Editing Paleozoic

{{Short description|First era of the Phanerozoic Eon}}
{{redirect|Primitive period|the use in mathematics|Periodic function}}
{{Infobox geologic timespan
| name                         = Paleozoic
| color                        = Paleozoic
| top_bar                      = Phanerozoic
| time_start                   = 538.8
| time_start_uncertainty       = 0.2
| time_end                     = 251.9
| time_end_uncertainty         = 0.024
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<!--Chronology-->  
| timeline                     = Paleozoic
| proposed_boundaries1         =
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<!--Etymology-->
| name_formality               = Formal
| name_accept_date             = 
| alternate_spellings          = Palaeozoic
| synonym1                     =
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<!--Usage Information--> 
| celestial_body               = earth
| usage                        = Global ([[International Commission on Stratigraphy|ICS]])
| timescales_used              = ICS Time Scale
| formerly_used_by             =
| not_used_by                  =
<!--Definition-->
| chrono_unit                  = Era
| strat_unit                   = Erathem
| proposed_by                  =
| timespan_formality           = 
| lower_boundary_def           = Appearance of the [[Trace fossil|Ichnofossil]] ''[[Treptichnus pedum]]''
| lower_gssp_location          = [[Fortune Head|Fortune Head section]], [[Newfoundland]], [[Canada]]
| lower_gssp_coords            = {{Coord|47.0762|N|55.8310|W|display=inline}}
| lower_gssp_accept_date       = 1992
| upper_boundary_def           = First appearance of the Conodont ''[[Hindeodus parvus]]''.
| upper_gssp_location          = [[Meishan]], [[Zhejiang]], [[China]]
| upper_gssp_coords            = {{Coord|31.0798|N|119.7058|E|display=inline}}
| upper_gssp_accept_date       = 2001
}}
The '''Paleozoic''' ({{IPAc-en|ˌ|p|æ|l|i|.|ə|ˈ|z|oʊ|.|ɪ|k|,_|-|i|.|oʊ|-|,_|ˌ|p|eɪ|-}} {{respell|PAL-ee-ə-ZOH-ik}}, {{respell|-ee-oh-}}, {{respell|PAY-}};{{refn|{{Cite Collins Dictionary|Paleozoic|access-date=2023-08-30}}}} or '''Palaeozoic''') '''Era''' is the first of three [[Era (geology)|geological eras]] of the [[Phanerozoic]] Eon. Beginning 538.8 million years ago (Ma), it succeeds the [[Neoproterozoic]] (the last era of the [[Proterozoic]] Eon) and ends 251.9 Ma at the start of the [[Mesozoic]] Era.<ref>{{Cite web |title=International Commission on Stratigraphy |url=https://stratigraphy.org/chart |access-date=2023-08-01 |website=stratigraphy.org}}</ref> The Paleozoic is subdivided into six [[period (geology)|geologic periods]] (from oldest to youngest), [[Cambrian]], [[Ordovician]], [[Silurian]], [[Devonian]], [[Carboniferous]] and  [[Permian]]. Some geological timescales divide the Paleozoic informally into early and late sub-eras: the Early Paleozoic consisting of the Cambrian, Ordovician and Silurian; the Late Paleozoic consisting of the Devonian, Carboniferous and Permian.<ref>{{Cite web |title=Geological timechart |url=https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/geological-timechart/ |access-date=2023-08-01 |website=British Geological Survey |language=en-GB}}</ref>

The name ''Paleozoic'' was first used by [[Adam Sedgwick]] (1785–1873) in 1838<ref name="Sedgwick-1838">{{cite journal |last=Sedgwick |first=Adam |author-link=Adam Sedgwick |year= 1838 |title=A synopsis of the English series of stratified rocks inferior to the Old Red Sandstone – with an attempt to determine the successive natural groups and formations |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015031294112;view=1up;seq=601 |url-status=live |journal=Proceedings of the Geological Society of London |volume= 2 |issue=58 |pages=675–685, esp. p.&nbsp;685 |archive-url=https://web.archive.org/web/20230410042253/https://babel.hathitrust.org/cgi/pt?id=mdp.39015031294112;view=1up;seq=601 |archive-date=2023-04-10 |access-date=2018-07-15}}</ref> to describe the Cambrian and Ordovician periods. It was redefined by [[John Phillips (geologist)|John Phillips]] (1800–1874) in 1840 to cover the Cambrian to Permian periods.<ref>{{Cite web |title=Penny cyclopaedia of the Society for the Diffusion of Useful Knowledge. v.17 Org-Per. |url=https://hdl.handle.net/2027/hvd.hn4zr7?urlappend=%3Bseq=163 |access-date=2023-08-01 |website=HathiTrust |language=en}}</ref> It is derived from the [[Ancient Greek|Greek]] ''palaiós'' (παλαιός, "old") and ''zōḗ'' (ζωή, "life") meaning "ancient life".<ref name="OnlineEtDict">{{cite OEtymD|Paleozoic }}</ref>

