- WASHINGTON (Reuters) - A
recently discovered layer of glassy fragments could only have been made
by a meteor slamming into Earth and helps prove such an impact nearly wiped
out life on the planet 250 million years ago, scientists said on Thursday.
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- They outlined what they believe is an ancient crater
left by the impact off the coast of what is now Australia.
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- "What we found is a melt sheet which is defining
the top of this very large feature out in the ocean," geologist Luann
Becker of the University of California Santa Barbara told a news conference.
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- "It is buried under a deep pile of sediment,"
she added.
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- "This is very likely the impact site we've been
looking for," added Robert Poreda, a professor of earth and environmental
sciences at the University of Rochester in New York.
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- "For years we've been observing evidence that a
meteor or comet hit the Southern Hemisphere 251 million years ago, and
this structure matches everything we've been expecting.
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- The findings, published in Friday's issue of the journal
Science, are controversial and the scientists say they need much more evidence.
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- But they believe they have found the smoking gun that
shows a meteor sparked the "Great Dying," much as an asteroid
wiped out the dinosaurs 65 million years ago forming what is now the Chicxulub
crater off Mexico's Yucatan Peninsula.
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- During the Permian extinction, 90 percent of life in
the seas and up to 70 percent of the species on land died off very quickly.
No one has been able to show what caused it.
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- Poreda, Becker and colleagues have been gathering evidence
an asteroid, comet or meteor was responsible.
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- Such an impact would have blown up a pall of dust and
rock that would dim the sun's light, and leave telltale evidence globally.
It would also have set off volcanic eruptions.
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- Evidence of those have been found. Layers of basalt dating
to 250 million or so years ago have been found in Siberia.
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- In 2001, Poreda and Becker found specific isotopes, or
varieties, of helium and argon trapped inside a 250 million-year-old layer
of carbon shells called buckyballs, which could only have come from space.
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- They have also found larger pieces of what they believe
could be the meteorite scattered in Antarctica. They include "shocked"
quartz that looks like it was splattered by a powerful force -- something
called impact breccia.
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- Now they describe a 125-mile- wide crater called Bedout
off the northwestern coast of Australia.
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- Becker had heard oil companies drilled two cores into
the Bedout structure thinking it looked like an oil dome in the 1970s and
1980s. All they found was volcanic debris and they abandoned the site.
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- Her team looked at the cores.
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- "Bob and I were absolutely flabbergasted at this
core because it does look just exactly like impact brecchia," Becker
told a news conference. In the cores, Becker's team found evidence for
a layer of melted glass formed by an impact.
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- "We realized that this was no ordinary volcanic
rock," Poreda added.
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- Critics disagree. Bevan French of the National Museum
of Natural History in Washington told Science it could be explained by
volcanic activity.
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- "I see nothing that would convince me there was
an impact," agreed Christian Kolberl of the University of Vienna in
Austria.
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- Becker and colleagues say they have to do more work to
prove their theory. They say it will be much more difficult to prove Bedout
is a crater than it was for Chicxulub, because it is older and underwater.
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- Bedout and Chicxulub look to be about the same size,
suggesting they were formed by similar events, the researchers said.
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