"csl-entry\">Gomes, R., Levison, H.F., Tsiganis, K., and Morbidelli, A., 2005, Origin of the cataclysmic [pb_glossary id=\"2206\"]Late Heavy Bombardment[\/pb_glossary] period of the [pb_glossary id=\"2902\"]terrestrial[\/pb_glossary] planets: Nature, v. 435, no. 7041, p. 466\u2013469.<\/li>\n \t<li class=\"csl-entry\">Hatcher, R.D., Jr, Thomas, W.A., and Viele, G.W., 1989, The Appalachian-Ouachita Orogen in the United States: Geological Society of America.<\/li>\n \t<li class=\"csl-entry\">Hosono, N., Karato, S., Makino, J., and Saitoh, T.R., 2019, [pb_glossary id=\"2902\"]Terrestrial[\/pb_glossary] [pb_glossary id=\"2672\"]magma[\/pb_glossary] ocean origin of the Moon: Nature Geoscience, p. 1., doi: <a href=\"https:\/\/doi.org\/10.1038\/s41561-019-0354-2\">10.1038\/s41561-019-0354-2<\/a>.<\/li>\n \t<li class=\"csl-entry\">Hsiao, E., 2004, Possibility of life on Europa:<\/li>\n \t<li class=\"csl-entry\">Hubble, E., 1929, A relation between distance and radial velocity among extra-galactic nebulae: Proc. Natl. Acad. Sci. U. S. A., v. 15, no. 3, p. 168\u2013173.<\/li>\n \t<li class=\"csl-entry\">Ingersoll, R.V., 1982, Triple-junction instability as cause for late [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] [pb_glossary id=\"1445\"]extension[\/pb_glossary] and fragmentation of the western United States: Geology, v. 10, no. 12, p. 621\u2013624.<\/li>\n \t<li class=\"csl-entry\">Johnson, C.M., 1991, Large-scale [pb_glossary id=\"2580\"]crust[\/pb_glossary] [pb_glossary id=\"2960\"]formation[\/pb_glossary] and [pb_glossary id=\"2590\"]lithosphere[\/pb_glossary] modification beneath Middle to Late [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] calderas and [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] fields, western North America: J. Geophys. Res. [Solid Earth], v. 96, no. B8, p. 13485\u201313507.<\/li>\n \t<li class=\"csl-entry\">Kass, M.S., 1999, Prognathodon stadtmani:(Mosasauridae) a new species from the Mancos [pb_glossary id=\"2839\"]Shale[\/pb_glossary] (lower Campanian) of western Colorado: [pb_glossary id=\"3380\"]Vertebrate[\/pb_glossary] Paleontology in Utah, Utah Geological.<\/li>\n \t<li class=\"csl-entry\">Livaccari, R.F., 1991, Role of crustal thickening and [pb_glossary id=\"1445\"]extensional[\/pb_glossary] collapse in the [pb_glossary id=\"2576\"]tectonic[\/pb_glossary]\u00a0evolution of the Sevier-Laramide [pb_glossary id=\"2585\"]orogeny[\/pb_glossary], western United States: Geology, v. 19, no. 11, p. 1104\u20131107.<\/li>\n \t<li class=\"csl-entry\">McMenamin, M.A., and Schulte McMenamin, D.L., 1990, The Emergence of Animals: The [pb_glossary id=\"2224\"]Cambrian[\/pb_glossary] Breakthrough: Columbia University Press.<\/li>\n \t<li class=\"csl-entry\">Mitrovica, J.X., Beaumont, C., and Jarvis, G.T., 1989, Tilting of [pb_glossary id=\"2575\"]continental[\/pb_glossary] interiors by the dynamical effects of [pb_glossary id=\"2602\"]subduction[\/pb_glossary]: [pb_glossary id=\"2576\"]Tectonics[\/pb_glossary].<\/li>\n \t<li class=\"csl-entry\">R\u00fccklin, M., Donoghue, P.C.J., Johanson, Z., Trinajstic, K., Marone, F., and Stampanoni, M., 2012, Development of teeth and jaws in the earliest jawed [pb_glossary id=\"2222\"]vertebrates[\/pb_glossary]: Nature, v. 491, no. 7426, p. 748\u2013751.<\/li>\n \t<li class=\"csl-entry\">Sahney, S., and Benton, M.J., 2008, Recovery from the most profound [pb_glossary id=\"2223\"]mass extinction[\/pb_glossary] of all time: Proc. Biol. Sci., v. 275, no. 1636, p. 759\u2013765.<\/li>\n \t<li class=\"csl-entry\">Salaris, M., and Cassisi, S., 2005, Evolution of stars and stellar populations: John Wiley &amp; Sons.<\/li>\n \t<li class=\"csl-entry\">Schoch, R.R., 2012, Amphibian Evolution: The life of Early Land [pb_glossary id=\"2222\"]Vertebrates[\/pb_glossary]: Wiley-Blackwell.<\/li>\n \t<li class=\"csl-entry\">Sharp, B.J., 1958, MINERALIZATION IN THE [pb_glossary id=\"1939\"]INTRUSIVE[\/pb_glossary] ROCKS IN LITTLE COTTONWOOD CANYON, UTAH: GSA Bulletin, v. 69, no. 11, p. 1415\u20131430., doi: <a href=\"https:\/\/doi.org\/10.1130\/0016-7606(1958)69[1415:MITIRI]2.0.CO;2\">10.1130\/0016-7606(1958)69[1415:MITIRI]2.0.CO;2<\/a>.<\/li>\n \t<li class=\"csl-entry\">Wiechert, U., Halliday, A.N., Lee, D.C., Snyder, G.A., Taylor, L.A., and Rumble, D., 2001, Oxygen [pb_glossary id=\"2701\"]isotopes[\/pb_glossary] and the moon-forming giant impact: Science, v. 294, no. 5541, p. 345\u2013348.<\/li>\n \t<li class=\"csl-entry\">Wilde, S.A., Valley, J.W., Peck, W.H., and Graham, C.M., 2001, Evidence from [pb_glossary id=\"3363\"]detrital[\/pb_glossary] [pb_glossary id=\"2175\"]zircons[\/pb_glossary] for the existence of [pb_glossary id=\"2575\"]continental crust[\/pb_glossary] and oceans on the Earth 4.4 Gyr ago: Nature, v. 409, no. 6817, p. 175\u2013178.<\/li>\n \t<li class=\"csl-entry\">Wood, R.A., 2019, The rise of Animals.: Scientific American, v. 320, no. 6, p. 24\u201331.<\/li>\n<\/ol>\n<\/div>","rendered":"<figure id=\"attachment_3273\" aria-describedby=\"caption-attachment-3273\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/CdC1-scaled.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3273 size-large\" title=\"By Matt Affolter\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/CdC1-scaled-1.jpg\" alt=\"The rock is a 750' spire.\" width=\"1024\" height=\"683\" \/><\/a><figcaption id=\"caption-attachment-3273\" class=\"wp-caption-text\">Spider Rock, within Canyon de Chelly National Monument, not only has a long human history with the Din\u00e9 tribe, but also has a long geologic history. The rocks are Permian in age, and formed in the desert conditions that dominated North America toward the end of the Paleozoic through the middle Mesozoic. Erosion of the canyon occurred in the Cenozoic.<\/figcaption><\/figure>\n<p><strong>KEY CONCEPTS<\/strong><\/p>\n<p><strong>By the end of this chapter, students should be able to:<\/strong><\/p>\n<ul>\n<li>Explain the big-bang <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a> and origin of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a><\/li>\n<li>Explain the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a>\u2019s origin and the consequences for Earth.<\/li>\n<li>Describe the turbulent beginning of Earth during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2203\">Hadean<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eons<\/a><\/li>\n<li>Identify the transition to modern <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">plate tectonics<\/a>, and evolution that occurred in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a><\/li>\n<li>Describe the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> evolution and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> of invertebrates with hard parts, fish, amphibians, reptiles, tetrapods, and land plants; and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonics<\/a> and sedimentation associated with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinent<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a><\/li>\n<li>Describe the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> evolution and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> of birds, dinosaurs, and mammmals; and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonics<\/a> and sedimentation associated with the breakup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a><\/li>\n<li>Describe the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> evolution of mammals and birds, paleoclimate, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonics<\/a> that shaped the modern world<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<figure id=\"attachment_2486\" aria-describedby=\"caption-attachment-2486\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/GeologicClock.png\"><img decoding=\"async\" class=\"wp-image-52 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-2486\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/GeologicClock-300&#215;288.png&#8221; alt=&#8221;The circle starts at 4.6 billion years ago, then loops around to zero.&#8221; width=&#8221;300&#8243; height=&#8221;288&#8243;&gt; Geologic time on Earth, represented circularly, to show the individual time divisions and important events. Ga=billion years ago, Ma=million years ago.<\/figcaption><\/figure>\n<p>Entire courses and careers have been based on the wide-ranging topics covering Earth\u2019s history. Throughout the long history of Earth, change has been the norm. Looking back in time, an untrained eye would see many unfamiliar life forms and terrains. The main topics studied in Earth history are paleogeography, paleontology, and paleoecology and paleoclimatology\u2014respectively, past landscapes, past organisms, past ecosystems, and past environments. This chapter will cover briefly the origin of the universe and the 4.6 billion year history of Earth. This Earth history will <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3080\">focus<\/a> on the major physical and biological events in each <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eons<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>.<\/p>\n<h2><strong>8.1 Origin of the Universe<\/strong><\/h2>\n<figure id=\"attachment_3275\" aria-describedby=\"caption-attachment-3275\" style=\"width: 349px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/HubbleDeepField.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-518\" title=\"NASA, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-300x294.jpg\" alt=\"The picture has over 1500 galaxies.\" width=\"349\" height=\"342\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-300x294.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-1024x1003.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-768x752.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-1536x1505.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-65x64.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-225x220.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField-350x343.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HubbleDeepField.jpg 1568w\" sizes=\"auto, (max-width: 349px) 100vw, 349px\" \/><\/a><figcaption id=\"caption-attachment-3275\" class=\"wp-caption-text\">The Hubble Deep Field. This image, released in 1996, is a composite long-exposure picture of one of the darkest parts of the night sky. Every light on this image that does not have diffraction spikes is believed to be an entire galaxy, with hundreds of billions of stars, demonstrating the immense size and scope of the universe.<\/figcaption><\/figure>\n<p>The universe appears to have an infinite number of galaxies and solar systems and our <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> occupies a small section of this vast entirety. The origins of the universe and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> set the context for conceptualizing the Earth\u2019s origin and early history.<\/p>\n<h3><b>8.1.1 Big-Bang Theory<\/b><\/h3>\n<figure id=\"attachment_3276\" aria-describedby=\"caption-attachment-3276\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/UniverseTimeline.jpg\"><img decoding=\"async\" class=\"wp-image-519 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3276\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/UniverseTimeline-300&#215;195.jpg&#8221; alt=&#8221;It starts small, then explodes outward&#8221; width=&#8221;300&#8243; height=&#8221;195&#8243;&gt; Timeline of expansion of the Universe<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The mysterious details of events prior to and during the origin of the universe are subject to great scientific debate. The prevailing idea about how the universe was created is called the <strong>big-bang <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a><\/strong>. Although the ideas behind the big-bang <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a> feel almost mystical, they are supported by Einstein\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a> of general relativity. Other scientific evidence, grounded in empirical observations, supports the big-bang <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a>.<\/span><\/p>\n<p><span style=\"font-weight: 400\">The big-bang <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a> proposes the universe was formed from an infinitely dense and hot <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a> of material. The bang in the title suggests there was an explosive, outward expansion of all matter and space that created atoms. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2641\">Spectroscopy<\/a> confirms that hydrogen makes up about 74% of all matter in the universe. Since its creation, the universe has been expanding for 13.8 billion years and recent observations suggest the rate of this expansion is increasing<\/span><span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<h4><span style=\"font-weight: 400\">Spectroscopy<\/span><\/h4>\n<figure id=\"attachment_3277\" aria-describedby=\"caption-attachment-3277\" style=\"width: 383px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/EM_Spectrum_Properties_edit.svg_.png\"><img decoding=\"async\" class=\"wp-image-520\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3277\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEM_Spectrum_Properties_edit.svg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/EM_Spectrum_Properties_edit.svg_-300&#215;178.png&#8221; alt=&#8221;The figure shows the various wavelengths of electromagnetic light, the scale of the wavelength, the frequency, and the temperature of objects that produces waves.&#8221; width=&#8221;383&#8243; height=&#8221;227&#8243;&gt; The electromagnetic spectrum and properties of light across the spectrum.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2641\">Spectroscopy<\/a><\/strong> is the investigation and measurement of spectra produced when materials interacts with or emits electromagnetic radiation. <em>Spectra<\/em> is the plural for <em>spectrum<\/em> which is a particular <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3186\">wavelength<\/a> from the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2642\">electromagnetic spectrum<\/a><\/strong>. Common spectra include the different colors of visible light, X-rays, ultraviolet waves, microwaves, and radio waves. Each beam of light is a unique mixture of wavelengths that combine across the spectrum to make the color we see. The light wavelengths are created or absorbed inside atoms, and each <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3186\">wavelength<\/a> signature matches a specific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a>. Even white light from the Sun, which seems like an uninterrupted continuum of wavelengths, has gaps in some wavelengths. The gaps correspond to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a> present in the Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> that act as filters for specific wavelengths. These missing wavelengths were famously observed by Joseph von Fraunhofer (1787\u20131826) in the early 1800s<\/span><span style=\"font-weight: 400\">, but it took decades before scientists were able to relate the missing wavelengths to atmospheric filtering<\/span><span style=\"font-weight: 400\">. <\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2641\">Spectroscopy<\/a> shows that the Sun is mostly made of hydrogen and helium. Applying this process to light from distant stars, scientists can calculate the abundance of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a> in a specific star and visible universe as a whole. Also, this spectroscopic information can be used as an interstellar speedometer.<\/p>\n<h4><span style=\"font-weight: 400\">Redshift<\/span><\/h4>\n<figure id=\"attachment_3278\" aria-describedby=\"caption-attachment-3278\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Dopplerfrequenz.gif\"><img decoding=\"async\" class=\"wp-image-521 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3278\" class=\"wp-caption-text\">GFDL<\/a>, <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5-2.0-1.0&quot;\">CC BY-SA 2.5-2.0-1.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ADopplerfrequenz.gif&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Dopplerfrequenz-300&#215;75.gif&#8221; alt=&#8221;In this animated image, the car moves, and the waves are pushed in the front, and stretched behind it.&#8221; width=&#8221;300&#8243; height=&#8221;75&#8243;&gt; The Doppler effect is heard as a car moves. The waves in front of the car are compressed together, making the pitch higher. The waves in the back of the car are stretched, and and the pitch gets lower.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2643\">Doppler effect<\/a><\/strong> is the same process that changes the pitch of the sound of an approaching car or ambulance from high to low as it passes. When an object emits waves, such as light or sound, while moving toward an observer, the wavelengths get compressed. In sound, this results in a shift to a higher pitch. When an object moves away from an observer, the wavelengths are extended, producing a lower pitched sound. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2643\">Doppler effect<\/a> is used on light emitted from stars and galaxies to determine their speed and direction of travel<\/span><span style=\"font-weight: 400\">. Scientists, including Vesto Slipher (1875\u20131969)<\/span><span style=\"font-weight: 400\"> and Edwin Hubble (1889\u20131953)<\/span><span style=\"font-weight: 400\">, examined galaxies both near and far and found that almost all galaxies outside of our galaxy are moving away from each other, and us. Because the light wavelengths of receding objects are extended, visible light is shifted toward the red end of the spectrum, called a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2195\">redshift<\/a><\/strong>. In addition, Hubble noticed that galaxies that were farther away from Earth also had the greater amount of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2195\">redshift<\/a>, and thus, the faster they are traveling away from us. The only way to reconcile this information is to deduce the universe is still expanding. Hubble\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2651\">observation<\/a> forms the basis of big-bang <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a>.<\/span><\/p>\n<figure id=\"attachment_4252\" aria-describedby=\"caption-attachment-4252\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Example-of-Doppler-Shift-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-522\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Example-of-Doppler-Shift-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4252\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Example of Doppler Shift using car horn\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/a3RfULw7aAY?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h4><span style=\"font-weight: 400\">Cosmic Microwave Background Radiation<\/span><\/h4>\n<figure id=\"attachment_3279\" aria-describedby=\"caption-attachment-3279\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/CosmicBackground.png\"><img decoding=\"async\" class=\"wp-image-523 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3279\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/CosmicBackground-300&#215;150.png&#8221; alt=&#8221;The map is blue with slight bright spots of green\/yellow&#8221; width=&#8221;300&#8243; height=&#8221;150&#8243;&gt; Heat map, showing slight variations in background heat, which is related to cosmic background radiation.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Another strong indication of the big-bang is <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2196\">cosmic microwave background radiation<\/a><\/strong>. Cosmic radiation was accidentally discovered by Arno Penzias (1933\u2013) and Robert Woodrow Wilson (1936\u2013) <\/span>when they were trying to eliminate background noise from a communication satellite. They discovered very faint traces of energy or heat that are omnipresent across the universe. This energy was left behind from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2194\">big bang<\/a>, like an echo.<\/p>\n<h3><b>8.1.2 Stellar Evolution<\/b><\/h3>\n<figure id=\"attachment_3280\" aria-describedby=\"caption-attachment-3280\" style=\"width: 400px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Nucleosynthesis_periodic_table.svg_-1.png\"><img decoding=\"async\" class=\"wp-image-524\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3280\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a> or <a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ANucleosynthesis_periodic_table.svg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Nucleosynthesis_periodic_table.svg_-1-300&#215;150.png&#8221; alt=&#8221;This shows the period table. Some elements are made in the big bang, some are made in stellar processes.&#8221; width=&#8221;400&#8243; height=&#8221;200&#8243;&gt; Origin of the elements on the periodic table, showing the important role the star life cycle plays.<\/figcaption><\/figure>\n<p>Astronomers think the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2194\">big bang<\/a> created lighter <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a>, mostly hydrogen and smaller amounts of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a> helium, lithium, and beryllium. Another process must be responsible for creating the other 90 heavier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a>. The current model of stellar evolution explains the origins of these heavier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a>.<\/p>\n<h4><span style=\"font-weight: 400\">Birth of a star<\/span><\/h4>\n<figure id=\"attachment_3281\" aria-describedby=\"caption-attachment-3281\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Eagle_nebula_pillars.jpg\"><img decoding=\"async\" class=\"wp-image-525 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3281\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Eagle_nebula_pillars-300&#215;296.jpg&#8221; alt=&#8221;It is several large column of gas&#8221; width=&#8221;300&#8243; height=&#8221;296&#8243;&gt; Section of the Eagle Nebula known as &#8220;The Pillars of Creation.&#8221;<\/figcaption><\/figure>\n<p>Stars start their lives as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a> floating in cold, spinning clouds of gas and dust known as <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebulas<\/a><\/strong>. Gravitational attraction or perhaps a nearby stellar explosion causes the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a> to condense and spin into disk shape. In the center of this disk shape a new star is born under the force of gravity. The spinning whirlpool concentrates material in the center, and the increasing gravitational forces collect even more mass. Eventually, the immensely <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3333\">concentrated<\/a> mass of material reaches a critical point of such intense heat and pressure it initiates <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a>.<\/p>\n<h4><span style=\"font-weight: 400\">Fusion<\/span><\/h4>\n<figure id=\"attachment_3282\" aria-describedby=\"caption-attachment-3282\" style=\"width: 211px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/FusionintheSun.svg_.png\"><img decoding=\"async\" class=\"wp-image-526 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3282\" class=\"wp-caption-text\">Borb<\/a> [<a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFusionintheSun.svg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/FusionintheSun.svg_-211&#215;300.png&#8221; alt=&#8221;There are 3 steps&#8221; width=&#8221;211&#8243; height=&#8221;300&#8243;&gt; General diagram showing the series of fusion steps that occur in the sun.<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">Fusion<\/a> is not a chemical reaction. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">Fusion<\/a><\/strong> is a nuclear reaction in which two or more nuclei, the centers of atoms, are forced together and combine creating a new larger atom. This reaction gives off a tremendous amount of energy, usually as light and solar radiation. An <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a> such as hydrogen combines or fuses with other hydrogen atoms in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a> of a star to become a new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a>, in this case, helium. Another product of this process is energy, such as solar radiation that leaves the Sun and comes to the Earth as light and heat. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">Fusion<\/a> is a steady and predictable process, which is why we call this the main phase of a star\u2019s life. During its main phase, a star turns hydrogen into helium. Since most stars contain plentiful amounts of hydrogen, the main phase may last billions of years, during which their size and energy output remains relatively steady.<\/p>\n<figure id=\"attachment_3283\" aria-describedby=\"caption-attachment-3283\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Star_life_cycles_red_dwarf_en.svg_.png\"><img decoding=\"async\" class=\"wp-image-527 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3283\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStar_life_cycles_red_dwarf_en.svg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Star_life_cycles_red_dwarf_en.svg_-300&#215;200.png&#8221; alt=&#8221;It shows many steps&#8221; width=&#8221;300&#8243; height=&#8221;200&#8243;&gt; Two main paths of a star&#8217;s life cycle, depending on mass.<\/figcaption><\/figure>\n<p>The giant phase in a star\u2019s life occurs when the star runs out of hydrogen for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a>. If a star is large enough, it has sufficient heat and pressure to start fusing helium into heavier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a>. This style of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> is more energetic and the higher energy and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2689\">temperature<\/a> expand the star to a larger size and brightness. This giant phase is predicted to happen to our Sun in another few billion years, growing the radius of the Sun to Earth\u2019s orbit, which will render life impossible. The mass of a star during its main phase is the primary factor in determining how it will evolve. If the star has enough mass and reaches a point at which the primary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a>, such as helium, is exhausted, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> continues using new, heavier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a>. This occurs over and over in very large stars, forming progressively heavier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a> like carbon and oxygen. Eventually, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> reaches its limit as it forms iron and nickel. This progression explains the abundance of iron and nickel in rocky objects, like Earth, within the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a>. At this point, any further <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> absorbs energy instead of giving it off, which is the beginning of the end of the star\u2019s life<span style=\"font-weight: 400\">.<\/span><\/p>\n<h4><span style=\"font-weight: 400\">Death of a Star<\/span><\/h4>\n<figure id=\"attachment_3284\" aria-describedby=\"caption-attachment-3284\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Crab_Nebula.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-528 size-medium\" title=\"NASA and ESA image, public domain.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-300x300.jpg\" alt=\"The picture is of dust and gas.\" width=\"300\" height=\"300\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-300x300.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-1024x1024.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-150x150.jpg 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-768x768.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-65x65.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-225x225.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula-350x350.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Crab_Nebula.jpg 1200w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3284\" class=\"wp-caption-text\">Hubble space telescope image of the Crab Nebula, the remnants of a supernova that occurred in 1054 C.E.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The death of a star can range from spectacular to other-worldly (see figure). Stars like the Sun form a planetary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebula<\/a>, which comes from the collapse of the star\u2019s outer layers in an event like the implosion of a building. In the tug-of-war between gravity\u2019s inward pull and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion\u2019s<\/a> outward push, gravity instantly takes over when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> ends, with the outer gasses puffing away to form a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebula<\/a>. More <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> stars do this as well but with a more energetic collapse, which starts another type of energy release mixed with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a> creation known as a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2199\">supernova<\/a>. In a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2199\">supernova<\/a><\/strong>, the collapse of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a> suddenly halts, creating a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> outward-propagating shock wave. A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2199\">supernova<\/a> is the most energetic explosion in the universe short of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2194\">big bang<\/a>. The energy release is so significant the ensuing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a> can make every <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a> up through uranium<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3285\" aria-describedby=\"caption-attachment-3285\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/08.1_blackhole_NASA_2019.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-529 size-medium\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-300x175.png\" alt=\"Blurry telescope photo of a fuzzy red halo around an entirely black center. The black center represents the first photograph of an actual black hole captured in 2019.\" width=\"300\" height=\"175\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-300x175.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-768x447.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-65x38.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-225x131.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019-350x204.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/08.1_blackhole_NASA_2019.png 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3285\" class=\"wp-caption-text\">A black hole and its shadow have been captured in an image for the first time in 2019, a historic feat by an international network of radio telescopes called the Event Horizon Telescope (Source: NASA)<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The death of the star can result in the creation of white dwarfs, neutron stars, or black holes. Following their deaths, stars like the Sun turn into white dwarfs<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<p>White dwarfs are hot star embers, formed by packing most of a dying star\u2019s mass into a small and dense object about the size of Earth. Larger stars may explode in a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2199\">supernova<\/a> that packs their mass even tighter to become neutron stars. Neutron stars are so dense that protons combine with electrons to form neutrons. The largest stars collapse their mass even further, becoming objects so dense that light cannot escape their gravitational grasp. These are the infamous black holes and the details of the physics of what occurs in them are still up for debate.