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 40 km (25 mi), and another at the Popigai crater 100 km (62 mi) in central Siberia, scattering debris perhaps as far as Europe. New dating of the Popigai meteor suggests it may be a cause of the mass extinction.
A leading scientific theory on climate cooling at this time predicts a decrease in atmospheric carbon dioxide, which slowly declined in the mid to late Eocene and possibly reached some threshold about 34 million years ago. This boundary is closely linked with the Oligocene Oi-1 event, an oxygen isotope change which marks the beginning of ice sheet coverage on Antarctica.
References[change | change source]
- Ivany, Linda C.; Patterson, William P.; Lohmann, Kyger C. (2000). "Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary" (PDF). Nature. 407 (6806): 887–890. doi:10.1038/35038044. hdl:2027.42/62707. PMID 11057663. S2CID 4408282.
- Molina, Eustoquio; Gonzalvo, Concepción; Ortiz, Silvia; Cruz, Luis E. (2006-02-28). "Foraminiferal turnover across the Eocene–Oligocene transition at Fuente Caldera, southern Spain: No cause–effect relationship between meteorite impacts and extinctions". Marine Micropaleontology. 58 (4): 270–286. Bibcode:2006MarMP..58..270M. doi:10.1016/j.marmicro.2005.11.006.
- "Russia's Popigai Meteor Crash Linked to Mass Extinction". June 16, 2014.
- Zachos, James C.; Quinn, Terrence M.; Salamy, Karen A. (1996-06-01). "High-resolution (104 years) deep-sea foraminiferal stable isotope records of the Eocene-Oligocene climate transition". Paleoceanography. 11 (3): 251–266. Bibcode:1996PalOc..11..251Z. doi:10.1029/96PA00571. ISSN 1944-9186.
- Shackleton, N. J. (1986-10-01). "Boundaries and events in the Paleogene: Paleogene stable isotope events". Palaeogeography, Palaeoclimatology, Palaeoecology. 57 (1): 91–102. Bibcode:1986PPP....57...91S. doi:10.1016/0031-0182(86)90008-8.