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Catastrophes and Prehistory

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Author Topic: Catastrophes and Prehistory  (Read 6405 times)
Troy Exeter
Superhero Member
Posts: 2113

« on: March 18, 2007, 09:12:24 pm »

Collisions with Earth
65 million years ago
250 million years ago
4,400 million years ago


According to a University of Arizona Chicxulub crater web page:

"... a large impact crater that is
65 million years old ... on Mexico's Yucatan Peninsula ... is called Chicxulub,
a Maya word that roughly translates as "tail of the devil." The crater, now buried beneath a kilometer-thick sequence of sediments, ... appears to have a diameter of 145 to 180 km, which makes it one of the largest confirmed impact structures on Earth. Only Sudbury in Canada and the Vredefort structure in South Africa could potentially be larger. ...

... The asteroid or comet that produced the Chicxulub crater was roughly 10 km in diameter. When an object that size hits Earth's surface ...[ as shown in this painting

from a National Museum of Natural History web page ]... it causes a tremendous shock wave while transferring energy and momentum to the ground. The impact was similar to a large explosion, although the energy of the Chicxulub impact dwarfs anything modern civilization has experienced. The energy of the impact was comparable to 100 million megatons of TNT, 6 million times more energetic than the 1980 Mount St. Helens volcanic eruption. The impact ejected rock from several kilometers beneath the surface of the Earth and carved out a bowl-shaped crater nearly 100 km in diameter. In addition, the shock of the impact produced magnitude-10 earthquakes, which were greater than the magnitude of any we have ever measured in modern times. ...[ According to a Miami University of Ohio web page: "... In contrast to the 2 to 3 cm thick clay layer found worldwide, the K-T boundary in the Gulf of Mexico region and in Haiti is composed of much thicker very coarse clastic deposits. Sand beds indicative of high energy deposition at the K-T boundary at Brazos River, Texas, have been interpreted to be the result of a major disturbance of the depositional environment, such as a tsunami approximately 50 to 100 meters high. ...". ]... The initial bowl-shaped crater was very unstable, and its walls quickly collapsed along a series of faults that enlarged the final diameter to between 145 and 180 km.  At the same time, the rock that had been compressed beneath the crater by the impact rebounded, producing a peak-ring structure in the crater's center. These dramatic changes, which rapidly transported huge volumes of rock over distances of tens of kilometers, occurred within only a few minutes. ...

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