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{{
{{Infobox geologic timespan
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| time_end_uncertainty = 1.5
| image_map = Mollweide Paleographic Map of Earth, 465 Ma (Darriwilian Age).png
| caption_map = A map of Earth as it appeared 465 million years ago during the Middle Ordovician
| timeline = Ordovician
<!--Etymology-->
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| lower_gssp_location = Greenpoint section, [[Green Point, Newfoundland|Green Point]], [[Newfoundland]], [[Canada]]
| lower_gssp_coords = {{Coord|49.6829|N|57.9653|W|display=inline}}
| lower_gssp_accept_date = 2000<ref>{{cite journal |last1=Cooper |first1=Roger |last2=Nowlan |first2=Godfrey |last3=Williams |first3=S. H. |title=Global Stratotype Section and Point for base of the Ordovician System |journal=Episodes |date=March 2001 |volume=24 |issue=1 |pages=19–28 |doi=10.18814/epiiugs/2001/v24i1/005 |doi-access=free |url=https://stratigraphy.org/gssps/files/tremadocian.pdf |access-date=6 December 2020 |archive-date=11 January 2021 |archive-url=https://web.archive.org/web/20210111103733/https://stratigraphy.org/gssps/files/tremadocian.pdf |url-status=live }}</ref>
| upper_boundary_def = FAD of the [[Graptolite]] ''[[Akidograptus ascensus]]''
| upper_gssp_location = [[Dob's Linn]], [[Moffat]], [[United Kingdom|U.K.]]
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The Ordovician, named after the [[Celtic Britons|Welsh]] tribe of the [[Ordovices]], was defined by [[Charles Lapworth]] in 1879 to resolve a dispute between followers of [[Adam Sedgwick]] and [[Roderick Murchison]], who were placing the same [[Rock (geology)|rock]] beds in [[North Wales]] in the Cambrian and Silurian systems, respectively.<ref>Charles Lapworth (1879) [https://books.google.com/books?id=JJpZAAAYAAJ&pg=PA1 "On the Tripartite Classification of the Lower Palaeozoic Rocks"]{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}, ''Geological Magazine'', new series, '''6''' : 1-15. From pp. 13-14: "North Wales itself — at all events the whole of the great Bala district where Sedgwick first worked out the physical succession among the rocks of the intermediate or so-called ''Upper Cambrian'' or ''Lower Silurian'' system; and in all probability, much of the Shelve and the Caradoc area, whence Murchison first published its distinctive fossils — lay within the territory of the Ordovices; … Here, then, have we the hint for the appropriate title for the central system of the Lower Paleozoic. It should be called the Ordovician System, after this old British tribe."</ref> Lapworth recognized that the [[fossil]] [[fauna]] in the disputed [[Stratum|strata]] were different from those of either the Cambrian or the Silurian systems, and placed them in a system of their own. The Ordovician received international approval in 1960 (forty years after Lapworth's death), when it was adopted as an official period of the Paleozoic Era by the [[International Union of Geological Sciences|International Geological Congress]].
Life continued to flourish during the Ordovician as it
==Subdivisions{{anchor|Subdivisions}}==
{{anchor|Tremadocian}}
In 2008, the [[International Classification for Standards|ICS]] erected a formal international system of subdivisions for the Ordovician Period and System.<ref>Details on the Dapingian are available at {{Cite journal| first1 = X.| first2 = S.| first3 = X.| first4 = Z.| first5 = C.| title = Dapingian Stage: standard name for the lowermost global stage of the Middle Ordovician Series| journal = [[Lethaia]]| volume = 42| issue = 3| pages = 377–380| last1 = Wang| year = 2009| doi = 10.1111/j.1502-3931.2009.00169.x| last2 = Stouge| last3 = Chen| last4 = Li| last5 = Wang}}</ref> Pre-existing Baltoscandic, British, Siberian, North American, Australian, Chinese, Mediterranean and North-[[Gondwana]]n regional stratigraphic schemes are also used locally.<ref>{{cite web |title=The Ordovician Period |url=https://ordovician.stratigraphy.org/period |website=Subcommission on Ordovician Stratigraphy |publisher=International Commission on Stratigraphy |access-date=7 June 2021 |date=2020 |archive-date=11 May 2022 |archive-url=https://web.archive.org/web/20220511072916/https://ordovician.stratigraphy.org/period |url-status=live }}</ref>
=== Global/regional correlation ===
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| rowspan="5" |