The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the [[Cambrian explosion]], in which most modern [[phylum|phyla]] first appeared. [[Arthropod]]s, [[Mollusca|molluscs]], [[fish]], [[amphibian]]s, [[reptile]]s, and [[synapsid]]s all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, great [[forest]]s of primitive plants covered the continents, many of which formed the [[coal]] beds of [[Europe]] and eastern [[North America]]. Towards the end of the era, large, sophisticated synapsids and diapsids were dominant and the first modern plants ([[conifers]]) appeared.

The Paleozoic Era ended with the largest [[extinction event]] of the [[Phanerozoic Eon]],{{efn|name=only-counting-Phanerozoic-extinctions-note}} the [[Permian–Triassic extinction event]]. The effects of this catastrophe were so devastating that it took life on land 30&nbsp;million years into the Mesozoic Era to recover.<ref name=Sahney-Benton-2008>
{{cite journal |author1=Sahney, S. |author2=Benton, M.J. |name-list-style=amp |year=2008 |title=Recovery from the most profound mass extinction of all time |journal=Proceedings of the Royal Society B: Biological Sciences |volume=275 |issue=1636 |pages=759–65 |doi=10.1098/rspb.2007.1370 |pmid=18198148 |pmc=2596898}}
</ref>
Recovery of life in the sea may have been much faster.<ref>
{{cite magazine |title=Dead-ammonite bounce |date=5 July 2010 |department=Science & technology |magazine=[[The Economist]] |url=http://www.economist.com/node/16524904}}
</ref>

== Boundaries ==
The base of the Paleozoic is one of the major divisions in geological time representing the divide between the Proterozoic and Phanerozoic eons, the Paleozoic and Neoproterozoic eras and the [[Ediacaran]] and Cambrian periods.<ref name=":0">{{Cite journal |last=Geyer |first=Gerd |last2=Landing |first2=Ed |date=2016-11-02 |title=The Precambrian–Phanerozoic and Ediacaran–Cambrian boundaries: a historical approach to a dilemma |url=http://dx.doi.org/10.1144/sp448.10 |journal=Geological Society, London, Special Publications |volume=448 |issue=1 |pages=311–349 |doi=10.1144/sp448.10 |issn=0305-8719}}</ref> When Adam Sedgwick named the Paleozoic in 1835, he defined the base as the first appearance of complex life in the rock record as shown by the presence of [[trilobite]]-dominated fauna.<ref name="Sedgwick-1838" /> Since then evidence of complex life in older rock sequences has increased and by the second half of the 20th century, the first appearance of [[small shelly fauna]] (SSF), also known as early skeletal fossils, were considered markers for the base of the Paleozoic. However, whilst SSF are well preserved in [[Carbonate rock|carbonate]] sediments, the majority of Ediacaran to Cambrian rock sequences are composed of [[siliciclastic]] rocks where skeletal fossils are rarely preserved.<ref name=":0" /> This led the [[International Commission on Stratigraphy]] (ICS) to use [[trace fossil]]s as an indicator of complex life.<ref name=":1">{{Citation |last=Peng |first=S. C. |title=Chapter 19 – The Cambrian Period |date=2020-01-01 |url=https://www.sciencedirect.com/science/article/pii/B978012824360200019X |work=Geologic Time Scale 2020 |pages=565–629 |editor-last=Gradstein |editor-first=Felix M. |access-date=2023-08-24 |publisher=Elsevier |isbn=978-0-12-824360-2 |last2=Babcock |first2=L. E. |last3=Ahlberg |first3=P. |editor2-last=Ogg |editor2-first=James G. |editor3-last=Schmitz |editor3-first=Mark D. |editor4-last=Ogg |editor4-first=Gabi M.}}</ref> Unlike later in the fossil record, Cambrian trace fossils are preserved in a wide range of sediments and environments, which aids correlation between different sites around the world. Trace fossils reflect the complexity of the body plan of the organism that made them. Ediacaran trace fossils are simple, sub-horizontal feeding traces. As more complex organisms evolved, their more complex behaviour was reflected in greater diversity and complexity of the trace fossils they left behind.<ref name=":0" /> After two decades of deliberation, the ICS chose [[Fortune Head]], Burin Peninsula, Newfoundland as the basal Cambrian Global Stratotype Section and Point (GSSP) at the base of the ''[[Treptichnus|Treptichnus pedum]]'' assemblage of trace fossils and immediately above the last occurrence of the Ediacaran problematica fossils ''[[Harlaniella]] podolica'' and ''[[Palaeopascichnus|Palaeopsacichnus]]''.<ref name=":1" /> The base of the Phanerozoic, Paleozoic and Cambrian is dated at 538.8+/-0.2 Ma and now lies below both the first appearance of trilobites and SSF.<ref name=":0" /><ref name=":1" />

