August 31, 2008

Earth Faced Death in Permian

By Robert S. Boyd / McClatchy Newspapers

It was the greatest mass murder of all time - poison everywhere, billions slain - but the killers have never been positively identified.

An estimated 95 percent of marine species and 85 percent of land creatures died, said Peter Ward, a paleobiologist at the University of Washington in Seattle.

Scientists call it "The Great Dying." Life took millions of years to recover.

Scientific sleuths now think they're making progress toward learning what caused the extinction of most plants and animals 251 million years ago.

The perpetrator wasn't an asteroid or comet, like one that wiped out the dinosaurs 65 million years ago .

Instead, it was a cascade of events that began with a monstrous outpouring of hot, reeking lava in Siberia. Repeated floods of lava released massive amounts of carbon dioxide, creating a runaway greenhouse effect, with oxygen-starved oceans and poisoned air.

The slaughter is known as the Permian-Triassic Mass Extinction. It marked the end of a multimillion-year geologic period, the Permian, and the start of another, the Triassic.

To further unravel the mystery, the National Science Foundation has launched a study of the Siberian lava, led by Linda Elkins- Tanton, a geologist at the Massachusetts Institute of Technology.

"We have 28 scientists from seven countries and five years' worth of funding," Elkins-Tanton said.

Besides being a puzzling detective story, the P-T extinction is a cautionary tale for our time.

"The end-Permian catastrophe is an extreme version of the consequences of global warming," said Lee Kump, a geoscientist at The Pennsylvania State University. "It reminds us that there are unexpected consequences of CO2 buildup, and these can be quite dire, indeed."

The lessons are "directly applicable to the present," said John Isbell, a geoscientist at the University of Wisconsin in Milwaukee. He said the world is in danger of exceeding a CO2 threshold that could set off an environmental upheaval as great as the Permian one .

Isbell said CO2 levels in the atmosphere at the time of the P-T catastrophe reached 1,000 to 1,500 parts per million , far higher than today's 385 ppm. (That means there are 385 carbon dioxide molecules for every 1 million total molecules in the atmosphere.)

CO2 levels are rising by 2 ppm a year, and that's expected to rise to 3 ppm a year. If carbon emissions aren't reduced, some researchers fear that by the end of the next century, CO2 could approach levels like those in the P-T period.

What caused the ancient mass extinction is still unclear, but here's how researchers think it may have unfolded:

Over a period of a million years, an enormous quantity of lava from deep in the Earth's interior oozed up through giant cracks in Siberia's crust. The molten mass "froze" into steplike slabs of flood basalts, volcanic rocks known as the Siberian Traps.

Enough lava gushed out to cover an area almost as large as the continental United States.

At a conference of geologists in Vienna in April, Russian geoscientist Alexei Ivanov estimated the lava flow at 2.8 million square miles and the volume of the basalt at 960,000 cubic miles, enough to slather the entire Earth with a layer 10 or more feet thick. ( The 1980 eruption of Mount St. Helens unleashed about a quarter of a cubic mile of lava.)

The lava from the Siberian Traps sent huge quantities of carbon dioxide and methane (natural gas) into the atmosphere. These greenhouse gases caused an epic spell of global warming. Toxic acid rain drizzled , and the ozone shield thinned, letting deadly ultraviolet radiation pass through.

As is happening now, the Earth warmed more near the poles than at the equator. The smaller temperature difference slowed the great ocean currents that keep the waters circulating. The oceans stagnated and lost oxygen. Marine plants and animals suffocated.

What happened to snuff life on land is still debated. Some researchers think bacteria in the ocean, living on sulfur instead of oxygen, churned out vast quantities of hydrogen sulfide (H2S), a lethal gas with a rotten-egg smell. As the H2S emerged from the sea, it choked half of all land creatures.

While evidence points to natural processes in the P-T mass extinction, scientists warn that humans may be contributing to a repeat.

"Today we've stepped in as the villain," Kump said.


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