|-
| rowspan="5" |[[Middle Ordovician]]|| rowspan="3" |[[Darriwilian]]|| rowspan="2" |
| rowspan="3" |[[Darriwilian]]
|-
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==Paleogeography and tectonics==
[[File:Earth Paleogeography 480 Ma (Early Ordovician,
[[File:Earth Paleogeography 470 Ma (Early-Middle Ordovician, Dapingian).png|thumb|Paleogeographic map of the Earth in the middle Ordovician, 470 million years ago]]
[[File:Earth Paleogeography 450 Ma (Late Ordovician, Katian).png|thumb|Paleogeographic map of the Earth in the late Ordovician, 450 million years ago]]
During the Ordovician, the southern continents were assembled into [[Gondwana]], which reached from north of the [[equator]] to the [[South Pole]]. The Panthalassic Ocean, centered in the northern hemisphere, covered over half the globe.<ref>{{cite book |last1=Torsvik |first1=Trond H. |last2=Cocks |first2=L. Robin M. |title=Earth history and palaeogeography |date=2017 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |isbn=9781107105324 |page=102}}</ref> At the start of the period, the continents of [[Laurentia]] (in present-day [[North America]]), [[Siberia (continent)|Siberia]], and [[Baltica]] (present-day northern Europe) were separated from Gondwana by over {{convert|5000|km||}} of ocean. These smaller continents were also sufficiently widely separated from each other to develop distinct communities of benthic organisms.{{sfn|Torsvik|Cocks|2017|p=102}} The small continent of [[Avalonia]] had just rifted from Gondwana and began to move north towards Baltica and Laurentia, opening the [[Rheic Ocean]] between Gondwana and Avalonia.<ref>{{cite journal |last1=Pollock |first1=Jeffrey C. |last2=Hibbard |first2=James P. |last3=Sylvester |first3=Paul J. |title=Early Ordovician rifting of Avalonia and birth of the Rheic Ocean: U–Pb detrital zircon constraints from Newfoundland |journal=[[Journal of the Geological Society]] |date=May 2009 |volume=166 |issue=3 |pages=501–515 |doi=10.1144/0016-76492008-088|bibcode=2009JGSoc.166..501P |s2cid=129091590 }}</ref><ref>{{cite journal |last1=Nance |first1=R. Damian |last2=Gutiérrez-Alonso |first2=Gabriel |last3=Keppie |first3=J. Duncan |last4=Linnemann |first4=Ulf |last5=Murphy |first5=J. Brendan |last6=Quesada |first6=Cecilio |last7=Strachan |first7=Rob A. |last8=Woodcock |first8=Nigel H. |title=A brief history of the Rheic Ocean |journal=Geoscience Frontiers |date=March 2012 |volume=3 |issue=2 |pages=125–135 |doi=10.1016/j.gsf.2011.11.008|doi-access=free }}</ref>{{sfn|Torsvik|Cocks|2017|p=103}} Avalonia collided with Baltica towards the end of Ordovician.<ref>{{cite journal |last1=Trela |first1=Wieslaw |date=15 July 2005 |title=Condensation and phosphatization of the Middle and Upper Ordovician limestones on the Malopolska Block (Poland): Response to paleoceanographic conditions |url=https://www.sciencedirect.com/science/article/abs/pii/S0037073805001910 |journal=Sedimentary Geology |volume=117 |issue=3–4 |pages=219–236 |doi=10.1016/j.sedgeo.2005.05.005 |access-date=21 May 2023 |archive-date=22 May 2023 |archive-url=https://web.archive.org/web/20230522055504/https://www.sciencedirect.com/science/article/abs/pii/S0037073805001910 |url-status=live }}</ref>{{sfn|Torsvik|Cocks|2017|p=112}}
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The [[ash fall]] of the Millburg/Big Bentonite bed, at about 454 Ma, was the largest in the last 590 million years. This had a [[dense rock equivalent]] volume of as much as {{convert|1140|km3||}}. Remarkably, this appears to have had little impact on life.<ref>{{cite journal |last1=Huff |first1=Warren D. |last2=Bergström |first2=Stig M. |last3=Kolata |first3=Dennis R. |title=Gigantic Ordovician volcanic ash fall in North America and Europe: Biological, tectonomagmatic, and event-stratigraphic significance |journal=[[Geology (journal)|Geology]] |date=1992-10-01 |volume=20 |issue=10 |pages=875–878 |doi=10.1130/0091-7613(1992)020<0875:GOVAFI>2.3.CO;2|bibcode=1992Geo....20..875H }}</ref>
