Study details world's worst die-off: hell on Earth

November 17, 2011 - 4:11 PM

WASHINGTON (AP) — During the world's biggest mass extinction, Earth seemed pretty close to a description of hell — fiery, smoky and explosive — created by massive volcanic eruptions, according to research dug up in China.

In geologic terms, it was surprisingly quick, and it may provide a scary lesson about climate change for our future, authors of the new study say. It was the third of five extinctions in world history, occurring even before dinosaurs roamed.

This extinction killed off more than three-quarters of life on the planet in an event scientists have called the Great Dying. The Chinese dig sites provide new dates and details of the event, which occurred at the end of the Permian Era. It happened 252 million years ago and may have lasted less than 100,000 years, far shorter than scientists had thought, according to the study published Thursday in the journal Science.

The study also bolsters the prevailing scientific concept that the giant die-off was caused by a massive shift in climate — global warming, prehistoric style — triggered by volcanic activity that is far beyond modern levels. The research also makes the case that the burst of carbon dioxide and methane thrown into the atmosphere that triggered the die-off took only about 20,000 years, less than previously thought, though the ecological damage lasted longer.

And devastating fires raged worldwide, not just where the volcanoes exploded, the paper said.

"Imagine drying out the Amazon and burning it up," said study co-author Douglas Erwin, a paleobiology curator at the Smithsonian Institution. "It certainly was a very uncomfortable time. You're killing off 75 to 90 percent of everything on the planet. It's not going to be terribly pleasant."

The air at times could be like the thick smog outside an old Eastern European power plant, Erwin said.

It was the only mass extinction in history to kill off hardy insects, Erwin said. Afterward, there were very few species left worldwide, and they had little diversity among different regions. It was only later that dinosaurs and mammals roamed the Earth.

The study is based on more than two dozen cross-sections of soil, both on land and under water, over thousands of miles in southern China. But they should be representative of the entire world, given the shift of continents over the past 250 million years, said lead author Shu-zhong Shen of the Nanjing Institute of Geology and Paleontology. The study also offered the first evidence that the die-off in the sea and on land happened at the same time.

Erwin said the climate changed because of rapid infusions of carbon dioxide and methane into the air. This study doesn't determine how much it warmed, but other research has said temperatures rose by as much as 9 degrees Fahrenheit, making the climate at least 15 degrees warmer than it is today.

Those greenhouse gases that trap heat probably were released because of immense volcanic activity mostly in Siberia, he said. The eruptions — probably hundreds of them lasting thousands of years — spewed far more carbon and magma than Earth has witnessed for tens of millions of years. Just one such eruption would cover an area the size of Vermont, Erwin said.

Outside experts had mixed reaction to the study.

Richard Twitchett of Plymouth University in Great Britain called it "an excellent illustration of just how far we've come in getting to grips with the greatest extinction event in the history of life on Earth."

But Luanne Becker, a former geochemist at the University of California Santa Barbara, disagreed with Shen's conclusion about what caused the global die-off. Becker is a longtime proponent of the minority view that an asteroid or comet hitting Earth caused this extinction.

She said that while the study did a great job of defining what happened and how long it lasted, "I do not feel that volcanism alone can trigger some of the most catastrophic extinction events in the history of life on Earth. Rather it would take multiple catastrophes to occur synchronously (impact and volcanism) to trigger a mass extinction event," she wrote in an email.

But Erwin said that despite global searches, scientists haven't found signs of a comet or asteroid impact at the right time for this extinction.

Shen theorized that environmental stress was building and then hit a tipping point and "collapsed in a very rapid way."

"This is also a lesson for the modern times," Shen said. "We don't know what will happen or when it will happen."

This climate change "happened naturally, and it killed everything," Erwin said. But he said that if critics of global warming science think it shows that climate change is nothing to worry about because it has happened naturally in the past, that's the wrong conclusion.

"I think the lesson you take away from this is that you don't want to get anywhere close to a mass extinction," Erwin said. "It took 5 million years before life got better again."

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Science: http://www.sciencemag.org