When Life Nearly Ended

Sept. 12, 2007 — -- There's a place in south China where the Earth tells its own story of the cataclysmic end to most of the animals and plants that had once thrived in its oceans and on its land. For decades now, scientists have probed the steep slopes of the Great Bank of Guizhou, pulling out fossils to see what they can tell us about the largest mass extinction in the planet's history.

Are those long-dead critters talking to us today? Can they tell us anything about the possible consequences of a changing global climate?

For hundreds of millions of years, small animals and plants accumulated in the floor of a giant seabed, forming a massive field of limestone that today provides a rare window into the past. The abundance was great, and the biodiversity was large, until a relatively brief period 250 million years ago. It was at that time, the end of the Permian period and the beginning of the Triassic, that 90 percent of life on Earth was wiped out.

The evidence suggests that the atmosphere was extra rich with carbon dioxide, probably because of volcanic activity, that would have changed the concentrations of ambient gases in the atmosphere and in the oceans. A once hospitable planet became very unfriendly to most of its inhabitants.

To be sure, the situation then was quite different than the global climate change we see today, but scientists who are studying the record in south China are not real comfortable with what they are seeing.

"The parallels to what's going on now are astonishing and a little disquieting," said Jonathan Payne, assistant professor of geological and environmental sciences at Stanford University. "There are many similarities."

But, he quickly added, "the organisms alive today are quite different" from the animals that thrived then. "It's difficult to predict."

For more than five years now, Payne has climbed over sections of the Great Bank. Deposits on the ancient sea floor were laid down horizontally, but tectonic forces have tipped them over on their side, so it is theoretically possible to walk back in time for hundreds of millions of years.

But, it would be a difficult walk. The area of interest to scientists is more than 40 miles long, extending across the face of a forbidding mountain, and rising nearly 2,000 feet above a twisting mountain road.