Asteroid May Have Caused Massive Extinction Wave

ROCHESTER, New York, May 17, 2004 (ENS) - Scientists believe they have found the crater made when a massive asteroid slammed into the planet some 251 million years ago. They contend the impact caused the greatest extinction in Earth's history.

Scientists have long debated the cause of the event in the Permian-Triassic era, but there is no debate that something wiped out 90 percent of life on Earth.

After determining that a meteor was responsible for killing off the dinosaurs some 60 million years ago, researchers have explored the theory that a major meteorite caused the Permian-Triassic event.

In November researchers from the University of Rochester and the University of California at Santa Barbara published a study in the journal "Science," that determined a major meteorite did strike the Earth 251 million years ago, likely triggering climate change and unprecedented volcanic activity.

Now those same researchers have published a new paper in "Science" that claims they have found the impact site in northern Australia.

"This is very likely the impact site we have been looking for," said Robert Poreda, professor of earth and environmental sciences at the University of Rochester. "For years we have been observing evidence that a meteor or comet hit the southern hemisphere 251 million years ago, and this structure matches everything we have been expecting."

Poreda and his colleagues knew that the chances of finding the crater, even one from an impact large enough to nearly wipe out life on Earth, would be difficult because the majority of the Earth is covered by ocean.

Had the meteor struck there, its telltale crater would have long ago disappeared.

But in 1970 an oil drilling exploration team found a "dome" in the area of Bedout, just off the northwestern coast of Australia.

Now covered by two miles of sediment, this area was most likely dry land 251 million years ago.

Such domes typically herald large oil deposits, but in this case the drilling team found only what it labeled as "volcanic rock."

The core samples were shelved and forgotten for 25 years, until in 1995 a report in a journal aimed at the oil industry mentioned that the rock might have been formed from a meteor impact.

"Once we looked at Bedout with the understanding that it was likely a crater, the geophysics just fell into place," Poreda said.

Geophysical analysis shows the rock strata underlying the dome at Bedout is fractured exactly the way the team expected - showing rock strata older than 251 million years old broken apart, with younger rock above laid down without the fractures.

Simulations of a six mile wide rock striking the area suggest a crater rim should be visible about 60 miles from the central dome, and the researchers say there is evidence of a rim at that distance. The team has plans to explore the geophysical outlay of the region with more scrutiny.

The Bedout crater, at 120 miles across, is almost exactly the same size as the Chicxulub crater in the Caribbean that has been identified as the impact site of the meteorite that dealt the dinosaurs their death blow.

It is likely that the bodies that struck at each site were of the same size and traveling at similar speeds.

"There have been five mass extinctions throughout the Earth's history," Poreda said. "Now we have very strong evidence that massive meteor impacts happened precisely at two of those extinctions."