Re: [meteorite-list] Big Bang in Antarctica - Killer Crater Found UnderIce
Hi Ron, list, are they sure yet? http://adsabs.harvard.edu/abs/1979JGR84.5681B Just curious Stefan - Original Message - From: Ron Baalke [EMAIL PROTECTED] To: Meteorite Mailing List meteorite-list@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
Re: [meteorite-list] Big Bang in Antarctica - Killer Crater Found UnderIce
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 [EMAIL PROTECTED] To: Meteorite Mailing List meteorite-list@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
