Volcanoes blamed for worst mass extinction

The greatest mass extinction in the 3.5-billion-year history of life on Earth probably occurred as a result of climate change resulting from a series of huge volcanic eruptions, researchers believe.

The greatest mass extinction in the 3.5-billion-year history of life on Earth probably occurred as a result of climate change resulting from a series of huge volcanic eruptions, researchers believe.

They said a study of "the great dying", when 90 per cent of marine life became extinct and three-quarters of land animals and plants died out, had failed to support earlier suggestions of the Earth and a giant asteroid colliding.

Previous studies have suggested that a sudden catastrophic change in the global climate resulted from an asteroid collision 250 million years ago, when the greatest of five mass extinctions took place. But scientists investigating volcanic ash sediments in South Africa and China - fallout from the same volcanic eruptions in Siberia - believe that a relatively slow rate of extinction occurred over millions of years.

Peter Ward of the University of Washington, a leader of the joint American-South African research team, said the volcanoes probably triggered the release of massive quantities of greenhouse gases which led to catastrophic climate change. "Animals and plants both on land and in the sea were dying at the same time, and apparently from the same causes - too much heat and too little oxygen," he said.

His findings are published in the online version of Science.