HELL ON EARTH: The Great Dying

Archaeologists looking at soil in China have seen traces of a time when the earth burned, sulphur filled the air and three quarters of living creatures died.

Investigating the biggest mass extinction in the earth's history - a team led by Shu-zhong Shen of Nanjing Institute of Geology and Palaeontology examined two dozen cross-sections of soil in southern China for traces of the catastrophe 252 million years ago.

Known as The Great Dying and occurring at the end of the Permian period, it happened well before dinosaurs arrived on earth and it took life on earth about five million years to recover.

The research published yesterday in Science gave further backing to the belief that this hell-on-earth scenario was caused by volcanos. Shen and his colleagues analysed the volcanic minerals in the soil and dated them using the decay of radioactive uranium to lead.

They estimated that volcanos, most likely in Siberia, erupted thousands of times a year for about 20,000 years to produce the toxic climate that killed off approximately three quarters of life on land and possibly 90 per cent of life in the sea.

"What's striking is how fast the extinction was," says Douglas Erwin of the Smithsonian National Museum of Natural History in Washington, D.C., a co-author of the paper. The event had been seen as lasting half a million years, but the new dating limits it to no more than 200,000 years and quite possibly less than 100,000 years, Erwin says. "We're paleontologists studying events 250 million years ago," he adds, so "a hundred thousand years sounds like overnight to us".

The combination of methane, carbon dioxide and an acid-generating sulphur was enough to create the biggest and worst of the five great mass extinctions to occur on the planet. The Great Dying was only one to kill hardy insects as well as more delicate life-forms.

The first humans are estimated to have emerged 200,000 years ago; proto-primates emerged about 65 million years ago. ®

Research reported in Science