The boundary between the Paleozoic and Mesozoic eras and the Permian and Triassic periods is marked by the first occurrence of the [[conodont]] ''[[Hindeodus|Hindeodus parvus]]''. This is the first [[Biostratigraphy|biostratigraphic]] event found worldwide that is associated with the beginning of the recovery following the end-[[Permian–Triassic extinction event|Permian mass extinctions]] and environmental changes. In non-marine strata, the equivalent level is marked by the disappearance of the Permian [[Dicynodon]] [[tetrapod]]s.<ref name=":2">{{Citation |last=Ogg |first=J. G. |title=Chapter 25 – The Triassic Period |date=2020-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780128243602000255 |work=Geologic Time Scale 2020 |pages=903–953 |editor-last=Gradstein |editor-first=Felix M. |access-date=2023-08-24 |publisher=Elsevier |isbn=978-0-12-824360-2 |last2=Chen |first2=Z. -Q. |last3=Orchard |first3=M. J. |last4=Jiang |first4=H. S. |editor2-last=Ogg |editor2-first=James G. |editor3-last=Schmitz |editor3-first=Mark D. |editor4-last=Ogg |editor4-first=Gabi M.}}</ref> This means events previously considered to mark the Permian-Triassic boundary, such as the eruption of the [[Siberian Traps]] [[flood basalt]]s, the onset of greenhouse climate, [[Anoxic event|ocean anoxia]] and [[Ocean acidification|acidification]] and the resulting mass extinction are now regarded as being of latest Permian in age.<ref name=":2" /> The GSSP is near [[Meishan]], Zhejiang Province, southern China. [[Radiometric dating]] of volcanic clay layers just above and below the boundary confine its age to a narrow range of 251.902+/-0.024 Ma.<ref name=":2" />

==Geology==
The beginning of the Paleozoic Era witnessed the breakup of the supercontinent of [[Pannotia]]<ref name=Scotese-2009>
{{cite journal |last=Scotese |first=C.R. |year=2009 |title=Late Proterozoic plate tectonics and palaeogeography: A tale of two supercontinents, Rodinia and Pannotia |journal=Geological Society, London, Special Publications |volume=326 |issue=1 |page=68 |doi=10.1144/SP326.4 |bibcode=2009GSLSP.326...67S |s2cid=128845353 |url=https://www.researchgate.net/publication/249552299 |access-date=29 November 2015}}
</ref><ref name=Murphy-Nance-Cawood-2009>
{{cite journal |last1=Murphy |first1=J.B. |last2=Nance |first2=R.D. |last3=Cawood |first3=P.A. |name-list-style=amp |year=2009 |title=Contrasting modes of supercontinent formation and the conundrum of Pangea |journal=Gondwana Research |volume=15 |issue=3 |pages=408–20 |doi=10.1016/j.gr.2008.09.005 |bibcode=2009GondR..15..408M |url=https://www.researchgate.net/publication/222153136 |access-date=20 December 2019}}
</ref>
and ended while the supercontinent [[Pangaea]] was assembling.<ref name=Rogers-Santosh-2004>
{{cite book |author1=Rogers, J.J.W. |author2=Santosh, M. |name-list-style=amp |year=2004 |title=Continents and Supercontinents |publisher=Oxford University Press |place=Oxford, UK |isbn=978-0-19-516589-0 |page=146}}
</ref>
The breakup of Pannotia began with the opening of the [[Iapetus Ocean]] and other Cambrian seas and coincided with a dramatic rise in sea level.<ref name=Dalziel-1997>
{{cite journal |last=Dalziel |first=I.W. |year=1997 |title=Neoproterozoic-Paleozoic geography and tectonics: Review, hypothesis, environmental speculation |journal=Geological Society of America Bulletin |volume=109 |issue=1 |pages=16–42 |doi=10.1130/0016-7606(1997)109<0016:ONPGAT>2.3.CO;2 |bibcode=1997GSAB..109...16D}}
</ref>
[[Paleoclimatology|Paleoclimatic]] studies and evidence of [[glacier]]s indicate that [[Central Africa]] was most likely in the polar regions during the early Paleozoic. The breakup of Pannotia was followed by the assembly of the huge continent [[Gondwana]] ({{Ma|510}}). By the mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subducting plate uplifted eastern [[Australia]]. By the late Paleozoic, continental collisions formed the supercontinent of Pangaea and created great mountain chains, including the [[Appalachians]], [[Caledonides]], [[Ural Mountains]], and mountains of [[Tasmania]].<ref name=Rogers-Santosh-2004/>