There was vigorous tectonic activity along northwest margin of Gondwana during the Floian, 478 Ma, recorded in the Central Iberian Zone of Spain. The activity reached as far as Turkey by the end of Ordovician. The opposite margin of Gondwana, in Australia, faced a set of island arcs.{{sfn|Torsvik|Cocks|2017|p=102}} The accretion of these arcs to the eastern margin of Gondwana was responsible for the Benambran Orogeny of eastern Australia.<ref>{{cite journal |last1=Glen |first1=R. A. |last2=Meffre |first2=S. |last3=Scott |first3=R. J. |title=Benambran Orogeny in the Eastern Lachlan Orogen, Australia |journal=[[Australian Journal of Earth Sciences]] |date=March 2007 |volume=54 |issue=2–3 |pages=385–415 |doi=10.1080/08120090601147019|bibcode=2007AuJES..54..385G |s2cid=129843558 }}</ref>{{sfn|Torsvik|Cocks|2017|p=105}} Subduction also took place along what is now Argentina (Famatinian Orogeny) at 450 Ma.<ref>{{cite
Towards the end of the period, Gondwana began to drift across the South Pole. This contributed to the Hibernian glaciation and the associated extinction event.{{sfn|Torsvik|Cocks|2017|pp=103–105}}
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==Climate and sea level==
The Early Ordovician climate was very hot,<ref>{{Cite journal |last1=M. Marcilly |first1=Chloé |last2=Maffre |first2=Pierre |last3=Le Hir |first3=Guillaume |last4=Pohl |first4=Alexandre |last5=Fluteau |first5=Frédéric |last6=Goddéris |first6=Yves |last7=Donnadieu |first7=Yannick |last8=H. Heimdal |first8=Thea |last9=Torsvik |first9=Trond H. |date=15 September 2022 |title=Understanding the early Paleozoic carbon cycle balance and climate change from modelling |url=https://www.sciencedirect.com/science/article/pii/S0012821X22003533 |journal=[[Earth and Planetary Science Letters]] |volume=594 |pages=117717 |doi=10.1016/j.epsl.2022.117717 |issn=0012-821X |access-date=17 September 2023 |hdl=10852/94890 |hdl-access=free |archive-date=7 October 2023 |archive-url=https://web.archive.org/web/20231007025150/https://www.sciencedirect.com/science/article/pii/S0012821X22003533 |url-status=live }}</ref> with intense [[Greenhouse and icehouse Earth|greenhouse]] conditions and [[sea surface temperature]]s comparable to those during the Early Eocene Climatic Optimum.<ref>{{cite journal |last1=Bergmann |first1=Kristin D. |last2=Finnegan |first2=Seth |last3=Creel |first3=Roger |last4=Eiler |first4=John M. |last5=Hughes |first5=Nigel C. |last6=Popov |first6=Leonid E. |last7=Fischer |first7=Woodward W. |date=1 March 2018 |title=A paired apatite and calcite clumped isotope thermometry approach to estimating Cambro-Ordovician seawater temperatures and isotopic composition |journal=[[Geochimica et Cosmochimica Acta]] |volume=224 |pages=18–41 |doi=10.1016/j.gca.2017.11.015 |bibcode=2018GeCoA.224...18B |doi-access=free }}</ref> [[Carbon dioxide]] levels were very high at the Ordovician period's beginning.<ref>{{Cite journal |
The Ordovician saw the highest sea levels of the Paleozoic, and the low relief of the continents led to many shelf deposits being formed under hundreds of metres of water.<ref name=Munnecke2010/> The sea level rose more or less continuously throughout the Early Ordovician, leveling off somewhat during the middle of the period.<ref name=Munnecke2010/> Locally, some regressions occurred, but the sea level rise continued in the beginning of the Late Ordovician. Sea levels fell steadily due to the cooling temperatures for about 3 million years leading up to the Hirnantian glaciation. During this icy stage, sea level seems to have risen and dropped somewhat. Despite much study, the details remain unresolved.<ref name=Munnecke2010/> In particular, some researches interpret the fluctuations in sea level as pre-Hibernian glaciation,<ref>{{cite journal |last1=Rasmussen |first1=Christian M. Ø. |last2=Ullmann |first2=Clemens V. |last3=Jakobsen |first3=Kristian G. |last4=Lindskog |first4=Anders |last5=Hansen |first5=Jesper |last6=Hansen |first6=Thomas |last7=Eriksson |first7=Mats E. |last8=Dronov |first8=Andrei |last9=Frei |first9=Robert |last10=Korte |first10=Christoph |last11=Nielsen |first11=Arne T. |last12=Harper |first12=David A.T. |title=Onset of main Phanerozoic marine radiation sparked by emerging Mid Ordovician icehouse |journal=[[Scientific Reports]] |date=May 2016 |volume=6 |issue=1 |pages=18884 |doi=10.1038/srep18884|pmid=26733399 |pmc=4702064 |bibcode=2016NatSR...618884R }}</ref> but sedimentary evidence of glaciation is lacking until the end of the period.{{sfn|Torsvik|Cocks|2017|p=112}} There is evidence of [[glacier]]s during the Hirnantian on the [[Gondwana|land we now know]] as Africa and South America, which were near the [[South Pole]] at the time, facilitating the formation of the [[ice cap]]s of the Hirnantian glaciation.
