View source for Earth:Eocene–Oligocene extinction event

{{short description|Mass extinction event 33.9 million years ago}}
{{annotated image/Extinction
|annotations={{Annotation|293|155|'''E-O<small>G</small>'''}}
|caption=Eocene–Oligocene extinction is labeled E–<span style="letter-spacing:-1px">&thinsp;O'''{{font|G|size=65%}}'''</span>.}}
The '''Eocene–Oligocene extinction event''', also called the '''Eocene-Oligocene transition''' ('''EOT''') or '''{{lang|fr|Grande Coupure}}''' ([[Social:French language|French]] for "great cut"), is the transition between the end of the [[Earth:Eocene|Eocene]] and the beginning of the [[Earth:Oligocene|Oligocene]], an extinction event and faunal turnover occurring between 33.9 and 33.4 million years ago.<ref name="EbroBasin" /> It was marked by large-scale extinction and floral and faunal turnover, although it was relatively minor in comparison to the [[Biology:Extinction event|largest mass extinctions]].<ref name="CoolerWinters" />

==Causes==
===Glaciation===
The boundary between the Eocene and Oligocene epochs is marked by the glaciation of Antarctica and the consequent beginning of the [[Earth:Late Cenozoic Ice Age|Late Cenozoic Ice Age]].<ref>{{Cite journal |last=Lear |first=Caroline H. |last2=Bailey |first2=Trevor R. |last3=Pearson |first3=Paul N. |last4=Coxall |first4=Helen K. |last5=Rosenthal |first5=Yair |date=1 March 2008 |title=Cooling and ice growth across the Eocene-Oligocene transition |url=https://pubs.geoscienceworld.org/geology/article/36/3/251-254/29681 |journal=Geology |language=en |volume=36 |issue=3 |pages=251 |doi=10.1130/G24584A.1 |issn=0091-7613 |access-date=1 January 2024}}</ref> This enormous shift in climatic regime is the leading candidate for the extinction event's cause. Though ephemeral ice sheets may have existed on the Antarctic continent during parts of the Middle and Late Eocene,<ref name="LadantDonnadieuLefebvreDumas2014" /> this interval of severe global cooling marked the beginning of permanent [[Earth:Ice sheet|ice sheet]] coverage of [[Earth:Antarctica|Antarctica]],<ref>{{Cite journal |last1=Zachos |first1=James C. |last2=Quinn |first2=Terrence M. |last3=Salamy |first3=Karen A. |date=1996-06-01 |title=High-resolution (104 years) deep-sea foraminiferal stable isotope records of the Eocene-Oligocene climate transition |url=https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1160&context=msc_facpub |journal=[[Earth:Paleoceanography and Paleoclimatology|Paleoceanography and Paleoclimatology]] |language=en |volume=11 |issue=3 |pages=251–266 |bibcode=1996PalOc..11..251Z |doi=10.1029/96PA00571 |issn=1944-9186 |access-date=17 March 2023}}</ref><ref>{{Cite journal |last=Shackleton |first=N. J. |date=1 October 1986 |title=Boundaries and Events in the Paleogene Paleogene stable isotope events |url=https://www.sciencedirect.com/science/article/abs/pii/0031018286900088 |journal=[[Earth:Palaeogeography, Palaeoclimatology, Palaeoecology|Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=57 |issue=1 |pages=91–102 |bibcode=1986PPP....57...91S |doi=10.1016/0031-0182(86)90008-8 |access-date=17 March 2023}}</ref> and thus the end of the greenhouse climate of the Early Palaeogene.<ref>{{cite journal |last1=Prothero |first1=Donald Ross |date=May 1994 |title=The Late Eocene-Oligocene Extinctions |url=https://www.annualreviews.org/doi/abs/10.1146/annurev.ea.22.050194.001045?journalCode=earth |journal=[[Earth:Annual Review of Earth and Planetary Sciences|Annual Review of Earth and Planetary Sciences]] |volume=22 |pages=145–165 |bibcode=1994AREPS..22..145P |doi=10.1146/annurev.ea.22.050194.001045 |access-date=16 April 2023}}</ref> The global cooling also correlated with marked drying conditions in low-latitudes Asia,<ref>{{Cite journal |last1=Li |first1=Y. X. |last2=Jiao |first2=W. J. |last3=Liu |first3=Z. H. |last4=Jin |first4=J. H. |last5=Wang |first5=D. H. |last6=He |first6=Y. X. |last7=Quan |first7=C. |date=2016-02-11 |title=Terrestrial responses of low-latitude Asia to the Eocene–Oligocene climate transition revealed by integrated chronostratigraphy |journal=[[Earth:Climate of the Past|Climate of the Past]] |volume=12 |issue=2 |pages=255–272 |bibcode=2016CliPa..12..255L |doi=10.5194/cp-12-255-2016 |issn=1814-9332 |doi-access=free|hdl=10722/231824 |hdl-access=free }}</ref> though a causal relationship between the two has been contradicted by some research.<ref>{{Cite journal |last1=Zhang |first1=Chunxia |last2=Guo |first2=Zhengtang |date=1 October 2014 |title=Clay mineral changes across the Eocene–Oligocene transition in the sedimentary sequence at Xining occurred prior to global cooling |url=https://www.sciencedirect.com/science/article/pii/S0031018214003435 |journal=[[Earth:Palaeogeography, Palaeoclimatology, Palaeoecology|Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=411 |pages=18–29 |bibcode=2014PPP...411...18Z |doi=10.1016/j.palaeo.2014.06.031 |issn=0031-0182 |access-date=25 December 2023 |via=Elsevier Science Direct}}</ref>

