{"id":5500,"date":"2023-09-01T15:25:20","date_gmt":"2023-09-01T19:25:20","guid":{"rendered":"https:\/\/www.fas37.org\/wp\/?p=5500"},"modified":"2026-02-05T05:36:58","modified_gmt":"2026-02-05T10:36:58","slug":"geologic-time","status":"publish","type":"post","link":"https:\/\/www.fas37.org\/wp\/geologic-time\/","title":{"rendered":"A History of the Earth (Geologic Time)"},"content":{"rendered":"\n<p class=\"\"><strong>FAS Astronomers Blog, Volume 31, Number 10.<\/strong><\/p>\n\n\n\n<p class=\"\">The history of the Earth is described by geologists using something call Geologic Time. This is a timeline from the beginning of the Earth to the present day broken down into a hierarchy of four main groupings: <strong>Eons<\/strong>, <strong>Eras<\/strong>, <strong>Periods<\/strong>, and <strong>Epochs<\/strong>. Epochs are broken down further into <strong>Ages<\/strong>, but we won\u2019t go there.<\/p>\n\n\n\n<p class=\"\"><\/p>\n\n\n\n<!--more-->\n\n\n\n<figure class=\"wp-block-image aligncenter is-resized\"><a href=\"https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?ssl=1\"><img data-recalc-dims=\"1\" loading=\"lazy\" decoding=\"async\" width=\"818\" height=\"886\" data-attachment-id=\"5709\" data-permalink=\"https:\/\/www.fas37.org\/wp\/geologic-time\/geologic-time-chart-alt\/\" data-orig-file=\"https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?fit=818%2C886&amp;ssl=1\" data-orig-size=\"818,886\" data-comments-opened=\"0\" data-image-meta=\"{&quot;aperture&quot;:&quot;0&quot;,&quot;credit&quot;:&quot;&quot;,&quot;camera&quot;:&quot;&quot;,&quot;caption&quot;:&quot;&quot;,&quot;created_timestamp&quot;:&quot;0&quot;,&quot;copyright&quot;:&quot;&quot;,&quot;focal_length&quot;:&quot;0&quot;,&quot;iso&quot;:&quot;0&quot;,&quot;shutter_speed&quot;:&quot;0&quot;,&quot;title&quot;:&quot;&quot;,&quot;orientation&quot;:&quot;0&quot;}\" data-image-title=\"Geologic Time Chart Alt\" data-image-description=\"\" data-image-caption=\"\" data-large-file=\"https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?fit=818%2C886&amp;ssl=1\" src=\"https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?resize=818%2C886&#038;ssl=1\" alt=\"\" class=\"wp-image-5709\" style=\"width:704px;height:auto\" srcset=\"https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?w=818&amp;ssl=1 818w, https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?resize=277%2C300&amp;ssl=1 277w, https:\/\/i0.wp.com\/www.fas37.org\/wp\/wp-content\/uploads\/2023\/08\/Geologic-Time-Chart-Alt.png?resize=768%2C832&amp;ssl=1 768w\" sizes=\"auto, (max-width: 818px) 100vw, 818px\" \/><\/a><\/figure>\n\n\n\n<div class=\"wp-block-group is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:1px;border-radius:10px;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\">The first three eons (<strong>Hadean<\/strong>, <strong>Archean<\/strong>, and <strong>Proterozoic<\/strong>) are often combined into the <strong>Precambrian<\/strong> supereon covering the first four billion years of the Earth\u2019s history &#8211; around 4 \u00bd billion years ago (Gya) up to 539 million years ago (Mya).<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\"><strong>Hadean<\/strong> eon (4.6 to 4.0 Gya) is when the Earth first formed. It was a hot molten sphere during a time when the Moon also formed, and the Late Heavy Bombardment rained asteroids down on the planet.<\/li>\n\n\n\n<li class=\"\"><strong>Archean<\/strong> eon (4.0 to 2.5 Gya) is when the Earth cooled forming the first rocks, and life emerged some 3.8 to 3.5 billion years ago &#8211; although some studies suggest it began earlier. The Sun\u2019s intensity was around 70% of today\u2019s levels, but greenhouse gases kept the Earth warm. Cyanobacteria began performing photosynthesis, which eventually produced the first oxygen.