Study: Death of dinosaurs was second event

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SEATTLE, Sept. 6 (UPI) -- The dying of dinosaurs 65 million years ago may have been the second of two extinction events, following one that killed marine life, U.S. scientists say.

The extinction of dinosaurs is thought to be due to an asteroid at least 6 miles in diameter slamming into Mexico's Yucatan Peninsula, but new evidence shows life on the seafloor was already perishing at the time of the impact because of the effects of huge volcanic eruptions on the Deccan Plateau in what is now India.

Researchers at the University of Washington said the eruptions would have spewed carbon dioxide and other greenhouse gases into the atmosphere to produce long-term warming that led to the first of the two mass extinctions.

"The eruptions started 300,000 to 200,000 years before the impact, and they may have lasted 100,000 years," Thomas Tobin, a doctoral student in Earth and space sciences, said in a UW release Thursday.

The eruptions would have filled the atmosphere with fine particles called aerosols that initially cooled the planet before the greenhouse gases reversed the climate into a warming mode.

"The aerosols are active on a year to 10-year time scale, while the carbon dioxide has effects on a scale of hundreds to tens of thousands of years," Tobin said.

There is no direct evidence the first extinction event had any effect on the second, but Tobin said he believes surviving species from the first event were compromised enough they were unable to survive the long-term environmental effects of the asteroid impact.

"It seems improbable to me that they are completely independent events," he said.