Posted on 05/14/2004 8:45:55 AM PDT by ckilmer
New clues to 2bn-year-old murder
Tim Radford, science editor Friday May 14, 2004
The Guardian
Scientists believe they are on the track of the biggest mass murderer in the two-billion year history of life. A buried crater off Australia could be the first direct evidence of a celestial assassin that wiped out more than 80% of life on Earth 250m years ago. Luann Becker, of the University of California, Santa Barbara, reports in Science online today on extensive evidence for a 125-mile wide crater called Bedout off the northwestern coast of Australia. The clues match the date of an event known to palaeontologists as the "great dying" - the spectacular mass extinction at the end of the Permian era, when 80% of all terrestrial creatures, and 95% of all marine life, were wiped out.
For decades researchers have argued about whether the damage was done by volcanism, climate change, glaciation, or a comet or asteroid. For the first time, there is evidence of a direct hit from a cosmic projectile.
While working in Antarctica, Dr Becker and colleagues found meteor fragments in sediment formed at the end of the Permian. But they also found something even more telling: fragments of "shocked quartz" - evidence of violently altered terrestrial rock - in Antarctica and Australia in the same stratum. At the time, Australia, Antarctica, Africa and the Americas were part of a huge supercontinent called Pangea.
The Bedout cores also looked similar to cores taken from Chicxulub, in the Yucatán peninsula, Mexico, the site linked to the end of the Cretaceous period 65m years ago when the dinosaur family was wiped out.
"We think mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Dr Becker said.
"This is what happened 65m years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout, I don't think we can call such catastrophes occurring together a coincidence any more."
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