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Dino-killing asteroid impact dwarfed by earlier space rock crash

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    Researchers speculate a giant fragment produced by a collision between two asteroids smashed into Earth 65 million years ago, creating the Chicxulub crater off the coast of the Yucatan.Don Davis

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    A graphical representation of the size of the asteroid thought to have killed the dinosaurs, and the crater it created, compared to an asteroid thought to have hit the Earth 3.26 billion years ago and the size of the crater it may have generateAmerican Geophysical Union

Scientists have reconstructed a long-ago asteroid impact that makes the strike that wiped out the dinosaurs 65 million years ago look like a playful chuck on the chin.

The enormous collision occurred 3.26 billion years ago and involved an asteroid 23 to 36 miles across — four to six times wider than the dino-killing space rock. The impact created a crater about 300 miles (500 km) wide and generated seismic waves far more powerful than those produced by any earthquake in recorded history, researchers said.

The asteroid impact was "far larger than anything in the last billion years," Jay Melosh of Purdue University, who was not involved in the new study, said in a statement. [Wipe Out: History's Most Mysterious Extinctions]

Researchers Norman Sleep and Donald Lowe, both of Stanford University, mapped out the details of the cataclysmic strike after studying rocks in a region of South Africa known as the Barberton greenstone belt.

The space rock probably hit far away from the Barberton formation, in a location that researchers may never find. But it left its imprint on the South African rocks and on the entire Earth, disrupting the planet's crust and possibly spurring a transition from an early tectonic regime to the more modern plate-tectonic system that prevails today, researchers said.

"This is providing significant support for the idea that the impact may have been responsible for this major shift in tectonics," said UCLA geologist Frank Kyte, who was not a member of the study team.

The mammoth collision likely posed a severe challenge for life on Earth, which first evolved about 3.8 billion years ago. The sky would have filled with dust and become incredibly hot, while the upper layers of the ocean would have boiled, researchers said.

The asteroid impact could have wiped out a large percentage of the planet's lifeforms, vacating niches that the survivors evolved to fill.

"We are trying to understand the forces that shaped our planet early in its evolution and the environments in which life evolved," Lowe said.

While incredibly dramatic, this enormous smashup was probably far from unique. Rather, it was one of many such strikes that occurred during a period called the Late Heavy Bombardment, which began around four billion years ago and lasted for perhaps one billion years.

That bombardment period also affected other bodies in the inner solar system, blasting huge holes into Mars, Venus, Mercury and Earth's moon.

The new study has been accepted for publication in the journal Geochemistry, Geophysics, Geosystems.