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Microbes indicted in ancient mass extinction

At the end of the Permian period, marine microbes may have given off so much methane and made the oceans so acidic that shelled creatures, similar to the fossils shown, would have gone extinct.

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About 252 million years ago an estimated 96 percent of all species were wiped from Earth, and now scientists have a new suspect in the killing — methane-belching microbes.

The archaea Methanosarcina got faster at making methane by acquiring a gene from another microbe and then reproducing quickly, fueled by nickel spewing from Siberian volcanoes. The extra methane would have made the oceans acidic and added sulfur compounds to the air, driving the extinction of life at sea and on land, a team of researchers suggests March 31 in the Proceedings of the National Academy of Sciences.  An earlier report estimated that the die-off happened in less than 60,000 years. 

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