<\/li>\n\n\n\n<li class=\"\"><strong>Proterozoic<\/strong> eon (2.5 to .539 Gya) saw the<strong> Great Oxidation event<\/strong> (GOE) when aerobic (oxygen breathing life) began to dominate the planet. Around 700 million years ago, the planet froze during the <strong>Cryogenian ice age,<\/strong> creating a <strong>Snowball Earth<\/strong>. This&nbsp;led to the <strong>Ediacaran<\/strong> (<em>EE-dee-A-care-an<\/em>) period and possibly the first simple multi-cellular animal life.<\/li>\n<\/ul>\n<\/div>\n\n\n\n<p class=\"\">The <strong>Phanerozoic<\/strong> (<em>Fan-er-oh-zo-ik)<\/em> eon, beginning 539 million years ago, is when things started to get really interesting. The Phanerozoic is divided into three eras: the <strong>Paleozoic <\/strong>(age of complex life), <strong>Mesozoic <\/strong>(age of reptiles)<em>,<\/em> and <strong>Cenozoic <\/strong>(age of mammals).<\/p>\n\n\n\n<div class=\"wp-block-group is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:1px;border-radius:10px;padding-top:5px;padding-right:4px;padding-bottom:5px;padding-left:4px\">\n<p class=\"\">The <strong>Paleozoic<\/strong> era saw the greatest expansion of life and the greatest disappearance of life in the Earth\u2019s history. It was during this time that life diversified from simple structures to many complex forms similar to what we see today.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\"><strong>Cambrian <\/strong>(<em>Kam-bree-an<\/em>) period (541 to 485 Mya) began with the <strong>Cambrian Explosion<\/strong>. This was the most significant increase in the diversity of life. Many invertebrates including hard shelled organisms such as Trilobites appeared (and fossilized). The first vertebrates (jawless fish) also appeared. Life was found primarily in the seas, while the land was mostly barren.<\/li>\n\n\n\n<li class=\"\"><strong>Ordovician<\/strong><em> (Or-doh-vish-an<\/em>) period (485 to 444 Mya) began with the <strong>Great Ordovician Biodiversification Event<\/strong> (aka the <strong>Ordovician Radiation<\/strong>). This period ended with the <strong>Andean-Saharan ice age<\/strong> that resulted in the <strong>Ordovician-Silurian extinction<\/strong>.<\/li>\n\n\n\n<li class=\"\"><strong>Silurian<\/strong> (<em>Sih-lyoor-ee-an<\/em>) period (444 to 419 Mya) saw placoderms (armored fish with jaws) first appear. Fish then diversified with the appearance of cartilaginous and bony fish late in the period.<\/li>\n\n\n\n<li class=\"\"><strong>Devonian<\/strong> (<em>Dah-voh-knee-an<\/em>) period (419 to 359 Mya) is called the \u201cage of fishes\u201d. Placoderms, such as <em>Dunkleosteus<\/em>, dominated the oceans but vanished by the end of the period. Bony fish split into two groups. There were the ray-finned fish (with fins attached with a ray of bones) similar to many fish of today. However, it was the lobe-finned fish (with fins attached by a single bone) that led to the first land dwelling tetrapods (four legged amphibious vertebrates). The Devonian ended with the beginning of the <strong>Karoo ice age<\/strong> and the <strong>Devonian-Carboniferous extinction<\/strong>.<\/li>\n\n\n\n<li class=\"\"><strong>Carboniferous<\/strong> (<em>Carbon-if-er-us<\/em>) period (359 to 299 Mya) saw mossy swamps containing trees, which decayed to form coal deposits. Amphibians led to land-dwelling amniotes (tetrapods having eggs with a membrane). Amniotes diverged into mammal ancestors (synapsids) and reptile ancestors (sauropsids\/diapsids). Oxygen levels were higher than today, which supported large insects such as giant 2 \u00bd foot dragonflies <em>(Meganeura)<\/em> and 10-foot millipedes (<em>Arthropleura<\/em>).