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-48\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-48\" class=\"h5p-iframe\" data-content-id=\"48\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.1 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4240\" aria-describedby=\"caption-attachment-4240\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.1-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-530\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.1-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4240\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.1 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>8.2 Origin of the Solar System: The Nebular Hypothesis<\/strong><\/h2>\n<figure id=\"attachment_3286\" aria-describedby=\"caption-attachment-3286\" style=\"width: 252px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/M42proplyds.jpg\"><img decoding=\"async\" class=\"wp-image-531\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3286\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/M42proplyds-300&#215;224.jpg&#8221; alt=&#8221;It is a small cloud&#8221; width=&#8221;252&#8243; height=&#8221;188&#8243;&gt; Small protoplanetary discs in the Orion Nebula<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Our <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> formed at the same time as our Sun as described in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2200\">nebular hypothesis<\/a>. The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2200\">nebular hypothesis<\/a><\/strong> is the idea that a spinning cloud of dust made of mostly light <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">elements<\/a>, called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebula<\/a>, flattened into a protoplanetary disk, and became a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> consisting of a star with orbiting planets<\/span><span style=\"font-weight: 400\">. <\/span>The spinning <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebula<\/a> collected the vast majority of material in its center, which is why the sun Accounts for over 99% of the mass in our <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a>.<\/p>\n<p>&nbsp;<\/p>\n<h3><b>8.2.1 Planet Arrangement and Segregation<\/b><\/h3>\n<figure id=\"attachment_3287\" aria-describedby=\"caption-attachment-3287\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fomalhaut_Circumstellar_Disk.jpg\"><img decoding=\"async\" class=\"wp-image-532 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3287\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fomalhaut_Circumstellar_Disk-300&#215;240.jpg&#8221; alt=&#8221;The disc is lop sided&#8221; width=&#8221;300&#8243; height=&#8221;240&#8243;&gt; This disk is asymmetric, possibly because of a large gas giant planet orbiting relatively far from the star.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">As our <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> formed, the nebular cloud of dispersed particles developed distinct <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2689\">temperature<\/a> zones. Temperatures were very high close to the center, only allowing condensation of metals and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2709\">silicate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> with high melting points. Farther from the Sun, the temperatures were lower, allowing the condensation of lighter gaseous molecules such as methane, ammonia, carbon dioxide, and water<\/span><span style=\"font-weight: 400\">. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2689\">temperature<\/a> differentiation resulted in the inner four planets of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> becoming rocky, and the outer four planets becoming gas giants.<\/span><\/p>\n<figure id=\"attachment_3288\" aria-describedby=\"caption-attachment-3288\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/HL_Tau_protoplanetary_disk.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-533 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-300x300.jpg\" alt=\"The orange disk has zones that are darker, indicating the planets are growing by using that material in the disk.\" width=\"300\" height=\"300\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-300x300.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-150x150.jpg 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-65x65.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-225x225.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk-350x350.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/HL_Tau_protoplanetary_disk.jpg 480w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3288\" class=\"wp-caption-text\">Image by the ALMA telescope of HL Tauri and its protoplanetary disk, showing grooves formed as planets absorb material in the disk.<\/figcaption><\/figure>\n<p>Both rocky and gaseous planets have a similar growth model. Particles of dust, floating in the disc were attracted to each other by static charges and eventually, gravity. As the clumps of dust became bigger, they interacted with each other\u2014colliding, sticking, and forming proto-planets. The planets continued to grow over the course of many thousands or millions of years, as material from the protoplanetary disc was added. Both rocky and gaseous planets started with a solid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a>. Rocky planets built more rock on that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a>, while gas planets added gas and ice. Ice giants formed later and on the furthest edges of the disc, accumulating less gas and more ice. That is why the gas-giant planets Jupiter and Saturn are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2831\">composed<\/a> of mostly hydrogen and helium gas, more than 90%. The ice giants Uranus and Neptune are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2831\">composed<\/a> of mostly methane ices and only about 20% hydrogen and helium gases.<\/p>\n<figure id=\"attachment_4330\" aria-describedby=\"caption-attachment-4330\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-534 size-medium\" title=\"A. Angelich (NRAO\/AUI\/NSF)\/ALMA (ESO\/NAOJ\/NRAO)\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-300x255.jpg\" alt=\"It shows a ring of ice around the star\" width=\"300\" height=\"255\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-300x255.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-1024x870.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-768x652.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-65x55.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-225x191.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis-350x297.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Artists_impression_of_the_water_snowline_around_the_young_star_V883_Orionis.jpg 1280w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4330\" class=\"wp-caption-text\">This artist\u2019s impression of the water snowline around the young star V883 Orionis, as detected with ALMA.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>The planetary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2831\">composition<\/a> of the gas giants is clearly different from the rocky planets. Their size is also dramatically different for two reasons: First, the original planetary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebula<\/a> contained more gases and ices than metals and rocks. There was abundant hydrogen, carbon, oxygen, nitrogen, and less silicon and iron, giving the outer planets more building material. Second, the stronger gravitational pull of these giant planets allowed them to collect large quantities of hydrogen and helium, which could not be collected by weaker gravity of the smaller planets.<\/p>\n<figure id=\"attachment_2515\" aria-describedby=\"caption-attachment-2515\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/02.2_TolucaMeteorite.jpg\"><img decoding=\"async\" class=\"wp-image-83 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-2515\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ATolucaMeteorite.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/02.2_TolucaMeteorite-300&#215;225.jpg&#8221; alt=&#8221;The meteorite is polished showing the Widmanst\u00e4tten Pattern.&#8221; width=&#8221;300&#8243; height=&#8221;225&#8243;&gt; A polished fragment of the iron-rich Toluca Meteorite, with octahedral Widmanst\u00e4tten Pattern.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">Jupiter\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> gravity further shaped the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> and growth of the inner rocky planets. As the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2197\">nebula<\/a> started to coalesce into planets, Jupiter\u2019s gravity accelerated the movement of nearby materials, generating destructive collisions rather than constructively gluing material together<\/span><span style=\"font-weight: 400\">. <\/span>These collisions created the asteroid belt, an unfinished planet, located between Mars and Jupiter. This asteroid belt is the source of most <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a><\/strong> that currently impact the Earth. Study of asteroids and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a> help geologist to determine the age of Earth and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2831\">composition<\/a> of its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>. Jupiter\u2019s gravity may also explain Mars\u2019 smaller mass, with the larger planet consuming material as it migrated from the inner to outer edge of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a><span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<h4><span style=\"font-weight: 400\">Pluto and planet definition<\/span><\/h4>\n<figure id=\"attachment_3290\" aria-describedby=\"caption-attachment-3290\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/EightTNOs.png\"><img decoding=\"async\" class=\"wp-image-535 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3290\" class=\"wp-caption-text\">GFDL<\/a>, <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/2.5-2.0-1.0&quot;\">CC BY-SA 2.5-2.0-1.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEightTNOs.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/EightTNOs-300&#215;218.png&#8221; alt=&#8221;It shows many objects&#8221; width=&#8221;300&#8243; height=&#8221;218&#8243;&gt; Eight largest objects discovered past Neptune.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The outermost part of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> is known as the Kuiper belt, which is a scattering of rocky and icy bodies. Beyond that is the Oort cloud, a zone filled with small and dispersed ice traces. These two locations are where most comets form and continue to orbit, and objects found here have relatively irregular orbits compared to the rest of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a><\/span><span style=\"font-weight: 400\">. <\/span>Pluto, formerly the ninth planet, is located in this region of space. The XXVIth General Assembly of the International Astronomical Union (IAU) stripped Pluto of planetary status in 2006 because scientists discovered an object more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> than Pluto, which they named Eris. The IAU decided against including Eris as a planet, and therefore, excluded Pluto as well. The IAU narrowed the definition of a planet to three criteria: 1) enough mass to have gravitational forces that force it to be rounded, 2) not <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> enough to create <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2198\">fusion<\/a>, and 3) large enough to be in a cleared orbit, free of other planetesimals that should have been incorporated at the time the planet formed. Pluto passed the first two parts of the definition, but not the third. Pluto and Eris are currently classified as dwarf planets.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-49\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-49\" class=\"h5p-iframe\" data-content-id=\"49\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.2 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4241\" aria-describedby=\"caption-attachment-4241\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.2-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-536\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.2-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4241\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.2 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-size: 28px\">8.3 Hadean Eon<\/span><\/h2>\n<figure id=\"attachment_3270\" aria-describedby=\"caption-attachment-3270\" style=\"width: 232px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/17.18_Geologic_Time_Scale_with_years-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3270 size-medium\" title=\"Image by Belinda Madsen\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/17.18_Geologic_Time_Scale_with_years-1-1.jpg\" alt=\"The Geologic Time Scale with an age of each unit shown by a scale\" width=\"232\" height=\"300\" \/><\/a><figcaption id=\"caption-attachment-3270\" class=\"wp-caption-text\">Geologic Time Scale with ages shown<\/figcaption><\/figure>\n<p>Geoscientists use the geological time scale to assign relative age names to events and rocks, separating major events in Earth\u2019s history based on significant changes as recorded in rocks and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a>. This section summarizes the most notable events of each major time interval. For a breakdown on how these time intervals are chosen and organized, see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/7-geologic-time\/\">chapter 7<\/a>.<\/p>\n<p><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2203\">Hadean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a>, named after the Greek god and ruler of the underworld Hades, is the oldest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">eon<\/a> and dates from 4.5\u20134.0 billion years ago<\/span><span style=\"font-weight: 400\">. \u00a0<\/span><\/p>\n<figure id=\"attachment_3244\" aria-describedby=\"caption-attachment-3244\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Hadean.png\"><img decoding=\"async\" class=\"wp-image-491 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3244\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AHadean.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Hadean-300&#215;161.png&#8221; alt=&#8221;The surface of Earth is full of volcanoes.&#8221; width=&#8221;300&#8243; height=&#8221;161&#8243;&gt; Artist&#8217;s impression of the Earth in the Hadean.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">This time represents Earth\u2019s earliest history, during which the planet was characterized by a partially molten surface, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a>, and asteroid impacts. Several mechanisms made the newly forming Earth incredibly hot: gravitational <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1446\">compression<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2966\">radioactive<\/a> decay, and asteroid impacts. Most of this initial heat still exists inside the Earth. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2203\">Hadean<\/a> was originally defined as the birth of the planet occurring 4.0 billion years ago and preceding the existence of many rocks and life forms. However, geologists have dated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> at 4.4 billion years, with evidence that liquid water was present<\/span><span style=\"font-weight: 400\">. <\/span><span style=\"font-weight: 400\"> There is possibly even evidence of life existing over 4.0 billion years ago<\/span><span style=\"font-weight: 400\">. However, the most reliable record for early life, the microfossil record, starts at 3.5 billion years ago<\/span><span style=\"font-weight: 400\">. <\/span><\/p>\n<h3><b>8.3.1 Origin of Earth&#8217;s Crust<\/b><\/h3>\n<figure id=\"attachment_3291\" aria-describedby=\"caption-attachment-3291\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MohoDepth.png\"><img decoding=\"async\" class=\"wp-image-538 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3291\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMohomap.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MohoDepth-300&#215;167.png&#8221; alt=&#8221;Places with mountain building have a deeper moho.&#8221; width=&#8221;300&#8243; height=&#8221;167&#8243;&gt; The global map of the depth of the moho, or thickness of the crust.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">As Earth cooled from its molten state, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> started to crystallize and settle resulting in a separation of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> based on density and the creation of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a>, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a>. The earliest Earth was chiefly molten material and would have been rounded by gravitational forces so it resembled a ball of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2673\">lava<\/a> floating in space. As the outer part of the Earth slowly cooled, the high melting-point <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> (see <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1174\">Bowen\u2019s Reaction Series<\/a> in <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>) formed solid slabs of early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>. These slabs were probably unstable and easily reabsorbed into the liquid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2672\">magma<\/a> until the Earth cooled enough to allow numerous larger fragments to form a thin primitive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>. Scientists generally assume this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a> was <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2581\">oceanic<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1956\">mafic<\/a> in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2831\">composition<\/a>, and littered with impacts, much like the Moon\u2019s current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>. There is still some debate over when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">plate tectonics<\/a> started, which would have led to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1954\">felsic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a><\/span><span style=\"font-weight: 400\">. Regardless of this, as Earth cooled and solidified, less dense <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1954\">felsic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> floated to the surface of the Earth to form the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>, while the denser <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1956\">mafic<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1957\">ultramafic<\/a> materials sank to form the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a> and the highest-density iron and nickel sank into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a>. This differentiated the Earth from a homogenous planet into a heterogeneous one with layers of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1954\">felsic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1956\">mafic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1957\">ultramafic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a>, and iron and nickel <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a>.<\/span><\/p>\n<h3><b>8.3.2 Origin of the Moon<\/b><\/h3>\n<figure id=\"attachment_3292\" aria-describedby=\"caption-attachment-3292\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Back_side_of_the_Moon_AS16-3021.jpg\"><img decoding=\"async\" class=\"wp-image-539 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3292\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Back_side_of_the_Moon_AS16-3021-300&#215;298.jpg&#8221; alt=&#8221;It looks different then the side we don&#8217;t normally see.&#8221; width=&#8221;300&#8243; height=&#8221;298&#8243;&gt; Dark side of the Moon<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Several unique features of Earth\u2019s Moon have prompted scientists to develop the current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a> about its <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a>. The Earth and Moon are tidally locked, meaning that as the Moon orbits, one side always faces the Earth and the opposite side is not visible to us. Also and most importantly, the chemical compositions of the Earth and Moon show nearly identical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2701\">isotope<\/a> ratios<\/span><span style=\"font-weight: 400\"> and volatile content<\/span><span style=\"font-weight: 400\">. <\/span>Apollo missions returned from the Moon with rocks that allowed scientists to conduct very precise comparisons between Moon and Earth rocks. Other bodies in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a> do not share the same degree of similarity and show much higher variability. If the Moon and Earth formed together, this would explain why they are so chemically similar.<\/p>\n<figure id=\"attachment_3293\" aria-describedby=\"caption-attachment-3293\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/ArtistsConceptMoonFormation.jpg\"><img decoding=\"async\" class=\"wp-image-540 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3293\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/ArtistsConceptMoonFormation-300&#215;240.jpg&#8221; alt=&#8221;The Earth and this object are colliding in a giant explosion.&#8221; width=&#8221;300&#8243; height=&#8221;240&#8243;&gt; Artist&#8217;s concept of the giant impact from a Mars-sized object that could have formed the moon.<\/figcaption><\/figure>\n<p>Many ideas have been proposed for the origin of the Moon: The Moon could have been captured from another part of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> and formed in place together with the Earth, or the Moon could have been ripped out of the early Earth. None of proposed explanations can account for all the evidence. The currently prevailing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a> is the <strong>giant-impact <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a><\/strong><span style=\"font-weight: 400\">. <\/span>It proposes a body about half of Earth\u2019s size must have shared at least parts of Earth\u2019s orbit and collided with it, resulting in a violent mixing and scattering of material from both objects. Both bodies would be <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2831\">composed<\/a> of a combination of materials, with more of the lower density splatter coalescing into the Moon. This may explain why the Earth has a higher density and thicker <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a> than the Moon.<\/p>\n<figure id=\"attachment_4254\" aria-describedby=\"caption-attachment-4254\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-541\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4254\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-2\" title=\"NASA | Evolution of the Moon\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/UIKmSQqp8wY?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><em><span style=\"font-weight: 400\">Computer simulation of the evolution of the Moon (2 minutes).<\/span><\/em><\/p>\n<h3><b>8.3.3 Origin of Earth\u2019s Water<\/b><\/h3>\n<figure id=\"attachment_3294\" aria-describedby=\"caption-attachment-3294\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Comet_on_7_July_2015_NavCam.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-542 size-medium\" title=\"&quot;ESA\/Rosetta\/NAVCAM,\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-300x300.jpg\" alt=\"Jets are seen coming off of the comet.\" width=\"300\" height=\"300\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-300x300.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-150x150.jpg 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-768x768.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-65x65.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-225x225.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam-350x350.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Comet_on_7_July_2015_NavCam.jpg 1024w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3294\" class=\"wp-caption-text\">Water vapor leaves comet 67P\/Churyumov\u2013Gerasimenko.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Explanations for the origin of Earth\u2019s water include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> outgassing, comets, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> outgassing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a> for the origin of Earth\u2019s water is that it originated from inside the planet, and emerged via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> processes as vapor associated with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> eruptions<\/span><span style=\"font-weight: 400\">.\u00a0 Since all <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> eruptions contain some water vapor, at times more than 1% of the volume, these alone could have created Earth\u2019s surface water. Another likely source of water was from space. Comets are a mixture of dust and ice, with some or most of that ice being frozen water. Seemingly dry meteors can contain small but measurable amounts of water, usually trapped in their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">mineral<\/a> structures<\/span><span style=\"font-weight: 400\">. During heavy bombardment <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">periods<\/a> later in Earth\u2019s history, its cooled surface was pummeled by comets and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a>, which could be why so much water exists above ground. There isn\u2019t a definitive answer for what process is the source of ocean water. Earth\u2019s water isotopically matches water found in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a> much better than that of comets<\/span><span style=\"font-weight: 400\">. However, it is hard to know if Earth processes could have changed the water\u2019s isotopic signature over the last 4-plus billion years<\/span><span style=\"font-weight: 400\">. <\/span>It is possible that all three sources contributed to the origin of Earth\u2019s water.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-50\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-50\" class=\"h5p-iframe\" data-content-id=\"50\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.3 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4242\" aria-describedby=\"caption-attachment-4242\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.3-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-543\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.3-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4242\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.3 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>8.4 Archean Eon<\/strong><\/h2>\n<figure id=\"attachment_3295\" aria-describedby=\"caption-attachment-3295\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Archean.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-544 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-300x134.png\" alt=\"It shows volcanoes, impacts, and stromatolites.\" width=\"300\" height=\"134\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-300x134.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-1024x459.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-768x344.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-1536x688.png 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-65x29.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-225x101.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean-350x157.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Archean.png 2048w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3295\" class=\"wp-caption-text\">Artist&#8217;s impression of the Archean.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a><\/strong>, which lasted from 4.0\u20132.5 billion years ago, is named after the Greek word for beginning. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">eon<\/a> represents the beginning of the rock record. Although there is current evidence that rocks and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> existed during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2203\">Hadean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a><\/span><span style=\"font-weight: 400\">, <\/span>the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> has a much more robust rock and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<h3><b><\/b><span style=\"font-weight: 400\">8.4.1 Late Heavy Bombardment<\/span><\/h3>\n<figure id=\"attachment_3296\" aria-describedby=\"caption-attachment-3296\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Pluto-in-true-color_2x_JPEG-edit-frame.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-545 size-medium\" title=\"NASA, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-300x300.jpg\" alt=\"The smooth plain is different than the cratered surrounding surface.\" width=\"300\" height=\"300\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-300x300.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-150x150.jpg 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-65x65.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-225x225.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame-350x350.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pluto-in-true-color_2x_JPEG-edit-frame.jpg 600w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3296\" class=\"wp-caption-text\">2015 image from NASA&#8217;s New Horizons probe of Pluto. The lack of impacts found on the Tombaugh Regio (the heart-shaped plain, lower right) has been inferred as being younger than the Late Heavy Bombardment and the surrounding surface due to its lack of impacts.<\/figcaption><\/figure>\n<p>Objects were chaotically flying around at the start of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a>, building the planets and moons. There is evidence that after the planets formed, about 4.1\u20133.8 billion years ago, a second large spike of asteroid and comet impacted the Earth and Moon in an event called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2206\">late heavy bombardment<\/a><\/strong><span style=\"font-weight: 400\">. <\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">Meteorites<\/a> and comets in stable or semi-stable orbits became unstable and started impacting objects throughout the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a>. In addition, this event is called the lunar cataclysm because most of the Moons craters are from this event. During <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2206\">late heavy bombardment<\/a>, the Earth, Moon, and all planets in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> were pummeled by material from the asteroid and Kuiper belts. Evidence of this bombardment was found within samples collected from the Moon.