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Report: Asteroid storm pounded Earth, moon as life formed

craters
Investigations of the moon's cratered surface suggest it passed through a period of heavy bombardment along with the Earth about 4 billion years ago  

(CNN) -- A new study of lunar meteorites strongly suggests that the moon and Earth suffered a brief but cataclysmic bombardment of asteroids almost 4 billion years ago at roughly the same time that life formed on our planet.

The flurry of killer space rocks could have had major consequences on early Earth evolution, whether smashing the building blocks of primordial life or delivering them to the planet in the first place, researchers said.

The burst of impacts lasted from 20 million and 200 million years, flanked in time by periods of relative calm. The rain of meteorites or comets melted rocks, blasted out craters and reshaped the surface across the entire moon, according to a new report in the journal Science.

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The bombardment would have produced the great basins that now shape the man in the moon. On Earth, the same cataclysm would have affected the evolution of life, possibly forcing it to begin anew, according to scientists.

"Earth would have been bombarded by at least 10 times as many impact events as the moon, and these impact cratering processes are immense," lunar geologist David Kring said in a statement.

The findings are based studies of four lunar meteorites -- rocks that were ejected at random from the moon's surface and landed on Earth after a million or so years in space.

The scientists applied a sophisticated dating technique to the meteorites to determine when the lunar bombardment occurred.

The Chixculub crater in Mexico, which is linked to the mass extinction of dinosaurs 65 million years ago, "is puny by the scheme of we are talking about. Here we are talking about impacts that are 10 times larger, impacts that blasted craters rim to rim the size of continents on Earth today," he said.

The blasts would have vaporized the oceans and filled the atmosphere with a life-choking fog, all but eliminating terrestrial life if it existed.

"If there was life on Earth before the bombardment, the question is what, if anything survived," said lunar researcher Timothy Swindle in a statement.

Unlike the lifeless moon, where the ancient scarring remained easily visible, the Earth has blotted out signs of the cataclysm through erosion and natural geologic changes over the eons.

Rather than death, ancient meteorites or comets could have brought life, some scientists theorize. Proponents of a theory called "panspermia" suggest that complex organic molecules or even primitive life forms seeded the Earth after riding aboard rocky or icy cosmic debris.

Previous analysis on lunar rocks returned by the Apollo and Luna missions in the 1970s suggested that the moon took a pounding near the equator where the samples originated.

But a sophisticated examination of lunar meteorites now offers strong evidence that the maelstrom hammered the entire lunar surface, according to a December 1 report in the journal Science.

Barbara Cohen of the University of Tennessee-Knoxville was the lead author of the report, co-authored by Kring and Swindle, both of the University of Arizona's Lunar and Planetary Lab.



RELATED STORIES:
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October 24, 2000
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July 13, 2000
Glass holds grains of truth about Earth's meteor history
April 3, 2000

RELATED SITES:
Science
University of Tennessee
University of Arizona's Lunar and Planetary Lab


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