Editing Ordovician (section)

==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 |last1=Brandt |first1=Danita S. |last2=Elias |first2=Robert J. |date=1989 |title=Temporal variations in tempestite thickness may be a geologic record of atmospheric CO2 |url=https://pubs.geoscienceworld.org/geology/article/17/10/951-952/186520 |journal=[[Geology (journal)|Geology]] |language=en |volume=17 |issue=10 |pages=951 |doi=10.1130/0091-7613(1989)017<0951:TVITTM>2.3.CO;2 |issn=0091-7613 |access-date=30 September 2023}}</ref> By the late Early Ordovician, the Earth cooled,<ref name="MayaElrick">{{cite journal |last1=Elrick |first1=Maya |date=1 October 2022 |title=Orbital-scale climate changes detected in Lower and Middle Ordovician cyclic limestones using oxygen isotopes of conodont apatite |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=603 |page=111209 |doi=10.1016/j.palaeo.2022.111209 |bibcode=2022PPP...603k1209E |doi-access=free }}</ref> giving way to a more temperate climate in the Middle Ordovician,<ref>{{Cite journal|last1=Goldberg|first1=Samuel L.|last2=Present|first2=Theodore M.|last3=Finnegan|first3=Seth|last4=Bergmann|first4=Kristin D.|date=2021-02-09|title=A high-resolution record of early Paleozoic climate|journal=[[Proceedings of the National Academy of Sciences of the United States of America]]|language=en|volume=118|issue=6|pages=e2013083118|doi=10.1073/pnas.2013083118|pmid=33526667|pmc=8017688|bibcode=2021PNAS..11813083G|issn=0027-8424|doi-access=free }}</ref> with the Earth likely entering the [[Late Ordovician glaciation|Early Palaeozoic Ice Age]] during the Sandbian,<ref>{{cite journal |last1=Vandenbroucke |first1=Thijs R. A. |last2=Armstrong |first2=Howard A. |last3=Williams |first3=Mark |last4=Paris |first4=Florentin |last5=Sabbe |first5=Koen |last6=Zalasiewicz |first6=Jan A. |last7=Nõlvak |first7=Jaak |last8=Verniers |first8=Jacques |date=15 August 2010 |title=Epipelagic chitinozoan biotopes map a steep latitudinal temperature gradient for earliest Late Ordovician seas: Implications for a cooling Late Ordovician climate |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018209005215 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=294 |issue=3–4 |pages=202–219 |doi=10.1016/j.palaeo.2009.11.026 |bibcode=2010PPP...294..202V |access-date=29 December 2022 |archive-date=29 December 2022 |archive-url=https://web.archive.org/web/20221229202739/https://www.sciencedirect.com/science/article/abs/pii/S0031018209005215 |url-status=live }}</ref><ref>{{cite journal |last1=Rosenau |first1=Nicholas A. |last2=Hermann |first2=Achim D. |last3=Leslie |first3=Stephen A. |date=15 January 2012 |title=Conodont apatite δ18O values from a platform margin setting, Oklahoma, USA: Implications for initiation of Late Ordovician icehouse conditions |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018211005839 |journal=[[Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=315-316 |pages=172–180 |doi=10.1016/j.palaeo.2011.12.003 |bibcode=2012PPP...315..172R |access-date=29 December 2022 |archive-date=7 April 2019 |archive-url=https://web.archive.org/web/20190407015109/https://www.sciencedirect.com/science/article/pii/S0031018211005839 |url-status=live }}</ref> and possibly as early as the Darriwilian<ref name ="EPIA">{{cite journal |last1=Pohl |first1=Alexandre |last2=Donnadieu |first2=Yannick |last3=Le Hir |first3=Guillaume |last4=Ladant |first4=Jean-Baptiste |last5=Dumas |first5=Christophe |last6=Alvarez-Solas |first6=Jorge |last7=Vandenbroucke |first7=Thijs R. A. |date=28 May 2016 |title=Glacial onset predated Late Ordovician climate cooling |journal=[[Paleoceanography and Paleoclimatology]] |volume=31 |issue=6 |pages=800–821 |doi=10.1002/2016PA002928 |bibcode=2016PalOc..31..800P |s2cid=133243759 |doi-access=free |hdl=1854/LU-8057556 |hdl-access=free }}</ref> or even the Floian.<ref name="MayaElrick" /> The Dapingian and Sandbian saw major humidification events evidenced by trace metal concentrations in Baltoscandia from this time.<ref name="HumidClimaticEvents">{{Cite journal |last1=Kiipli |first1=Enli |last2=Kiipli |first2=Tarmo |last3=Kallaste |first3=Toivo |last4=Pajusaar |first4=Siim |date=December 2017 |title=Trace elements indicating humid climatic events in the Ordovician–early Silurian |url=https://linkinghub.elsevier.com/retrieve/pii/S0009281917300168 |journal=Geochemistry |language=en |volume=77 |issue=4 |pages=625–631 |doi=10.1016/j.chemer.2017.05.002 |access-date=23 July 2024 |via=Elsevier Science Direct}}</ref> Evidence suggests that global temperatures rose briefly in the early Katian (Boda Event), depositing bioherms and radiating fauna across Europe.<ref>{{cite journal |last1=Fortey |first1=Richard A. |last2=Cocks |first2=L. Robin M. |title=Late Ordovician global warming—The Boda event |journal=[[Geology (journal)|Geology]] |date=2005 |volume=33 |issue=5 |pages=405 |doi=10.1130/G21180.1|bibcode=2005Geo....33..405F }}</ref> The early Katian also witnessed yet another humidification event.<ref name="HumidClimaticEvents" /> Further cooling during the Hirnantian, at the end of the Ordovician, led to the [[Late Ordovician glaciation]].<ref>{{Cite journal|last1=Trotter|first1=J. A.|last2=Williams|first2=I. S.|last3=Barnes|first3=C. R.|last4=Lecuyer|first4=C.|last5=Nicoll|first5=R. S.|date=2008-07-25|title=Did Cooling Oceans Trigger Ordovician Biodiversification? Evidence from Conodont Thermometry|url=https://www.science.org/doi/10.1126/science.1155814|journal=[[Science (journal)|Science]]|language=en|volume=321|issue=5888|pages=550–554|doi=10.1126/science.1155814|pmid=18653889|bibcode=2008Sci...321..550T|s2cid=28224399|issn=0036-8075|access-date=2022-06-30|archive-date=2022-10-06|archive-url=https://web.archive.org/web/20221006184654/https://www.science.org/doi/10.1126/science.1155814|url-status=live}}</ref>

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, the sea level has 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.

As with [[North America]] and [[Europe]], [[Gondwana]] was largely covered with shallow seas during the Ordovician. Shallow clear waters over continental shelves encouraged the growth of organisms that deposit calcium carbonates in their shells and hard parts. The [[Panthalassic Ocean]] covered much of the [[Northern Hemisphere]], and other minor oceans included [[Proto-Tethys Ocean|Proto-Tethys]], [[Paleo-Tethys Ocean|Paleo-Tethys]], [[Khanty Ocean]], which was closed off by the Late Ordovician, [[Iapetus Ocean]], and the new [[Rheic Ocean]].