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

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sat Jun 3 13:46:51 2006
Message-ID: <005901c686e9$d65d79b0$ca714b44_at_ATARIENGINE>

Hiya!

    The journal Nature reports on the "find" very skeptically,
dragging in the Siberian Traps, the lack of geological deformation
in nearby Antarctic mountains, the "unproven-ness" of
Chicxulub (gimme a break), the lack of any applicable dating
method, and in general sniffing at the notion like it was a dead fish:
http://www.nature.com/news/2006/060529/full/060529-11.html

    The New Scientist is more reasonably skeptical, and
references an earlier article that suggests that giant impacts
cause ALL the major outbreaks of mantle plume outflows (like
The Traps) by punching through the Earth's crust, thus tying
three opposing theories (impacts, basalt floods, and poisonous
gases) together as one unified theory, satisfying the biases
of nobody and annoying pretty much everybody. Good work, guys.
http://www.newscientist.com/article/dn9268-giant-crater-may-lie-under-antarctic-ice.html

Nice large map of the crater location (roughly 120E 70S) in this article:
http://www.hindu.com/thehindu/holnus/008200606021451.htm

    The dating IS vague: younger than 400-500 mya (million years ago)
and older than 100 mya. Not exactly a smoking gun. But there is the
earlier publication of discoveries of excess meteoritic material in
Antarctica at the right date (250 mya), which was criticized because
they couldn't specify a crater location. And the discovery of "buckyballs"
or fullerenes from around the world with extraterrestrial gas in them at
the same date. Sounds to me like a case is being built. Slowly.

    What bothers me about the topography of the location is that we
are shown a single or simple basin that large with no signs that I can
see of further rims or arc segments of rims. A 30-mile impactor is
going to make a ring basin, not just a hole. Unless it was really
"only" a 10-mile impactor and the 300 mile arc is the outer ring
of a ring basin, which would make it only a bit bigger than
the Chicxuluber.

    But the Permian extinction is The Champ; it deserves a
Whopper of an impactor. 96% of all marine species went
bye-bye. So long to trilobites, farewell to pelycosaurs,
blastoids, acanthodians, placoderms, and the ever-popular
fusulinid foraminifera. Greatly reduced in variety and numbers
were the bryozoans, brachiopods, ammonoids, sharks,
bony fish, crinoids, eurypterids, ostracodes, and echinoderms.
For about five million years, corals disappeared from the
oceans altogether, then returned. If it was tough on sharks,
it wasn't an easy time.

    Personally, the absence of a huge crater does not affect my
notion of the likelihood of an impact at 250 mya. 70% of the globe's
area is deep ocean, and thanks to the policy of extensive Crustal
Renewal instituted by the Zargon Administration billions of years
ago, none of the submerged Crust is more than 200 million years
old. I hate an ocean cluttered with old run-down unsightly Crust,
don't you?

    You could have had a 60-mile-diameter impactor and a basin
800 miles across at 250 mya, and there wouldn't be a trace today,
if it had been in ocean. At 250 mya, the continents were still
gathered together in one premiere tourist destination known
as Gondwanaland, and the rest of the world was just ocean.
Lots and lots of ocean. East Antarctica was out at the southern-
most tip of Gondwanaland in fact, so if something hit there,
it ALMOST missed land. The fact that whatever it was so
greatly affected MARINE species may be a sort of clue,
you know. "Well, first, there was this tidal wave about ten
miles high, and then, right after that the water started to BOIL..."

    For those of us who want to see where our continents came from
and where they've been, here's a nice set of dated world maps, at
roughly 50 million year intervals, going back to 750 mya and very
readable, with present lands keyed in on the "old" continents.
http://www.uwgb.edu/dutchs/platetec/plhist94.htm

    For those who miss having a 50-kilometer body in potentially
Earth-intercepting orbit, you'll have to make do with 1866 Sisyphus,
the largest Apollo asteroid, at 10 km, about the size of the
Chicxuluber. Unless, as some contend, it was bigger than 10 km.
Impact odds on Sisyphus are pretty nil for thousands of years,
though.

    Or you could worry about the NEA with the highest ACTUAL
chance of striking the Earth, out of all the thousands of NEA's. That
would be 1950 DA, a 1100 meter asteroid, which stands a good
shot (33%) at whacking us on March 16, 2880. Mark it on your
calendar. Put up some water and canned goods in the basement.
A bag of cookies wouldn't hurt.


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-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
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
Received on Sat 03 Jun 2006 04:43:49 AM PDT