May 14, 2004
By John Stapleton and agencies

A GIANT submerged crater off the Australian coast could hold the key to the biggest extinction event in Earth's history - the so-called "Great Dying" 250million years ago.

The discovery, from oil drills on the northwest shelf of Australia, could reshape scientific theory on the evolution of animal life.

The extinction of the dinosaurs 65million years ago is usually blamed on the impact of a massive meteor that struck near Mexico. But what caused the earlier, much larger extinction, for which there is ample evidence in fossil records, has never been known.

While most theories have concentrated on a massive increase in volcanic activity, a new study published in the latest edition of the journal Science backs another theory that an asteroid strike could have played a significant part.

Jim Gehling, palaeontologist with the South Australian Museum, says scientists around the world will be fascinated to look at the new evidence. There is likely also to be considerable scepticism.

"This is one of the major mysteries on the history of life in the last few hundred million years," he said. "There will be a lot of doubters in the scientific community and more proof will be needed. It is potentially a very exciting discovery but doesn't necessarily prove that this is the crater that wiped out so many species.

"You need the smoking gun and the victim. We've got the victim but the smoking gun isn't yet in hand."

Among the species that disappeared in the Great Dying were the early forms of coral and many of the earliest ancestors of mammals. Also wiped out were trilobites, the most common of marine fossils and known to every amateur enthusiast.

The researchers cite clues that an impact crater the right age and perhaps 193km wide is buried off Australia's northwest corner. They're calling it the Bedout (pronounced Beh-doo) crater.

"We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," said lead researcher Luann Becker of the University of California, Santa Barbara.

Becker's team, funded by the National Aeronautics and Space Administration and the National Science Foundation, had been hunting a crater in the Southern Hemisphere after finding what appeared to be impact debris in Antarctica.

http://www.theaustralian.news.com.au/common/story_page/0,5744,9555271%255E30417,00.html