=== Cambrian Period ===
{{main|Cambrian}}
[[File:Trilobite Heinrich Harder.jpg|thumb|left|[[Trilobite]]s]]
The Cambrian spanned from 539–485&nbsp;million years ago and is the first period of the Paleozoic Era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the [[Cambrian explosion]] in which the largest number of creatures evolved in any single period of the history of the Earth. Creatures like [[algae]] evolved, but the most ubiquitous of that period were the armored arthropods, like trilobites. Almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, most of which later became the supercontinent Gondwana.<ref>{{cite web |title=Cambrian |website=www.ucmp.berkeley.edu |place=Berkeley, CA |publisher=[[University of California Museum of Paleontology]] |url=http://www.ucmp.berkeley.edu/cambrian/cambrian.php |access-date=2015-04-26 |archive-date=2012-05-15 |archive-url=https://web.archive.org/web/20120515190500/http://www.ucmp.berkeley.edu/cambrian/cambrian.php |url-status=live }}</ref>
{{Clear}}

=== Ordovician Period ===
{{main|Ordovician}}

[[File:Ostracoderm digital recreation..jpg|thumb|[[Cephalaspis]] (a jawless fish)]]
The Ordovician spanned from 485–444&nbsp;million years ago. The Ordovician was a time in Earth's history in which many of the [[Class (biology)|biological class]]es still prevalent today evolved, such as primitive fish, cephalopods, and coral. The most common forms of life, however, were trilobites, snails and shellfish. The first arthropods went ashore to colonize the empty continent of Gondwana. By the end of the Ordovician, Gondwana was at the south pole, early North America had collided with Europe, closing the intervening ocean. Glaciation of Africa resulted in a major drop in sea level, killing off all life that had established along coastal Gondwana. Glaciation may have caused the [[Ordovician–Silurian extinction events]], in which 60% of marine invertebrates and 25% of families became extinct, and is considered the first Phanerozoic mass extinction event, and the second deadliest.{{efn|name=only-counting-Phanerozoic-extinctions-note}}<ref>{{cite web |title=Ordovician |website=www.ucmp.berkeley.edu |place=Berkeley, CA |publisher=[[University of California Museum of Paleontology]] |url=http://www.ucmp.berkeley.edu/ordovician/ordovician.php |access-date=2015-04-26 |archive-date=2015-05-02 |archive-url=https://web.archive.org/web/20150502201732/http://www.ucmp.berkeley.edu/ordovician/ordovician.php |url-status=live }}</ref>

=== Silurian Period ===
{{main|Silurian}}

The Silurian spanned from 444–419&nbsp;million years ago. The Silurian saw the rejuvenation of life as the Earth recovered from the previous glaciation. This period saw the mass evolution of fish, as jawless fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as [[Eurypterida|sea scorpions]], were still [[apex predator]]s. Fully terrestrial life evolved, including early arachnids, fungi, and centipedes. The evolution of [[vascular plants]] (''[[Cooksonia]]'') allowed plants to gain a foothold on land. These early plants were the forerunners of all plant life on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, Siberia), Laurentia (North America), Baltica (Northern Europe), and Avalonia (Western Europe). The recent rise in sea levels allowed many new species to thrive in water.<ref>{{cite web |title=Silurian |website=www.ucmp.berkeley.edu |place=Berkeley, CA |publisher=[[University of California Museum of Paleontology]] |url=http://www.ucmp.berkeley.edu/silurian/silurian.php |access-date=2015-04-26 |archive-date=2017-06-16 |archive-url=https://web.archive.org/web/20170616141804/http://www.ucmp.berkeley.edu/silurian/silurian.php |url-status=live }}</ref>

