Geology

Surviving the Snowball

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Science  18 Apr 2003:
Vol. 300, Issue 5618, pp. 395-397
DOI: 10.1126/science.300.5618.395e

Before the pre-Cambrian-Cambrian boundary, there is geological evidence of periods of extraordinarily extreme climatic variation. Some postulate this veered from millions of years of total glaciation at −50°C to sudden shifts to surface temperatures averaging 40°C. The exact nature of the physical conditions is hotly debated, as are the effects of these extremes on the survival of prevailing life forms. In their examination of the microfossils of Death Valley, Corsetti et al. have found complex communities of prokaryotes and eukaryotes preserved in cherts and carbonate rocks, including various forms of stromalites and oncoids. The communities seen in the preglacial cherts are very similar to those in the postglacial carbonate films, and it appears that complex communities persisted for 200 million years of climatic vacillation. The new findings suggest that the environmental scars noted in the geological record were not so severe that mass extinction of shallow water microbiota occurred, at least in shallow tropical seas.—CA

Proc. Natl. Acad. Sci. U.S.A. 100, 4399 (2003).

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