[meteorite-list] Another Killer Crater Found -- Last Month

[Gerald Flaherty]

I'm convinced enough to "worry".
There's a something out there with Earth's name on it. I just can't see the 
date from here!
----- Original Message ----- 
From: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Sunday, June 04, 2006 12:24 AM
Subject: [meteorite-list] Another Killer Crater Found -- Last Month



> Hi,

>

>    Also, less than a month ago, there was a similar "proof"

> that the Bedout High, off the coast of north-western Australia,

> was a crater remnant, with impact melts, breccias, and an Ar/Ar

> date of 250.1 mya. Nobody much liked it, either...

> http://news.bbc.co.uk/1/hi/sci/tech/3707023.stm

>    The announcement was made by Dr Luann Becker, of the

> University of California, Santa Barbara. The Bedout High is

> a seabed feature.

>    Jay Melosh, of the University of Arizona in Tucson, commented:

> "This thing just rings off alarm bells in my mind. If it is an impact

> it's the most darn peculiar one I've ever seen."

>    In some cases, there's no suspect at all. In others, there's

> just way too many suspects.

>

>

> Sterling K. Webb

> ----------------------------------------------------------------

> ----- 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 11:37 AM

>> 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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