View source for Phanerozoic

===Paleozoic Era===
{{Main|Paleozoic}}
The Paleozoic is a time in Earth's history when active complex life forms evolved, took their first foothold on dry land, and when the forerunners of all multicellular life on Earth began to diversify. There are six periods in the Paleozoic era: [[Cambrian]], [[Ordovician]], [[Silurian]], [[Devonian]], [[Carboniferous]] and [[Permian]].<ref>{{cite web|url=http://www.ucmp.berkeley.edu/paleozoic/paleozoic.php|title=Paleozoic|author=University of California|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20150502123522/http://www.ucmp.berkeley.edu/paleozoic/paleozoic.php|archive-date=2 May 2015}}</ref>

====Cambrian Period====
{{Main|Cambrian}}The Cambrian is the first period of the Paleozoic Era and ran from 539 million to 485&nbsp;million years ago. The Cambrian sparked a [[evolutionary radiation|rapid expansion in the diversity]] of animals, in an event known as the [[Cambrian explosion]], during which the greatest number of animal [[body plan]]s evolved in a single period in the history of Earth. Complex [[algae]] evolved, and the fauna was dominated by armoured arthropods (such as [[trilobite]]s and [[radiodontid]]s) and to a lesser extent shelled [[cephalopod]]s (such as [[orthocone]]s). Almost all [[Phylum|phyla]] of marine animals evolved in this period. During this time, the super-continent [[Pannotia]] began to break up, most of which later recombined into the super-continent [[Gondwana]].<ref>{{cite web|url=http://www.ucmp.berkeley.edu/cambrian/cambrian.php|title=Cambrian|author=University of California|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20120515190500/http://www.ucmp.berkeley.edu/cambrian/cambrian.php|archive-date=15 May 2012}}</ref>

====Ordovician Period====
{{Main|Ordovician}}
The Ordovician spans from 485 million to 444&nbsp;million years ago. The Ordovician was a time in Earth's history in which many groups still prevalent today evolved or diversified, such as primitive [[nautiloid]]s, [[vertebrate]]s (then only [[jawless fish]]) and [[corals]]. This process is known as the [[Great Ordovician Biodiversification Event]] or GOBE. Trilobites began to be replaced by [[articulate brachiopod]]s, and [[crinoid]]s also became an increasingly important part of the fauna.<ref name="Cooper1986">{{cite book |title=A Trip Through Time: Principles of Historical Geology |last=Cooper |first=John D. |author2=Miller, Richard H. |author3=Patterson, Jacqueline |year=1986 |publisher=Merrill Publishing Company |location=Columbus |isbn=978-0-675-20140-7 |pages=[https://archive.org/details/tripthroughtimep0000coop/page/247 247, 255&ndash;259] |url=https://archive.org/details/tripthroughtimep0000coop/page/247 }}</ref> The first [[arthropod]]s crept ashore to colonise [[Gondwana]], a continent empty of animal life. A group of freshwater [[green algae]], the [[streptophyte]]s, also survived being washed ashore and began to colonize the [[flood plain]]s and [[riparian zone]]s, giving rise to primitive [[land plant]]s.

By the end of the Ordovician, Gondwana had moved from the equator to the [[South Pole]], and [[Laurentia]] had collided with [[Baltica]], closing the [[Iapetus Ocean]]. The glaciation of Gondwana resulted in a major drop in sea level, killing off all life that had established along its coast. Glaciation caused an [[icehouse Earth]], leading to the [[Ordovician–Silurian extinction events|Ordovician–Silurian extinction]], during which 60% of marine invertebrates and 25% of families became extinct. Though one of the deadliest mass extinctions in earth's history, the O–S extinction did not cause profound ecological changes between the periods.<ref>{{cite web|url=http://www.ucmp.berkeley.edu/ordovician/ordovician.php|title=Ordovician|author=University of California|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20150502201732/http://www.ucmp.berkeley.edu/ordovician/ordovician.php|archive-date=2 May 2015}}</ref>