<\/li>\n\n\n\n<li class=\"\"><strong>Permian<\/strong> (<em>Per-me-an<\/em>) period (299 to 252 Mya) saw the Carboniferous Rainforest Collapse bringing a more arid climate. Seed-bearing plants and larger mammal ancestors (pelycosaurs and therapsids) became prevalent. The supercontinent of Pangaea formed during this time.<\/li>\n<\/ul>\n\n\n\n<p class=\"\">The <strong>Paleozoic<\/strong> era ended with the <strong>Permian-Triassic (P-T) extinction<\/strong> (aka the Great Dying) that wiped out around 90% of Earth\u2019s marine species and 70% of the land species. This was the greatest mass extinction in Earth\u2019s history.&nbsp;According to Michael Benton in <em>When Life Nearly Died<\/em> and Andrew Knoll in <em>A Brief History of Earth, <\/em>the P-T extinction was most likely caused by volcanic eruptions that created the Siberian Traps in northern Russia. The eruptions produced a general increase in CO<sub>2<\/sub> levels, which resulted in a catastrophic effect on the planet including a runaway Greenhouse effect with reduced oceanic oxygen levels, acid rain, and global warming.<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-group is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:1px;border-radius:10px;padding-top:5px;padding-right:4px;padding-bottom:5px;padding-left:4px\">\n<p class=\"\">The <strong>Mesozoic <\/strong>era brought the age of reptiles and particularly the dinosaurs. The Mesozoic is divided into three periods (<strong>Triassic<\/strong>, <strong>Jurassic<\/strong>, and <strong>Cretaceous<\/strong>).<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\"><strong>Triassic<\/strong> period (252 to 201 Mya) saw life slowly recover from the Great Dying. Early on, the last big therapsid, the two-tusked <em>Lystrosaurus<\/em>, spread across Pangaea before dying off. Archosaurs (ruling reptiles) eventually dominated the Triassic, while the first small mammals and dinosaurs appeared. The Earth\u2019s land mass started to split in two during the latter part of the Triassic. The Triassic period ended with the <strong>Triassic-Jurassic extinction<\/strong>.<\/li>\n\n\n\n<li class=\"\"><strong>Jurassic<\/strong> period (201 to 145 Mya) saw large plant eating sauropods (e.g., <em>Apatosaurus<\/em>\/<em>Brontosaurus<\/em>) and the first of the large two-legged meat eating theropods (e.g., <em>Allosaurus<\/em>) roam the Earth. Large dinosaur like reptiles (ichthyosaurs, plesiosaurs, and pliosaurs) swam the depths of the seas. The first of the Pterosaurs, <em>Pterodactyl<\/em>, circled overhead. The supercontinent of Pangaea continued to split apart into Laurasia (in the north) and Gondwana (in the south).<\/li>\n\n\n\n<li class=\"\"><strong>Cretaceous<\/strong> period (145 to 66 Mya) saw the giant theropods, such as <em>T. rex<\/em>, rule the Earth. Large sauropods called titanosaurs continued through the Cretaceous. Mosasaurs replaced the earlier giant marine reptiles of the Jurassic. Larger Pterosaurs such as <em>Pteranodon <\/em>and <em>Quetzalcoatlus<\/em> were found in the skies. Laurasia and Gondwana each continued to break up into continents somewhat similar to those we find today.<\/li>\n<\/ul>\n\n\n\n<p class=\"\">The <strong>Mesozoic<\/strong> era ended 66 million years ago with the <strong>Cretaceous-Paleogene (K-Pg) extinction<\/strong> that wiped out around 70% of the Earth\u2019s species including the dinosaurs. The K-Pg extinction is thought to be the result of a 6- to 9-mile-wide asteroid that smashed into the Earth near the present-day town of Chicxulub, Mexico on the Yucatan Peninsula.<\/p>\n<\/div>\n\n\n\n<div class=\"wp-block-group is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:1px;border-radius:10px;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\">The <strong>Cenozoic<\/strong> (<em>Sign-oh-zo-ik<\/em>) era brought the age of mammals. The modern divisions include the <strong>Paleogene<\/strong>, <strong>Neogene<\/strong>, and<strong> Quaternary<\/strong> periods.