A leading model of climate cooling at this time predicts a decrease in atmospheric [[Chemistry:Carbon dioxide|carbon dioxide]], which slowly declined over the course of the Middle to Late Eocene.<ref>{{cite journal |last1=Villa |first1=Giuliana |last2=Fioroni |first2=Chiara |last3=Persico |first3=Davide |last4=Roberts |first4=Andrew P. |last5=Florindo |first5=Fabio |date=20 December 2013 |title=Middle Eocene to Late Oligocene Antarctic glaciation/deglaciation and Southern Ocean productivity |journal=[[Earth:Paleoceanography and Paleoclimatology|Paleoceanography and Paleoclimatology]] |volume=29 |issue=3 |pages=223–237 |doi=10.1002/2013PA002518 |doi-access=free }}</ref><ref>{{cite journal |last1=Cappelli |first1=C. |last2=Bown |first2=P. R. |last3=Westerhold |first3=T. |last4=Bohaty |first4=S. M. |last5=De Riu |first5=M. |last6=Loba |first6=V. |last7=Yamamoto |first7=Y. |last8=Agnini |first8=C. |date=15 November 2019 |title=The Early to Middle Eocene Transition: An Integrated Calcareous Nannofossil and Stable Isotope Record From the Northwest Atlantic Ocean (Integrated Ocean Drilling Program Site U1410) |journal=[[Earth:Paleoceanography and Paleoclimatology|Paleoceanography and Paleoclimatology]] |volume=34 |issue=12 |pages=1913–1930 |doi=10.1029/2019PA003686 |bibcode=2019PaPa...34.1913C |s2cid=210245165 |doi-access=free |hdl=11577/3322441 |hdl-access=free }}</ref><ref>{{Cite journal |last=Pagani |first=Mark |last2=Zachos |first2=James C. |last3=Freeman |first3=Katherine H. |last4=Tipple |first4=Brett |last5=Bohaty |first5=Stephen |date=22 July 2005 |title=Marked Decline in Atmospheric Carbon Dioxide Concentrations During the Paleogene |url=https://www.science.org/doi/10.1126/science.1110063 |journal=Science |language=en |volume=309 |issue=5734 |pages=600–603 |doi=10.1126/science.1110063 |issn=0036-8075 |access-date=1 January 2024}}</ref> Significant cooling took place in the final hundreds of thousands of years prior to the start of major Antarctic glaciation.<ref>{{cite journal |last1=Evans |first1=David |last2=Wade |first2=Bridget S. |last3=Henehan |first3=Michael |last4=Erez |first4=Jonathan |last5=Müller |first5=Wolfgang |date=6 April 2016 |title=Revisiting carbonate chemistry controls on planktic foraminifera Mg / Ca: implications for sea surface temperature and hydrology shifts over the Paleocene–Eocene Thermal Maximum and Eocene–Oligocene transition |url=https://cp.copernicus.org/articles/12/819/2016/ |journal=[[Earth:Climate of the Past|Climate of the Past]] |volume=12 |issue=4 |pages=819–835 |doi=10.5194/cp-12-819-2016 |bibcode=2016CliPa..12..819E |access-date=5 April 2023|doi-access=free }}</ref> This cooling reached some threshold approximately 34 million years ago,<ref>{{cite journal |last1=Hutchinson |first1=David K. |last2=Coxall |first2=Helen K. |last3=Lunt |first3=Daniel J. |last4=Steinthorsdottir |first4=Margret |last5=De Boer |first5=Agatha M. |last6=Baatsen |first6=Michiel |last7=Von der Heydt |first7=Anna |last8=Huber |first8=Matthew |last9=Kennedy-Asser |first9=Alan T. |last10=Kunzmann |first10=Lutz |last11=Ladant |first11=Jean-Baptiste |last12=Lear |first12=Caroline H. |last13=Moraweck |first13=Karolin |last14=Pearson |first14=Paul N. |last15=Piga |first15=Emanuela |last16=Pound |first16=Matthew J. |last17=Salzmann |first17=Ulrich |last18=Scher |first18=Howie D. |last19=Sijp |first19=Willem P. |last20=Śliwińska |first20=Kasia K. |last21=Wilson |first21=Paul A. |last22=Zhang |first22=Zhongshi |date=28 January 2021 |title=The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons |url=https://cp.copernicus.org/articles/17/269/2021/ |journal=[[Earth:Climate of the Past|Climate of the Past]] |volume=17 |issue=1 |pages=269–315 |doi=10.5194/cp-17-269-2021 |bibcode=2021CliPa..17..269H |s2cid=234099337 |access-date=17 March 2023|doi-access=free }}</ref><ref name="PearsonFosterWade2009">{{cite journal |last1=Pearson |first1=Paul N. |last2=Foster |first2=Gavin L. |last3=Wade |first3=Bridget S. |date=13 September 2009 |title=Atmospheric carbon dioxide through the Eocene–Oligocene climate transition |url=https://www.nature.com/articles/nature08447?error=cookies_not_supported&code=c515a74b-c1ef-480a-a7ee-98cdbd1b84c3 |journal=Nature |volume=461 |issue=7267 |pages=1110–1113 |doi=10.1038/nature08447 |pmid=19749741 |bibcode=2009Natur.461.1110P |s2cid=205218274 |access-date=17 March 2023}}</ref><ref name="LadantDonnadieuLefebvreDumas2014" /> precipitating the formation of a large ice sheet in [[Earth:East Antarctica|East Antarctica]] in response to falling carbon dioxide levels.<ref>{{cite journal |last1=Galeotti |first1=Simone |last2=Deconto |first2=Robert |last3=Naish |first3=Timothy |last4=Stocchi |first4=Paolo |last5=Florindo |first5=Fabio |last6=Pagani |first6=Mark |last7=Barrett |first7=Peter |last8=Bohaty |first8=Steven M. |last9=Lanci |first9=Luca |last10=Pollard |first10=David |last11=Sandroni |first11=Sonia |last12=Talarico |first12=Franco M. |last13=Zachos |first13=James C. |date=10 March 2016 |title=Antarctic Ice Sheet variability across the Eocene-Oligocene boundary climate transition |journal=Science |volume=352 |issue=6281 |pages=76–80 |doi=10.1126/science.aab0669 |pmid=27034370 |bibcode=2016Sci...352...76G |s2cid=24154493 |doi-access=free |hdl=11365/1007376 |hdl-access=free }}</ref><ref name="WestAntarcticPalaeotopography">{{cite journal |last1=Wilson |first1=Douglas S. |last2=Luyendyk |first2=Bruce P. |date=25 August 2009 |title=West Antarctic paleotopography estimated at the Eocene-Oligocene climate transition |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2009GL039297 |journal=[[Earth:Geophysical Research Letters|Geophysical Research Letters]] |volume=36 |issue=16 |pages=1–4 |doi=10.1029/2009GL039297 |bibcode=2009GeoRL..3616302W |s2cid=163074 |access-date=8 December 2022}}</ref> The cause of the drop in [[Chemistry:PCO2|''p''CO<sub>2</sub>]] was the drift of the [[Earth:Indian subcontinent|Indian Subcontinent]] into equatorial latitudes, supercharging the [[Chemistry:Carbonate–silicate cycle|silicate weathering]] of the [[Earth:Deccan Traps|Deccan Traps]].<ref>{{Cite journal |last=Kent |first=Dennis V. |last2=Muttoni |first2=Giovanni |date=21 October 2008 |title=Equatorial convergence of India and early Cenozoic climate trends |url=https://pnas.org/doi/full/10.1073/pnas.0805382105 |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=105 |issue=42 |pages=16065–16070 |doi=10.1073/pnas.0805382105 |issn=0027-8424 |pmc=2570972 |pmid=18809910 |access-date=1 January 2024}}</ref> Another factor was the opening of the Drake Passage and the creation of the [[Earth:Antarctic Circumpolar Current|Antarctic Circumpolar Current]] (ACC), which had the effect of creating [[Physics:Ocean gyre|ocean gyre]]s that promote [[Earth:Upwelling|upwelling]] of cold bottom waters and diminishing heat transport to Antarctica by isolating the water around it.<ref>{{Cite journal |last=Barker |first=P.F. |last2=Thomas |first2=E. |date=June 2004 |title=Origin, signature and palaeoclimatic influence of the Antarctic Circumpolar Current |url=https://linkinghub.elsevier.com/retrieve/pii/S0012825203001272 |journal=[[Earth:Earth-Science Reviews|Earth-Science Reviews]] |language=en |volume=66 |issue=1-2 |pages=143–162 |doi=10.1016/j.earscirev.2003.10.003 |access-date=1 January 2024 |via=Elsevier Science Direct}}</ref> Likewise, the Tasmanian Gateway also opened up around the time of the EOT.<ref>{{Citation |last=Kennett |first=James P. |title=Paleoceanographic evolution of the Tasmanian Seaway and its climatic implications |date=2004 |url=https://onlinelibrary.wiley.com/doi/10.1029/151GM19 |work=Geophysical Monograph Series |volume=151 |pages=345–367 |editor-last=Exon |editor-first=Neville F. |access-date=2024-01-02 |place=Washington, D. C. |publisher=American Geophysical Union |language=en |doi=10.1029/151gm19 |isbn=978-0-87590-416-0 |last2=Exon |first2=Neville F. |editor2-last=Kennett |editor2-first=James P. |editor3-last=Malone |editor3-first=Mitchell J.}}</ref> Ocean circulation changes were, however, not as significant in engendering cooling as the decline in ''p''CO<sub>2</sub>.<ref>{{Cite journal |last=Huber |first=Matthew |last2=Nof |first2=Doron |date=February 2006 |title=The ocean circulation in the southern hemisphere and its climatic impacts in the Eocene |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018205004785 |journal=[[Earth:Palaeogeography, Palaeoclimatology, Palaeoecology|Palaeogeography, Palaeoclimatology, Palaeoecology]] |language=en |volume=231 |issue=1-2 |pages=9–28 |doi=10.1016/j.palaeo.2005.07.037 |access-date=1 January 2024 |via=Elsevier Science Direct}}</ref> On top of that, the timing of the creation of the ACC is uncertain.<ref>{{Cite journal |last=Barker |first=Peter F. |last2=Filippelli |first2=Gabriel M. |last3=Florindo |first3=Fabio |last4=Martin |first4=Ellen E. |last5=Scher |first5=Howard D. |date=October–November 2007 |title=Onset and role of the Antarctic Circumpolar Current |url=https://linkinghub.elsevier.com/retrieve/pii/S0967064507001786 |journal=Deep Sea Research Part II: Topical Studies in Oceanography |language=en |volume=54 |issue=21-22 |pages=2388–2398 |doi=10.1016/j.dsr2.2007.07.028 |access-date=1 January 2024 |via=Elsevier Science Direct}}</ref>