<\/p>\n<figure id=\"attachment_3297\" aria-describedby=\"caption-attachment-3297\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Lhborbits.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-546 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-300x100.png\" alt=\"It shows 3 pictures.\" width=\"300\" height=\"100\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-300x100.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-1024x342.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-768x256.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-65x22.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-225x75.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits-350x117.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Lhborbits.png 1360w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3297\" class=\"wp-caption-text\">Simulation of before, during, and after the late heavy bombardment.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">It is universally accepted that the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a> experienced extensive asteroid and comet bombardment at its start; however, some other process must have caused the second increase in impacts hundreds of millions of years later. A leading <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a> blames gravitational <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3103\">resonance<\/a> between Jupiter and Saturn for disturbing orbits within the asteroid and Kuiper belts <\/span>based on a similar process observed in the Eta Corvi star <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2664\">system<\/a><span style=\"font-weight: 400\">.<\/span><\/p>\n<h3><b>8.4.2 Origin of the Continents<\/b><\/h3>\n<figure id=\"attachment_2512\" aria-describedby=\"caption-attachment-2512\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Earth-cutaway-schematic-english.svg_-1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-51\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1-300x211.png\" alt=\"The crust and lithosphere are on the outside of the Earth and are thin. Below the crust is the mantle and core. Below the lithosphere is the asthenosphere.\" width=\"300\" height=\"211\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1-300x211.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1-65x46.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1-225x158.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1-350x246.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Earth-cutaway-schematic-english.svg_-1.png 640w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-2512\" class=\"wp-caption-text\">The layers of the Earth. Physical layers include lithosphere and asthenosphere; chemical layers are crust, mantle, and core.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">In order for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">plate tectonics<\/a> to work as it does currently, it necessarily must have continents. However, the easiest way to create <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> material is via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1178\">assimilation<\/a> and differentiation of existing continents (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>). This chicken-and-egg quandary over how continents were made in the first place is not easily answered because of the great age of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> material and how much evidence has been lost during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonics<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2677\">erosion<\/a>. While the timing and specific processes are still debated, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> action must have brought the first <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> material to the Earth\u2019s surface during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2203\">Hadean<\/a>, 4.4 billion years ago<\/span><span style=\"font-weight: 400\">. <\/span>This model does not solve the problem of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continent<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a>, since <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1179\">magmatic differentiation<\/a> seems to need thicker <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a>. Nevertheless, the continents formed by some incremental process during the early history of Earth<span style=\"font-weight: 400\">. The best idea is that density differences allowed lighter <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1954\">felsic<\/a> materials to float upward and heavier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1957\">ultramafic<\/a> materials and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3345\">metallic<\/a> iron to sink. These density differences led to the layering of the Earth, the layers that are now detected by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3087\">seismic<\/a> studies. Early protocontinents accumulated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1954\">felsic<\/a> materials as developing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a>&#8211;<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> processes brought lighter material from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a> to the surface<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3299\" aria-describedby=\"caption-attachment-3299\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fig21oceanocean.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3299 size-medium\" title=\"USGS, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fig21oceanocean-1.gif\" alt=\"The ocean plate subducts beneath a different ocean plate.\" width=\"300\" height=\"173\" \/><\/a><figcaption id=\"caption-attachment-3299\" class=\"wp-caption-text\">Subduction of an oceanic plate beneath another oceanic plate, forming a trench and an island arc. Several island arcs might combine and eventually evolve into a continent.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The first solid evidence of modern <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">plate tectonics<\/a> is found at the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a>, indicating at least some <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2590\">lithosphere<\/a> must have been in place. This evidence does not necessarily mark the starting point of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">plate tectonics<\/a>; remnants of earlier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> activity could have been erased by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2671\">rock cycle<\/a><\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_2523\" aria-describedby=\"caption-attachment-2523\" style=\"width: 419px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/CratonGeolProv.jpg\"><img decoding=\"async\" class=\"wp-image-92\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-2523\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/CratonGeolProv-300&#215;159.jpg&#8221; alt=&#8221;The legend shows shields, platforms, orogens, basins, large igneous provinces, and extended crust.&#8221; width=&#8221;419&#8243; height=&#8221;222&#8243;&gt; Geologic provinces of Earth. Cratons are pink and orange.<\/figcaption><\/figure>\n<p>The stable interiors of the current continents are called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">cratons<\/a><\/strong> and were mostly formed in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a>. A <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">craton<\/a> has two main parts: the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2207\">shield<\/a><\/strong>, which is crystalline <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1971\">basement<\/a> rock near the surface, and the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2208\">platform<\/a><\/strong> made of sedimentary rocks covering the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2207\">shield<\/a>. Most <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">cratons<\/a> have remained relatively unchanged with most <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> activity having occurred around <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">cratons<\/a> instead of within them. Whether they were created by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">plate tectonics<\/a> or another process, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> continents gave rise to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> continents that now dominate our planet.<\/p>\n<figure id=\"attachment_3300\" aria-describedby=\"caption-attachment-3300\" style=\"width: 258px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Zealandia_topography.jpg\"><img decoding=\"async\" class=\"wp-image-548 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3300\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Zealandia_topography-258&#215;300.jpg&#8221; alt=&#8221;It shows Zealandia&#8221; width=&#8221;258&#8243; height=&#8221;300&#8243;&gt; The continent of Zealandia<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The general guideline as to what constitutes a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continent<\/a> and differentiates <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2581\">oceanic<\/a> from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental crust<\/a> is under some debate. At passive margins, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental crust<\/a> grades into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2581\">oceanic crust<\/a> at passive margins, making a distinction difficult<\/span><span style=\"font-weight: 400\">. Even island-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2609\">arc<\/a> and hot-spot material can seem more closely related to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental crust<\/a> than <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2581\">oceanic<\/a>. Continents usually have a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">craton<\/a> in the middle with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1954\">felsic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2675\">igneous<\/a> rocks. There is evidence that submerged masses like Zealandia, that includes present-day New Zealand, would be considered a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continent<\/a><\/span><span style=\"font-weight: 400\">. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">Continental crust<\/a> that does not contain a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">craton<\/a> is called a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> fragment, such as the island of Madagascar off the east <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of Africa<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<h3><b>8.4.3 First Life on Earth<\/b><\/h3>\n<figure id=\"attachment_3301\" aria-describedby=\"caption-attachment-3301\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MicrobialMats.jpg\"><img decoding=\"async\" class=\"wp-image-549 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3301\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ARunzelmarken.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MicrobialMats-300&#215;167.jpg&#8221; alt=&#8221;Rocks with a wrinkled texture, formed by microbial mats&#8221; width=&#8221;300&#8243; height=&#8221;167&#8243;&gt; Fossils of microbial mats from Sweden<\/figcaption><\/figure>\n<p>Life most likely started during the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2203\">Hadean<\/a> or early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eons<\/a>. The earliest evidence of life are chemical signatures, microscopic filaments, and microbial mats. Carbon found in 4.1 billion year old <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2175\">zircon<\/a> grains have a chemical signature suggesting an organic origin. Other evidence of early life are 3.8\u20134.3 billion-year-old microscopic filaments from a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2921\">hydrothermal<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1187\">vent<\/a> deposit in Quebec, Canada. While the chemical and microscopic filaments evidence is not as robust as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a>, there is significant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> evidence for life at 3.5 billion years ago. These first well-preserved <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> are photosynthetic microbial mats, called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2213\">stromatolites<\/a>, found in Australia.<\/p>\n<figure id=\"attachment_3302\" aria-describedby=\"caption-attachment-3302\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/15.2_greenhouse-gas-molecules.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-550 size-medium\" title=\"https:\/\/climate.nasa.gov\/system\/internal_resources\/details\/original\/249_Causes-greenhouse-gas-molecules-cropped-more-55.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-300x192.jpg\" alt=\"Illustration of the molecular shape of greenhouse gases.\" width=\"300\" height=\"192\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-300x192.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-65x42.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-225x144.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-350x224.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules.jpg 746w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3302\" class=\"wp-caption-text\">Greenhouse gases were more common in Earth\u2019s early atmosphere.<\/figcaption><\/figure>\n<p>Although the origin of life on Earth is unknown, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypotheses<\/a> include a chemical origin in the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> and ocean, deep-sea <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2921\">hydrothermal<\/a> vents, and delivery to Earth by comets or other objects. One <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a> is that life arose from the chemical environment of the Earth\u2019s early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> and oceans, which was very different than today. The oxygen-free <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> produced a reducing environment with abundant methane, carbon dioxide, sulfur, and nitrogen compounds. This is what the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> is like on other bodies in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2201\">solar system<\/a>. In the famous Miller-Urey <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2653\">experiment<\/a>, researchers simulated early Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> and lightning within a sealed vessel. After igniting sparks within the vessel, they discovered the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a> of amino acids, the fundamental building blocks of proteins.\u00a0 In 1977, when scientists discovered an isolated ecosystem around <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2921\">hydrothermal<\/a> vents on a deep-sea <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">mid-ocean ridge<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/4-igneous-processes-and-volcanoes\/\">Chapter 4<\/a>), it opened the door for another explanation of the origin of life. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2921\">hydrothermal<\/a> vents have a unique ecosystem of critters with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1184\">chemosynthesis<\/a> as the foundation of the food chain instead of photosynthesis. The ecosystem is deriving its energy from hot chemical-rich waters pouring out of underground towers. This suggests that life could have started on the deep <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2885\">ocean floor<\/a> and derived energy from the heat from the Earth\u2019s interior via <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1184\">chemosynthesis<\/a>. Scientists have since expanded the search for life to more unconventional places, like Jupiter\u2019s icy moon Europa.<\/p>\n<figure id=\"attachment_4244\" aria-describedby=\"caption-attachment-4244\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.4.3-Animation-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-551\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4.3-Animation-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4244\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this animation via this QR Code.<\/figcaption><\/figure>\n<div style=\"width: 854px;\" class=\"wp-video\"><video class=\"wp-video-shortcode\" id=\"video-600-1\" width=\"854\" height=\"480\" preload=\"metadata\" controls=\"controls\"><source type=\"video\/webm\" src=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Miller-Urey_experiment_-_Work_by_the_C3BC_consortium_licensed_under_CC-BY-3.0.webm.480p.webm?_=1\" \/><a href=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Miller-Urey_experiment_-_Work_by_the_C3BC_consortium_licensed_under_CC-BY-3.0.webm.480p.webm\">http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/03\/Miller-Urey_experiment_-_Work_by_the_C3BC_consortium_licensed_under_CC-BY-3.0.webm.480p.webm<\/a><\/video><\/div>\n<p><em>Animation of the original Miller-Urey 1959 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2653\"><em>experiment<\/em><\/a> that simulated the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\"><em>atmosphere<\/em><\/a> and created amino acids from simple <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\"><em>elements<\/em><\/a> and compounds. <\/em><\/p>\n<p>Another possibility is that life or its building blocks came to Earth from space, carried aboard comets or other objects. Amino acids, for example, have been found within comets and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a>. This intriguing possibility also implies a high likelihood of life existing elsewhere in the cosmos.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-51\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-51\" class=\"h5p-iframe\" data-content-id=\"51\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.4 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4243\" aria-describedby=\"caption-attachment-4243\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.4-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-552\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.4-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4243\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.4 via this QR Code.<\/figcaption><\/figure>\n<h2><strong><span style=\"font-size: 28px\">8.5 Proterozoic Eon<\/span><\/strong><\/h2>\n<figure id=\"attachment_3303\" aria-describedby=\"caption-attachment-3303\" style=\"width: 216px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Photosynthesis.gif\"><img decoding=\"async\" class=\"wp-image-553 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3303\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APhotosynthesis.gif&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Photosynthesis-216&#215;300.gif&#8221; alt=&#8221;Water and carbon dioxide go into plants, making sugar and oxygen.&#8221; width=&#8221;216&#8243; height=&#8221;300&#8243;&gt; Diagram showing the main products and reactants in photosynthesis. The one product that is not shown is sugar, which is the chemical energy that goes into constructing the plant, and the energy that is stored in the plant which is used later by the plant or by animals that consume the plant.<\/figcaption><\/figure>\n<p>The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a><\/strong>, meaning \u201cearlier life,\u201d comes after the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a> and ranges from 2.5 billion to 541 million years old. During this time, most of the central parts of the continents had formed and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> processes had started. Photosynthesis by microbial organisms, such as single-celled cyanobacteria, had been slowly adding oxygen to the oceans. As cyanobacteria evolved into multicellular organisms, they completely transformed the oceans and later the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> by adding <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> amounts of free oxygen gas (O<sub>2<\/sub>) and initiated what is called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2210\">Great Oxygenation Event<\/a> (GOE<\/strong>). This drastic environmental change decimated the anaerobic bacteria, which could not survive in the presence of free oxygen. On the other hand, aerobic organisms could thrive in ways they could not earlier<span style=\"font-weight: 400\">. <\/span><\/p>\n<p>An oxygenated world also changed the chemistry of the planet in significant ways. For example, iron remained in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2705\">solution<\/a> in the non-oxygenated environment of the earlier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a>. In chemistry, this is known as a reducing environment. Once the environment was oxygenated, iron combined with free oxygen to form solid precipitates of iron <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1919\">oxide<\/a>, such as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">mineral<\/a> hematite or magnetite. These precipitates accumulated into large <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">mineral<\/a> deposits with red <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2849\">chert<\/a> known as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2931\">banded<\/a>-iron <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formations<\/a>, which are dated at about 2 billion years<span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3304\" aria-describedby=\"caption-attachment-3304\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/MichiganBIF-1.jpg\"><img decoding=\"async\" class=\"wp-image-371 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3304\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/MichiganBIF-1-300&#215;206.jpg&#8221; alt=&#8221;The rock shows red and brown layering.&#8221; width=&#8221;300&#8243; height=&#8221;206&#8243;&gt; Alternating bands of iron-rich and silica-rich mud, formed as oxygen combined with dissolved iron.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a> of iron <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1919\">oxide<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">minerals<\/a> and red <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2849\">chert<\/a> (see figure) in the oceans lasted a long time and prevented oxygen levels from increasing significantly, since <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2707\">precipitation<\/a> took the oxygen out of the water and deposited it into the rock <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2857\">strata<\/a>. As oxygen continued to be produced and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">mineral<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2707\">precipitation<\/a> leveled off, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2815\">dissolved<\/a> oxygen gas eventually <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2706\">saturated<\/a> the oceans and started bubbling out into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a>. Oxygenation of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> is the single biggest event that distinguishes the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> environments. In addition to changing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">mineral<\/a> and ocean chemistry, the GOE is also tabbed as triggering Earth\u2019s first <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">glaciation<\/a> event around 2.1 billion years ago, the Huron <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">Glaciation<\/a>. Free oxygen reacted with methane in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> to produce carbon dioxide. Carbon dioxide and methane are called greenhouse gases because they <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3342\">trap<\/a> heat within the Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a>, like the insulated glass of a greenhouse. Methane is a more effective insulator than carbon dioxide, so as the proportion of carbon dioxide in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> increased, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1715\">greenhouse effect<\/a> decreased, and the planet cooled.<\/p>\n<h3><b>8.5.1 Rodinia<\/b><\/h3>\n<figure id=\"attachment_3305\" aria-describedby=\"caption-attachment-3305\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Rodinia_reconstruction.jpg\"><img decoding=\"async\" class=\"wp-image-554 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3305\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Rodinia_reconstruction-300&#215;267.jpg&#8221; alt=&#8221;The image shows the continents arrange in a possible orientation of Rodinia.&#8221; width=&#8221;300&#8243; height=&#8221;267&#8243;&gt; One possible reconstruction of Rodinia 1.1 billion years ago. Source: John Goodge, modified from (Dalziel 1997).<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">By the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a>, lithospheric plates had formed and were moving according to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> forces that were similar to current times. As the moving <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plates<\/a> collided, the ocean basins closed to form a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinent<\/a><\/strong> called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2211\">Rodinia<\/a><\/strong>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinent<\/a> formed about 1 billion years ago and broke up about 750 to 600 million years ago, at the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a><\/span><span style=\"font-weight: 400\">. <\/span>One of the resulting fragments was a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> mass called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2212\">Laurentia<\/a><\/strong> that would later become North America. Geologists have reconstructed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2211\">Rodinia<\/a> by matching and aligning ancient mountain chains, assembling the pieces like a jigsaw puzzle, and using paleomagnetics to orient to magnetic north.<\/p>\n<p><span style=\"font-weight: 400\">The disagreements over these complex reconstructions is exemplified by geologists proposing at least six different models for the breakup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2211\">Rodinia<\/a> to create Australia<\/span><span style=\"font-weight: 400\">, Antarctica<\/span><span style=\"font-weight: 400\">, parts of China<\/span><span style=\"font-weight: 400\">, the Tarim <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">craton<\/a> north of the Himalaya<\/span><span style=\"font-weight: 400\">, Siberia<\/span><span style=\"font-weight: 400\">, or the Kalahari <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2640\">craton<\/a> of eastern Africa<\/span><span style=\"font-weight: 400\">. <\/span>This breakup created lots of shallow-water, biologically favorable environments that fostered the evolutionary breakthroughs marking the start of the next <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">eon<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a>.<\/p>\n<p>&nbsp;<\/p>\n<h3><b>8.5.2 Life Evolves<\/b><\/h3>\n<figure id=\"attachment_3306\" aria-describedby=\"caption-attachment-3306\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Stromatolites_in_Sharkbay.jpg\"><img decoding=\"async\" class=\"wp-image-555 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3306\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStromatolites_in_Sharkbay.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Stromatolites_in_Sharkbay-300&#215;223.jpg&#8221; alt=&#8221;Picture of modern cyanobacteria (as stromatolites) in Shark Bay, Australia. The brown, blobby stromatolites are slightly sticking out of the shallow water of the ocean.&#8221; width=&#8221;300&#8243; height=&#8221;223&#8243;&gt; Modern cyanobacteria (as stromatolites) in Shark Bay, Australia.<\/figcaption><\/figure>\n<p>Early life in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2205\">Archean<\/a> and earlier is poorly documented in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record. Based on chemical evidence and evolutionary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2655\">theory<\/a>, scientists propose this life would have been single-celled photosynthetic organisms, such as the cyanobacteria that created <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2213\">stromatolites<\/a><\/strong>. Cyanobacteria produced free oxygen in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a> through photosynthesis. Cyanobacteria, archaea, and bacteria are <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2214\">prokaryotes<\/a><\/strong>\u2014primitive organisms made of single cells that lack cell nuclei and other organelles.<\/p>\n<figure id=\"attachment_3307\" aria-describedby=\"caption-attachment-3307\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Stromatolites_hoyt.jpg\"><img decoding=\"async\" class=\"wp-image-556 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3307\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AStromatolites_hoyt_mcr1.JPG&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Stromatolites_hoyt-300&#215;200.jpg&#8221; alt=&#8221;Round structures of grey limestone are remnants of the blobby nature of the living stromatolites, fossilized in rock.&#8221; width=&#8221;300&#8243; height=&#8221;200&#8243;&gt; Fossil stromatolites in Saratoga Springs, New York.<\/figcaption><\/figure>\n<p>A large evolutionary step occurred during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a> with the appearance of <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2215\">eukaryotes<\/a><\/strong> around 2.1 to 1.6 billion years ago. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2215\">Eukaryotic<\/a> cells are more complex, having nuclei and organelles. The nuclear DNA is capable of more complex replication and regulation than that of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2214\">prokaryotic<\/a> cells. The organelles include mitochondria for producing energy and chloroplasts for photosynthesis. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2215\">eukaryote<\/a> branch in the tree of life gave rise to fungi, plants, and animals.<\/p>\n<p>Another important event in Earth\u2019s biological history occurred about 1.2 billion years ago when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2215\">eukaryotes<\/a> invented sexual reproduction. Sharing genetic material from two reproducing individuals, male and female, greatly increased genetic variability in their offspring. This genetic mixing accelerated evolutionary change, contributing to more complexity among individual organisms and within ecosystems (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/7-geologic-time\/\">Chapter 7<\/a>).