Thursday, March 11, 2010

Impact Craters on Earth

Most people think that that meteor crater in Arizona, Barringer Crater, is a "one time thing," though that is not ay all the case.

In a sense, the answer to the question, "Has the Earth been hit with meteors frequently?" is in the sky, above your head, on the surface of the Moon.

Essentially, the Earth would have been bombarded with the same array of "cosmic cannon fire" -- meteorites, asteroids, and comets -- as the Moon.

There would be some difference because of the atmosphere. Meteorites smaller than a certain size frequently don't make it down to ground level, in Earth's case, because unlike the Moon the Earth has an atmosphere, and friction, when they slam into the atmosphere, heats them, melts them and vaporizes them.

But there would also be a difference arising from the fact that the Earth is much larger than the Moon. Our gravity, about 6 times that of the Moon, attracts a lot more naturally-occurring "space junk," and therefore many more impacts.

The main reason why the Earth does not look like the Moon is because our atmosphere and the life forms it supports quickly fills in craters with deposits which masks their existence. Earth would look like the Moon were it not for our atmosphere.

Despite the healing effects of Earth's atmosphere, many impact craters are still visible all over the Earth.

Before Barringer Crater was formed by a 20 megaton impact about 49,000 years ago, a meterorite slammed into Wolf Creek, Australia, around 300,000 B.C.

A large piece of rock slammed into Bosumtwi, Ghana, around 1,000,000 years ago with an enormous impact of 7,000 megatons.

The Manicougan, Quebec crater, generated by an impact about 214,ooo,ooo years ago, has a substantial deposit of rebound material in the center of it, after the meteorite slammed into the Earth and buried itself there.

The Brent, Ontaria crater was genetated by a 250 megaton impact about 400,000,000 years ago.

Many other impact craters on Earth have been photographed from space.

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