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\"><strong>Paleogene<\/strong> period (66 to 23 Mya) saw a warm climate with jungles and the first expansion of mammals including early primates.&nbsp;The Paleogene is further divided into the <strong>Paleocene,<\/strong> <strong>Eocene,<\/strong> and <strong>Oligocene<\/strong> epochs.<\/li>\n\n\n\n<li class=\"\"><strong>Neogene<\/strong> period (23 to 2.6 Mya) brought a cooling climate and more grasslands. Hominids, including the ancestors of humans, orangutans, gorillas, and chimpanzees, appeared roughly 15 Mya during the <b>Miocene <\/b>epoch (23 to 5.2 Mya). The human tree, hominins, branched off from the others around 7 Mya. <em>Australopithecus<\/em> appeared around 4 Mya near the beginning of the <b>Pliocene <\/b>epoch (5.3 to 2.6 Mya). Lurking under the water during this time was the bus sized shark, <em>Megalodon<\/em>.<\/li>\n<\/ul>\n\n\n\n<p class=\"\">The <strong>Quaternary<\/strong> (<em>Kwah-tur-nah-ree<\/em>) period is divided into two epochs and continues to this day. This period experienced the last great ice age (<strong>Quaternary\/Pleistocene ice age<\/strong>) with periods of \u201cglacials\u201d and \u201cinterglacials\u201d.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\"><strong>Pleistocene<\/strong> (<em>Ply-stoh-seen<\/em>) epoch (2.6 Mya to 11.7 Kya) was the age of saber-tooth tigers, woolly mammoths, and mastodons. The human genus <em>Homo<\/em> appeared around 2 Mya, and the species <em>Homo sapiens<\/em> around 300 thousand years ago (Kya). The most recent period of glaciation (i.e., THE ice age) began around 115,000 years ago.<\/li>\n\n\n\n<li class=\"\"><strong>Holocene <\/strong>epoch (11.7 Kya to now) is the \u201cage of humans\u201d with a warming and stable climate as the last period of glaciation ended and humans came to dominate the planet.<\/li>\n<\/ul>\n<\/div>\n\n\n\n<p class=\"\">4 \u00bd billion years is a long time, so if you missed the highlights \u2013 here they are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">The Earth formed 4 \u00bd billion years ago at the beginning of the <strong>Hadean<\/strong><\/li>\n\n\n\n<li class=\"\">Life began some 3.8 to 3.5 billion years ago during the <strong>Archean<\/strong><\/li>\n\n\n\n<li class=\"\">The <em>Great Oxidation Event<\/em> (GOE) transformed the Earth\u2019s atmosphere during the <strong>Proterozoic<\/strong><\/li>\n\n\n\n<li class=\"\">Life diversified in the <em>Cambrian Explosion<\/em> during the <strong>Cambrian<\/strong><\/li>\n\n\n\n<li class=\"\">Fish crawled out of the sea during the <strong>Devonian<\/strong><\/li>\n\n\n\n<li class=\"\">Large mammal ancestors appeared during the <strong>Permian<\/strong> period but were wiped out in the <strong>P-T extinction<\/strong>.<\/li>\n\n\n\n<li class=\"\">Dinosaurs took over during the <strong>Mesozoic<\/strong> era but were wiped out in the <strong>K-Pg extinction<\/strong>.<\/li>\n\n\n\n<li class=\"\">Mammals rebounded during the <strong>Cenozoic<\/strong> era after the <strong>K-Pg extinction.<\/strong><\/li>\n\n\n\n<li class=\"\">The last ice age occurred during the <strong>Quaternary<\/strong> period, with the last period of glaciation occurring during the <strong>Pleistocene<\/strong><\/li>\n\n\n\n<li class=\"\">Saber-tooth tigers, woolly mammoths, and mastodons were found during the <strong>Pleistocene<\/strong><\/li>\n\n\n\n<li class=\"\">Humans first appeared during the late <strong>Pleistocene<\/strong> epoch and came to dominate the planet during the <strong>Holocene<\/strong><\/li>\n<\/ul>\n\n\n\n<p class=\"\">For more details on geologic time, the IUGS <a href=\"https:\/\/stratigraphy.org\/\" target=\"_blank\" rel=\"noreferrer noopener\">International Commission on