[[Philosophy:Evidence|Evidence]] points to the glaciation of Antarctica occurring in two steps, with the first step, the less pronounced and more modest step of the two, taking place at the Eocene-Oligocene boundary itself. This first step is referred to as EOT-1.<ref name="LadantDonnadieuLefebvreDumas2014">{{cite journal |last1=Ladant |first1=Jean-Baptiste |last2=Donnadieu |first2=Yannick |last3=Lefebvre |first3=Vincent |last4=Dumas |first4=Christophe |date=11 August 2014 |title=The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition |journal=[[Earth:Paleoceanography and Paleoclimatology|Paleoceanography and Paleoclimatology]] |volume=29 |issue=8 |pages=810–823 |doi=10.1002/2013PA002593 |bibcode=2014PalOc..29..810L |s2cid=54093596 |doi-access=free }}</ref> Carbon dioxide concentrations dropped from about 885 ppm to about 560 ppm.<ref name="EoceneOligoceneTransitionReview">{{Cite journal |last1=Hutchinson |first1=David K. |last2=Coxall |first2=Helen K. |last3=Lunt |first3=Daniel J. |last4=Steinthorsdottir |first4=Margret |last5=de Boer |first5=Agatha M. |last6=Baatsen |first6=Michiel |last7=von der Heydt |first7=Anna |last8=Huber |first8=Matthew |last9=Kennedy-Asser |first9=Alan T. |last10=Kunzmann |first10=Lutz |last11=Ladant |first11=Jean-Baptiste |last12=Lear |first12=Caroline H. |last13=Moraweck |first13=Karolin |last14=Pearson |first14=Paul N. |last15=Piga |first15=Emanuela |last16=Pound |first16=Matthew J. |last17=Salzmann |first17=Ulrich |last18=Scher |first18=Howie D. |last19=Sijp |first19=Willem P. |last20=Śliwińska |first20=Kasia K. |last21=Wilson |first21=Paul A. |last22=Zhang |first22=Zhongshi |date=28 January 2021 |title=The Eocene–Oligocene transition: a review of marine and terrestrial proxy data, models and model–data comparisons |url=https://cp.copernicus.org/articles/17/269/2021/ |journal=[[Earth:Climate of the Past|Climate of the Past]] |language=en |volume=17 |issue=1 |pages=269–315 |doi=10.5194/cp-17-269-2021 |bibcode=2021CliPa..17..269H |issn=1814-9332 |access-date=25 December 2023 |doi-access=free }}</ref> The Oligocene Oi-1 event, an oxygen isotope excursion that occurred around 33.55 million years ago,<ref name="JovaneEtAl2006GGG">{{cite journal |last1=Jovane |first1=Luigi |last2=Florindo |first2=Fabio |last3=Sprovieri |first3=Mario |last4=Pälike |first4=Heiko |date=27 July 2006 |title=Astronomic calibration of the late Eocene/early Oligocene Massignano section (central Italy) |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2005GC001195 |journal=[[Chemistry:Geochemistry, Geophysics, Geosystems|Geochemistry, Geophysics, Geosystems]] |volume=7 |issue=7 |pages=1–10 |doi=10.1029/2005GC001195 |bibcode=2006GGG.....7.7012J |s2cid=127299427 |access-date=6 December 2022}}</ref> was the second major pulse of Antarctic ice sheet formation.<ref name="LadantDonnadieuLefebvreDumas2014" />