=== Devonian Period ===
{{main|Devonian }}

[[File:Eogyrinus BW.jpg|thumb|[[Eogyrinus]] (an amphibian) of the Carboniferous]]
The Devonian spanned from 419–359&nbsp;million years ago. Also known as "The Age of the Fish", the Devonian featured a huge diversification of fish, including armored fish like ''[[Dunkleosteus]]'' and lobe-finned fish which eventually evolved into the first tetrapods. On land, plant groups diversified rapidly in an event known as the [[Devonian explosion]] when plants made [[lignin]], leading to taller growth and vascular tissue; the first trees and seeds evolved. These new habitats led to greater arthropod diversification. The first amphibians appeared and fish occupied the top of the food chain. Earth's second Phanerozoic mass extinction event (a group of several smaller extinction events), the [[Late Devonian extinction]], ended 70% of existing species.{{efn|name=only-counting-Phanerozoic-extinctions-note}}<ref>{{cite web |title=Devonian |website=www.ucmp.berkeley.edu |place=Berkeley, CA |publisher=[[University of California Museum of Paleontology]] |url=http://www.ucmp.berkeley.edu/devonian/devonian.php |access-date=2015-04-26 |archive-date=2012-05-11 |archive-url=https://web.archive.org/web/20120511155551/http://www.ucmp.berkeley.edu/devonian/devonian.php |url-status=live }}</ref>

=== Carboniferous Period ===
{{main|Carboniferous}}

The Carboniferous is named after the large coal deposits laid down during the period. It spanned from 359–299&nbsp;million years ago. During this time, average global temperatures were exceedingly high; the early Carboniferous averaged at about 20&nbsp;degrees Celsius (but cooled to 10&nbsp;°C during the Middle Carboniferous).<ref>{{cite web |author=Hieb, Monte |title=Carboniferous Era |website=geocraft.com |url=http://www.geocraft.com/WVFossils/Carboniferous_climate.html |access-date=2015-04-26 |archive-date=2014-12-20 |archive-url=https://web.archive.org/web/20141220004649/http://www.geocraft.com/WVFossils/Carboniferous_climate.html |url-status=live }}</ref> An important evolutionary development of the time was the evolution of [[Amniote|amniotic eggs]], which allowed amphibians to move farther inland and remain the dominant vertebrates for the duration of this period. Also, the first reptiles and [[synapsid]]s evolved in the swamps. Throughout the Carboniferous, there was a cooling trend, which led to the Permo-Carboniferous glaciation or the [[Carboniferous Rainforest Collapse]]. [[Gondwana]] was glaciated as much of it was situated around the south pole.<ref>{{cite web |title=Carboniferous |website=www.ucmp.berkeley.edu |place=Berkeley, CA |publisher=University of California Museum of Paleontology |url=http://www.ucmp.berkeley.edu/carboniferous/carboniferous.php |access-date=2015-04-26 |archive-date=2012-02-10 |archive-url=https://web.archive.org/web/20120210070913/http://www.ucmp.berkeley.edu/carboniferous/carboniferous.php |url-status=live }}</ref>

=== Permian Period ===
{{main|Permian}}
[[File:Dimetrodon grandis in "high walk" pose.png|thumb|Synapsid: ''[[Dimetrodon|Dimetrodon grandis]]'']]
The Permian spanned from 299–252&nbsp;million years ago and was the last period of the Paleozoic Era. At the beginning of this period, all continents joined together to form the supercontinent Pangaea, which was encircled by one ocean called [[Panthalassa]]. The land mass was very dry during this time, with harsh seasons, as the climate of the interior of Pangaea was not regulated by large bodies of water. [[Diapsid]]s and [[synapsid]]s flourished in the new dry climate. Creatures such as ''[[Dimetrodon]]'' and ''[[Edaphosaurus]]'' ruled the new continent. The first conifers evolved, and dominated the terrestrial landscape. Near the end of the Permian, however, Pangaea grew drier. The interior was desert, and new taxa such as ''[[Scutosaurus]]'' and [[Gorgonopsia|Gorgonopsids]] filled it. Eventually they disappeared, along with 95% of all life on Earth, in a cataclysm known as "[[Permian–Triassic extinction event|The Great Dying]]", the third and most severe Phanerozoic mass extinction.{{efn|name=only-counting-Phanerozoic-extinctions-note}}<ref>{{cite web |title=The Great Dying |website=www.nhm.ac.uk |place=London, UK |publisher=[[Natural History Museum, London|Natural History Museum]] |url=http://www.nhm.ac.uk/nature-online/life/dinosaurs-other-extinct-creatures/mass-extinctions/end-permian-mass-extinction/ |access-date= |archive-date=2015-04-20 |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/ |url-status=dead}}</ref><ref>{{cite web |title=Permian Era |website=www.ucmp.berkeley.edu |place=Berkeley, CA |publisher=[[University of California Museum of Paleontology]] |url=http://www.ucmp.berkeley.edu/permian/permian.php |access-date=2015-05-24 |archive-date=2017-07-04 |archive-url=https://web.archive.org/web/20170704140229/http://www.ucmp.berkeley.edu/permian/permian.php |url-status=live }}</ref>

