[meteorite-list] Big Bang in Antarctica - Killer Crater Found UnderIce

From: Stefan Brandes <brandes_at_meteoritecentral.com>
Date: Sat Jun 3 13:44:53 2006
Message-ID: <000e01c686e5$f1e30e60$f49a2fd5_at_FORCEMACHINE>

Hi Ron, list,

are they sure yet?

http://adsabs.harvard.edu/abs/1979JGR....84.5681B

Just curious
Stefan


----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Friday, June 02, 2006 6:37 PM
Subject: [meteorite-list] Big Bang in Antarctica - Killer Crater Found
UnderIce


>
> http://researchnews.osu.edu/archive/erthboom.htm
>
> BIG BANG IN ANTARCTICA -- KILLER CRATER FOUND UNDER ICE
> Ohio State Research News
> June 1, 2006
>
> Ancient mega-catastrophe paved way for the dinosaurs, spawned Australian
> continent
>
> COLUMBUS, Ohio -- Planetary scientists have found evidence of a meteor
> impact much larger and earlier than the one that killed the dinosaurs --
> an impact that they believe caused the biggest mass extinction in
> Earth's history.
>
> The 300-mile-wide crater lies hidden more than a mile beneath the East
> Antarctic Ice Sheet. And the gravity measurements that reveal its
> existence suggest that it could date back about 250 million years -- the
> time of the Permian-Triassic extinction, when almost all animal life on
> Earth died out.
>
> Its size and location -- in the Wilkes Land region of East Antarctica,
> south of Australia -- also suggest that it could have begun the breakup
> of the Gondwana supercontinent by creating the tectonic rift that pushed
> Australia northward.
>
> Scientists believe that the Permian-Triassic extinction paved the way
> for the dinosaurs to rise to prominence. The Wilkes Land crater is more
> than twice the size of the Chicxulub crater in the Yucatan
> peninsula, which marks the impact that may have ultimately killed the
> dinosaurs 65 million years ago. The Chicxulub meteor is thought to have
> been 6 miles wide, while the Wilkes Land meteor could have been up to 30
> miles wide -- four or five times wider.
>
> "This Wilkes Land impact is much bigger than the impact that killed the
> dinosaurs, and probably would have caused catastrophic damage at the
> time," said Ralph von Frese, a professor of geological sciences at Ohio
> State University.
>
> He and Laramie Potts, a postdoctoral researcher in geological sciences,
> led the team that discovered the crater. They collaborated with other
> Ohio State and NASA scientists, as well as international partners from
> Russia and Korea. They reported their preliminary results in a recent
> poster session at the American Geophysical Union Joint Assembly meeting
> in Baltimore.
>
> The scientists used gravity fluctuations measured by NASA's GRACE
> satellites to peer beneath Antarctica's icy surface, and found a
> 200-mile-wide plug of mantle material -- a mass concentration, or
> "mascon" in geological parlance -- that had risen up into the Earth's
> crust.
>
> Mascons are the planetary equivalent of a bump on the head. They form
> where large objects slam into a planet's surface. Upon impact, the
> denser mantle layer bounces up into the overlying crust, which holds it
> in place beneath the crater.
>
> When the scientists overlaid their gravity image with airborne radar
> images of the ground beneath the ice, they found the mascon perfectly
> centered inside a circular ridge some 300 miles wide -- a crater easily
> large enough to hold the state of Ohio.
>
> Taken alone, the ridge structure wouldn't prove anything. But to von
> Frese, the addition of the mascon means "impact." Years of studying
> similar impacts on the moon have honed his ability to find them.
>
> "If I saw this same mascon signal on the moon, I'd expect to see a
> crater around it," he said. "And when we looked at the ice-probing
> airborne radar, there it was."
>
> "There are at least 20 impact craters this size or larger on the moon,
> so it is not surprising to find one here," he continued. "The active
> geology of the Earth likely scrubbed its surface clean of many more."
>
> He and Potts admitted that such signals are open to interpretation. Even
> with radar and gravity measurements, scientists are only just beginning
> to understand what's happening inside the planet. Still, von Frese said
> that the circumstances of the radar and mascon signals support their
> interpretation.
>
> "We compared two completely different data sets taken under different
> conditions, and they matched up," he said.
>
> To estimate when the impact took place, the scientists took a clue from
> the fact that the mascon is still visible.
>
> "On the moon, you can look at craters, and the mascons are still there,"
> von Frese said. "But on Earth, it's unusual to find mascons, because the
> planet is geologically active. The interior eventually recovers and the
> mascon goes away." He cited the very large and much older Vredefort
> crater in South Africa that must have once had a mascon, but no evidence
> of it can be seen now.
>
> "Based on what we know about the geologic history of the region, this
> Wilkes Land mascon formed recently by geologic standards -- probably
> about 250 million years ago," he said. "In another half a billion years,
> the Wilkes Land mascon will probably disappear, too."
>
> Approximately 100 million years ago, Australia split from the ancient
> Gondwana supercontinent and began drifting north, pushed away by the
> expansion of a rift valley into the eastern Indian Ocean. The rift cuts
> directly through the crater, so the impact may have helped the rift to
> form, von Frese said.
>
> But the more immediate effects of the impact would have devastated life
> on Earth.
>
> "All the environmental changes that would have resulted from the impact
> would have created a highly caustic environment that was really hard to
> endure. So it makes sense that a lot of life went extinct at that time,"
> he said.
>
> He and Potts would like to go to Antarctica to confirm the finding. The
> best evidence would come from the rocks within the crater. Since the
> cost of drilling through more than a mile of ice to reach these rocks
> directly is prohibitive, they want to hunt for them at the base of the
> ice along the coast where the ice streams are pushing scoured rock into
> the sea. Airborne gravity and magnetic surveys would also be very useful
> for testing their interpretation of the satellite data, they said.
>
> NSF funded this work. Collaborators included Stuart Wells and Orlando
> Hernandez, graduate students in geological sciences at Ohio State;
> Luis Gaya-Piqu?and Hyung Rae Kim, both of NASA's Goddard Space
> Flight Center; Alexander Golynsky of the All-Russia Research Institute
> for Geology and Mineral Resources of the World Ocean; and Jeong Woo Kim
> and Jong Sun Hwang, both of Sejong University in Korea.
>
> #
>
> Contact: Ralph von Frese, (614) 292-5635; Von-frese.3_at_osu.edu
>
> Laramie Potts, (614) 292-7365; Potts.3_at_osu.edu
>
> Written by Pam Frost Gorder, (614) 292-9475; Gorder.1_at_osu.edu
>
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Received on Sat 03 Jun 2006 04:15:58 AM PDT