When Life Nearly Ended

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.

"It's quite dramatic when you see it," Payne said. "It is an enormous scale. When you stand there, you are an ant looking at a mountain."

But, what's even more impressive is the story that mountain has to tell.

The line that separates the Permian period from the Triassic is so fine, "you can put your fingernail on it," Payne said. The rocks below your fingernail, from the late Permian, would be rich with marine fossils.

"In many areas, the proportion of the rock that's made up of shells of animals and algae is as much as 20 or 30 percent," Payne said. "When you think about the limitations of packing shells together, you realize you can't make it 100 percent of the volume. So, 20 or 30 percent basically means you have shells cheek-to-jowl, and stacked for 50 to 100 meters."

But, above your fingernail — the beginning of the Triassic — would be a very different story.

"Above (the line), you have very low diversity of fossils, very few fossils, and that remains the case for 4 to 5 million years," explained Payne. "We find that extremely intriguing, because decreasing the diversity in the world doesn't necessarily mean you decrease the abundance of animals.

  • 1
  • |
  • 2
Join the Discussion
blog comments powered by Disqus
You Might Also Like...