==Climate==
[[File:Life in the early Paleozoic Age.jpg|thumb|Life in the early Paleozoic]]
[[File:Swamp Forest in the Carboniferous Age.jpg|thumb|Swamp forest in the Carboniferous]]
The early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained [[sea level rise]] in the Phanerozoic got underway. However, as if to offset this trend, Gondwana moved south, so that, in Ordovician time, most of West Gondwana (Africa and South America) lay directly over the [[South Pole]].

The early Paleozoic climate was strongly zonal, with the result that the "climate", in an abstract sense, became warmer, but the living space of most organisms of the time – the continental shelf marine environment – became steadily colder. However, [[Baltica]] (Northern Europe and Russia) and [[Laurentia]] (eastern North America and Greenland) remained in the tropical zone, while China and Australia lay in waters which were at least temperate. The early Paleozoic ended, rather abruptly, with the short, but apparently severe, late Ordovician ice age. This cold spell caused the second-greatest [[mass extinction]] of the Phanerozoic Eon.<ref>{{cite journal |last1=Saupe |first1=Erin E. |last2=Qiao |first2=Huijie |last3=Donnadieu |first3=Yannick |last4=Farnsworth |first4=Alexander |last5=Kennedy-Asser |first5=Alan T. |last6=Ladant |first6=Jean-Baptiste |last7=Lunt |first7=Daniel J. |last8=Pohl |first8=Alexandre |last9=Valdes |first9=Paul |last10=Finnegan |first10=Seth |date=16 December 2019 |title=Extinction intensity during Ordovician and Cenozoic glaciations explained by cooling and palaeogeography |url=https://www.nature.com/articles/s41561-019-0504-6#citeas |journal=[[Nature Geoscience]] |volume=13 |issue=1 |pages=65–70 |doi=10.1038/s41561-019-0504-6 |s2cid=209381464 |access-date=22 October 2022|hdl=1983/c88c3d46-e95d-43e6-aeaf-685580089635 |hdl-access=free }}</ref>{{efn|name=only-counting-Phanerozoic-extinctions-note}} Over time, the warmer weather moved into the Paleozoic Era.

The Ordovician and Silurian were warm greenhouse periods, with the highest sea levels of the Paleozoic (200&nbsp;m above today's); the warm climate was interrupted only by a {{Ma|30|million year}} cool period, the [[Early Palaeozoic Icehouse]], culminating in the [[Hirnantian]] glaciation, {{Ma|445}} at the end of the Ordovician.<ref name=Munnecke-Calner-etal-2010>
{{cite journal |last1=Munnecke |first1=A. |last2=Calner |first2=M. |last3=Harper |first3=D.A.T. |author3-link=David Harper (palaeontologist) |last4=Servais |first4=T. |title=Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=296 |issue=3–4 |pages=389–413 |year=2010 |doi=10.1016/j.palaeo.2010.08.001 |bibcode=2010PPP...296..389M}}
</ref>

The middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the ice age, but slowly recovered over the course of the Silurian and Devonian. The slow merger of Baltica and Laurentia, and the northward movement of bits and pieces of Gondwana created numerous new regions of relatively warm, shallow sea floor. As plants took hold on the continental margins, [[oxygen]] levels increased and [[carbon dioxide]] dropped, although much less dramatically. The north–south temperature gradient also seems to have moderated, or [[metazoan life]] simply became hardier, or both. At any event, the far southern continental margins of [[Antarctica]] and West Gondwana became increasingly less barren. The Devonian ended with a series of [[Turnover-pulse hypothesis|turnover pulses]] which killed off much of middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.