<\/p>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> land surfaces were barren of plants and animals and geologic processes actively shaped the environment differently because land surfaces were not protected by leafy and woody vegetation. For example, rain and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3134\">rivers<\/a> would have caused <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2677\">erosion<\/a> at much higher rates on land surfaces devoid of plants. This resulted in thick accumulations of pure <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1915\">quartz<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2834\">sandstone<\/a> from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a> such as the extensive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2935\">quartzite<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formations<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2589\">core<\/a> of the Uinta Mountains in Utah.<\/p>\n<figure id=\"attachment_3308\" aria-describedby=\"caption-attachment-3308\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/DickinsoniaCostata.jpg\"><img decoding=\"async\" class=\"wp-image-557 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3308\" class=\"wp-caption-text\">Verisimilus<\/a> at <a href=\"denied:&quot;https:\/\/en.wikipedia.org\/wiki\/&quot;\" class=\"&quot;extiw&quot;\" title=\"&quot;wikipedia:&quot;\">English Wikipedia<\/a> [<a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a>, <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by\/2.5&quot;\">CC BY 2.5<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ADickinsoniaCostata.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/DickinsoniaCostata-300&#215;225.jpg&#8221; alt=&#8221;The fossil is a flat, leaf-shaped&#8221; width=&#8221;300&#8243; height=&#8221;225&#8243;&gt; Dickinsonia, a typical Ediacaran fossil.<\/figcaption><\/figure>\n<p>Fauna during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2216\">Ediacaran<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a>, 635.5 to 541 million years ago are known as the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2216\">Ediacaran fauna<\/a><\/strong>, and offer a first glimpse at the diversity of ecosystems that evolved near the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a>. These soft-bodied organisms were among the first multicellular life forms and probably were similar to jellyfish or worm-like. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2216\">Ediacaran fauna<\/a> did not have hard parts like shells and were not well preserved in the rock records. However, studies suggest they were widespread in the Earth\u2019s oceans. Scientists still debate how many species were evolutionary dead-ends that became <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinct<\/a> and how many were ancestors of modern groupings. The transition of soft-bodied <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2216\">Ediacaran<\/a> life to life forms with hard body parts occurred at the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> and beginning of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eons<\/a>. This evolutionary explosion of biological diversity made a dramatic difference in scientists\u2019 ability to understand the history of life on Earth.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-52\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-52\" class=\"h5p-iframe\" data-content-id=\"52\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.5 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4245\" aria-describedby=\"caption-attachment-4245\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.5-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-558\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.5-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4245\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.5 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>8.6 Phanerozoic Eon: Paleozoic Era<\/strong><\/h2>\n<figure id=\"attachment_3249\" aria-describedby=\"caption-attachment-3249\" style=\"width: 243px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/ElrathiakingiUtahWheelerCambrian.jpg\"><img decoding=\"async\" class=\"wp-image-497 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3249\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/ElrathiakingiUtahWheelerCambrian-243&#215;300.jpg&#8221; alt=&#8221;It has three lobes&#8221; width=&#8221;243&#8243; height=&#8221;300&#8243;&gt; The trilobites had a hard exoskeleton, and is an early arthropod, the same group that includes modern insects, crustaceans, and arachnids.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a><\/strong> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">Eon<\/a> is the most recent, 541 million years ago to today, <\/span>and means \u201cvisible life\u201d because the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a> rock record is marked by an abundance of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a> organisms had hard body parts like claws, scales, shells, and bones that were more easily preserved as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a>. Rocks from the older <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2218\">Precambrian<\/a> time are less commonly found and rarely include <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> because these organisms had soft body parts. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a> rocks are younger, more common, and contain the majority of extant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a>. The study of rocks from this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2190\">eon<\/a> yields much greater detail. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2217\">Phanerozoic<\/a> is subdivided into three <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">eras<\/a>, from oldest to youngest they are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> (\u201cancient life\u201d), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> (\u201cmiddle life\u201d), and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> (\u201crecent life\u201d) and the remaining three chapter headings are on these three important <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">eras<\/a>.<\/p>\n<figure id=\"attachment_3309\" aria-describedby=\"caption-attachment-3309\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Trilobite_Heinrich_Harder.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-559 size-medium\" title=\"Trilobites, by Heinrich Harder, 1916.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder-300x186.jpg\" alt=\"The trilobites are crawling over the sea floor\" width=\"300\" height=\"186\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder-300x186.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder-65x40.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder-225x140.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder-350x217.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Trilobite_Heinrich_Harder.jpg 650w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3309\" class=\"wp-caption-text\">Trilobites, by Heinrich Harder, 1916.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Life in the early <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a><\/strong> was dominated by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> organisms but by the middle of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">era<\/a> plants and animals evolved to live and reproduce on land. Fish evolved jaws and fins evolved into jointed limbs. The development of lungs allowed animals to emerge from the sea and become the first air-breathing tetrapods (four-legged animals) such as amphibians. From amphibians evolved reptiles with the amniotic egg. From reptiles evolved an early ancestor to birds and mammals <\/span><span style=\"font-weight: 400\">and their scales became feathers and fur. Near the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1429\">Carboniferous<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a> had some of the most extensive forests in Earth\u2019s history. Their fossilized remains became the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2856\">coal<\/a> that powered the industrial revolution<\/span><\/p>\n<h3><strong>8.6.1 Paleozoic Tectonics and Paleogeography<\/strong><\/h3>\n<figure id=\"attachment_3310\" aria-describedby=\"caption-attachment-3310\" style=\"width: 256px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/North_america_craton_nps.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-560 size-medium\" title=\"USGS, public domain\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/North_america_craton_nps-256x300.gif\" alt=\"It is a map of North America\" width=\"256\" height=\"300\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/North_america_craton_nps-256x300.gif 256w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/North_america_craton_nps-65x76.gif 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/North_america_craton_nps-225x263.gif 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/North_america_craton_nps-350x409.gif 350w\" sizes=\"auto, (max-width: 256px) 100vw, 256px\" \/><\/a><figcaption id=\"caption-attachment-3310\" class=\"wp-caption-text\">Laurentia, which makes up the North American craton.<\/figcaption><\/figure>\n<p>During the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>, sea-levels rose and fell four times. With each sea-level rise, the majority of North America was covered by a shallow tropical ocean. Evidence of these submersions are the abundant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> sedimentary rocks such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2851\">limestone<\/a> with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> corals and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2845\">ooids<\/a>. Extensive sea-level <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3119\">falls<\/a> are documented by widespread <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2961\">unconformities<\/a>. Today, the midcontinent has extensive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> sedimentary rocks from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> and western North America has thick layers of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2851\">limestone<\/a> on block faulted mountain ranges such as Mt. Timpanogos near Provo, Utah<span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<figure id=\"attachment_3311\" aria-describedby=\"caption-attachment-3311\" style=\"width: 267px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Pangaea_continents.png\"><img decoding=\"async\" class=\"wp-image-3311 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3311\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3APangaea_continents.svg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pangaea_continents-1.png&#8221; alt=&#8221;Pangaea has a crescent shape.&#8221; width=&#8221;267&#8243; height=&#8221;300&#8243;&gt; A reconstruction of Pangaea, showing approximate positions of modern continents.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The assembly of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinent<\/a> <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a><\/strong>, sometimes spelled <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangaea<\/a>, was completed by the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>. The name <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> was originally coined by Alfred Wegener and means \u201call land.\u201d <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> is the when all of the major continents were grouped together as one by a series of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> events including <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> island-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2609\">arc<\/a> accretion, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> collisions, and ocean-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1461\">basin<\/a> closures. In North America, these <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> events occurred on the east <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> and are known as the Taconic, Acadian, Caledonian, and Alleghanian orogenies<\/span><span style=\"font-weight: 400\">.<\/span><span style=\"font-weight: 400\"> The Appalachian Mountains are the erosional remnants of these mountain building events in North America. Surrounding <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> was a global ocean <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1461\">basin<\/a> known as the Panthalassa. Continued <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> movement extended the ocean into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a>, forming a large bay called the Tethys Sea that eventually divided the land mass into two smaller <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinents<\/a>, Laurasia and Gondwana. Laurasia consisted of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2212\">Laurentia<\/a> and Eurasia, and Gondwana consisted of the remaining continents of South America, Africa, India, Australia, and Antarctica. <\/span><\/p>\n<figure id=\"attachment_4254\" aria-describedby=\"caption-attachment-4254\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-541\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/NASA-Evolution-of-the-Moon-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4254\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-3\" title=\"Continental Drift\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/ovT90wYrVk4?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><em>Animation of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\"><em>plate<\/em><\/a> movement the last 3.3 billion years. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\"><em>Pangea<\/em><\/a> occurs at the 4:40 mark.<\/em><\/p>\n<p>While the east <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of North America was tectonically active during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>, the west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> remained mostly inactive as a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2598\">passive margin<\/a> during the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a>. The western edge of North American <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continent<\/a> was near the present-day Nevada-Utah border and was an expansive shallow <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2891\">continental shelf<\/a> near the paleoequator. However, by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2227\">Devonian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a>, the Antler <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a> started on the west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> and lasted until the Pennsylvanian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a>. The Antler <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a> was a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2619\">island arc<\/a> that was accreted onto western North America with the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> direction away from North America. This created a mountain range on the west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of North American called the Antler highlands and was the first part of building the land in the west that would eventually make most of California, Oregon, and Washington states. By the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a>, the Sonoma <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a> began on the west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> and was another <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2620\">collision<\/a> of an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2619\">island arc<\/a>. The Sonoma <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a> marks the change in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> direction to be toward North America with a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2617\">volcanic arc<\/a> along the entire west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of North America by late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> to early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Eras<\/a><span style=\"font-weight: 400\">.<\/span><\/p>\n<p>By the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>, the east <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of North America had a very high mountain range due to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2620\">collision<\/a> and the creation of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a>. The west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of North America had smaller and isolated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> highlands associated with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2619\">island arc<\/a> accretion. During the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a>, the size of the mountains on either side of North America would flip, with the west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> being a more tectonically active <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2592\">plate boundary<\/a> and the east <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> changing into a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2598\">passive margin<\/a> after the breakup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a>.<\/p>\n<h3><strong>8.6.2 Paleozoic Evolution<\/strong><\/h3>\n<figure id=\"attachment_3312\" aria-describedby=\"caption-attachment-3312\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Anomalocaris.jpg\"><img decoding=\"async\" class=\"wp-image-562 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3312\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAnomalocaris_canadensis_-_reconstruction_-_MUSE.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Anomalocaris-300&#215;200.jpg&#8221; alt=&#8221;The animal has two arms and large eyes.&#8221; width=&#8221;300&#8243; height=&#8221;200&#8243;&gt; Anomalocaris reconstruction by the MUSE science museum in Italy.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The beginning of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a> is marked by the first appearance of hard body parts like shells, spikes, teeth, and scales; and the appearance in the rock record of most animal phyla known today. That is, most basic animal body plans appeared in the rock record during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a>. This sudden appearance of biological diversity is called the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2220\">Cambrian Explosion<\/a>. <\/strong>Scientists debate whether this sudden appearance is more from a rapid evolutionary diversification as a result of a warmer <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a> following the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2910\">glacial<\/a> environments, better preservation and fossilization of hard parts, or artifacts of a more complete and recent rock record. For example, fauna may have been diverse during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2216\">Ediacaran<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a>, setting the state for the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2220\">Cambrian Explosion<\/a>, but they lacked hard body parts and would have left few <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> behind<\/span><span style=\"font-weight: 400\">. Regardless, during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a> 541\u2013485 million years ago marked the appearance of most animal phyla<\/span><span style=\"font-weight: 400\">. <\/span><\/p>\n<figure id=\"attachment_3313\" aria-describedby=\"caption-attachment-3313\" style=\"width: 112px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Opabinia.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-563 size-medium\" title=\"&quot;Charles\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-112x300.jpg\" alt=\"The animal has a long trunk with claws at the end.\" width=\"112\" height=\"300\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-112x300.jpg 112w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-381x1024.jpg 381w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-65x175.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-225x604.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia-350x940.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Opabinia.jpg 446w\" sizes=\"auto, (max-width: 112px) 100vw, 112px\" \/><\/a><figcaption id=\"caption-attachment-3313\" class=\"wp-caption-text\">Original plate from Walcott&#8217;s 1912 description of Opabinia, with labels: fp = frontal appendage, e = eye, ths = thoracic somites, i = intestine, ab = abdominal segment.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">One of the best <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> sites for the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2220\">Cambrian Explosion<\/a> was discovered in 1909 by <a href=\"http:\/\/www.nasonline.org\/member-directory\/deceased-members\/20000936.html\">Charles Walcott (1850\u20131927)<\/a> in the <strong>Burgess <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2839\">Shale<\/a><\/strong> in western Canada. The Burgess <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2839\">Shale<\/a> is a <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2221\">Lagerst\u00e4tte<\/a><\/strong>, a site of exceptional <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> preservation that includes impressions of soft body parts. This discovery allowed scientists to study <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a> animals in immense detail because soft body parts are not normally preserved and fossilized. Other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2221\">Lagerst\u00e4tte<\/a> sites of similar age in China and Utah have allowed scientist to form a detailed picture of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a> biodiversity. The biggest mystery surrounds animals that do not fit existing lineages and are unique to that time. This includes many famous fossilized creatures: the first compound-eyed trilobites; <em>Wiwaxia<\/em>, a creature covered in spiny <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plates<\/a>;<em> Hallucigenia<\/em>, a walking worm with spikes;<em> Opabinia<\/em>, a five-eyed arthropod with a grappling claw; and <em>Anomalocaris<\/em>, the alpha predator of its time, complete with grasping appendages and circular <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2698\">mouth<\/a> with sharp <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plates<\/a><\/span><span style=\"font-weight: 400\">. <\/span>Most notably appearing during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a> is an important ancestor to humans. A segmented worm called <em>Pikaia<\/em> is thought to be the earliest ancestor of the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">Chordata<\/a><\/strong> phylum that includes <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrates<\/a>, animals with backbones<span style=\"font-weight: 400\">.\u00a0<\/span><\/p>\n<figure id=\"attachment_3314\" aria-describedby=\"caption-attachment-3314\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Coral_Outcrop_Flynn_Reef-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-564\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1-300x225.jpg\" alt=\"The reef has many intricacies.\" width=\"300\" height=\"225\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1-225x169.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1-350x263.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Coral_Outcrop_Flynn_Reef-1.jpg 640w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3314\" class=\"wp-caption-text\">A modern coral reef.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p>By the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a>, mollusks, brachiopods, nautiloids, gastropods, graptolites, echinoderms, and trilobites covered the sea floor. Although most animal phyla appeared by the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a>, the biodiversity at the family, genus, and species level was low until the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2225\">Ordovician<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a>. During the <strong>Great <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2225\">Ordovician<\/a> Biodiversification Event<\/strong>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrates<\/a> and invertebrates (animals without backbone) became more diverse and complex at family, genus, and species level. The cause of the rapid speciation event is still debated but some likely causes are a combination of warm temperatures, expansive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> shelves near the equator, and more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a> along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">mid-ocean ridges<\/a>. Some have shown evidence that an asteroid breakup event and consequent heavy <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorite<\/a> impacts correlate with this diversification event. The additional <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a> added nutrients to ocean water helping support a robust ecosystem. Many life forms and ecosystems that would be recognizable in current times appeared at this time. Mollusks, corals, and arthropods in particular multiplied to dominate the oceans<span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3315\" aria-describedby=\"caption-attachment-3315\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Guadalupe_Nima2.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-565 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-300x206.jpg\" alt=\"The entire mountain is one big fossil.\" width=\"300\" height=\"206\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-300x206.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-1024x701.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-768x526.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-1536x1052.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-65x45.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-225x154.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2-350x240.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Guadalupe_Nima2.jpg 1600w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3315\" class=\"wp-caption-text\">Guadalupe National Park is made of a giant fossil reef.<\/figcaption><\/figure>\n<p>One important evolutionary advancement during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2225\">Ordovician<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a> was <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2898\">reef<\/a>-building organisms, mostly colonial coral. Corals took advantage of the ocean chemistry, using <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1918\">calcite<\/a> to build large structures that resembled modern <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2898\">reefs<\/a> like the Great Barrier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2898\">Reef<\/a> off the coast of Australia. These reefs housed thriving ecosystems of organisms that swam around, hid in, and crawled over them. Reefs are important to paleontologists because of their preservation potential, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> size, and in-place ecosystems. Few other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> offer more diversity and complexity than <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2898\">reef<\/a> assemblages<span style=\"font-weight: 400\">.<\/span><\/p>\n<p><span style=\"font-weight: 400\">According to evidence from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2910\">glacial<\/a> deposits,\u00a0 a small <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">ice age<\/a> caused sea-levels to drop and led to a major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a> by the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2225\">Ordovician<\/a>. This is the earliest of five <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a><\/strong> events documented in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record. During this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a>, an unusually large number of species abruptly disappear in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record (see video).\u00a0<\/span><\/p>\n<p><span style=\"font-weight: 400\">Life bounced back during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2226\">Silurian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a><\/span><span style=\"font-weight: 400\">.<\/span><span style=\"font-weight: 400\">\u00a0The major evolutionary event was the development of the forward pair of gill arches into jaws, allowing fish new feeding strategies and opening up new ecological niches.<\/span><\/p>\n<figure id=\"attachment_4253\" aria-describedby=\"caption-attachment-4253\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-566\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/How-Many-Mass-Extinctions-Youtube-QR-Code.png 1148w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4253\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-4\" title=\"How Many Mass Extinctions Have There Been?\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/aO9mOAKXvJs?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p><em>3-minute video describing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\"><em>mass extinctions<\/em><\/a> and how they are\u00a0defined.<\/em><\/p>\n<figure id=\"attachment_3316\" aria-describedby=\"caption-attachment-3316\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Placoderm.jpg\"><img decoding=\"async\" class=\"wp-image-567 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3316\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0&quot;\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABothriolepis_panderi.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Placoderm-300&#215;264.jpg&#8221; alt=&#8221;This fish is covered with armor.&#8221; width=&#8221;300&#8243; height=&#8221;264&#8243;&gt; The placoderm Bothriolepis panderi from the Devonian of Russia<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Life bounced back during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2226\">Silurian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>\u2019s major evolutionary event was the development of jaws from the forward pair of gill arches in bony fishes and sharks. Hinged jaws allowed fish to exploit new food sources and ecological niches. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a> also included the start of armored fishes, known as the placoderms. In addition to fish and jaws, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2226\">Silurian<\/a> rocks provide the first evidence of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> or land-dwelling plants and animals<\/span><span style=\"font-weight: 400\">. The first vascular plant, <em>Cooksonia,<\/em> had woody tissues, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3116\">pores<\/a> for gas exchange, and veins for water and food transport<\/span><span style=\"font-weight: 400\">. Insects, spiders, scorpions, and crustaceans began to inhabit moist, freshwater <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> environments<\/span><span style=\"font-weight: 400\">. \u00a0<\/span><\/p>\n<figure id=\"attachment_3317\" aria-describedby=\"caption-attachment-3317\" style=\"width: 392px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fishapods.png\"><img decoding=\"async\" class=\"wp-image-568\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3317\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/4.0-3.0-2.5-2.0-1.0&quot;\">CC BY-SA 4.0-3.0-2.5-2.0-1.