Posted on 06/01/2006 2:26:58 PM PDT by PatrickHenry
Ancient mega-catastrophe paved way for the dinosaurs, spawned Australian continent.
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 and NASA funded this work. Collaborators included Stuart Wells and Orlando Hernandez, graduate students in geological sciences at Ohio State; Luis Gaya-Piqué 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.
Whoops! sorry about the double post...
I was looking for the THING reference, and I found it! LOL!
There is no telling how big the Snake River collider would have been since the ensuing vulcanism would pretty much erase all traces of the crater. To cause impact volcanism a smaller high speed iron meteorite traveling at high speed and striking at a high angle could do the job nicely.
This impact theory is very controversial but there really isn't another explanation as to how a hot spot could have appeared out of nowhere.
Your post #219 reminded me of a TV program, I saw a few months ago, about all the volcanic activity and this hotspot that you speak of, lying under the whole of the geologically active Yellowstone area...it was really quite scarey to watch this program, with the experts surmising what may happen to that area in the future....its truly a place to watch...
Obviously, to some, it was Bush's fault.
Hey, I hate to burst your bubble, but it ain't happening.
Besides Mars, and the moon, I mean. ~ aNYCguy
IOW, this generation isn't clever enough to figure out a way.
Therefore it can never be done....
An Antarctic Bone BedW. Zinsmeister was accustomed to scoff at the idea that the Age of Dinosaurs ended violently with the impact of a giant asteroid some 65 million years ago. He always asked: "Where's the layer of burnt and twisted dinosaur bones?" His certainty was shaken, however, when he began mapping fossil deposits on Seymour Island, Antarctica. He didn't find the dinosaur bones but rather a giant bed of fish bones at least 50 square kilometers in area. Some sort of catastrophe must have annihilated untold millions of fish. And guess what? This great bone bed was deposited directly on top of that layer of extraterrestrial iridium that marks the 65-million-year-old Cretaceous Tertiary boundary at many sites around the world.
William R. Corliss
Science Frontiers
No. 104: Mar-Apr 1996
"'New Scientist' article from 2002 discussing the link between impact events and volcanism."
It is nice to see that science has endorsed the proposal about boloids and the Traps that I made in comment #168.
When you're hot, you're hot...
"Some sort of catastrophe must have annihilated untold millions of fish."
In a book by (I think) the younger Alvarez, he describes visiting a 65mya site in Denmark (?) where there were also signs of of many dead fish. His impression was that something very catastrophic and nasty had happened there. He commented on the fact that this layer smelled bad, and I think there was also iridium found. I wish I could find the darn book in one of my piles.
"I suppose for truth you'd prefer to invent pleasing axioms out of whole cloth and deduce pleasing conclusions from them. That's fine for you, I suppose. It's a nice exercise and inconvenient observations won't rain on your parade.
Myself, I prefer the provisional, inductive truth of the scientific method."
If you define truth as provisional and inductive, how do you define opinion? How can you call it truth if it can change at any time? You have demonstrated the problem with scientism, it mocks (by assertion without argument) any source of truth outside the scientific method but then must, in the end, admit that the truth of scientism is provisional and inductive, in other words, just the latest opinion waiting to be supplanted by the next big idea. Ever learning but never able to come to the knowledge of the truth. Science is operational not cognitive.
:')
Nah, I really think the crater evolved over millions of years.
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