Stratigraphy<\/a> maintains <a href=\"https:\/\/stratigraphy.org\/gssps\/\" target=\"_blank\" rel=\"noreferrer noopener\">Global Boundary Stratotype Section and Points<\/a> (GSSP) along with a detailed <a href=\"https:\/\/stratigraphy.org\/chart\" target=\"_blank\" rel=\"noreferrer noopener\">chart of Geologic Time<\/a>. Two additional charts are provided by <a href=\"https:\/\/www.geosociety.org\/GSA\/Education_Careers\/Geologic_Time_Scale\/GSA\/timescale\/home.aspx\" target=\"_blank\" rel=\"noreferrer noopener\">The Geological Society of America<\/a>, and the <a href=\"https:\/\/pubs.usgs.gov\/fs\/2010\/3059\/\">U. S. Geological Survey<\/a>.<\/p>\n\n\n\n<p class=\"\">The folks at dinosaurpicture.org have a nice <a href=\"https:\/\/dinosaurpictures.org\/ancient-earth#300\" target=\"_blank\" rel=\"noreferrer noopener\">website<\/a> that will show you what the Earth looked like at any point in geologic time.<\/p>\n\n\n\n<div class=\"wp-block-group has-background is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:2px;border-radius:10px;background-color:#eaf4ec;margin-top:1rem;margin-bottom:1rem;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\"><u>Selected Sources and Further Reading (Geologic Time Charts)<\/u><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">\u201c<a href=\"https:\/\/stratigraphy.org\/chart\" target=\"_blank\" rel=\"noreferrer noopener\">Chart.<\/a>\u201d International Commission on Stratigraphy.\u201d <\/li>\n\n\n\n<li class=\"\">U.S. Geological Survey Geologic Names Committee. \u201c<a href=\"https:\/\/pubs.usgs.gov\/fs\/2010\/3059\/\" target=\"_blank\" rel=\"noreferrer noopener\">Divisions of Geologic Time-Major Chronostratigraphic and Geochronologic Units<\/a>.\u201d <a href=\"https:\/\/pubs.usgs.gov\/fs\/2010\/3059\/pdf\/FS10-3059.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">PDF<\/a>. USGS. Fact Sheet 2010-3059. July 20, 2010. <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/www.geosociety.org\/GSA\/Education_Careers\/Geologic_Time_Scale\/GSA\/timescale\/home.aspx\" target=\"_blank\" rel=\"noreferrer noopener\">GSA Geologic Time Scale, Version 5.0.<\/a>\u201d The Geological Society of America. August 2018. <a href=\"https:\/\/www.geosociety.org\/documents\/gsa\/timescale\/timescl.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">https:\/\/www.geosociety.org\/documents\/gsa\/timescale\/timescl.pdf<\/a><\/li>\n\n\n\n<li class=\"\">Hobart M King, Ph.D. \u201c<a href=\"https:\/\/geology.com\/time.htm\" target=\"_blank\" rel=\"noreferrer noopener\">Geologic Time Scale, A Time Line for Geological Sciences<\/a>.\u201d Geology.com. (Accessed August 18, 2020). <a href=\"https:\/\/geology.com\/time\/geologic-time-scale.pdf\" target=\"_blank\" rel=\"noreferrer noopener\">https:\/\/geology.com\/time\/geologic-time-scale.pdf<\/a><\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-group has-background is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:2px;border-radius:10px;background-color:#eaf4ec;margin-top:1rem;margin-bottom:1rem;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\"><u>Selected Sources and Further Reading (IUGS &amp; ICS)<\/u><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">\u201c<a href=\"https:\/\/www.iugs.org\/\" target=\"_blank\" rel=\"noreferrer noopener\">IUGS \u2013 International Union of Geological Science<\/a>.\u201d <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/stratigraphy.org\/\" target=\"_blank\" rel=\"noreferrer noopener\">International Commission on Stratigraphy<\/a>.\u201d International Union of Geological Science. <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/stratigraphy.org\/gssps\/\">Global Boundary Stratotype Section and Points (GSSP)<\/a>.\u201d International Commission on Stratigraphy.