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.
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.
One of the interesting aspects of the find is that:
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.
Speaking of plate tectonics, Science Daily has an article on that as well:
The new study found that continents sometimes break along preexisting lines of weakness created during earlier continental collisions. Geologists had long suspected that break lines were created by the attachment of pieces onto larger land masses, but Nance and his co-authors were the first group to be able to prove this theory.
How did they do it:
About 525 million years ago, that land mass broke apart, with North America on one side and South America, Africa and the small island pieces on the other. The two plates drifted apart, forming the Iapetus Ocean.
Twenty-five million years later – at the time of the first fish and land plants – the strip of land that used to be the small islands broke off South America and Africa and began moving across Iapetus towards North America. This movement closed the Iapetus Ocean while at the same time opening the Rheic Ocean.
Nance and his co-authors focused on these two particular breaks because they occurred along a “line of weakness” – namely the spot where the small islands had attached to the larger land mass. As the internal structure of the continent was already less stable there than it was across the two solid outside pieces, the continent broke along this preexisting line.
The scientists used geochemical “fingerprinting” to show that the small pieces of land, which today are found in the Appalachians, were originally created in an ocean. The radioactive element Samarium, which breaks down into various types of the element Neodymium, was used to determine the age of the rock (about one billion years). The amount of each element was typical of rock created in the ocean, away from larger continental masses.
Finally, New Scientist has an article on why there are more left-handed amino acids than right-handed amino acids:
Donna Blackmond at Imperial College London and colleagues dissolved a mixture of solid L and D versions of the amino acid serine in water. They found that a small difference in the initial proportion of one version gets amplified in the resulting solution. So a 100:1 mixture of L- and D-serine produces a solution made up almost entirely of L-serine, but so does a 100:99 mixture
Added Later: This is cool!
Deep within Earth, halfway to its center in an area where Earth’s core meets its mantle, lies a massive folded slab of rock that once was the ocean floor, reports a team of researchers (including one from Arizona State University) in the current issue of Nature. (Image courtesy of Arizona State University)
The slab, which sank beneath North America some 50 million years ago, holds important clues as to the behavior and composition of the deep interior of Earth and it could help explain how surface features such as volcanos and earthquakes form, the researchers say.
The discovery sheds new light on the processes that drive the movement of Earth’s tectonic plates. Earth’s outermost layer, its lithosphere, is broken into large, rigid plates composed of the crust and the outer layer of the mantle. New plate material is created at mid-oceanic ridges, where the ocean floor spreads apart, and old plate material is consumed in subduction zones, where one plate dives beneath another. But the fate of subducted lithosphere has been uncertain, at least until this slab was detected.
Garnero said there is an on going debate over whether subducted slabs sink all the way down to the base of the mantle or get trapped in the upper mantle. The new evidence favors the presence of subducted slabs in the deep mantle and, if this is the case, then finding this slab could have significant ramifications for our understanding of the inner workings of Earth.
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