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Craters and Impactites |
Department of Palaeontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
The Phanerozoic history of life has been interrupted by at least 17 different stage-level episodes of elevated extinction intensity. These range from major turnovers that affected the majority of the Earth’s extant biota (e.g. the Tatarian, Ashgill, and Maastrichtian events) to much smaller and perhaps more geographically localized disruptions. Review of available stage-level stratigraphic evidence suggests that bolide impacts do not exhibit a compelling correspondence to the Phanerozoic record of marine invertebrate extinctions. A much stronger case can be made for the repeated association of extinction events and episodes of long-term eustatic sea-level fall and/or major episodes of continental flood basalt volcanism. Moreover, during the last 250 Ma particularly severe extinction events have occurred during times of simultaneous continental flood basalt eruption and eustatic sea-level fall (e.g. Tatarian, Norian, Maastrichtian). Attempts to employ patterns of extinction selectivity to infer the physical cause of extinction events have foundered on the non-specificity of biological predictions as well as the seemingly unique biotic nature of each event. Although a few high-resolution biostratigraphic analyses have demonstrated that largely progressive patterns of faunal turnovers are consistent with co-extinction models under certain assumptions, this does not constitute a strong confirmation of the co-extinction model as a necessary or sufficient general explanation for Phanerozoic extinction events. In all likelihood, the nature of the fossil record precludes precise identification of extinction causal mechanisms. Nevertheless, comparative studies are able to evaluate the role both large and small extinction events have played in altering the long-term course of Earth’s biological history.
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