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFishapods.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fishapods-300&#215;153.png&#8221; alt=&#8221;Six different fish\/amphibians are shown, with variation between totally swimming and fully walking.&#8221; width=&#8221;392&#8243; height=&#8221;200&#8243;&gt; Several different types of fish and amphibians that led to walking on land.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2227\">Devonian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">Period<\/a> is called the Age of Fishes due to the rise in plated, jawed, and lobe-finned fishes . The lobe-finned fishes, which were related to the modern lungfish and coelacanth, are important for their eventual evolution into tetrapods, four-limbed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrate<\/a> animals that can walk on land. \u00a0The first lobe-finned land-walking fish, named <em>Tiktaalik<\/em>, appeared about 385 million years ago and serves as a transition <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> between fish and early tetrapods<\/span><span style=\"font-weight: 400\">. <\/span>Though Tiktaalik was clearly a fish, it had some tetrapod structures as well. Several <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2227\">Devonian<\/a> are more tetrapod like than fish like but these weren\u2019t fully <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a>. The first fully <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> tetrapod arrived in the Mississippian (early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1429\">Carboniferous<\/a>) <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>. By the Mississippian (early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1429\">Carboniferous<\/a>) <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>, tetrapods had evolved into two main groups, amphibians and amniotes, from a common tetrapod ancestor. The amphibians were able to breathe air and live on land but still needed water to nurture their soft eggs. The first reptile (an amniote) could live and reproduce entirely on land with hard-shelled eggs that wouldn\u2019t dry out.<\/p>\n<p><span style=\"font-weight: 400\">\u00a0Land plants had also evolved into the first trees and forests<\/span><span style=\"font-weight: 400\">. Toward the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2227\">Devonian<\/a>, another <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a> event occurred. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a>, while severe, is the least temporally defined, with wide variations in the timing of the event or events. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2898\">Reef<\/a> building organisms were the hardest hit, leading to dramatic changes in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> ecosystems<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3318\" aria-describedby=\"caption-attachment-3318\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Arthropleura.png\"><img decoding=\"async\" class=\"wp-image-569 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3318\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArthropleura.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Arthropleura-300&#215;156.png&#8221; alt=&#8221;The millipede is about 2 meters long.&#8221; width=&#8221;300&#8243; height=&#8221;156&#8243;&gt; A reconstruction of the giant arthropod (insects and their relatives) Arthropleura.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The next time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>, called the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1429\">Carboniferous<\/a> (North American geologists have subdivided this into the Mississippian and Pennsylvanian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">periods<\/a>), saw the highest levels of oxygen ever known, with forests (e.g., ferns, club mosses) and swamps dominating the landscape <\/span><span style=\"font-weight: 400\">. This helped cause\u00a0the largest arthropods ever<\/span><span style=\"font-weight: 400\">, like the millipede <\/span><i><span style=\"font-weight: 400\">Arthropleura<\/span><\/i><span style=\"font-weight: 400\">, at 2.5 meters (6.4 feet) long! It also saw the rise of a new group of animals, the reptiles. The evolutionary advantage that reptiles have over amphibians is the amniote egg (egg with a protective shell), which allows them to rely on non-aquatic environments for reproduction. This widened the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> reach of reptiles compared to amphibians. This booming life, especially plant life, created cooling temperatures as carbon dioxide<\/span><span style=\"font-weight: 400\">\u00a0was removed from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a><\/span><span style=\"font-weight: 400\">. By the middle <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1429\">Carboniferous<\/a>, these cooler temperatures led to an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">ice age<\/a> (called the Karoo <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">Glaciation<\/a>) and less-productive forests. The reptiles fared much better than the amphibians, leading to their diversification<\/span><span style=\"font-weight: 400\">. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2910\">glacial<\/a> event lasted into the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1428\">Permian<\/a><\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3319\" aria-describedby=\"caption-attachment-3319\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Dimetrodon_grandis.jpg\"><img decoding=\"async\" class=\"wp-image-570 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3319\" class=\"wp-caption-text\">DiBgd<\/a> at <a href=\"denied:&quot;https:\/\/en.wikipedia.org\/wiki\/&quot;\" class=\"&quot;extiw&quot;\" title=\"&quot;wikipedia:&quot;\">English Wikipedia<\/a> [<a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a>, <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by\/2.5&quot;\">CC BY 2.5<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ADimetrodon_grandis.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Dimetrodon_grandis-300&#215;169.jpg&#8221; alt=&#8221;The animal has a large mouth with sharp teeth and a large sail on its back.&#8221; width=&#8221;300&#8243; height=&#8221;169&#8243;&gt; Reconstruction of Dimetrodon.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">By the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1428\">Permian<\/a>, with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> assembled, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinent<\/a> led to a dryer <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a>, and even more diversification and domination by the reptiles<\/span><span style=\"font-weight: 400\">. The groups that developed in this warm <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a> eventually radiated into dinosaurs. Another group, known as the synapsids, eventually evolved into mammals<\/span><span style=\"font-weight: 400\">. Synapsids, including the famous sail-backed <\/span><i><span style=\"font-weight: 400\">Dimetrodon<\/span><\/i><span style=\"font-weight: 400\"> are commonly confused with dinosaurs.<\/span><span style=\"font-weight: 400\">\u00a0Pelycosaurs (of the Pennsylvanian to early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1428\">Permian<\/a> like <\/span><i><span style=\"font-weight: 400\">Dimetrodon) <\/span><\/i><span style=\"font-weight: 400\">are the first group of synapsids that exhibit the beginnings of mammalian characteristics such as well-differentiated dentition: incisors, highly developed canines in lower and upper jaws and cheek teeth, premolars and molars. Starting in the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1428\">Permian<\/a>, a second group of synapsids, called the therapsids (or mammal-like reptiles) evolve<\/span><span style=\"font-weight: 400\">, and become the ancestors to mammals.<\/span><\/p>\n<h4><span style=\"font-weight: 400\">Permian Mass Extinction<\/span><\/h4>\n<figure id=\"attachment_2911\" aria-describedby=\"caption-attachment-2911\" style=\"width: 399px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/World-map-or-flood-basalts.jpg\"><img decoding=\"async\" class=\"wp-image-307\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-2911\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFlood_Basalt_Map.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/World-map-or-flood-basalts-300&#215;168.jpg&#8221; alt=&#8221;World map of flood basalts. Note the largest is the Siberian Traps&#8221; width=&#8221;399&#8243; height=&#8221;223&#8243;&gt; World map of flood basalts. Note the largest is the Siberian Traps<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">The end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">era<\/a> is marked by the largest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a> in earth history. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">era<\/a> had two smaller <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinctions<\/a>, \u00a0but these were not as large as the <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1430\">Permian Mass Extinction<\/a><\/b><span style=\"font-weight: 400\">, also known as the <\/span><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1430\">Permian-Triassic Extinction Event<\/a><span style=\"font-weight: 400\">. It is estimated that up to 96% of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> species and 70% of land-dwelling (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a>) <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrates<\/a> went extinct<\/span><span style=\"font-weight: 400\">. Many famous organisms, like sea scorpions and trilobites, were never seen again in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record. <\/span><span style=\"font-weight: 400\">What caused such a widespread <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> event? The exact cause is still debated, though the leading idea relates to extensive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a> associated with the <strong>Siberian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3342\">Traps<\/a><\/strong>, which are one of the largest deposits of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1197\">flood basalts<\/a> known on Earth, dating to the time of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> event<\/span><span style=\"font-weight: 400\">. The eruption size is estimated at over 3 million cubic kilometers<\/span><span style=\"font-weight: 400\"> that is approximately 4,000,000 times larger than the famous 1980 Mt. St. Helens eruption in Washington. \u00a0The unusually large <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> eruption would have contributed a large amount of toxic gases, aerosols, and greenhouse gasses into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a>. Further, some evidence suggests that the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a> burned vast <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2856\">coal<\/a> deposits releasing methane (a greenhouse gas) into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a><\/span><span style=\"font-weight: 400\">. As discussed in <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/15-global-climate-change\/\">Chapter 15<\/a>, greenhouse gases cause the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a> to warm. This extensive addition of greenhouse gases from the Siberian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3342\">Traps<\/a> may have caused a runaway <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1715\">greenhouse effect<\/a> that rapidly changed the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a>, acidified the oceans, disrupted food chains, disrupted carbon cycling, and caused the largest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a><\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-53\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-53\" class=\"h5p-iframe\" data-content-id=\"53\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.6 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4248\" aria-describedby=\"caption-attachment-4248\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Video-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-571\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4248\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this interactive activity via this QR Code.<\/figcaption><\/figure>\n<h2><b>8.7 Phanerozoic Eon: Mesozoic Era<\/b><\/h2>\n<figure id=\"attachment_3321\" aria-describedby=\"caption-attachment-3321\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Fighting_dinosaurs.jpg\"><img decoding=\"async\" class=\"wp-image-572 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3321\" class=\"wp-caption-text\">CC BY 2.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AFighting_dinosaurs_(1).jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Fighting_dinosaurs-300&#215;173.jpg&#8221; alt=&#8221;The dinosaurs are fighting&#8221; width=&#8221;300&#8243; height=&#8221;173&#8243;&gt; Perhaps the greatest fossil ever found, a velociraptor attacked a protoceratops, and both were fossilized mid sequence.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Following the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1430\">Permian Mass Extinction<\/a>, the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a><\/strong> (&#8220;middle life&#8221;) was from 252 million years ago to 66 million years ago. As <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> started to break apart, mammals, birds, and flowering plants developed. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> is probably best known as the age of reptiles, most notably, the dinosaurs.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">8.7.1 Mesozoic Tectonics and Paleogeography<\/span><\/h3>\n<figure id=\"attachment_3322\" aria-describedby=\"caption-attachment-3322\" style=\"width: 200px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Pangea_animation_03.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-573\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pangea_animation_03.gif\" alt=\"The continents separate into their current configuration.\" width=\"200\" height=\"160\" \/><\/a><figcaption id=\"caption-attachment-3322\" class=\"wp-caption-text\">Animation showing Pangea breaking up<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> started breaking up (in a region that would become eastern Canada and United States) around 210 \u00a0million years ago in the Late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a><\/span><span style=\"font-weight: 400\">. Clear evidence for this includes the age of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2678\">sediments<\/a> in the Newark Supergroup <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2624\">rift<\/a> basins and the Palisades <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1970\">sill<\/a> of the eastern part of North America and the age of the Atlantic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2885\">ocean floor<\/a>. Due to sea-floor spreading, the oldest rocks on the Atlantic\u2019s floor are along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of northern Africa and the east coast of \u00a0North America, while the youngest are along the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">mid-ocean ridge<\/a>.<\/span><\/p>\n<figure id=\"attachment_3323\" aria-describedby=\"caption-attachment-3323\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/age_oceanic_lith.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-3323 size-medium\" title=\"Image via NOAA https:\/\/www.ngdc.noaa.gov\/mgg\/ocean_age\/data\/2008\/image\/age_oceanic_lith.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/age_oceanic_lith-1.jpg\" alt=\"The map shoes colors that represent different ages.\" width=\"300\" height=\"191\" \/><\/a><figcaption id=\"caption-attachment-3323\" class=\"wp-caption-text\">Age of oceanic lithosphere, in millions of years. Notice the differences in the Atlantic Ocean along the coasts of the continents.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">This age pattern shows how the Atlantic Ocean opened as the young Mid-Atlantic Ridge began to create the seafloor. This means the Atlantic ocean started opening and was first formed here. The southern Atlantic opened next, with South America separating from central and southern Africa. Last (happening after the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> ended) was the northernmost Atlantic, with Greenland and Scandinavia parting ways.\u00a0<\/span><span style=\"font-weight: 400\">The breaking points of each <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2624\">rifted<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> margin eventually turned into the passive <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> boundaries of the east <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of the Americas today.<\/span><\/p>\n<figure id=\"attachment_4248\" aria-describedby=\"caption-attachment-4248\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Video-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-571\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Video-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4248\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this interactive activity via this QR Code.<\/figcaption><\/figure>\n<div style=\"width: 300px;\" class=\"wp-video\"><video class=\"wp-video-shortcode\" id=\"video-600-2\" width=\"300\" height=\"200\" preload=\"metadata\" controls=\"controls\"><source type=\"video\/mp4\" src=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2016\/07\/PangeaEADef.mp4?_=2\" \/><a href=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2016\/07\/PangeaEADef.mp4\">http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2016\/07\/PangeaEADef.mp4<\/a><\/video><\/div>\n<p><em><a href=\"http:\/\/emvc.geol.ucsb.edu\/2_infopgs\/IP1GTect\/aPangeaAnim.html\">Video<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\"><em>Pangea<\/em><\/a> breaking apart and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\"><em>plates<\/em><\/a> moving to their present locations. By Tanya Atwater.<\/em><\/p>\n<figure id=\"attachment_3324\" aria-describedby=\"caption-attachment-3324\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sevierorogeny.jpg\"><img decoding=\"async\" class=\"wp-image-575 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3324\" class=\"wp-caption-text\">CC0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASevierorogeny.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Sevierorogeny-300&#215;113.jpg&#8221; alt=&#8221;It shows faulting and a volcanic arc&#8221; width=&#8221;300&#8243; height=&#8221;113&#8243;&gt; Sketch of the major features of the Sevier Orogeny.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">In western North America, an active <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> margin had started with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a>, controlling most of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonics<\/a> of that region in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a>. Another possible island-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2609\">arc<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2620\">collision<\/a> created the Sonoman <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">Orogeny<\/a> in Nevada during the latest <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a><\/span><span style=\"font-weight: 400\">. In the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a>, another island-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2609\">arc<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2620\">collision<\/a> caused the Nevadan <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">Orogeny<\/a>, a large Andean-style <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2617\">volcanic arc<\/a> and thrust belt<\/span><span style=\"font-weight: 400\">. The Sevier Orogeny followed in the Cretaceous, which was mainly a volcanic arc to the west and a thin-skinned fold and thrust belt to the east<\/span><span style=\"font-weight: 400\">, meaning stacks of shallow <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3065\">faults<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1455\">folds<\/a> built up the topography. Many of the structures in the Rocky Mountains today date from this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a>.<\/span><\/p>\n<figure id=\"attachment_3325\" aria-describedby=\"caption-attachment-3325\" style=\"width: 250px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Cretaceous_seaway.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-576 size-full\" title=\"USGS, public domain.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Cretaceous_seaway.png\" alt=\"Water is covering the middle of North America.\" width=\"250\" height=\"301\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cretaceous_seaway.png 250w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cretaceous_seaway-65x78.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Cretaceous_seaway-225x271.png 225w\" sizes=\"auto, (max-width: 250px) 100vw, 250px\" \/><\/a><figcaption id=\"caption-attachment-3325\" class=\"wp-caption-text\">The Cretaceous Interior Seaway in the mid-Cretaceous.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">Tectonics<\/a> had an influence in one more important geographic feature in North America: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1440\">Cretaceous<\/a> Western Interior Foreland <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1461\">Basin<\/a>, which flooded during high sea levels forming the <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1433\">Cretaceous\u00a0Interior Seaway<\/a><\/strong>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">Subduction<\/a> from the west was the Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">Plate<\/a>, an <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2581\">oceanic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> connected to the Pacific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">Plate<\/a> (seen today as remnants such as the Juan de Fuca <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">Plate<\/a>, off the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of the Pacific Northwest). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">Subduction<\/a> was shallow at this time because a very young, hot and less dense portion of the Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> was <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subducted<\/a>. This shallow <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> caused a downwarping in the central part of North America<\/span><span style=\"font-weight: 400\">. High sea levels due to shallow <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a>, and increasing rates of seafloor spreading and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a>, high temperatures, and melted ice also contributed to the high sea levels<\/span><span style=\"font-weight: 400\">. These factors allowed a shallow epicontinental seaway that extended from the Gulf of Mexico to the Arctic Ocean to divide North America into two separate land masses<\/span><span style=\"font-weight: 400\">, Laramidia to the west and Appalachia to the east, for 25 million years<\/span><span style=\"font-weight: 400\">. Many of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2856\">coal<\/a> deposits in Utah and Wyoming formed from swamps along the shores of this seaway<\/span><span style=\"font-weight: 400\">. By the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1440\">Cretaceous<\/a>, cooling temperatures caused the seaway to regress<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">8.7.2 Mesozoic Evolution<\/span><\/h3>\n<figure id=\"attachment_3326\" aria-describedby=\"caption-attachment-3326\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Mesozoic_Scene.jpg\"><img decoding=\"async\" class=\"wp-image-577 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3326\" class=\"wp-caption-text\">CC BY-SA 2.5<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AEuropasaurus_holgeri_Scene_2.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Mesozoic_Scene-300&#215;225.jpg&#8221; alt=&#8221;Several dinosaurs and their relatives are in the scene.&#8221; width=&#8221;300&#8243; height=&#8221;225&#8243;&gt; A Mesozoic scene from the late Jurassic.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">era<\/a> is dominated by reptiles, and more specifically, the dinosaurs. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a> saw devastated ecosystems that took over 30 million years to fully re-emerge after the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1430\">Permian Mass Extinction<\/a><\/span><span style=\"font-weight: 400\">. \u00a0The first appearance of many modern groups of animals that would later flourish occurred at this time. \u00a0This includes frogs (amphibians), turtles (reptiles), <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> ichthyosaurs and plesiosaurs (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> reptiles), mammals, and the archosaurs. \u00a0The archosaurs (\u201cruling reptiles\u201d) include ancestral groups that went <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinct<\/a> at the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a>, as well as the flying pterosaurs, crocodilians, and the dinosaurs. \u00a0Archosaurs, like the placental mammals after them, occupied all major environments: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> (dinosaurs), in the air (pterosaurs), aquatic (crocodilians) and even fully <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> habitats (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> crocodiles). The pterosaurs, the first <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrate<\/a>\u00a0group to take flight, like the dinosaurs and mammals, start small in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a>.<\/span><\/p>\n<figure id=\"attachment_3327\" aria-describedby=\"caption-attachment-3327\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Augustasaurus_BW.jpg\"><img decoding=\"async\" class=\"wp-image-578 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3327\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by\/3.0&quot;\">CC BY 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AAugustasaurus_BW.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Augustasaurus_BW-300&#215;189.jpg&#8221; alt=&#8221;It is a swimming reptile with a long neck&#8221; width=&#8221;300&#8243; height=&#8221;189&#8243;&gt; A drawing of the early plesiosaur Agustasaurus from the Triassic of Nevada.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">At the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a><\/span><span style=\"font-weight: 400\">, another <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a> event occurred, the fourth major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a> in the geologic record. This was perhaps caused by the Central Atlantic Magmatic Province <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1197\">flood basalt<\/a><\/span><span style=\"font-weight: 400\">. The end-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> made certain lineages go extinct and helped spur the evolution of survivors like mammals, pterosaurs (flying reptiles), ichthyosaurs\/plesiosaurs\/mosasaurs (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> reptiles), and dinosaurs<\/span><span style=\"font-weight: 400\">. <\/span><\/p>\n<figure id=\"attachment_3328\" aria-describedby=\"caption-attachment-3328\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Megazostrodon_sp._Natural_History_Museum_-_London.jpg\"><img decoding=\"async\" class=\"wp-image-579 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3328\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AMegazostrodon_sp._Natural_History_Museum_-_London.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Megazostrodon_sp._Natural_History_Museum_-_London-300&#215;200.jpg&#8221; alt=&#8221;It is small, less than 5 inches, and looks like a shrew&#8221; width=&#8221;300&#8243; height=&#8221;200&#8243;&gt; Reconstruction of the small (&lt;5&#8243;) Megazostrodon, one of the first animals considered to be a true mammal.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Mammals, as previously mentioned, got their start from a reptilian synapsid ancestor possibly in the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a><\/span><span style=\"font-weight: 400\">. Mammals stayed small, in mainly nocturnal niches, with insects being their largest prey. The development of warm-blooded circulation and fur may have been a response to this lifestyle<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3329\" aria-describedby=\"caption-attachment-3329\" style=\"width: 226px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Ornithischia.png\"><img decoding=\"async\" class=\"wp-image-580\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3329\" class=\"wp-caption-text\">GFDL<\/a> or <a href=\"denied:&quot;http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/&quot;\">CC-BY-SA-3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AOrnithischia.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ornithischia-150&#215;150.png&#8221; alt=&#8221;The bones of the pubis and ischium are close to each other.&#8221; width=&#8221;226&#8243; height=&#8221;186&#8243;&gt; Closed structure of a ornithischian hip, which is similar to a birds.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">In the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a>, species that were previously common, flourished due to a warmer and more tropical <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a><\/span><span style=\"font-weight: 400\">. The dinosaurs were relatively small animals in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a>, but became truly <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1933\">massive<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a>. \u00a0Dinosaurs are split into two groups based on their hip structure<\/span><span style=\"font-weight: 400\">, i.e. orientation of the pubis and ischium bones in relationship to each other. \u00a0This is referred to as the \u201creptile hipped\u201d saurischians and the \u201cbird hipped\u201d ornithischians. This has recently been brought into question by a new idea for dinosaur lineage.<\/span><\/p>\n<figure id=\"attachment_3330\" aria-describedby=\"caption-attachment-3330\" style=\"width: 227px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Saurischia.png\"><img decoding=\"async\" class=\"wp-image-581\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3330\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ASaurischia_pelvis_structure.svg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Saurischia.png&#8221; alt=&#8221;The bones of the pubis and ischium are away from each other.&#8221; width=&#8221;227&#8243; height=&#8221;214&#8243;&gt; Open structure of a saurischian hip, which is similar to a lizards.