There are many unanswered questions about the late Paleozoic. The [[Mississippian age|Mississippian]] (early Carboniferous Period) began with a spike in atmospheric oxygen, while carbon dioxide plummeted to new lows. This destabilized the climate and led to one, and perhaps two, ice ages during the Carboniferous. These were far more severe than the brief Late Ordovician ice age; but, this time, the effects on world biota were inconsequential. By the [[Cisuralian]] Epoch, both oxygen and carbon dioxide had recovered to more normal levels. On the other hand, the assembly of Pangaea created huge arid inland areas subject to temperature extremes. The [[Lopingian]] Epoch is associated with falling sea levels, increased carbon dioxide and general climatic deterioration, culminating in the devastation of the Permian extinction.

==Flora==
[[File:Devonianscene-green.jpg|thumb|An artist's impression of early land plants]]
While macroscopic plant life appeared early in the Paleozoic Era and possibly late in the Neoproterozoic Era of the earlier eon, plants mostly remained aquatic until the Silurian Period, about 420&nbsp;million years ago, when they began to transition onto dry land. Terrestrial flora reached its climax in the Carboniferous, when towering [[lycopsid]] rainforests dominated the tropical belt of [[Euramerica]]. [[Climate change]] caused the [[Carboniferous Rainforest Collapse]] which fragmented this habitat, diminishing the diversity of plant life in the late Carboniferous and Permian periods.<ref name=Sahney-Benton-Falcon-2010/>

==Fauna==
A noteworthy feature of Paleozoic life is the sudden appearance of nearly all of the [[invertebrate]] animal phyla in great abundance at the beginning of the Cambrian. The first vertebrates appeared in the form of primitive fish, which greatly diversified in the Silurian and Devonian Periods. The first animals to venture onto dry land were the arthropods. Some fish had lungs, and powerful bony fins that in the late Devonian, 367.5&nbsp;million years ago, allowed them to crawl onto land. The bones in their fins eventually evolved into legs and they became the first tetrapods, {{Ma|390}}, and began to develop lungs. Amphibians were the dominant tetrapods until the mid-Carboniferous, when climate change greatly reduced their diversity, allowing amniotes to take over. Amniotes would split into two clades shortly after their origin in the Carboniferous; the synapsids, which was the dominant group, and the [[Sauropsida|sauropsids]]. The synapsids continued to prosper and increase in number and variety till the end of the Permian period. In late middle Permian the [[Pareiasauria|pareiasaurs]] originated, successful herbivores and the only sauropsids that could reach sizes comparable to some of the largest synapsids.<ref name=Sahney-Benton-Falcon-2010>{{cite journal |author1=Sahney, S. |author2=Benton, M.J. |author3=Falcon-Lang, H.J. |name-list-style=amp |year=2010 |title=Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica |journal=Geology |volume=38 |issue=12 |pages=1079–1082 |doi=10.1130/G31182.1 |bibcode=2010Geo....38.1079S |url=http://geology.geoscienceworld.org/cgi/content/abstract/38/12/1079 |format=PDF abstract |access-date=2012-02-17 |archive-date=2011-10-11 |archive-url=https://web.archive.org/web/20111011144357/http://geology.geoscienceworld.org/cgi/content/abstract/38/12/1079 |url-status=live }}</ref><ref>[https://www.livescience.com/43219-permian-period-climate-animals-plants.html Permian Period: Climate, Animals & Plants]</ref><ref>[https://www.wits.ac.za/news/latest-news/opinion/2023/2023-07/gigantic-extinct-reptile-weighed-as-much-as-a-black-rhino.html Gigantic extinct reptile weighed as much as a black rhino]</ref>

The Palaeozoic marine fauna was notably lacking in predators relative to the present day. Predators made up about 4% of the fauna in Palaeozoic assemblages while making up 17% of temperate Cenozoic assemblages and 31% of tropical ones. Infaunal animals made up 4% of soft substrate Palaeozoic communities but about 47% of Cenozoic communities. Additionally, the Palaeozoic had very few facultatively motile animals that could easily adjust to disturbance, with such creatures composing 1% of its assemblages in contrast to 50% in Cenozoic faunal assemblages. Non-motile animals untethered to the substrate, extremely rare in the Cenozoic, were abundant in the Palaeozoic.<ref>{{Cite journal |last=Bush |first=Andrew M. |last2=Bambach |first2=Richard K. |last3=Daley |first3=Gwen M. |date=January 2007 |title=Changes in theoretical ecospace utilization in marine fossil assemblages between the mid-Paleozoic and late Cenozoic |url=https://www.cambridge.org/core/journals/paleobiology/article/abs/changes-in-theoretical-ecospace-utilization-in-marine-fossil-assemblages-between-the-midpaleozoic-and-late-cenozoic/40836F638A27707DD59E25FAE3B01B31 |journal=[[Paleobiology (journal)|Paleobiology]] |language=en |volume=33 |issue=1 |pages=76–97 |doi=10.1666/06013.1 |issn=0094-8373 |access-date=10 December 2023}}</ref>