These large climate changes have been linked to biotic turnovers. Even before the Eocene-Oligocene boundary itself, during the early Priabonian, extinction rates went up in connection with falling global temperatures.<ref name="EoceneOligoceneTransitionReview" /> Radiolarians suffered major losses thanks to a decrease in nutrient availability in deep and intermediate waters.<ref>{{Cite journal |last1=Moore |first1=T. C. |last2=Kamikuri |first2=Shin-ichi |last3=Erhardt |first3=Andrea M. |last4=Baldauf |first4=Jack |last5=Coxall |first5=Helen K. |last6=Westerhold |first6=Thomas |date=1 April 2015 |title=Radiolarian stratigraphy near the Eocene–Oligocene boundary |url=https://www.sciencedirect.com/science/article/pii/S0377839815000134 |journal=Marine Micropaleontology |volume=116 |pages=50–62 |doi=10.1016/j.marmicro.2015.02.002 |bibcode=2015MarMP.116...50M |issn=0377-8398 |access-date=25 December 2023 |via=Elsevier Science Direct}}</ref> In the Gulf of Mexico, marine turnover is associated with climatic change, though the ultimate cause according to the study was not the drop in average temperatures themselves but colder winters and increased seasonality.<ref name="CoolerWinters">{{Cite journal|last1=Ivany|first1=Linda C.|last2=Patterson|first2=William P.|last3=Lohmann|first3=Kyger C.|title=Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary|journal=Nature|volume=407|issue=6806|pages=887–890|doi=10.1038/35038044|pmid=11057663|year=2000|hdl=2027.42/62707|url=https://deepblue.lib.umich.edu/bitstream/2027.42/62707/1/407887a0.pdf|bibcode=2000Natur.407..887I|s2cid=4408282|hdl-access=free}}</ref>

