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Death by magma

Long-term volcanic eruptions triggered mass undersea extinctions

11:56am, July 16, 2008

Widespread extinctions in the world’s oceans millions of years ago may have been triggered by massive underwater volcanic eruptions that created much of the Caribbean seafloor.


About 93.5 million years ago, many types of deep-sea creatures, including large clams and various microorganisms that lived on the seafloor, died out. At the same time, thick layers of organic-rich marine sediments accumulated at several sites worldwide, says Steven C. Turgeon, a geochemist at the University of Alberta in Edmonton.


The layers, such as a 1.2-meter-thick black shale layer off the northeastern coast of South America that contains as much as 23 percent organic matter, suggest that the waters bathing ocean floors across the globe at the time contained little if any dissolved oxygen, he notes.


Similar events, which scientists have dubbed oceanic anoxic events, pepper the geologic record, and their causes have long remained unexplained.

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