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">Most of the dinosaurs of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1438\">Triassic<\/a> were saurischians, but all of them were bipedal. The major adaptive advantage dinosaurs had was changes in the hip and ankle bones, tucking the legs under the body for improved locomotion as opposed to the semi-erect gait of crocodiles or the sprawling posture of reptiles. In the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a>, limbs (or a lack thereof) were also important to another group of reptiles, leading to the evolution of <\/span><i><span style=\"font-weight: 400\">Eophis<\/span><\/i><span style=\"font-weight: 400\">, the oldest snake<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3331\" aria-describedby=\"caption-attachment-3331\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Beipiao1mmartyniuk.png\"><img decoding=\"async\" class=\"wp-image-582 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3331\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABeipiao1mmartyniuk.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Beipiao1mmartyniuk-300&#215;158.png&#8221; alt=&#8221;It is a feathered dinosaur with large hand claws&#8221; width=&#8221;300&#8243; height=&#8221;158&#8243;&gt; Therizinosaurs, like Beipiaosaurus (shown in this restoration), are known for their enormous hand claws.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">There is a paucity of dinosaur <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a> from the Early and Middle <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a><\/span><span style=\"font-weight: 400\">, but by the Late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a> they were dominating the planet<\/span><span style=\"font-weight: 400\">. The saurischians diversified into the giant herbivorous (plant-eating) long-necked sauropods weighing up to 100 tons and bipedal carnivorous theropods, with the possible exception of the <\/span><i><span style=\"font-weight: 400\">Therizinosaurs<\/span><\/i><span style=\"font-weight: 400\">. All of the ornithischians (e.g <\/span><i><span style=\"font-weight: 400\">Stegosaurus, Iguanodon, Triceratops, Ankylosaurus,\u00a0<\/span><\/i><i>Pachycephhlosaurus<\/i>) were herbivorous with a strong tendency to have a \u201cturtle-like\u201d beak at the tips of their mouths.<\/p>\n<figure id=\"attachment_2488\" aria-describedby=\"caption-attachment-2488\" style=\"width: 222px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/09\/Archaeopteryx_lithographica_Berlin_specimen.jpg\"><img decoding=\"async\" class=\"wp-image-54 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-2488\" class=\"wp-caption-text\">CC BY-SA 3.0<\/a> or <a href=\"denied:&quot;http:\/\/www.gnu.org\/copyleft\/fdl.html&quot;\">GFDL<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArchaeopteryx_lithographica_(Berlin_specimen).jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Archaeopteryx_lithographica_Berlin_specimen-222&#215;300.jpg&#8221; alt=&#8221;The fossil has bird and dinosaur features.&#8221; width=&#8221;222&#8243; height=&#8221;300&#8243;&gt; Iconic \u201cBerlin specimen\u201d Archaeopteryx lithographica fossil from Germany.<\/figcaption><\/figure>\n<p>&nbsp;<\/p>\n<p><span style=\"font-weight: 400\">The pterosaurs grew and diversified in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a>, and another notable arial organism developed and thrived in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a>: birds. When <\/span><i><span style=\"font-weight: 400\">Archeopteryx<\/span><\/i><span style=\"font-weight: 400\"> was found in the Solnhofen <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2221\">Lagerst\u00e4tte<\/a> of Germany<\/span><span style=\"font-weight: 400\">, a seeming dinosaur-bird hybrid, it started the conversation on the origin of birds. The idea that birds evolved from dinosaurs occurred very early in the history of research into evolution, only a few years after Darwin\u2019s <\/span><i><span style=\"font-weight: 400\">On the Origin of Species<\/span><\/i><span style=\"font-weight: 400\">. This study used a remarkable <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> of <\/span><i><span style=\"font-weight: 400\">Archeopteryx<\/span><\/i><span style=\"font-weight: 400\"> from a transitional animal between dinosaurs and birds. Small meat-eating theropod dinosaurs were likely the branch that became birds due to their similar features<\/span><span style=\"font-weight: 400\">. A significant debate still exists over how and when powered flight evolved. Some have stated a running-start model<\/span><span style=\"font-weight: 400\">, while others have favored a tree-leaping gliding model<\/span><span style=\"font-weight: 400\"> or even a semi-combination: flapping to aid in climbing<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3333\" aria-describedby=\"caption-attachment-3333\" style=\"width: 199px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Argentinosaurus_DSC_2943.jpg\"><img decoding=\"async\" class=\"wp-image-583 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3333\" class=\"wp-caption-text\">GFDL 1.2<\/a> or <a href=\"denied:&quot;http:\/\/artlibre.org\/licence\/lal\/en&quot;\">FAL<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AArgentinosaurus_DSC_2943.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Argentinosaurus_DSC_2943-199&#215;300.jpg&#8221; alt=&#8221;The dinosaur is huge! 130&#8242; long and 24&#8242; high.&#8221; width=&#8221;199&#8243; height=&#8221;300&#8243;&gt; Reconstructed skeleton of Argentinosaurus, from Naturmuseum Senckenberg in Germany.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1440\">Cretaceous<\/a> saw a further diversification, specialization, and domination of the dinosaurs and other fauna. One of the biggest changes on land was the transition to angiosperm-dominated flora. Angiosperms, which are plants with flowers and seeds, had originated in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1440\">Cretaceous<\/a><\/span><span style=\"font-weight: 400\">, switching many plains to grasslands by the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a><\/span><span style=\"font-weight: 400\">. By the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>, they had replaced gymnosperms (evergreen trees) and ferns as the dominant plant in the world\u2019s forests. Haplodiploid eusocial insects (bees and ants) are descendants from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1439\">Jurassic<\/a> wasp-like ancestors that co-evolved with the flowering plants during this time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a><\/span><span style=\"font-weight: 400\">. The breakup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a> not only shaped our modern world\u2019s geography, but biodiversity at the time as well. Throughout the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a>, animals on the isolated, now separated island continents (formerly parts of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3366\">Pangea<\/a>), took strange evolutionary turns. This includes giant titanosaurian sauropods (<\/span><i><span style=\"font-weight: 400\">Argentinosaurus<\/span><\/i><span style=\"font-weight: 400\">) and theropods (<\/span><i><span style=\"font-weight: 400\">Giganotosaurus<\/span><\/i><span style=\"font-weight: 400\">) from South America<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<h4><span style=\"font-weight: 400\">K-T Extinction<\/span><\/h4>\n<figure id=\"attachment_3334\" aria-describedby=\"caption-attachment-3334\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Extinction_intensity.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-584 size-medium\" title=\"After: Raup, D. &amp; Sepkoski, J. (1982). &quot;Mass extinctions in the marine fossil record&quot;. Science 215: 1501\u20131503. DOI:10.1126\/science.215.4539.1501. Rohde, R.A. &amp; Muller, R.A. (2005). &quot;Cycles in fossil diversity&quot;. Nature 434: 209-210. DOI:10.1038\/nature03339. Sepkoski, J. (2002) A Compendium of Fossil Marine Animal Genera (eds. Jablonski, D. &amp; Foote, M.) Bull. Am. Paleontol. no. 363 (Paleontological Research Institution, Ithaca, NY). Signor, P. and J. Lipps (1982) &quot;Sampling bias, gradual extinction patterns and catastrophes in the fossil record&quot;, in Geologic Implications of Impacts of Large Asteroids and Comets on the Earth, I. Silver and P. Silver Eds, Geol. Soc. Amer. Special Paper 190, Boulder Colo. p. 291-296.\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-300x183.png\" alt=\"There are many spikes, but the K\/T spike is second largest to the end Perlman.\" width=\"300\" height=\"183\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-300x183.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-1024x625.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-768x469.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-65x40.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-225x137.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_-350x214.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Extinction_intensity.svg_.png 1062w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3334\" class=\"wp-caption-text\">Graph of the rate of extinctions. Note the large spike at the end of the Cretaceous (labeled as K).<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Similar to the end of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">era<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">Era<\/a> ended with the <\/span><b>K-Pg <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">Mass Extinction<\/a> <\/b><span style=\"font-weight: 400\">(previously known as the <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1434\">K-T Extinction<\/a><\/b><span style=\"font-weight: 400\">) 66 million years ago<\/span><span style=\"font-weight: 400\">.<\/span><span style=\"font-weight: 400\"> This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> event was likely caused by a large <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1435\">bolide<\/a> <\/b>(<span style=\"font-weight: 400\">an extraterrestrial impactor such as an asteroid, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteoroid<\/a>, or comet) that collided with earth<\/span><span style=\"font-weight: 400\">. Ninety percent of plankton species, 75% of plant species, and all the dinosaurs went <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinct<\/a> at this time.<\/span><\/p>\n<figure id=\"attachment_3335\" aria-describedby=\"caption-attachment-3335\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Impact_event.jpg\"><img decoding=\"async\" class=\"wp-image-585 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3335\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Impact_event-300&#215;209.jpg&#8221; alt=&#8221;The rock is slamming into the Earth&#8221; width=&#8221;300&#8243; height=&#8221;209&#8243;&gt; Artist&#8217;s depiction of an impact event<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">One of the strongest pieces of evidence comes from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2700\">element<\/a> iridium. Quite rare on Earth, and more common in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2202\">meteorites<\/a>, it has been found all over the world in higher concentrations at a particular layer of rock that formed at the time of the K-T boundary. Soon other scientists started to find evidence to back up the claim. Melted rock spheres<\/span><span style=\"font-weight: 400\">, a special type of \u201cshocked\u201d <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1915\">quartz<\/a> called stishovite, that only is found at impact sites, was found in many places around the world <\/span><span style=\"font-weight: 400\">. T<\/span><span style=\"font-weight: 400\">he huge impact created a strong thermal pulse that could be responsible for global forest fires<\/span><span style=\"font-weight: 400\">, strong acid rains<\/span><span style=\"font-weight: 400\">, a corresponding abundance of ferns, the first colonizing plants after a forest fire<\/span><span style=\"font-weight: 400\">, enough debris thrown into the air to significantly cool temperatures afterward<\/span><span style=\"font-weight: 400\">, and a 2-km high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3194\">tsunami<\/a> inferred from deposits found from Texas to Alabama<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3336\" aria-describedby=\"caption-attachment-3336\" style=\"width: 268px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Chicxulub_radar_topography.jpg\"><img decoding=\"async\" class=\"wp-image-586 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3336\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Chicxulub_radar_topography-268&#215;300.jpg&#8221; alt=&#8221;The crater is circular.&#8221; width=&#8221;268&#8243; height=&#8221;300&#8243;&gt; The land expression of the Chicxulub crater. The other side of the crater is within the Gulf of M\u00e9xico.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Still, with all this evidence, one large piece remained missing: the crater where the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1435\">bolide<\/a> impacted. It was not until 1991 <\/span><span style=\"font-weight: 400\">that the crater was confirmed using <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3337\">petroleum<\/a> company geophysical data. Even though it is the third largest confirmed crater on Earth at roughly 180 km wide, the <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1437\">Chicxulub Crater<\/a><\/b><span style=\"font-weight: 400\"> was hard to find due to being partially underwater and partially obscured by the dense forest canopy of the Yucatan Peninsula<\/span><span style=\"font-weight: 400\">. Coring of the center of the impact called the peak ring contained <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1962\">granite<\/a>, indicating the impact was so powerful that it lifted <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1971\">basement<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2678\">sediment<\/a> from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a> several miles toward the surface<\/span><span style=\"font-weight: 400\">. In 2010, an international team of scientists reviewed 20 years of research and blamed the impact for the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a><\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_3337\" aria-describedby=\"caption-attachment-3337\" style=\"width: 298px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/India_Geology_Zones.jpg\"><img decoding=\"async\" class=\"wp-image-587 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3337\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/India_Geology_Zones-298&#215;300.jpg&#8221; alt=&#8221;It covers more than 200,000 square miles&#8221; width=&#8221;298&#8243; height=&#8221;300&#8243;&gt; Geology of India, showing purple as Deccan Traps-related rocks.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">With all of this information, it seems like the case would be closed. However, there are other events at this time which could have partially aided the demise of so many organisms. For example, sea levels are known to be slowly decreasing at the time of the K-T event, which is tied to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> extinctions<\/span><span style=\"font-weight: 400\">, though any study on gradual vs. sudden changes in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record is flawed due to the incomplete nature of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record<\/span><span style=\"font-weight: 400\">. <\/span><span style=\"font-weight: 400\">Another big event at this time was the <\/span><b>Deccan <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3342\">Traps<\/a><\/b><span style=\"font-weight: 400\">\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1197\">flood basalt<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a> in India. At over 1.3 million cubic kilometers of material, it was certainly a large source of material hazardous to ecosystems at the time, and it has been suggested as at least partially responsible for the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a><\/span><span style=\"font-weight: 400\">. Some have found the impact and eruptions too much of a coincidence, and have even linked the two together<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-54\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-54\" class=\"h5p-iframe\" data-content-id=\"54\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.7 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4247\" aria-describedby=\"caption-attachment-4247\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.7-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-588\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.7-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4247\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.7 via this QR Code.<\/figcaption><\/figure>\n<h2><strong>8.8 Phanerozoic Eon: Cenozoic Era<\/strong><\/h2>\n<figure id=\"attachment_3338\" aria-describedby=\"caption-attachment-3338\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Paracertherium.png\"><img decoding=\"async\" class=\"wp-image-589 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3338\" class=\"wp-caption-text\">CC BY-SA 4.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3AIndricotherium.png&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Paracertherium-300&#215;234.png&#8221; alt=&#8221;It is grey and tall.&#8221; width=&#8221;300&#8243; height=&#8221;234&#8243;&gt; Paraceratherium, seen in this reconstruction, was a massive (15-20 ton, 15 foot tall) ancestor of rhinos.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a><\/strong>, meaning \u201cnew life,\u201d is known as the age of mammals because it is in this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2191\">era<\/a> that mammals came to be a dominant and large life form, including human ancestors. Birds, as well, flourished in the open niches left by the dinosaur\u2019s demise. Most of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> has been relatively warm, with the main exception being the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">ice age<\/a> that started about 2.558 million years ago and (despite recent warming) continues today<\/span><span style=\"font-weight: 400\">. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">Tectonic<\/a> shifts in the west caused <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a>, but eventually changed the long-standing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> zone into a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2601\">transform<\/a> boundary.<\/span><\/p>\n<h3><span style=\"font-weight: 400\">8.8.1 Cenozoic Tectonics and Paleogeography<\/span><\/h3>\n<figure id=\"attachment_4255\" aria-describedby=\"caption-attachment-4255\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Plate-Tectonics-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-4255\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Plate-Tectonics-Youtube-QR-Code-1.png\" alt=\"\" width=\"150\" height=\"150\" \/><\/a><figcaption id=\"caption-attachment-4255\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-5\" title=\"Plate Tectonics in a Nutshell (Tanya Atwater)\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/IDTBY5WDELg?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<p>&nbsp;<\/p>\n<p><em>Animation of the last 38 million years of movement in western North America. Note, that after the ridge is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\"><em>subducted<\/em><\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2600\"><em>convergent<\/em><\/a> turns to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2601\"><em>transform<\/em><\/a> (with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2599\"><em>divergent<\/em><\/a> inland).<\/em><\/p>\n<figure id=\"attachment_3339\" aria-describedby=\"caption-attachment-3339\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Shallow_subduction_Laramide_orogeny.png\"><img decoding=\"async\" class=\"wp-image-3339 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3339\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Shallow_subduction_Laramide_orogeny-1.png&#8221; alt=&#8221;The subducting plate goes right under the overriding plate&#8221; width=&#8221;300&#8243; height=&#8221;142&#8243;&gt; Shallow subduction during the Laramide Orogeny.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">In the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plates<\/a> of the Earth moved into more familiar places, with the biggest change being the closing of the Tethys Sea with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2620\">collisions<\/a> such as the Alps, Zagros, and Himalaya, a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2620\">collision<\/a> that started about 57 million years ago, and continues today<\/span><span style=\"font-weight: 400\">. Maybe the most significant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a> feature that occurred in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> of North America was the conversion of the west <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of California from a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2600\">convergent<\/a> boundary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> zone to a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2601\">transform<\/a> boundary. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">Subduction<\/a> off the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2890\">coast<\/a> of the western United States, which had occurred throughout the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a>, had continued in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a>. After the Sevier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">Orogeny<\/a> in the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1432\">Mesozoic<\/a>, a subsequent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a> called the Laramide <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">Orogeny<\/a>, occurred in the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a><\/span><span style=\"font-weight: 400\">. The Laramide was <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2612\">thick-skinned<\/a>, different than the Sevier <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">Orogeny<\/a>. It involved deeper crustal rocks, and produced bulges that would become mountain ranges like the Rockies, Black Hills, Wind <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3134\">River<\/a> Range, Uinta Mountains, and the San Rafael Swell. Instead of descending directly into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subducting<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> shallowed out and moved eastward beneath the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> affecting the overlying <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continent<\/a> hundreds of miles east of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> margin and building high mountains.\u00a0 This occurred because the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subducting<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> was so young and near the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">spreading center<\/a> and the density of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> was therefore low and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> was hindered.\u00a0<\/span><\/p>\n<figure id=\"attachment_3340\" aria-describedby=\"caption-attachment-3340\" style=\"width: 217px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Sanandreas.jpg\"><img decoding=\"async\" class=\"wp-image-3340 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3340\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Sanandreas-1.jpg&#8221; alt=&#8221;The fault runs through California.&#8221; width=&#8221;217&#8243; height=&#8221;300&#8243;&gt; Map of the San Andreas fault, showing relative motion.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">As the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">mid-ocean ridge<\/a> itself started to subduct, the relative motion had changed. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">Subduction<\/a> caused a relative convergence between the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subducting<\/a> Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> and the North American <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a>. On the other side of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">mid-ocean ridge<\/a> from the Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a> was the Pacific <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a>, which was moving away from the North American <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2591\">plate<\/a>. Thus, as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> zone consumed the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2630\">mid-ocean ridge<\/a>, the relative movement became <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2601\">transform<\/a> instead of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2600\">convergent<\/a>, which went on to become the San Andreas Fault System<\/span><span style=\"font-weight: 400\">. As the San Andreas grew, it caused east-west directed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1445\">extensional<\/a> forces to spread over the western United States, creating the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2462\">Basin and Range<\/a> province<\/span><span style=\"font-weight: 400\">. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2601\">transform<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3065\">fault<\/a> switched position over the last 18 million years, twisting the mountains around Los Angeles<\/span><span style=\"font-weight: 400\">, and new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3065\">faults<\/a> in the southeastern California deserts may become a future San Andreas-style <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3065\">fault<\/a><\/span><span style=\"font-weight: 400\">. During this switch from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a> to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2601\">transform<\/a>, the nearly horizontal Farallon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2605\">slab<\/a> began to sink into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2586\">mantle<\/a>. This caused magmatism as the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subducting<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2605\">slab<\/a> sank, allowing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2593\">asthenosphere<\/a> material to rise around it. This event is called the Oligocene ignimbrite flare-up, which was one of the most significant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">periods<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanism<\/a> ever<\/span><span style=\"font-weight: 400\">, including the largest single confirmed eruption, the 5000 cubic kilometer Fish Canyon <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1953\">Tuff<\/a><\/span><span style=\"font-weight: 400\">. <\/span><\/p>\n<h3><span style=\"font-weight: 400\">8.8.2 Cenozoic Evolution<\/span><\/h3>\n<figure id=\"attachment_3341\" aria-describedby=\"caption-attachment-3341\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Hominidae_chart.svg_.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-593 size-medium\" title=\"&quot;By\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-300x101.png\" alt=\"Humans are most replated to Pan (chimpanzee)\" width=\"300\" height=\"101\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-300x101.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-768x259.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-65x22.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-225x76.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_-350x118.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Hominidae_chart.svg_.png 800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-3341\" class=\"wp-caption-text\">Family tree of Hominids (Hominadae).<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">There are five groups of early mammals in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> record, based primarily on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> teeth, the hardest bone in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrate<\/a> skeletons<\/span><span style=\"font-weight: 400\">. For the purpose of this text, the most important group are the Eupantotheres, that diverge into the two main groups of mammals, the marsupials (like <\/span><i><span style=\"font-weight: 400\">Sinodelphys<\/span><\/i><span style=\"font-weight: 400\">) and placentals or eutherians (like <\/span><i><span style=\"font-weight: 400\">Eomaia<\/span><\/i><span style=\"font-weight: 400\">) in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1440\">Cretaceous<\/a> and then diversified in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a>. \u00a0The marsupials dominated on the isolated island continents of South America and Australia, and many went <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinct<\/a> in South America with the introduction of placental mammals. Some well-known mammal groups have been highly studied with interesting evolutionary stories in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a>. For example, horses started small with four toes, ended up larger and having just one toe<\/span><span style=\"font-weight: 400\">. Cetaceans (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2883\">marine<\/a> mammals like whales and dolphins) started on land from small bear-like (mesonychids) creatures in the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> and gradually took to water<\/span><span style=\"font-weight: 400\">. However, no study of evolution has been more studied than human evolution. <\/span><b>Hominids<\/b><span style=\"font-weight: 400\">, the name for human-like primates, started in eastern Africa several\u00a0million years ago.<\/span><\/p>\n<figure id=\"attachment_3342\" aria-describedby=\"caption-attachment-3342\" style=\"width: 199px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Lucy_Skeleton.jpg\"><img decoding=\"async\" class=\"wp-image-594 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3342\" class=\"wp-caption-text\">CC BY-SA 2.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ALucy_Skeleton.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Lucy_Skeleton-199&#215;300.jpg&#8221; alt=&#8221;The fossil is about 1\/2 complete&#8221; width=&#8221;199&#8243; height=&#8221;300&#8243;&gt; Lucy skeleton, showing real fossil (brown) and reconstructed skeleton (white).