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

[Stefan Brandes]

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-Piquéand 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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