<\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-group has-background is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:2px;border-radius:10px;background-color:#eaf4ec;margin-top:1rem;margin-bottom:1rem;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\"><u>Selected Sources and Further Reading<\/u><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">\u201c<a href=\"https:\/\/earthhow.com\/category\/geology\/geologic-timeline\/\" target=\"_blank\" rel=\"noreferrer noopener\">Geologic Timeline<\/a>.\u201d EarthHow. <\/li>\n\n\n\n<li class=\"\">Charles. \u201c<a href=\"https:\/\/earthlyuniverse.com\/hadean-earth-violent-creation-of-our-world\/\" target=\"_blank\" rel=\"noreferrer noopener\">A Journey through the History of the Earth<\/a>.\u201d Earthly Universe. November 2016 \u2013 March 2017. (Part 1 of 15 starts here.) <\/li>\n\n\n\n<li class=\"\">Andrew Alden. &#8220;<a href=\"https:\/\/www.thoughtco.com\/geologic-time-scale-eons-eras-periods-1440796\" target=\"_blank\" rel=\"noreferrer noopener\">Geologic Time Scale: Eons, Eras, and Periods.<\/a>&#8221; ThoughtCo, Mar. 3, 2021, thoughtco.com\/geologic-time-scale-eons-eras-periods-1440796. <\/li>\n\n\n\n<li class=\"\">Heather Scoville. &#8220;<a href=\"https:\/\/www.thoughtco.com\/the-5-major-mass-extinctions-4018102\" target=\"_blank\" rel=\"noreferrer noopener\">The 5 Major Mass Extinctions<\/a>.&#8221; ThoughtCo, Jul. 27, 2021, thoughtco.com\/the-5-major-mass-extinctions-4018102. <\/li>\n\n\n\n<li class=\"\">Scott Dutfield. \u201c<a href=\"https:\/\/www.livescience.com\/mass-extinction-events-that-shaped-Earth.html\" target=\"_blank\" rel=\"noreferrer noopener\">The 5 mass extinction events that shaped the history of the Earth \u2013 and the 6<sup>th<\/sup> that\u2019s happening now.<\/a>\u201d Live Science. May 17, 2021. <\/li>\n\n\n\n<li class=\"\">Ian Webster. \u201c<a href=\"https:\/\/dinosaurpictures.org\/ancient-earth#300\" target=\"_blank\" rel=\"noreferrer noopener\">What Did The Earth Look Like<\/a>.\u201d Ancient Earth\/dinosaurpictures.org. <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/youtu.be\/tkxWmh-tFGs\" target=\"_blank\" rel=\"noreferrer noopener\">Four ways to understand the Earth&#8217;s age &#8211; Joshua M. Sneideman.<\/a>\u201d TED-Ed\/YouTube.&nbsp;August 29, 2013.&nbsp;<\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-group has-background is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:2px;border-radius:10px;background-color:#eaf4ec;margin-top:1rem;margin-bottom:1rem;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\"><u>Selected Sources and Further Reading (A deeper dive)<\/u><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">\u201c<a href=\"https:\/\/opengeology.org\/historicalgeology\/geologic-time\/\" target=\"_blank\" rel=\"noreferrer noopener\">Geologic Time.<\/a>\u201d Historical Geology. <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/slcc.pressbooks.pub\/introgeology\/chapter\/7-geologic-time\/\" target=\"_blank\" rel=\"noreferrer noopener\">7 Geologic Time<\/a>.\u201d An Introduction to Geology. Salt Lake Community College. <\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-group has-background is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:2px;border-radius:10px;background-color:#eaf4ec;margin-top:1rem;margin-bottom:1rem;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\"><u>Selected Sources and Further Reading (Books)<\/u><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">Andrew H. Knoll. <em><a href=\"https:\/\/www.goodreads.com\/book\/show\/54390506-a-brief-history-of-earth\" target=\"_blank\" rel=\"noreferrer noopener\">A Brief History of Earth, Four Billion Years in Eight Chapters<\/a><\/em>. Custom House. 2021.