On land, the increased seasonality brought on by this abrupt cooling caused the Grande Coupure faunal turnover in Europe.<ref>{{Cite journal |last1=Weppe |first1=Romain |last2=Condamine |first2=Fabien L. |last3=Guinot |first3=Guillaume |last4=Maugoust |first4=Jacob |last5=Orliac |first5=Maëva J. |date=26 December 2023 |title=Drivers of the artiodactyl turnover in insular western Europe at the Eocene–Oligocene Transition |url=https://pnas.org/doi/10.1073/pnas.2309945120 |journal=Proceedings of the National Academy of Sciences of the United States of America |language=en |volume=120 |issue=52 |doi=10.1073/pnas.2309945120 |s2cid=266359889 |issn=0027-8424 |access-date=25 December 2023}}</ref> In the Ebro Basin, major aridification occurred amidst the Grande Coupure, suggesting causality.<ref name="EbroBasin">{{cite journal |last1=Costa |first1=Elisenda |last2=Garcés |first2=Miguel |last3=Sáez |first3=Alberto |last4=Cabrera |first4=Lluís |last5=López-Blanco |first5=Miguel |date=15 February 2011 |title=The age of the "Grande Coupure" mammal turnover: New constraints from the Eocene–Oligocene record of the Eastern Ebro Basin (NE Spain) |url=https://www.sciencedirect.com/science/article/abs/pii/S0031018211000083 |journal=[[Earth:Palaeogeography, Palaeoclimatology, Palaeoecology|Palaeogeography, Palaeoclimatology, Palaeoecology]] |volume=301 |issue=1–4 |pages=97–107 |doi=10.1016/j.palaeo.2011.01.005 |bibcode=2011PPP...301...97C |hdl=2445/34510 |access-date=25 August 2022 |hdl-access=free }}</ref> The remarkable cooling period in the ocean is correlated with pronounced mammalian faunal replacement within continental Asia as well. The Asian biotic reorganization events are comparable to the {{lang|fr|Grande Coupure}} in Europe and the Mongolian Remodeling of mammalian communities.<ref>{{cite journal |last1=Zhang |first1=R. |last2=Kravchinsky |first2=V.A. |last3=Yue |first3=L. |date=21 May 2012 |title=Link between Global Cooling and Mammalian Transformation across the Eocene–Oligocene Boundary in the Continental Interior of Asia |url=https://link.springer.com/article/10.1007/s00531-012-0776-1 |journal=International Journal of Earth Sciences |volume=101 |issue=8 |pages=2193–2200 |bibcode=2012IJEaS.101.2193Z |doi=10.1007/s00531-012-0776-1 |s2cid=55409146 |access-date=17 March 2023}}</ref>