====Silurian Period====
{{Main|Silurian}}
[[File:Dalmanites limulurus trilobite silurian.jpg|left|thumb|177x177px|''[[Dalmanites|Dalmanites limulurus]]'', a species of Silurian [[trilobite]]s]]
The Silurian spans from 444 million to 419&nbsp;million years ago, which saw a warming from an icehouse Earth. This period saw the [[evolution of fish|mass diversification of fish]], as jawless fish became more numerous, and early [[jawed fish]] and [[freshwater fish|freshwater species]] appeared in the fossil record. Arthropods remained abundant, and some groups, such as [[eurypterid]]s, became [[apex predator]]s in the ocean. Fully terrestrial life established itself on land, including early [[fungi]], [[arachnid]]s, [[Hexapoda|hexapod]]s and [[myriapod]]s. The evolution of [[vascular plant]]s (mainly [[spore]]-producing [[fern]]s such as ''[[Cooksonia]]'') allowed land plants to gain a foothold further inland as well. During this time, there were four continents: [[Gondwana]] (Africa, South America, Australia, Antarctica, India), [[Laurentia]] (North America with parts of Europe), [[Baltica]] (the rest of Europe), and [[Siberia (continent)|Siberia]] (Northern Asia).<ref>{{cite web|url=http://www.ucmp.berkeley.edu/silurian/silurian.php|author=University of California|title=Silurian|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20170616141804/http://www.ucmp.berkeley.edu/silurian/silurian.php|archive-date=16 June 2017}}</ref>

====Devonian Period====
{{Main|Devonian}}
[[File:Ostracoderm digital recreation..jpg|thumb|left|''[[Cephalaspis]]'', a jawless fish]]
The Devonian spans from 419 million to 359&nbsp;million years ago. Also informally known as the "Age of the Fish", the Devonian features a huge diversification in fish such as the jawless [[conodont]]s and [[ostracoderm]]s, as well as jawed fish such as the armored [[placoderm]]s (e.g. ''[[Dunkleosteus]]''), the spiny [[acanthodian]]s and early [[bony fish]]. The Devonian also saw the primitive appearance of modern fish groups such as [[Chondrichthyes|chondricthyan]]s ([[cartilaginous fish]]) and [[osteichthyan]]s (bony fish), the latter of which include two [[clade]]s — the [[actinopterygian]]s ([[ray-finned fish]]) and [[sarcopterygian]]s ([[lobe-finned fish]]). One lineage of sarcopterygians, [[Rhipidistia]], evolved [[Tetrapodomorpha|the first four-limbed vertebrates]], which would eventually become [[tetrapod]]s. On land, plant groups diversified after the [[Silurian-Devonian Terrestrial Revolution]]; the first [[woody plant|woody]] ferns and the earliest [[seed plant]]s evolved during this period. By the Middle Devonian, shrub-like forests existed: [[Lycopodiophyta|lycophytes]], [[Equisetales|horsetails]] and [[progymnosperm]]. This [[greening]] event also allowed the diversification of [[arthropod]]s as they took advantage of the new habitat. Near the end of the Devonian, 70% of all species became extinct in a sequence of mass extinction events, collectively known as the [[Late Devonian extinction]].<ref>{{cite web|url=http://www.ucmp.berkeley.edu/devonian/devonian.php|title=Devonian|author=University of California|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20120511155551/http://www.ucmp.berkeley.edu/devonian/devonian.php|archive-date=11 May 2012}}</ref>