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[[File:Isotelus trilobite from Wisconsin.jpg|thumb|The trilobite ''[[Isotelus]]'' from [[Wisconsin]]]]
On the whole, the fauna that emerged in the Ordovician were the template for the remainder of the Palaeozoic. The fauna was dominated by tiered communities of suspension feeders, mainly with short food chains. The ecological system reached a new grade of complexity far beyond that of the Cambrian fauna, which has persisted until the present day.<ref name=Munnecke2010>{{Cite journal| last1 = Munnecke| first1 = Axel| last2 = Calner| first2 = M.| last3 = Harper| first3 = David A. T.| author-link3 = David Harper (palaeontologist)| last4 = Servais| first4 = Thomas| title = Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis| journal = [[Palaeogeography, Palaeoclimatology, Palaeoecology]]| url = https://www.sciencedirect.com/science/article/abs/pii/S0031018210004785| volume = 296| issue = 3–4| pages = 389–413| year = 2010| doi = 10.1016/j.palaeo.2010.08.001| bibcode = 2010PPP...296..389M| access-date = 16 August 2023| archive-date = 17 August 2023| archive-url = https://web.archive.org/web/20230817055224/https://www.sciencedirect.com/science/article/abs/pii/S0031018210004785| url-status = live}}</ref> Though less famous than the [[Cambrian explosion]], the [[Ordovician radiation]] (also known as the Great Ordovician Biodiversification Event){{sfn|Torsvik|Cocks|2017|p=102}} was no less remarkable; marine faunal [[genus|genera]] increased fourfold, resulting in 12% of all known [[Phanerozoic]] marine fauna.<ref name="Dixon2001">{{cite book |title=Atlas of Life on Earth |last=Dixon |first=Dougal |year=2001 |publisher=Barnes & Noble Books |location=New York |isbn=978-0-7607-1957-2 |pages=87 |display-authors=etal}}</ref> Several animals also went through a miniaturization process, becoming much smaller than their Cambrian counterparts.{{Citation needed|date=September 2023}} Another change in the fauna was the strong increase in [[Filter feeder|filter-feeding]] organisms.<ref>[http://www.palaeos.com/Paleozoic/Ordovician/Ordovician.htm Palaeos Paleozoic : Ordovician : The Ordovician Period] {{webarchive|url=https://web.archive.org/web/20071221094614/http://www.palaeos.com/Paleozoic/Ordovician/Ordovician.htm |date=21 December 2007}}</ref> The trilobite, inarticulate brachiopod, [[Archaeocyatha|archaeocyathid]], and [[Eocrinoidea|eocrinoid]] faunas of the Cambrian were succeeded by those that dominated the rest of the Paleozoic, such as articulate brachiopods, [[cephalopod]]s, and [[crinoid]]s. Articulate brachiopods, in particular, largely replaced trilobites in [[continental shelf|shelf]] communities. Their success epitomizes the greatly increased diversity of [[calcium carbonate|carbonate]] shell-secreting organisms in the Ordovician compared to the Cambrian.<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, 255–259] |url=https://archive.org/details/tripthroughtimep0000coop/page/247 }}</ref>[[File:20191205 Aegirocassis benmoulai Aegirocassis benmoulae.png|left|thumb|''[[Aegirocassis]]'', a large filter-feeding [[Hurdiidae|hurdiid]] [[Radiodonta|radiodont]] from [[Morocco]] ]]