=== Extraterrestrial impact ===
Another speculation points to several large [[Astronomy:Meteorite|meteorite]] impacts near this time, including those of the Chesapeake Bay crater {{cvt|40|km||}} and the [[Earth:Popigai impact structure|Popigai impact structure]] {{cvt|100|km||}} of central Siberia, which scattered debris perhaps as far as Europe. New dating of the Popigai meteor strengthens its association with the extinction.<ref>{{cite web |date=June 16, 2014 |title=Russia's Popigai Meteor Crash Linked to Mass Extinction |url=https://news.yahoo.com/russias-popigai-meteor-crash-linked-mass-extinction-113359696.html}}</ref> However, other studies have failed to find any association between the extinction event and any impact event.<ref>{{Cite journal |last1=Molina |first1=Eustoquio |last2=Gonzalvo |first2=Concepción |last3=Ortiz |first3=Silvia |last4=Cruz |first4=Luis E. |date=2006-02-28 |title=Foraminiferal turnover across the Eocene–Oligocene transition at Fuente Caldera, southern Spain: No cause–effect relationship between meteorite impacts and extinctions |journal=Marine Micropaleontology |volume=58 |issue=4 |pages=270–286 |bibcode=2006MarMP..58..270M |doi=10.1016/j.marmicro.2005.11.006}}</ref>

=== Solar activity ===
Imprints of sunspot cycles from the Bohai Bay Basin (BBB) show no evidence that any significant change in solar activity occurred across the EOT.<ref>{{Cite journal |last=Shi |first=Juye |last2=Jin |first2=Zhijun |last3=Liu |first3=Quanyou |last4=Fan |first4=Tailiang |last5=Gao |first5=Zhiqian |date=1 October 2021 |title=Sunspot cycles recorded in Eocene lacustrine fine-grained sedimentary rocks in the Bohai Bay Basin, eastern China |url=https://www.sciencedirect.com/science/article/pii/S0921818121001995 |journal=[[Earth:Global and Planetary Change|Global and Planetary Change]] |volume=205 |pages=103614 |doi=10.1016/j.gloplacha.2021.103614 |issn=0921-8181 |access-date=1 January 2024 |via=Elsevier Science Direct}}</ref>

==Extinction patterns==

=== Terrestrial biota ===

==== {{lang|fr|Grande Coupure}} ====
The {{lang|fr|Grande Coupure}}, or 'great break' in [[Social:French language|French]],<ref>also termed the MP 21 event.</ref> with a major European turnover in mammalian fauna about 33.5 Ma, marks the end of the last phase of Eocene assemblages, the [[Earth:Priabonian|Priabonian]], and the arrival in Europe of Asian species. The {{lang|fr|Grande Coupure}} is characterized by widespread extinctions and [[Biology:Allopatric speciation|allopatric speciation]] in small isolated [[Biology:Relict|relict population]]s.<ref>Called "dispersal-generated origination" in Hooker et al. 2004</ref> It was given its name in 1910 by the {{wipe|Switzerland}} palaeontologist Hans Georg Stehlin, to characterise the dramatic turnover of European mammalian fauna, which he placed at the Eocene–Oligocene boundary.<ref>{{cite journal |last1=Stehlen |first1=H.G. |year=1910 |title=Remarques sur les faunules de Mammifères des couches eocenes et oligocenes du Bassin de Paris |journal={{lang|fr|Bulletin de la Société Géologique de France|italic=unset}} |volume=4 |issue=9 |pages=488–520}}</ref> A comparable turnover in Asian fauna has since been called the "Mongolian Remodelling".

