What is Eocene–Oligocene extinction event?
[[File:Extinction intensity.svg|thumb|250px|Extinction events]] The end of the [[Eocene]] was the beginning of the [[Oligocene]] (33.9 million years ago). It is marked by a large-scale [[floral]] and [[fauna]]l turnover.<ref>{{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|s2cid=4408282|url=https://deepblue.lib.umich.edu/bitstream/2027.42/62707/1/407887a0.pdf}}</ref> Most of the affected organisms were marine or aquatic in nature. They included the last of the ancient [[cetaceans]], the [[Archaeoceti]]. This was a time of major [[Climate change|climatic change]], especially cooling. At first, it was not linked with any single major impact or any catastrophic [[volcanic]] 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|doi=10.1016/j.marmicro.2005.11.006|bibcode=2006MarMP..58..270M}}</ref> But volcanic activity may have caused the extinction event. Several large [[meteorite]] impacts occurred about this time. One such event caused the [[Chesapeake Bay impact crater]] {{cvt|40|km||}}, and another at the [[Popigai crater]] {{cvt|100|km||}} in central [[Siberia]], scattering debris perhaps as far as [[Europe]]. New dating of the Popigai meteor suggests it may be a cause of the [[List of extinction events|mass extinction]].<ref>{{cite web|title=Russia's Popigai Meteor Crash Linked to Mass Extinction|url=https://news.yahoo.com/russias-popigai-meteor-crash-linked-mass-extinction-113359696.html|date=June 16, 2014}