New theory for mass extinction is offered

LOS ANGELES, Oct. 29 (UPI) -- U.S. scientists say the great mass extinction of 250 million years ago might not have been caused by a meteor strike, but, rather, by environmental stresses.

University of Southern California doctoral student Catherine Powers said stresses such as volcanic eruptions and global warming were the likely causes of a slow decline in the diversity of some common marine organisms.

The study by Powers and Professor David Bottjer suggests the decline began millions of years before the disappearance of 90 percent of Earth’s species at the end of the Permian era. The study also found organisms in the deep ocean started dying first, followed by those on ocean shelves and reefs, and finally those living near shore.

"Something has to be coming from the deep ocean," Powers said. "Something has to be coming up the water column and killing these organisms."

She and Bottj said they believe hydrogen sulfide might have been the culprit. They said previous studies, combined with their new data, support a model attributing the extinction to enormous volcanic eruptions that released carbon dioxide and methane, triggering rapid global warming.

The scientists detail their findings in the November issue of the journal Geology.