The {{lang|fr|Grande Coupure}} marks a break between endemic European faunas before the break and mixed faunas with a strong Asian component afterwards. J. J. Hooker and his team summarized the break:<ref name=Hooker>{{Cite journal|doi=10.1144/0016-764903-091 |title=Eocene–Oligocene mammalian faunal turnover in the Hampshire Basin, UK: calibration to the global time scale and the major cooling event |year=2004 |last1=Hooker |first1=J.J. |journal=Journal of the Geological Society |volume=161 |issue=2 |pages=161–172 |last2=Collinson |first2=M.E. |last3=Sille |first3=N.P.|bibcode=2004JGSoc.161..161H |s2cid=140576090 |url=http://doc.rero.ch/record/13418/files/PAL_E228.pdf }}</ref>
:"Pre-{{lang|fr|Grande Coupure}} faunas are dominated by the perissodactyl family [[Biology:Palaeotheriidae|Palaeotheriidae]] (distant [[Biology:Horse|horse]] relatives), six families of artiodactyls (cloven-hoofed mammals) ([[Biology:Anoplotheriidae|Anoplotheriidae]], [[Biology:Xiphodontidae|Xiphodontidae]], [[Biology:Choeropotamidae|Choeropotamidae]], Cebochoeridae, [[Biology:Dichobunidae|Dichobunidae]] and Amphimerycidae), the rodent family Pseudosciuridae, the primate families [[Biology:Omomyidae|Omomyidae]] and [[Biology:Adapiformes|Adapidae]], and the [[Biology:Archonta|archonta]]n family [[Biology:Nyctitheriidae|Nyctitheriidae]].

:"Post-{{lang|fr|Grande Coupure}} faunas include the true rhinoceros (family [[Biology:Rhinocerotidae|Rhinocerotidae]]), three artiodactyl families ([[Biology:Entelodontidae|Entelodontidae]], [[Biology:Anthracotheriidae|Anthracotheriidae]] and [[Biology:Gelocidae|Gelocidae]]) related respectively to [[Biology:Suidae|pig]]s, [[Biology:Hippopotamus|hippo]]s and [[Biology:Ruminant|ruminant]]s, the [[Biology:Rodent|rodent]] families [[Biology:Eomyidae|Eomyidae]], [[Biology:Cricetidae|Cricetidae]] ([[Biology:Hamster|hamster]]s) and [[Biology:Castoridae|Castoridae]] ([[Biology:Beaver|beaver]]s), and the lipotyphlan family [[Biology:Erinaceidae|Erinaceidae]] ([[Biology:Hedgehog|hedgehog]]s). The speciose genus ''Palaeotherium'' plus ''[[Biology:Anoplotherium|Anoplotherium]]'' and the families Xiphodontidae and Amphimerycidae were observed to disappear completely.

:"Only the [[Biology:Marsupial|marsupial]] family [[Biology:Herpetotheriidae|Herpetotheriidae]], the artiodactyl family [[Biology:Cainotheriidae|Cainotheriidae]], and the rodent families Theridomyidae and Gliridae (dormice) crossed the faunal divide undiminished."

An element of the paradigm of the {{lang|fr|Grande Coupure}} was the apparent [[Biology:Extinction|extinction]] of all European primates at the {{lang|fr|Coupure}}. However, the 1999 discovery of a [[Biology:Mouse|mouse]]-sized early Oligocene omomyid, reflecting the better survival chances of small mammals, undercut the {{lang|fr|Grand Coupure}} [[Philosophy:Paradigm|paradigm]].<ref>{{Cite journal |author1=Köhler, M |author2=Moyà-Solà, S |date=December 1999 |title=A finding of Oligocene primates on the European continent |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=96 |issue=25 |pages=14664–7 |bibcode=1999PNAS...9614664K |doi=10.1073/pnas.96.25.14664 |issn=0027-8424 |pmc=24493 |pmid=10588762 |doi-access=free}}</ref>

Additionally, a second dispersal event of Asian taxa into Europe, known as the Bachitherium dispersal event, occurred later, around 31 Ma. Unlike the Grande Coupure, which took place via Central and Northern Asia, this later dispersal occurred via a southern corridor.<ref>{{Cite journal |last=Mennecart |first=Bastien |last2=Aiglstorfer |first2=Manuela |last3=Li |first3=Yikun |last4=Li |first4=Chunxiao |last5=Wang |first5=ShiQi |date=6 September 2021 |title=Ruminants reveal Eocene Asiatic palaeobiogeographical provinces as the origin of diachronous mammalian Oligocene dispersals into Europe |url=https://www.nature.com/articles/s41598-021-96221-x |journal=Scientific Reports |language=en |volume=11 |issue=1 |pages=17710 |doi=10.1038/s41598-021-96221-x |issn=2045-2322 |access-date=1 January 2024|doi-access=free |pmc=8421421 }}</ref>

