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Oceans may have poisoned early animals

Add sulfur, subtract oxygen, and a deadly brew results

1:09pm, January 5, 2011

Soon after complex animals made their first great strides onto the stage of life, the oceans brewed up a toxic chemical mix that put the brakes on evolutionary innovation, suggests a paper in the Jan. 6 Nature.

The culprits? Too little oxygen and too much sulfur dissolved in coastal waters, reports a team led by geochemist Benjamin Gill of Harvard University. Ancient creatures such as trilobites and brachiopods could not cope with the changes, and many of them went extinct.

The “remarkable” new data are the first to link a changing ocean environment to some of the extinctions that took place between about 490 million and 520 million years ago, says Graham Shields-Zhou, a geologist at University College London who was not on the research team.

Perhaps not surprisingly, marine creatures are exquisitely sensitive to their surroundings, suffocating when oxygen levels drop. Other big extinctions, like one that occurred around 400 million year

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