By Ben Hirschler

LONDON, March 20 (Reuters) - Gas-belching volcanoes may be to blame for a series of mass extinctions over the last 545 million years, including that of the dinosaurs, new evidence suggested on Thursday.

A series of eruptions that formed the Deccan Traps in what is now India pumped huge amounts of sulphur into the atmosphere 65 million years ago, with likely devastating repercussions for the Earth's climate, scientists said.

Gigantic eruptions, forming so-called "flood basalts", are one of two leading explanations for a series of mass extinctions that have killed off species periodically throughout history.

The other theory involves asteroid impacts -- generally considered the prime suspect in the case of the extinction of dinosaurs 65 million years ago.

There have been doubts about the killing power of volcanoes because, until now, researchers have struggled to measure just how much toxic gas would have been released.

But after finding rare inclusions of glass in the Deccan rock, a British-based team has found vital preserved information about its original gas content.

Writing in the journal Science, they concluded that the massive of amounts of both sulphur and chlorine released would probably have had a "severe" environmental impact.

"It certainly bolsters the case, though it doesn't prove it," Stephen Self, formerly of Britain's Open University and now senior volcanologist with the U.S. Nuclear Regulatory Commission, said in an interview.

"There have been several major mass extinctions and most of those have, uncannily, occurred while one of these huge flood basalt provinces was being formed."

The volcanoes may have spewed 10 times as much sulphur into the atmosphere every year as humans have done recently by burning coal in power stations and through other industrial activities.

The result would have been widespread acid rain and aerosols of sulphuric acid in atmosphere, cooling the surface of the Earth and upsetting normal patterns of circulation.

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