&nbsp; <\/li>\n\n\n\n<li class=\"\">Robert M. Hazen. <em><a href=\"https:\/\/archive.org\/details\/isbn_9780670023554\" target=\"_blank\" rel=\"noreferrer noopener\">The Story of Earth: The First 4.5 Billion Years<\/a><\/em>. Viking Penguin. New York. 2012. <\/li>\n\n\n\n<li class=\"\">Henry Gee. <em><a href=\"https:\/\/us.macmillan.com\/books\/9781250276650\/averyshorthistoryoflifeonearth\" target=\"_blank\" rel=\"noreferrer noopener\">A (Very) Short History of Life on Earth, 4.6 Billion Years in 12 Pithy Chapters<\/a><\/em>. MacMillan. November 9, 2021. <\/li>\n\n\n\n<li class=\"\">Felix M. Gradstein, James G. Ogg, Mark D. Schmitz, and Gabi M. Ogg (editors). <a href=\"https:\/\/www.sciencedirect.com\/book\/9780444594259\/the-geologic-time-scale\"><em>The Geologic Time Scale<\/em>.<\/a> Science Direct. 2012. <a href=\"https:\/\/www.sciencedirect.com\/book\/9780444594259\/the-geologic-time-scale\" target=\"_blank\" rel=\"noreferrer noopener\">h<\/a><\/li>\n<\/ul>\n<\/div>\n\n\n\n<div class=\"wp-block-group has-background is-layout-flow wp-block-group-is-layout-flow\" style=\"border-style:solid;border-width:2px;border-radius:10px;background-color:#eaf4ec;margin-top:1rem;margin-bottom:1rem;padding-top:5px;padding-right:5px;padding-bottom:5px;padding-left:5px\">\n<p class=\"\"><u>Selected Sources and Further Reading (Videos)<\/u><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li class=\"\">\u201c<a href=\"https:\/\/youtu.be\/UZ1YE68HszU\" target=\"_blank\" rel=\"noreferrer noopener\">Intro to the Geologic Time Chart | Big History Project.<\/a>\u201d OER Project\/YouTube. December 23, 2013. <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/www.youtube.com\/playlist?list=PLi6K9w_UbfFSFIpEU9VMavTM5MIbOAiW5\" target=\"_blank\" rel=\"noreferrer noopener\">Journeys Through Geologic Time<\/a>.\u201d PBS Eons\/YouTube. <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/youtu.be\/rWp5ZpJAIAE\" target=\"_blank\" rel=\"noreferrer noopener\">A Brief History of Geologic Time.<\/a>\u201d PBS Eons\/YouTube. November 6, 2017. (12:06). <\/li>\n\n\n\n<li class=\"\">\u201c<a href=\"https:\/\/www.youtube.com\/playlist?list=PL6L8fqJFoWXdUJUT81VO9kzzAPU3TYbdV\" target=\"_blank\" rel=\"noreferrer noopener\">Mix \u2013 Paleo Analysis<\/a>.\u201d Paleo Analysis\/YouTube. <\/li>\n<\/ul>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>FAS Astronomers Blog, Volume 31, Number 10. The history of the Earth is described by geologists using something call Geologic Time. This is a timeline from the beginning of the Earth to the present day broken down into a hierarchy of four main groupings: Eons, Eras, Periods, and Epochs. Epochs are broken down further into [&hellip;]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[9],"tags":[800,795,799,798,797,796,802,414],"class_list":["post-5500","post","type-post","status-publish","format-standard","hentry","category-fasastroblog","tag-cenozoic-era","tag-geologic-time","tag-mesozoic-era","tag-paleozoic-era","tag-phanerozoic-eon","tag-precambrian-supereon","tag-september-2023","tag-the-fas-astronomers-blog"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2VHcz-1qI","jetpack_likes_enabled":false,"_links":{"self":[{"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/posts\/5500","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/comments?post=5500"}],"version-history":[{"count":5,"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/posts\/5500\/revisions"}],"predecessor-version":[{"id":23533,"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/posts\/5500\/revisions\/23533"}],"wp:attachment":[{"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/media?parent=5500"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/categories?post=5500"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.fas37.org\/wp\/wp-json\/wp\/v2\/tags?post=5500"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}