Extinction's Cause and Effect

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Science  04 Feb 2011:
Vol. 331, Issue 6017, pp. 512
DOI: 10.1126/science.331.6017.512-b

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CREDIT: GRASBY ET AL., NAT. GEOSCI. 4, 10.1038/NGEO1069 (2011)

At the Permian-Triassic boundary ∼250 million years ago, nearly 90% of marine animals went extinct. Unlike the dinosaurs' demise attributed to a giant asteroid impact ∼185 million years later, this extinction event was at least partially related to a long series of volcanic eruptions. A series of feedbacks in the ocean-atmosphere system as a response to these eruptions would have turned the oceans anoxic and suffocating to animals, but how marine life recovered is not well constrained. To track primary productivity after the mass extinction, Meyer et al. examined the carbon isotope signature from limestone deposits in south China. Large variations in the isotopic record suggest that autotrophic productivity was so high after the mass extinction that it maintained anoxia and choked out larger marine life, though the isotopes say little about how such a situation would have originated. Toward that end, a study by Grasby et al. suggests that volcanism also combusted nearby coal deposits in a series of events that are roughly coincident with downturns in productivity leading up to the mass extinction. The charred remains (shown left in comparison with modern combustion residue), which were found in sedimentary deposits in the Canadian arctic, may have added toxins, such as chromium, to ocean basins that could also have contributed to the declining state of marine biodiversity.

Earth Planet Sci. Lett. 10.1016/j.epsl.2010.12.033 (2011); Nat. Geosci. 4, 10.1038/ngeo1069 (2011).

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