<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">The first critical event in this story is an environmental change from jungle to more of a savanna<\/span><span style=\"font-weight: 400\">, probably caused by changes in Indian Ocean circulation. While bipedalism is known to have evolved before this shift<\/span><span style=\"font-weight: 400\">, it is generally believed that our bipedal ancestors (like <\/span><i><span style=\"font-weight: 400\">Australopithecus<\/span><\/i><span style=\"font-weight: 400\">) had an advantage by covering ground more easily in a more open environment compared to their non-bipedal evolutionary cousins. There is also a growing body of evidence, including the famous \u201cLucy\u201d <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossil<\/a> of an Australopithecine, that our early ancestors lived in trees<\/span><span style=\"font-weight: 400\">. Arboreal animals usually demand a high intelligence to navigate through a three-dimensional world. It is from this lineage that humans evolved, using endurance running as a means to acquire more resources and possibly even hunt<\/span><span style=\"font-weight: 400\">. This can explain many uniquely human features, from our long legs, strong achilles, lack of lower gut protection, and our wide range of running efficiencies. <\/span><\/p>\n<figure id=\"attachment_3343\" aria-describedby=\"caption-attachment-3343\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Spreading_homo_sapiens.png\"><img decoding=\"async\" class=\"wp-image-595 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3343\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Spreading_homo_sapiens-300&#215;141.png&#8221; alt=&#8221;They started in Africa and migrated toward Asia and beyond.&#8221; width=&#8221;300&#8243; height=&#8221;141&#8243;&gt; The hypothesized movement of the homo genus. Years are marked as to the best guess of the timing of movement.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Now that the hands are freed up, the next big step is a large brain. There have been arguments from a switch to more meat eating<\/span><span style=\"font-weight: 400\">, cooking with fire<\/span><span style=\"font-weight: 400\">, tool use<\/span><span style=\"font-weight: 400\">, and even the construct of society itself<\/span><span style=\"font-weight: 400\"> to explain this increase in brain size. Regardless of how, it was this increased cognitive power that allowed humans to reign as their ancestors moved out of Africa and explored the world, ultimately entering the Americas through land bridges like the Bering Land Bridge<\/span><span style=\"font-weight: 400\">. The details of this worldwide migration and the different branches of the hominid evolutionary tree are very complex, and best reserved for its own\u00a0course.<\/span><\/p>\n<h4><span style=\"font-weight: 400\">Anthropocene and Extinction<\/span><\/h4>\n<figure id=\"attachment_3344\" aria-describedby=\"caption-attachment-3344\" style=\"width: 293px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/8.8_Extinctions_Africa_Austrailia_NAmerica_Madagascar.gif\"><img decoding=\"async\" class=\"wp-image-596 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3344\" class=\"wp-caption-text\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8_Extinctions_Africa_Austrailia_NAmerica_Madagascar-293&#215;300.gif&#8221; alt=&#8221;The mammals generally decrease after humans come.&#8221; width=&#8221;293&#8243; height=&#8221;300&#8243;&gt; Graph showing abundance of large mammals and the introduction of humans.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Humans have had an influence on the Earth, its ecosystems and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a>. Yet, human activity can not explain all of the changes that have occurred in the recent past. The start of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1443\">Quaternary<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>, the last and current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a>, is marked by the start of our current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1700\">ice age<\/a> 2.58 million years ago<\/span><span style=\"font-weight: 400\">. During this time <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2467\">ice sheets<\/a> advanced and retreated, most likely due to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1701\">Milankovitch cycles<\/a> (see <a href=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/15-global-climate-change\/\">ch. 15<\/a>). Also at this time, various cold-adapted megafauna emerged (like giant sloths, saber-tooth cats, and woolly mammoths), and most of them went <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinct<\/a> as the Earth warmed from the most recent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2910\">glacial<\/a> maximum. A long-standing debate is over the cause of these and other extinctions. Is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1710\">climate<\/a> warming to blame, or were they caused by humans<\/span><span style=\"font-weight: 400\">? Certainly, we know of recent human extinctions of animals like the dodo or passenger pigeon. Can we connect modern extinctions to extinctions in the recent past? If so, there are several ideas as to how this happened. Possibly the most widely accepted and oldest is the hunting\/overkill <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a><\/span><span style=\"font-weight: 400\">. The idea behind this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a> is that humans hunted large herbivores for food, then carnivores could not find food, and human arrival times in locations has been shown to be tied to increased <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> rates in many cases.<\/span><\/p>\n<figure id=\"attachment_3345\" aria-describedby=\"caption-attachment-3345\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2021\/12\/Bingham_Canyon_mine_2016.jpg\"><img decoding=\"async\" class=\"wp-image-597 size-medium\" src=\"src\" alt=\"image\" \/><figcaption id=\"caption-attachment-3345\" class=\"wp-caption-text\">CC BY 2.0<\/a>], <a href=\"denied:&quot;https:\/\/commons.wikimedia.org\/wiki\/File%3ABingham_Canyon_mine_2016.jpg&quot;\">via Wikimedia Commons<\/a>&#8221; src=&#8221;https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Bingham_Canyon_mine_2016-300&#215;180.jpg&#8221; alt=&#8221;The image is a large hole in a mountainside.&#8221; width=&#8221;300&#8243; height=&#8221;180&#8243;&gt; Bingham Canyon Mine, Utah. This open pit mine is the largest man-made removal of rock in the world.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Modern human impact on the environment and the Earth as a whole is unquestioned. In fact, many scientists are starting to suggest that the rise of human civilization ended and\/or replaced the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1444\">Holocene<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2193\">epoch<\/a> and defines a new geologic time interval: the <\/span><b><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1442\">Anthropocene<\/a><\/b><span style=\"font-weight: 400\">. Evidence for this change includes extinctions, increased tritium (hydrogen with two neutrons) due to nuclear testing, rising pollutants like carbon dioxide, more than 200 never-before seen <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2687\">mineral<\/a> species that have occurred only in this <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2193\">epoch<\/a><\/span><span style=\"font-weight: 400\">, materials such as plastic and metals which will be\u00a0long lasting &#8220;<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">fossils<\/a>&#8221; in the geologic record, and large amounts of earthen material moved<\/span><span style=\"font-weight: 400\">. The biggest scientific debate with this topic is the starting point. Some say that humans\u2019 invention of agriculture would be recognized in geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2857\">strata<\/a> and that should be the starting point, around 12,000 years ago<\/span><span style=\"font-weight: 400\">. Others link the start of the industrial revolution and the subsequent addition of vast amounts of carbon dioxide in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a><\/span><span style=\"font-weight: 400\">. Either way, the idea is that alien geologists visiting Earth in the distant future would easily recognize the impact of humans on the Earth as the beginning of a new geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2192\">period<\/a>.<\/span><\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-55\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-55\" class=\"h5p-iframe\" data-content-id=\"55\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"8.8 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4249\" aria-describedby=\"caption-attachment-4249\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/8.8-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-598\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/8.8-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4249\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 8.8 via this QR Code.<\/figcaption><\/figure>\n<h2>Summary<\/h2>\n<p>The changes that have occurred since the inception of Earth are vast and significant. From the oxygenation of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2667\">atmosphere<\/a>, the progression of life forms, the assembly and deconstruction of several <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2623\">supercontinents<\/a>, to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a> of more life forms than exist today, having a general understanding of these changes can put present change into a more rounded perspective.<\/p>\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n<div id=\"h5p-56\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-56\" class=\"h5p-iframe\" data-content-id=\"56\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Chapter 8 Review\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4250\" aria-describedby=\"caption-attachment-4250\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/01\/Ch.8-Review-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-599\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.8-Review-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4250\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the review quiz for Chapter 8 via this QR Code.<\/figcaption><\/figure>\n<h2><b>References<\/b><\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n<li class=\"csl-entry\">Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V., 1980, Extraterrestrial cause for the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1440\">cretaceous<\/a>-tertiary <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a>: Science, v. 208, no. 4448, p. 1095\u20131108.<\/li>\n<li class=\"csl-entry\">Beerling, D., 2008, The emerald planet: how plants changed Earth\u2019s history: OUP Oxford.<\/li>\n<li class=\"csl-entry\">Boyce, J.W., Liu, Y., Rossman, G.R., Guan, Y., Eiler, J.M., Stolper, E.M., and Taylor, L.A., 2010, Lunar apatite with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> volatile abundances: Nature, v. 466, no. 7305, p. 466\u2013469.<\/li>\n<li class=\"csl-entry\">Brueckner, H.K., and Snyder, W.S., 1985, Structure of the Havallah sequence, Golconda allochthon, Nevada: Evidence for prolonged evolution in an accretionary prism: Geol. Soc. Am. Bull., v. 96, no. 9, p. 1113\u20131130.<\/li>\n<li class=\"csl-entry\">Brusatte, S.L., Benton, M.J., Ruta, M., and Lloyd, G.T., 2008, The first 50 Myr of dinosaur evolution: macroevolutionary pattern and morphological disparity: Biol. Lett., v. 4, no. 6, p. 733\u2013736.<\/li>\n<li class=\"csl-entry\">Canup, R.M., and Asphaug, E., 2001, Origin of the Moon in a giant impact near the end of the Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a>: Nature, v. 412, no. 6848, p. 708\u2013712.<\/li>\n<li class=\"csl-entry\">Clack, J.A., 2009, The Fish\u2013Tetrapod Transition: New <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2176\">Fossils<\/a> and Interpretations: Evolution: Education and Outreach, v. 2, no. 2, p. 213\u2013223., doi: <a href=\"https:\/\/doi.org\/10\/cz257q\">10\/cz257q<\/a>.<\/li>\n<li class=\"csl-entry\">Cohen, K.M., Finney, S.C., Gibbard, P.L., and Fan, J.-X., 2013, The ICS International Chronostratigraphic Chart: Episodes, v. 36, no. 3, p. 199\u2013204.<\/li>\n<li class=\"csl-entry\">Colbert, E.H., and Morales, M.A., 1991, History of the Backboned Animals Through Time: New York: Wiley.<\/li>\n<li class=\"csl-entry\">De Laubenfels, M.W., 1956, Dinosaur <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1708\">extinction<\/a>: one more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2652\">hypothesis<\/a>: J. Paleontol.<\/li>\n<li class=\"csl-entry\">Gomes, R., Levison, H.F., Tsiganis, K., and Morbidelli, A., 2005, Origin of the cataclysmic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2206\">Late Heavy Bombardment<\/a> period of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">terrestrial<\/a> planets: Nature, v. 435, no. 7041, p. 466\u2013469.<\/li>\n<li class=\"csl-entry\">Hatcher, R.D., Jr, Thomas, W.A., and Viele, G.W., 1989, The Appalachian-Ouachita Orogen in the United States: Geological Society of America.<\/li>\n<li class=\"csl-entry\">Hosono, N., Karato, S., Makino, J., and Saitoh, T.R., 2019, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2902\">Terrestrial<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2672\">magma<\/a> ocean origin of the Moon: Nature Geoscience, p. 1., doi: <a href=\"https:\/\/doi.org\/10.1038\/s41561-019-0354-2\">10.1038\/s41561-019-0354-2<\/a>.<\/li>\n<li class=\"csl-entry\">Hsiao, E., 2004, Possibility of life on Europa:<\/li>\n<li class=\"csl-entry\">Hubble, E., 1929, A relation between distance and radial velocity among extra-galactic nebulae: Proc. Natl. Acad. Sci. U. S. A., v. 15, no. 3, p. 168\u2013173.<\/li>\n<li class=\"csl-entry\">Ingersoll, R.V., 1982, Triple-junction instability as cause for late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1445\">extension<\/a> and fragmentation of the western United States: Geology, v. 10, no. 12, p. 621\u2013624.<\/li>\n<li class=\"csl-entry\">Johnson, C.M., 1991, Large-scale <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2580\">crust<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2960\">formation<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2590\">lithosphere<\/a> modification beneath Middle to Late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1441\">Cenozoic<\/a> calderas and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1181\">volcanic<\/a> fields, western North America: J. Geophys. Res. [Solid Earth], v. 96, no. B8, p. 13485\u201313507.<\/li>\n<li class=\"csl-entry\">Kass, M.S., 1999, Prognathodon stadtmani:(Mosasauridae) a new species from the Mancos <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2839\">Shale<\/a> (lower Campanian) of western Colorado: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3380\">Vertebrate<\/a> Paleontology in Utah, Utah Geological.<\/li>\n<li class=\"csl-entry\">Livaccari, R.F., 1991, Role of crustal thickening and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1445\">extensional<\/a> collapse in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">tectonic<\/a>\u00a0evolution of the Sevier-Laramide <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2585\">orogeny<\/a>, western United States: Geology, v. 19, no. 11, p. 1104\u20131107.<\/li>\n<li class=\"csl-entry\">McMenamin, M.A., and Schulte McMenamin, D.L., 1990, The Emergence of Animals: The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2224\">Cambrian<\/a> Breakthrough: Columbia University Press.<\/li>\n<li class=\"csl-entry\">Mitrovica, J.X., Beaumont, C., and Jarvis, G.T., 1989, Tilting of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental<\/a> interiors by the dynamical effects of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2602\">subduction<\/a>: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2576\">Tectonics<\/a>.<\/li>\n<li class=\"csl-entry\">R\u00fccklin, M., Donoghue, P.C.J., Johanson, Z., Trinajstic, K., Marone, F., and Stampanoni, M., 2012, Development of teeth and jaws in the earliest jawed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">vertebrates<\/a>: Nature, v. 491, no. 7426, p. 748\u2013751.<\/li>\n<li class=\"csl-entry\">Sahney, S., and Benton, M.J., 2008, Recovery from the most profound <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2223\">mass extinction<\/a> of all time: Proc. Biol. Sci., v. 275, no. 1636, p. 759\u2013765.<\/li>\n<li class=\"csl-entry\">Salaris, M., and Cassisi, S., 2005, Evolution of stars and stellar populations: John Wiley &amp; Sons.<\/li>\n<li class=\"csl-entry\">Schoch, R.R., 2012, Amphibian Evolution: The life of Early Land <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2222\">Vertebrates<\/a>: Wiley-Blackwell.<\/li>\n<li class=\"csl-entry\">Sharp, B.J., 1958, MINERALIZATION IN THE <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_1939\">INTRUSIVE<\/a> ROCKS IN LITTLE COTTONWOOD CANYON, UTAH: GSA Bulletin, v. 69, no. 11, p. 1415\u20131430., doi: <a href=\"https:\/\/doi.org\/10.1130\/0016-7606(1958)69[1415:MITIRI]2.0.CO;2\">10.1130\/0016-7606(1958)69[1415:MITIRI]2.0.CO;2<\/a>.<\/li>\n<li class=\"csl-entry\">Wiechert, U., Halliday, A.N., Lee, D.C., Snyder, G.A., Taylor, L.A., and Rumble, D., 2001, Oxygen <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2701\">isotopes<\/a> and the moon-forming giant impact: Science, v. 294, no. 5541, p. 345\u2013348.<\/li>\n<li class=\"csl-entry\">Wilde, S.A., Valley, J.W., Peck, W.H., and Graham, C.M., 2001, Evidence from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_3363\">detrital<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2175\">zircons<\/a> for the existence of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_600_2575\">continental crust<\/a> and oceans on the Earth 4.4 Gyr ago: Nature, v. 409, no. 6817, p. 175\u2013178.<\/li>\n<li class=\"csl-entry\">Wood, R.A., 2019, The rise of Animals.: Scientific American, v. 320, no. 6, p. 24\u201331.<\/li>\n<\/ol>\n<\/div>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_600_2655\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2655\"><div tabindex=\"-1\"><p>An accepted scientific idea that explains a process using the best available information.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2700\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2700\"><div tabindex=\"-1\"><p>A group of all atoms with a specific number of protons, having specific, universal, and unique properties.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2201\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2201\"><div tabindex=\"-1\"><p>A collection of planets orbiting around a star.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2203\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2203\"><div tabindex=\"-1\"><p>Eon that represents the time from Earth's formation to 4 billion years ago. Noted for high levels of volcanism, impacts, and very low preservation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2205\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2205\"><div tabindex=\"-1\"><p>Eon defined as the time between 4 billion years ago to 2.5 billion years ago. Most of the oldest rocks on Earth, including large portions of the continents, formed at this time.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2190\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2190\"><div tabindex=\"-1\"><p>The largest span of time recognized by geologists, larger than an era. We are currently in the Phanerozoic eon. Rocks of a specific eon are called eonotherms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2667\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2667\"><div tabindex=\"-1\"><p>The gases that are part of the Earth, which are mainly nitrogen and oxygen.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2576\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2576\"><div tabindex=\"-1\"><p>The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2209\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2209\"><div tabindex=\"-1\"><p>Meaning \"earlier life,\" the third eon of Earth's history, starting at 2.5 billion years ago and ending at 541 million years ago. Marked by increasing atmospheric oxygen and the supercontinent Rodinia.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2219\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2219\"><div tabindex=\"-1\"><p>Meaning \"ancient life,\" the era that started 541 million years ago and ending 252 million years ago. Vertebrates (including fish, amphibians, and reptiles) and arthropods (including insects) evolved and diversified throughout the Paleozoic. Pangea formed toward the end of the Paleozoic.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1708\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1708\"><div tabindex=\"-1\"><p>When a species no longer exists.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2623\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2623\"><div tabindex=\"-1\"><p>An arrangement of many continental masses collided together into one larger mass. According to the Wilson Cycle, this occurs every half billion years or so.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3366\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3366\"><div tabindex=\"-1\"><p>The most recent supercontinent, which formed over 300 million years ago and started breaking apart less than 200 million years ago. Africa and South America, as well as Europe and North America, bordered each other.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1432\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1432\"><div tabindex=\"-1\"><p>Meaning \"middle life,\" it is the middle era of the Phanerozoic, starting at 252 million years ago and ending 66 million years ago. Known as the Age of Reptiles.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1441\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1441\"><div tabindex=\"-1\"><p>The last (and current) era of the Phanerozoic eon, starting 66 million years ago and spanning through the present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3080\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3080\"><div tabindex=\"-1\"><p>Initiation point of an earthquake or fault movement.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2191\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2191\"><div tabindex=\"-1\"><p>The second largest span of time recognized by geologists; smaller than a eon, larger than a period. We are currently in the Cenozoic era. Rocks of a specific era are called eratherms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2589\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2589\"><div tabindex=\"-1\"><p>The innermost chemical layer of the Earth, made chiefly of iron and nickel. It has both liquid and solid components.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2641\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2641\"><div tabindex=\"-1\"><p>The study of the details of light, which can tell you the chemical makeup of light and even the movement of a light source.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3186\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3186\"><div tabindex=\"-1\"><p>The distance between any two repeating portions of a wave (e.g., two successive wave crests).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2642\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2642\"><div tabindex=\"-1\"><p>Visible light and its related energetic waves, including X-rays, UV rays, and radio waves.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2643\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2643\"><div tabindex=\"-1\"><p>A change in wavelength and frequency of a wave due to the source of a wave moving relative to the observer of a wave.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2195\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2195\"><div tabindex=\"-1\"><p>A change in starlight that occurs as light moves away from a source.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2651\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2651\"><div tabindex=\"-1\"><p>The act of gathering new information from the senses or from a scientific instrument.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2196\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2196\"><div tabindex=\"-1\"><p>Trace amounts of energy found throughout the Universe<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2194\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2194\"><div tabindex=\"-1\"><p>The theory that the Universe started with a expansive explosion. Shortly after, elements were created (mostly hydrogen) and galaxies started to form.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2197\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2197\"><div tabindex=\"-1\"><p>A cloud of gas and dust in space that can form a new star\/solar system if it collapses.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3333\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3333\"><div tabindex=\"-1\"><p>A mechanical process which takes ore and separates it from gangue material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2198\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2198\"><div tabindex=\"-1\"><p>A process inside stars where smaller atoms combine and form larger atoms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2689\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2689\"><div tabindex=\"-1\"><p>The measure of the vibrational (kinetic) energy of a substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1933\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1933\"><div tabindex=\"-1\"><p>A feature with no internal structure, habit, or layering.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2199\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2199\"><div tabindex=\"-1\"><p>Large explosion when the largest stars end fusion; cause of the formation of the largest elements in the Universe, like gold and uranium.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2200\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2200\"><div tabindex=\"-1\"><p>The idea that a nebula can collapse and form a star with planets.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2709\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2709\"><div tabindex=\"-1\"><p>Mineral group in which the silica tetrahedra, SiO4-4, is the building block.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2687\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2687\"><div tabindex=\"-1\"><p>A natural substance that is typically solid, has a crystalline structure, and is typically formed by inorganic processes. Minerals are the building blocks of most rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2831\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2831\"><div tabindex=\"-1\"><p>The mineral make up of a rock, i.e. which minerals are found within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2202\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2202\"><div tabindex=\"-1\"><p>A stoney and\/or metallic object from our solar system which was never incorporated into a planet and has fallen onto Earth. Meteorite is used for the rock on Earth, meteoroid for the object in space, and meteor as the object travels in Earth's atmosphere.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2586\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2586\"><div tabindex=\"-1\"><p>Middle chemical layer of the Earth, made of mainly iron and magnesium silicates. It is generally denser than the crust (except for older oceanic crust) and less dense than the core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2580\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2580\"><div tabindex=\"-1\"><p>The outermost chemical layer of the Earth, defined by its low density and higher concentrations of lighter elements. The crust has two types: <strong>continental<\/strong>, which is the thick, more ductile, and lowest density, and <strong>oceanic<\/strong>, which is higher density, more brittle, and thinner.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2176\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2176\"><div tabindex=\"-1\"><p>Any evidence of ancient life.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1181\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1181\"><div tabindex=\"-1\"><p>Place where lava is erupted at the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1446\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1446\"><div tabindex=\"-1\"><p>Stresses that push objects together into a smaller surface area or volume; contracting forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2966\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2966\"><div tabindex=\"-1\"><p>The process of atoms breaking down randomly and spontaneously.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2673\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2673\"><div tabindex=\"-1\"><p>Liquid rock on the surface of the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1174\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1174\"><div tabindex=\"-1\"><p>A series of mineral formation temperatures that can explain the minerals that form in specific igneous rocks. For example, pyroxene will form with olivine and amphibole, but not quartz.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2672\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2672\"><div tabindex=\"-1\"><p>Liquid rock within the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2581\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2581\"><div tabindex=\"-1\"><p>The thin, outer layer of the Earth which makes up the rocky bottom of the ocean basins. It is made of rocks similar to basalt, and as it cools, even become more dense than the upper mantle below.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1956\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1956\"><div tabindex=\"-1\"><p>Can refer to a volcanic rock with lower silica composition, or the minerals that make up those rocks, namely olivine, pyroxene, amphibole, and biotite. Mafic rocks are darker in color and contain more minerals that are dark in color, but can contain some plagioclase feldspar. Primary mafic rocks are basalt (extrusive) and gabbro (intrusive).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2960\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2960\"><div tabindex=\"-1\"><p>An extensive, distinct, and mapped set of geologic layers.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2575\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2575\"><div tabindex=\"-1\"><p>The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust. Continental crust is defined as having higher concentrations of&nbsp;very light elements like K, Na, and Ca, and is the lowest density rocky layer of Earth. Its average composition is similar to granite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1954\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1954\"><div tabindex=\"-1\"><p>Can refer to a volcanic rock with higher silica composition, or the minerals that make up those rocks, namely quartz, feldspar (both potassium feldspar and plagioclase feldspar), and muscovite mica. Felsic rocks are lighter in color and contain more minerals that are light in color, but can contain some biotite and amphibole. Primary felsic rocks are rhyolite (extrusive) and granite (intrusive).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1957\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1957\"><div tabindex=\"-1\"><p>An igneous rock with extremely low silica composition, being made of almost all olivine and pyroxene. Ultramafic rocks contain very low amount of silica and are common in the mantle. Primary ultramafic rocks are komatiite (extrusive) and peridotite (intrusive).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2652\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2652\"><div tabindex=\"-1\"><p>A proposed explanation for an observation that can be tested.