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Giant meteorite rocked life on young Earth?

Ancient space rock would have dwarfed the one that killed the dinosaurs.
Ancient space rock would have dwarfed the one that killed the dinosaurs.  

By Richard Stenger

(CNN) -- The oldest confirmed meteorite slammed into the Earth about 3.5 billion years ago, setting off worldwide tsunamis and dust clouds that possibly affected the primordial life forms, scientists said this week.

Based on rock studies from sites on two continents, geologists were able to determine that a space boulder about 12 miles (20 kilometers) across struck our planet when only about 1 billion years old.

The killer rock would have been twice the size of the one thought to have hastened the end of the dinosaurs about 65 million years ago, the team said.

"It would have taken only a second or two for a meteor that's 20 kilometers in diameter to pass through the ocean and impact the rock beneath," said Stanford professor Donald Lowe, co-author of a report in the August 23 edition of the journal Science.

"That would generate enormous waves kilometers high that would spread out from the impact site, sweep across the ocean and produce just incredible tsunamis -- causing a tremendous amount of erosion on the microcontinents and tearing up the bottom of the ocean," he said.

At the time, the young Earth was probably much hotter and wetter, with at most only a handful of small continents, Lowe speculated.

The episode might have produced a dust cloud in the atmosphere that significantly cooled the planet from an average temperature of about 185 degrees F (85 degrees C), he said.

It certainly affected the primordial global ecosystem, but how remains unknown.

Mineralogical sample that helped peg the impact date to 3.47 billion years ago.
Mineralogical sample that helped peg the impact date to 3.47 billion years ago.  

"The most advanced organisms at the time were bacteria, so there isn't a big extinction event you can identify as cut-and-dry as the extinction of the dinosaurs," Lowe said.

To make their conclusions, Lowe, Gary Byerly of Louisiana State University, lead author of the Science report, and colleagues studied samples from geologic sites in South Africa and Australia, known to contain rocks more than 3 billion years old.

By analyzing tiny particles in the rocks known as sphericles, a common byproduct of meteorite strikes, they were able to date the samples to about 3.47 billion years ago. Other chemical studies confirmed their extraterrestrial origin.

The space boulder that snuffed out the dinosaurs created spherical beds about 0.8 inches (2 centimeters) thick worldwide, the scientists said.

The deposits in South Africa and Australia, however, are between eight and 12 inches (20 and 30 centimeters) deep.

"When the meteor hits the surface, it instantaneously melts and vaporizes rock, and that rock vapor is sucked right back up the hole into the atmosphere," Lowe said.

"It spreads around the Earth as a rock vapor cloud that eventually condenses and forms droplets that solidify into spherules, which rain back down onto the surface."

"We have no idea where the actual impact might have been [but it] left deposits in both South Africa and Australia."




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