Ordovician geography had its effect on the diversity of fauna; Ordovician invertebrates displayed a very high degree of provincialism.<ref>{{cite journal |last1=Heim |first1=Noel A. |date=8 April 2016 |title=A null biogeographic model for quantifying the role of migration in shaping patterns of global taxonomic richness and differentiation diversity, with implications for Ordovician biogeography |url=https://www.cambridge.org/core/journals/paleobiology/article/abs/null-biogeographic-model-for-quantifying-the-role-of-migration-in-shaping-patterns-of-global-taxonomic-richness-and-differentiation-diversity-with-implications-for-ordovician-biogeography/2FB3853AA935DAD151FC1FB35181A986 |journal=[[Paleobiology (journal)|Paleobiology]] |volume=34 |issue=2 |pages=195–209 |doi=10.1666/0094-8373(2008)034[0195:ANBMFQ]2.0.CO;2 |access-date=18 May 2023 |archive-date=19 May 2023 |archive-url=https://web.archive.org/web/20230519042939/https://www.cambridge.org/core/journals/paleobiology/article/abs/null-biogeographic-model-for-quantifying-the-role-of-migration-in-shaping-patterns-of-global-taxonomic-richness-and-differentiation-diversity-with-implications-for-ordovician-biogeography/2FB3853AA935DAD151FC1FB35181A986 |url-status=live }}</ref> The widely separated continents of Laurentia and Baltica, then positioned close to the tropics and boasting many shallow seas rich in life, developed distinct trilobite faunas from the trilobite fauna of Gondwana,<ref>{{Cite journal |last1=Cocks |first1=L. Robin M. |last2=Torsvik |first2=Trond H. |date=December 2021 |title=Ordovician palaeogeography and climate change
[[File:Eurypterids Pentecopterus Vertical.jpg|thumb|''[[Pentecopterus]]'', the earliest known eurypterid, and found in [[Iowa]]]]
[[Trilobite]]s in particular were rich and diverse, and experienced rapid diversification in many regions.<ref>{{Cite journal |
In the Early Ordovician, trilobites were joined by many new types of organisms, including [[Tabulata|tabulate]] corals, [[Strophomenida|strophomenid]], [[Rhynchonellida|rhynchonellid]], and many new [[Orthida|orthid]] brachiopods, bryozoans, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first [[Starfish|sea stars]]. Nevertheless, the arthropods remained abundant; all the Late Cambrian orders continued, and were joined by the new group [[Phacopida]]. The first evidence of land plants also appeared (see [[evolutionary history of life]]).
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=== Microbiota ===
Though stromatolites had declined from their peak in the Proterozoic, they continued to exist in localised settings.<ref>{{Cite journal |
==End of the period==
{{Main|Ordovician–Silurian extinction events}}
[[File:Anji Biota.jpg|thumb|The Anji Biota (Wenchang Formation, [[Zhejiang]] Province, [[China]]) preserves abundant and diverse [[Hexactinellid|glass sponges]] and graptolites as well as rare examples of other marine animals (such as the eurypterid [[Archopterus]]) living at a depth of several hundred metres. It is dated to just after the [[Late_Ordovician_mass_extinction|Hirnantian mass extinction]] at the end of the Ordovician period.<ref>{{Cite journal |last1=Wang |first1=Han |last2=Braddy |first2=Simon J. |last3=Botting |first3=Joseph |last4=Zhang |first4=Yuandong |date=2023 |title=The first documentation of an Ordovician eurypterid (Chelicerata) from China |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/first-documentation-of-an-ordovician-eurypterid-chelicerata-from-china/2F0762857D48061467555E2C91387957 |journal=Journal of Paleontology |language=en |volume=97 |issue=3 |pages=606–611 |doi=10.1017/jpa.2023.21 |issn=0022-3360}}</ref>]]
The Ordovician came to a close in a series of [[extinction event]]s that, taken together, comprise the second largest of the five major extinction events in [[History of Earth|Earth's history]] in terms of percentage of [[genus|genera]] that became extinct. The only larger one was the [[Permian–Triassic extinction event]].
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