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2701\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2701\"><div tabindex=\"-1\"><p>An atom that has different number of neutrons but the same number of protons. While most properties are based on the number of protons in an element, isotopes can have subtle changes between them, including temperature fractionation and radioactivity.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2192\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2192\"><div tabindex=\"-1\"><p>The third largest span of time recognized by geologists; smaller than a era, larger than a epoch. We are currently in the Quaternary period. Rocks of a specific period are called systems.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2206\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2206\"><div tabindex=\"-1\"><p>A hypothesis that states that movement of Jupiter and Saturn about 4 billion years ago caused a destabilization of orbits in the Asteroid and Kuiper Belts, which then caused a spike in impacts throughout of solar system.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3103\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3103\"><div tabindex=\"-1\"><p>An amplification of earthquake waves due to a structure of buildings or structures.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2664\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2664\"><div tabindex=\"-1\"><p>An interconnected set of parts that combine and make up a whole.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1178\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1178\"><div tabindex=\"-1\"><p>Bedrock around the magma chamber being incorporated into the magma, sometimes changing the composition of the magma.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2677\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2677\"><div tabindex=\"-1\"><p>The transport and movement of weathered sediments.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1179\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1179\"><div tabindex=\"-1\"><p>The process of changing a magma's composition, usually through assimilation or fractionation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3345\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3345\"><div tabindex=\"-1\"><p>Minerals with a luster similar to metal and contain metals, including valuable elements like lead, zinc, copper, tin, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3087\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3087\"><div tabindex=\"-1\"><p>Energy that radiates from fault movement via earthquakes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2591\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2591\"><div tabindex=\"-1\"><p>A solid part&nbsp;of the lithosphere which moves as a unit, i.e. the entire plate generally moves the same direction at the same speed.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2590\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2590\"><div tabindex=\"-1\"><p>The outermost physical layer of the Earth, made of the entire crust and upper mantle. It is brittle and broken into a series of plates, and these plates move in various ways (relative to one another), causing the features of the theory of plate tectonics.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2671\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2671\"><div tabindex=\"-1\"><p>The process of changing rocks on Earth into different forms, namely igneous, sedimentary, and metamorphic.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2640\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2640\"><div tabindex=\"-1\"><p>The stable interior part of a continent, typically more than a billion years old, and sometimes as old as &nbsp;2.5-3 billion years. When exposed on the surface, a craton is called a shield.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2207\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2207\"><div tabindex=\"-1\"><p>An exposed part of a craton.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1971\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1971\"><div tabindex=\"-1\"><p>Term for the underlying lithified rocks that make up the geologic record in an area. This term can sometimes refer to only the deeper, crystalline (non-layered) rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2208\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2208\"><div tabindex=\"-1\"><p>Part of a craton that is covered, mainly by sedimentary rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2609\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2609\"><div tabindex=\"-1\"><p>A chain of volcanic activity, typically in a curved pattern, rising from a subduction zone. The arc is on the overriding plate, typically a few hundred kilometers from the trench, but parallel to the trench.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2675\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2675\"><div tabindex=\"-1\"><p>Rocks that are formed from liquid rock, i.e. from volcanic processes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2890\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2890\"><div tabindex=\"-1\"><p>The entire area which is related to land-sea interactions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2175\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2175\"><div tabindex=\"-1\"><p>ZrSiO4.&nbsp;Relatively chemically inert with a hardness of 8.5. Common accessory mineral in igneous and metamorphic rocks, as well as detrital sediments. Uranium can substitute for zirconium, making zircon a valuable mineral in radiometric dating.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2921\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2921\"><div tabindex=\"-1\"><p>Metamorphism which occurs with hot fluids going within rocks, altering and changing the rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1187\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1187\"><div tabindex=\"-1\"><p>Opening of a volcano where lava can erupt.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2213\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2213\"><div tabindex=\"-1\"><p>A fossil that forms as algal mats grow and capture sediment into mounds.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2653\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2653\"><div tabindex=\"-1\"><p>A test of an idea in which new information can be gathered to either accept or reject a hypothesis.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2630\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2630\"><div tabindex=\"-1\"><p>A divergent boundary within an oceanic plate, where new lithosphere and crust is created as the two plates spread apart. Mid-ocean ridge and spreading center are synonyms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1184\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1184\"><div tabindex=\"-1\"><p>A biologic process of gaining energy from chemicals from within the Earth, similar to using the energy of the sun in photosynthesis.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2885\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2885\"><div tabindex=\"-1\"><p>Relatively flat ocean floor, which accumulates very fine grained detrital and chemical sediments.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2210\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2210\"><div tabindex=\"-1\"><p>A period of the early Proterozoic (around 2.5-2 billion years ago) where atmospheric oxygen levels dramatically increased, killing many non-oxygen-breathing organisms and allowing oxygen-breathing organisms to thrive.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2705\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2705\"><div tabindex=\"-1\"><p>The act of taking a solid and dissolving it into a liquid. This commonly occurs with salts and other minerals in water.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1919\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1919\"><div tabindex=\"-1\"><p>Minerals in which ions are bonded to oxygen, such as in ice, H2O.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2849\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2849\"><div tabindex=\"-1\"><p>A very fine grained version of silica deposited with or without microfossils.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2931\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2931\"><div tabindex=\"-1\"><p>A separation of light (felsic) and dark (mafic) minerals in higher grade metamorphic rocks like gneiss.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2707\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2707\"><div tabindex=\"-1\"><p>The act of a solid coming out of solution, typically resulting from a drop in temperature or a decrease of the dissolving material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2857\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2857\"><div tabindex=\"-1\"><p>Discernible layers of rock, typically from a sedimentary rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2815\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2815\"><div tabindex=\"-1\"><p>The process in which solids (like minerals) are disassociated and the ionic components are dispersed in a liquid (usually water).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2706\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2706\"><div tabindex=\"-1\"><p>A solution that has the maximum allowed dissolved component, and is unable to dissolve more.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1700\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1700\"><div tabindex=\"-1\"><p>A period of cooler temperatures on Earth in which ice sheets can grow on continents.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3342\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3342\"><div tabindex=\"-1\"><p>A geologic circumstance (such as a fold, fault, change in lithology, etc.) which allows petroleum resources to collect.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1715\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1715\"><div tabindex=\"-1\"><p>The ability for the atmosphere to absorb heat that is emitted by a planet's surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2211\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2211\"><div tabindex=\"-1\"><p>The supercontinent that existed before Pangea, about 1 billion years ago. North America was positioned in the center of the land mass.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2212\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2212\"><div tabindex=\"-1\"><p>Geologic name for the craton that makes up North America.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2217\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2217\"><div tabindex=\"-1\"><p>Meaning \"visible life,\" the most recent eon in Earth's history, starting at 541 million years ago and extending through the present. Known for the diversification and evolution of life, along with the formation of Pangea.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2214\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2214\"><div tabindex=\"-1\"><p>A type of single-celled organism with no nucleus.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2215\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2215\"><div tabindex=\"-1\"><p>A type of organism in with a cell or cells that contains a nucleus.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3134\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3134\"><div tabindex=\"-1\"><p>A channelled body of water.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1915\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1915\"><div tabindex=\"-1\"><p>SiO2. Transparent, but can be any color imaginable with impurities. No cleavage, hard, and commonly forms equant masses. Perfect crystals are hexagonal prisms topped with pyramidal shapes. One of the most common minerals, and is found in many different geologic settings, including the dominant component of sand on the surface of Earth. Structure is a three-dimensional network of silica tetrahedra, connected as much as possible to each other.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2834\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2834\"><div tabindex=\"-1\"><p>A rock primarily made of sand.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2935\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2935\"><div tabindex=\"-1\"><p>A metamorphosed sandstone.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2216\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2216\"><div tabindex=\"-1\"><p>A group of relatively complex organisms that existed at the end of the Proterozoic.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2218\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2218\"><div tabindex=\"-1\"><p>A term for the collective time before the Phanerozoic (pre-541 million years ago), including the Hadean, Archean, and Proterozoic. Known for a lack of easy-to-find fossils.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2883\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2883\"><div tabindex=\"-1\"><p>Places that are under ocean water at all times.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1429\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1429\"><div tabindex=\"-1\"><p>The fifth (second to last) period in the Paleozoic, 359-299 million years ago. In North America, the Carboniferous is split into two different periods, the Mississippian (359-323 million years ago) and the Pennsylvanian (323-299 million years ago).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2856\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2856\"><div tabindex=\"-1\"><p>Former swamp-derived (plant) material that is part of the rock record.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2851\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2851\"><div tabindex=\"-1\"><p>A chemical or biochemical rock made of mainly calcite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2845\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2845\"><div tabindex=\"-1\"><p>Spheres of calcite that form in saline waters with slight wave agitation. Ooid refers to the sphere, oolite the rock with the spheres.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3119\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3119\"><div tabindex=\"-1\"><p>Detached, free-falling rocks from very steep slopes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2961\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2961\"><div tabindex=\"-1\"><p>Missing time in the rock record, either because of a lack of deposition and\/or erosion.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2602\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2602\"><div tabindex=\"-1\"><p>A process where an oceanic plate descends bellow a less dense plate, causing the removal of the plate from the surface. Subduction causes the largest earthquakes possible, as the subducting plate can lock as it goes down. Volcanism is also caused as the plate releases volatiles into the mantle, causing melting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1461\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1461\"><div tabindex=\"-1\"><p>A down-warped feature in the crust.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2598\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2598\"><div tabindex=\"-1\"><p>A boundary between continental and oceanic plates that has no relative movement, making it a place where an oceanic plate is connected to a continental plate, but it is not a plate boundary.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2891\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2891\"><div tabindex=\"-1\"><p>Submerged part of the continental mass, with a gentle slope.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2227\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2227\"><div tabindex=\"-1\"><p>Known as the \"Age of Fishes,\" the 4th period of the Paleozoic, about 419-359 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2585\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2585\"><div tabindex=\"-1\"><p>The process of uplifting mountain within mountain belts, primarily via tectonic movement. <strong>Orogenic belts<\/strong> are the mountain belts that result from these movements, and <strong>orogenesis<\/strong> is the name for the process of forming mountain belts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2619\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2619\"><div tabindex=\"-1\"><p>Place where oceanic-oceanic subduction causes volcanoes to form on an overriding oceanic plate, making a chain of active volcanoes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2620\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2620\"><div tabindex=\"-1\"><p>When two continents crash, with no subduction (and thus little to no volcanism), since each continent is to buoyant. Many of the largest mountain ranges and broadest zones of seismic activity come from collisions.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2617\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2617\"><div tabindex=\"-1\"><p>Place with a chain of mountain volcanism on a continent, from oceanic-continental subduction.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2592\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2592\"><div tabindex=\"-1\"><p>Location where two plates are in contact, allowing a relative motion between the two plates. These are the locations where&nbsp;most earthquakes and volcanoes are found.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2224\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2224\"><div tabindex=\"-1\"><p>The first period of the Paleozoic, 541 million years ago-485 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2220\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2220\"><div tabindex=\"-1\"><p>A period of time in the early Cambrian (about 541-516 million years ago) in which a large diversification of life forms was found in the fossil record. Many of the modern phyla of organisms evolved in this time span.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1710\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1710\"><div tabindex=\"-1\"><p>Long term averages and variations within the conditions of the atmosphere.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2910\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2910\"><div tabindex=\"-1\"><p>Deposition and erosion tied to glacier movement.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2839\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2839\"><div tabindex=\"-1\"><p>A very fine-grained rock with very thin layering (fissile).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2221\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2221\"><div tabindex=\"-1\"><p>An exceptionally-well preserved fossil locality, often including soft tissues.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2698\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2698\"><div tabindex=\"-1\"><p>The end of a river out of which water flows into a sea or other large body of water.<\/p>\n<p>Source:&nbsp;https:\/\/en.wiktionary.org\/wiki\/mouth<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2222\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2222\"><div tabindex=\"-1\"><p>Organisms that possess vertebrate or some form of a spinal column, including humans.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2225\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2225\"><div tabindex=\"-1\"><p>The second period of the Paleozoic era, 485-444 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2898\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2898\"><div tabindex=\"-1\"><p>A topographic high found away from the beach in deeper water, but still on the continental shelf. Typically, these are formed in tropical areas by organisms such as corals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1918\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1918\"><div tabindex=\"-1\"><p>CaCO3. Pure form is clear, but can take on many different colors with impurities. It is soft, fizzes in acid, and has three cleavages that are not at 90\u00b0. Thus, it can form slanted blocks, though it is visually common to be without any structure. Found in many sedimentary rocks from marine settings, rarely in igneous rocks, in the metamorphic rock marble, but is common as a secondary mineral throughout surface rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2223\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2223\"><div tabindex=\"-1\"><p>A pronounced increase in the extinction rate, typically caused by significant environmental change. There have been 5 mass extinctions in geologic history, and a sixth that has been suggested to be currently occurring.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2226\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2226\"><div tabindex=\"-1\"><p>The third period of the Paleozoic, 444-420 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2902\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2902\"><div tabindex=\"-1\"><p>Depositional environments that are on land.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3116\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3116\"><div tabindex=\"-1\"><p>Empty space in a geologic material, either within sediments, or within rocks. Can be filled by air, water, or hydrocarbons.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1428\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1428\"><div tabindex=\"-1\"><p>The last period of the Paleozoic, 299-252 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1430\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1430\"><div tabindex=\"-1\"><p>The largest mass extinction in history, where an estimated 83% of genera went extinct. Linked to the Siberian Trapps as a cause.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1197\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1197\"><div tabindex=\"-1\"><p>Rare very low viscosity eruption that covers vast areas. None have been observed in human history.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1438\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1438\"><div tabindex=\"-1\"><p>The first period of the Mesozoic era, from 252-201 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2678\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2678\"><div tabindex=\"-1\"><p>Pieces of rock that have been weathered and possibly eroded.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2624\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2624\"><div tabindex=\"-1\"><p>Area of extended continental lithosphere, forming a depression. Rifts can be narrow (focused in one place) or broad (spread out over a large area with&nbsp;many faults).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1970\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1970\"><div tabindex=\"-1\"><p>A type of dike that is parallel to bedding planes within the bedrock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1439\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1439\"><div tabindex=\"-1\"><p>The middle period of the Mesozoic era, 201-145 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3065\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3065\"><div tabindex=\"-1\"><p>Planer feature where two blocks of bedrock move past each other via earthquakes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1455\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1455\"><div tabindex=\"-1\"><p>A rock layer that has been bent in a ductile way instead of breaking (as with faulting).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1440\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1440\"><div tabindex=\"-1\"><p>The last period of the Mesozoic, 145-66 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1433\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1433\"><div tabindex=\"-1\"><p>A waterway that existed in North America around 100 million years ago. Western North America was separated from eastern North America.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1434\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1434\"><div tabindex=\"-1\"><p>The most recent mass extinction, which killed the non-avian dinosaurs and paved the way for the diversification of mammals. Occurred when a bolide hit near Chicxulub, Mexico 66 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1435\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1435\"><div tabindex=\"-1\"><p>A large extraterrestrial object, such as a meteor or asteroid, that hits the surface of the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3194\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3194\"><div tabindex=\"-1\"><p>Formally known as a tidal wave, it is a large wave produced from a sudden movement of the floor of a ocean basin, caused by events such as earthquakes, volcanic eruptions, landslides, and bolide impacts.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3337\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3337\"><div tabindex=\"-1\"><p>A fossil fuel derived from shallow marine rocks. Consists of oil and natural gas.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1437\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1437\"><div tabindex=\"-1\"><p>A 180 kilometer (110 mile) crater that exists near&nbsp;Chicxulub, Mexico on the Yucatan Peninsula. Made during the K-T extinction.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1962\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1962\"><div tabindex=\"-1\"><p>General name of a felsic rock that is intrusive. Has more felsic minerals than mafic minerals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2601\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2601\"><div tabindex=\"-1\"><p>Place where two plates slide past each other, creating strike slip faults.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2600\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2600\"><div tabindex=\"-1\"><p>Place where two plates come together, casing subduction or collision.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2599\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2599\"><div tabindex=\"-1\"><p>Place where two plates are moving apart, creating either a rift (continental lithosphere) or a mid-ocean ridge (oceanic lithosphere).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2612\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2612\"><div tabindex=\"-1\"><p>Faulting that is deep into the crust, and typically involves crystalline basement rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1445\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1445\"><div tabindex=\"-1\"><p>Stresses that pull objects apart into a larger surface area or volume; stretching forces.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2462\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2462\"><div tabindex=\"-1\"><p>Term for the extensional tectonic province that extends from California's Sierra Nevada Mountains in the west, to Utah's Wasatch Mountains to the east, to southern Oregon and Idaho to the north, to northern Mexico to the south. Known as a wide rift, as each graben 'basin,' bounded by horst 'ranges.' Each set of horsts with a graben has some individual extension, adding up to the overall rifting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2605\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2605\"><div tabindex=\"-1\"><p>Name given to the subducting plate, where volatiles are driven out at depth, causing volcanism.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2593\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2593\"><div tabindex=\"-1\"><p>A ductile physical layer of the Earth, below the lithosphere. Movement within the asthenosphere is the main driver of plate motion, as the overriding lithosphere is pushed by this.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1953\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1953\"><div tabindex=\"-1\"><p>Rocks made from pyroclastic tephra: either ash, lapilli, and\/or bombs. Tephra type can be used as an adjective, i.e. ash-fall tuff. If deposited hot, where material can fuse together while hot, the rock is then called a welded tuff.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1443\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1443\"><div tabindex=\"-1\"><p>The most recent, and current, period within the Cenozoic era, starting 2.58 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2467\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2467\"><div tabindex=\"-1\"><p>Thick glaciers that cover continents during ice ages.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1701\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1701\"><div tabindex=\"-1\"><p>A series of changes to the Earth's orbit which can fluctuate climate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1444\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1444\"><div tabindex=\"-1\"><p>The most recent epoch of geologic time, from 11,700 years ago to present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_2193\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_2193\"><div tabindex=\"-1\"><p>The second smallest span of time recognized by geologists; smaller than a period, larger than as age. We are currently in the Holocene epoch. Rocks of a specific epoch are called series.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1442\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1442\"><div tabindex=\"-1\"><p>A newly-proposed time segment (an epoch) that would be representative of time since humans have changed (and left evidence behind within) the geologic record.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3380\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3380\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_1939\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_1939\"><div tabindex=\"-1\"><p>Igneous rock cooling, and thus forming, inside of the Earth, i.e. under the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_600_3363\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_600_3363\"><div tabindex=\"-1\"><p>Sedimentary rocks made of mineral grains weathered as mechanical detritus of previous rocks, e.g. sand, gravel, etc.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":83,"menu_order":8,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-600","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":19,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/600","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/users\/83"}],"version-history":[{"count":3,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/600\/revisions"}],"predecessor-version":[{"id":3409,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/600\/revisions\/3409"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/parts\/19"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/600\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/media?parent=600"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapter-type?post=600"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/contributor?post=600"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/license?post=600"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}