It has been suggested that this was caused by [[Earth:Climate change (general concept)|climate change]] associated with the earliest polar glaciations and a major fall in sea levels, or by competition with taxa dispersing from Asia. However, few argue for an [[Earth:Oligocene#Climate|isolated single cause]]. Other possible causes are related to the impact of one or more large bolides in northern hemisphere at [[Earth:Popigai crater|Popigai]], [[Earth:Toms Canyon impact crater|Toms Canyon]] and Chesapeake Bay.<ref>A major cooling event preceded the {{lang|fr|Grande Coupure}}, based on pollen studies in the Paris Basin conducted by Chateauneuf (J.J. Chateauneuf, 1980. "{{lang|fr|Palynostratigraphie et paleoclimatologie de l'Éocene superieur et de l'Oligocene du Bassin de [[Place:Paris|Paris]] ({{wipe|France}})|italic=no}}" in {{lang|fr|Mémoires du Bureau de Recherches Géologiques et Minières}}, '''116''' 1980).</ref> Improved correlation of northwest European successions to global events confirms the {{lang|fr|Grande Coupure}} as occurring in the earliest Oligocene, with a hiatus of about 350 millennia prior to the first record of post-{{lang|fr|Grande Coupure}} Asian immigrant taxa.<ref name="Hooker" /> Research suggests that in the Ebro Basin of Spain, the turnover lagged the Eocene-Oligocene boundary by at most 500 kyr.<ref name="EbroBasin" />

=== Marine biota ===
In the marine realm, the frequency of drilling in recovery faunas, especially among bivalves, was drastically higher than in assemblages before the extinction event, a phenomenon attributed to a high extinction rate among escalated prey taxa with highly evolved defences against predators.<ref>{{cite journal |last1=Kelley |first1=Patricia H. |last2=Hansen |first2=Thor A. |date=4 April 1996 |title=Recovery of the naticid gastropod predator–prey system from the Cretaceous–Tertiary and Eocene–Oligocene extinctions |url=https://www.lyellcollection.org/doi/abs/10.1144/gsl.sp.1996.001.01.27 |journal=Geological Society, London, Special Publications |volume=102 |issue=1 |pages=373–386 |doi=10.1144/gsl.sp.1996.001.01.27 |bibcode=1996GSLSP.102..373K |s2cid=129920064 |access-date=16 April 2023}}</ref> Veneroid bivalves experienced a short-term size increase during the biotic recovery.<ref>{{cite journal |last1=Lockwood |first1=Rowan |date=1 January 2005 |title=Body size, extinction events, and the early Cenozoic record of veneroid bivalves: a new role for recoveries? |url=https://pubs.geoscienceworld.org/paleobiol/article-abstract/31/4/578/110297/Body-size-extinction-events-and-the-early-Cenozoic |journal=Paleobiology |volume=31 |issue=4 |pages=578–590 |doi=10.1666/0094-8373(2005)031[0578:BSEEAT]2.0.CO;2 |access-date=16 April 2023}}</ref> Orthophragminid foraminifera disappeared in the extinction event; in Alpine carbonates, [[Biology:Bryozoa|bryozoa]]n facies show an expansion in response to the loss of orthophragminids.<ref>{{cite journal |last1=Nebelsick |first1=James H. |last2=Rasser |first2=Michael W. |last3=Bassi |first3=Davide |date=5 July 2005 |title=Facies dynamics in Eocene to Oligocene circumalpine carbonates |url=https://link.springer.com/article/10.1007/s10347-005-0069-2?error=cookies_not_supported&code=2d2d9552-62f2-4b2f-a5b8-0fc96481a292 |journal=Facies |volume=51 |issue=1–4 |pages=197–217 |doi=10.1007/s10347-005-0069-2 |bibcode=2005Faci...51..197N |s2cid=140576829 |access-date=10 May 2023}}</ref>

Some sites contain evidence that the Eocene–Oligocene extinction was not a sudden event but a prolonged biotic transition drawn out over as much as 6 million years. Localities near Eugene, Oregon, record a plant extinction 33.4 Ma and a marine invertebrate turnover 33.2 Ma; both of these turnovers post-date the supposed extinction event by hundreds of thousands of years.<ref>{{cite journal |last1=Retallack |first1=Gregory J. |last2=Orr |first2=William N. |last3=Prothero |first3=Donald Ross |last4=Duncan |first4=Robert A. |last5=Kester |first5=Paul R. |last6=Ambers |first6=Clifford P. |date=1 July 2004 |title=Eocene–Oligocene extinction and paleoclimatic change near Eugene, Oregon |url=https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/116/7-8/817/2099/Eocene-Oligocene-extinction-and-paleoclimatic |journal=Geological Society of America Bulletin |volume=116 |issue=7–8 |pages=817–839 |doi=10.1130/B25281.1 |bibcode=2004GSAB..116..817R |access-date=16 April 2023}}</ref>

==References==
{{reflist}}

==External links==
* [http://www.ucmp.berkeley.edu/education/events/cowen1a.html ''Extinction'' an essay by Richard Cowen]

{{Extinction}}

{{DEFAULTSORT:Eocene-Oligocene Extinction Event}}
[[Category:Extinction events]]
[[Category:Eocene extinctions| ]]
[[Category:Oligocene extinctions| ]]

{{Sourceattribution|Eocene–Oligocene extinction event}}