==Microbiota==
Palaeozoic [[phytoplankton]] overall were both nutrient-poor themselves and adapted to nutrient-poor environmental conditions. This phytoplankton nutrient poverty has been cited as an explanation for the Palaeozoic's relatively low biodiversity.<ref>{{Cite journal |last=Martin |first=Ronald E. |last2=Quigg |first2=Antonietta |last3=Podkovyrov |first3=Victor |date=27 February 2008 |title=Marine biodiversification in response to evolving phytoplankton stoichiometry |url=https://www.sciencedirect.com/science/article/pii/S0031018207005688 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=258 |issue=4 |pages=277–291 |doi=10.1016/j.palaeo.2007.11.003 |issn=0031-0182 |access-date=30 September 2023}}</ref>

==See also==
* {{annotated link|Geologic time scale}}
* {{annotated link|Precambrian}}
* {{annotated link|Cenozoic}}
* {{annotated link|Mesozoic}}
* {{annotated link|Phanerozoic}}

==Footnotes==
{{notelist|notes=

{{efn|
name=only-counting-Phanerozoic-extinctions-note|
The list of the "big 5" [[mass extinctions]] only counts extinctions in the [[Phanerozoic Eon]], since up to [[Ediacaran|the end of]] the [[Proterozoic Eon]], life was [[Ediacaran biota|all soft-bodied]]. The meagre [[Ediacaran biota|fossil traces of earlier life]] make it essentially impossible to identify [[species]] or [[genus|genera]], and it is the disappearance of large proportions of existing genera from the fossil record that is the standard for comparing [[extinction event]]s of the Phanerozoic "big 5". The one known [[extinction event]] in the [[eon (geology)|eons]] before the Phanerozoic was the '''[[Oxygen Catastrophe]]''', or the '''[[Great Oxygenation Event]]''', when the previously [[Anoxic waters|anoxic]] seas  were poisoned with [[oxygen]] by [[Evolution of photosynthesis|newly photosynthesizing bacteria]]. By some estimates, that event killed almost all life on the Earth, and might qualify as the "greatest ever" mass extinction, if its consequences for soft-bodied genera could be measured. Further, there might have been ''other'' extinction events in the [[precambrian]] eons, whose traces in the [[geologic record]] (if any) are less obvious than the [[Great Oxygenation Event|Oxygenation Event]].
}}

}} <!-- end "notes=" -->

==References==
{{reflist|25em}}

==Further reading==
{{refbegin|colwidth=25em}}
* {{cite web |title=International Commission on Stratigraphy (ICS) |type=home page |url=http://www.stratigraphy.org/ |access-date=September 19, 2005 |archive-date=September 20, 2005 |archive-url=https://web.archive.org/web/20050920105136/http://www.stratigraphy.org/ |url-status=live }}
* {{cite book |title=British Palaeozoic Fossils |year=1975 |edition=4th |orig-year=1964 |series=British Museum publications on Natural History |volume=624 |place=London, UK |publisher=[[Natural History Museum, London|Natural History Museum]] |isbn=9780565056247 |lccn=77354077 |url=https://archive.org/details/britishpalaeozoi0000brit |access-date=2022-10-06 |via=Internet Archive (archive.org) }} {{isbn|0565056247}}
{{refend}}

==External links==
{{Commons category|Paleozoic}}
{{Wikisource portal|Paleozoic}}
* [http://www.foraminifera.eu/querydb.php?&period=Carboniferous&aktion=suche 60+ images of Paleozoic Foraminifera]
* [https://ghkclass.com/ghkC.html?paleozoic Paleozoic (chronostratigraphy scale)]

{{Geological history|p|p|state=collapsed}}
{{Authority control}}

[[Category:Paleozoic| ]]
[[Category:Geological eras]]