====Carboniferous Period====
{{Main|Carboniferous}}
[[File:Proterogyrinus DB.jpg|thumb|239x239px|''[[Proterogyrinus]]'', a Carboniferous amphibian (non-[[amniote]] tetrapod)]]
The Carboniferous spans from 359 million to 299&nbsp;million years ago.<ref>{{cite web |url=http://www.geocraft.com/WVFossils/Carboniferous_climate.html |title=Carboniferous Era|author=Monte Hieb|work=unknown|url-status=live|archive-url=https://web.archive.org/web/20141220004649/http://www.geocraft.com/WVFossils/Carboniferous_climate.html|archive-date=20 December 2014}}</ref> Tropical [[swamp]]s dominated the Earth, and the large amounts of trees [[carbon sequestration|sequestered]] much of the carbon that became [[coal]] deposits (hence the name Carboniferous and the term "[[coal forest]]"). About 90% of all coal beds were deposited in the Carboniferous and Permian periods, which represent just 2% of the Earth's geologic history.<ref>{{cite book |last1=McGhee |first1=George R. |title=Carboniferous giants and mass extinction: the late Paleozoic Ice Age world |date=2018 |publisher=Columbia University Press |location=New York |isbn=978-0-231-18097-9 |pages=98}}</ref> The high [[dioxygen in biological reactions|oxygen]] levels caused by these wetland rainforests allowed arthropods, normally limited in size by [[respiratory system of insects|their respiratory systems]], to proliferate and increase in size. Tetrapods also diversified during the Carboniferous as [[semiaquatic]] [[amphibian]]s such as the [[temnospondyl]]s, and one lineage developed [[extraembryonic membrane]]s that allowed their [[egg]]s to survive outside of the water. These tetrapods, the [[amniotes]], included the first [[sauropsid]]s (which evolved the [[reptile]]s, [[dinosaur]]s and [[bird]]s) and [[synapsid]]s (the ancestors of [[mammals]]). Throughout the Carboniferous, there was a cooling pattern, which eventually led to the glaciation of [[Gondwana]] as much of it was situated around the [[South Pole]]. This event was known as the [[Permo-Carboniferous Glaciation]] and resulted in a major loss of coal forests, known as the [[Carboniferous rainforest collapse]].<ref>{{cite web|url=http://www.ucmp.berkeley.edu/carboniferous/carboniferous.php|title=Carboniferous|author=University of California|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20120210070913/http://www.ucmp.berkeley.edu/carboniferous/carboniferous.php|archive-date=10 February 2012}}</ref>

====Permian Period====
{{Main|Permian}}
[[File:Dimetrodon grandis 3D Model Reconstruction.png|left|thumb|''[[Dimetrodon|Dimetrodon grandis]],'' a synapsid from the early Permian]]
The Permian spans from 299 million to 251&nbsp;million years ago and was the last period of the Paleozoic era. At its beginning, all landmasses came together to form the supercontinent [[Pangaea]], surrounded by one expansive ocean called [[Panthalassa]]. The Earth was relatively dry compared to the Carboniferous, with [[Pangean megamonsoon|harsh seasons]], as the climate of the interior of Pangaea was not moderated by large bodies of water. [[Amniote]]s still flourished and diversified in the new dry climate, particularly [[synapsid]]s such as ''[[Dimetrodon]],'' ''[[Edaphosaurus]]'' and [[therapsid]]s, which gave rise to the ancestors of modern mammals. The first [[conifer]]s evolved during this period, then dominated the terrestrial landscape. The Permian ended with at least one [[mass extinction]], an event sometimes known as "[[Permian–Triassic extinction event|the Great Dying]]", caused by large [[Flood basalt|floods of lava]] (the [[Siberian Traps]] in Russia and the [[Emeishan Traps]] in China). This extinction was the largest in Earth's history and led to the loss of 95% of all species of life.<ref>{{cite web|url=http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/mass-extinctions/end-permian-mass-extinction/|title=The Great Dying|author=Natural History Museum|work=Natural History Museum|url-status=live|archive-url=https://web.archive.org/web/20150420192109/http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/mass-extinctions/end-permian-mass-extinction/|archive-date=20 April 2015}}</ref><ref>{{cite web|url=http://www.ucmp.berkeley.edu/permian/permian.php|title=Permian Era|author=University of California|work=University of California|url-status=live|archive-url=https://web.archive.org/web/20170704140229/http://www.ucmp.berkeley.edu/permian/permian.php|archive-date=4 July 2017}}</ref>