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Scientists reconstruct ancient impact that dwarfs dinosaur-extinction blast

asteroid

BY NANCI BOMPEY 

A new study by Norm Sleep and Don Lowe reveals the power and scale of a cataclysmic asteroid strike on the Earth that happened 3.26 billion years ago.

Picture this: A massive asteroid almost as wide as Rhode Island and about three to five times larger than the rock thought to have wiped out the dinosaurs slams into Earth. The collision punches a crater into the planet’s crust that’s nearly 500 kilometers (about 300 miles) across: greater than the distance from Washington, D.C. to New York City, and up to two and a half times larger in diameter than the hole formed by the dinosaur-killing asteroid. Seismic waves bigger than any recorded earthquakes shake the planet for about half an hour at any one location – about six times longer than the huge earthquake that struck Japan three years ago. The impact also sets off tsunamis many times deeper than the one that followed the Japanese quake.

Although scientists had previously hypothesized enormous ancient impacts, much greater than the one that may have eliminated the dinosaurs 65 million years ago, now a new study reveals the power and scale of a cataclysmic event some 3.26 billion years ago which is thought to have created geological features found in a South African region known as the Barberton greenstone belt.  The research has been accepted for publication in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union.

The huge impactor – between 37 and 58 kilometers (23 to 36 miles) wide – collided with the planet at 20 kilometers per second (12 miles per second). The jolt, bigger than a 10.8 magnitude earthquake, propelled seismic waves hundreds of kilometers through the Earth, breaking rocks and setting off other large earthquakes. Tsunamis thousands of meters deep – far bigger than recent tsunamis generated by earthquakes — swept across the oceans that covered most of the Earth at that time.

“We knew it was big, but we didn’t know how big,” Donald Lowe, a geologist at Stanford University and a co-author of the study, said of the asteroid.

Lowe, who discovered telltale rock formations in the Barberton greenstone a decade ago, thought their structure smacked of an asteroid impact. The new research models for the first time how big the asteroid was and the effect it had on the planet, including the possible initiation of a more modern plate tectonic system that is seen in the region, according to Lowe.

The study marks the first time scientists have mapped in this way an impact that occurred more than 3 billion years ago, Lowe added, and is likely one of the first times anyone has modeled any impact that occurred during this period of the Earth’s evolution.

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