When large meteorites strike Earth, as pictured above in an artist's conception, they often vaporize and change the ratio of certain chemicals in ocean water and sediments.
A new technique that analyzes these chemical clues suggests that the meteorite that wiped out the dinosaurs 65 million years ago might have been less than half the size previously thought.
Image by Don Davis/NASA</major_cutline>

"Dino Killer" Asteroid Was Half the Size Predicted?

Ker Than
for National Geographic News

April 10, 2008

The meteorite that wiped out the dinosaurs might have been less than half the size of what previous models predicted.

That's the finding of a new technique being developed to estimate the size of ancient impactors that left little or no remaining physical evidence of themselves after they collided with Earth.<!---->

Scientists working on the technique used chemical signatures in seawater and ocean sediments to study the dino-killing impact that occurred at the end of the Cretaceous period, about 65 million years ago.

They also looked at two impact events at the end of the Eocene epoch, roughly 33.9 million years ago.

In what could be a major scientific puzzle, the team's new size estimate for the dino-killing meteorite is a mere 2.5 to 3.7 miles (4 to 6 kilometers) across.

The most recent computer models predicted a size of 9 to 12 miles (15 to 19 kilometers) across.

The team notes that their findings could also mean that the makeup of the impactor is different from what scientists commonly assume.

"We are hoping this will lead to further work," said study leader Gregory Ravizza of the University of Hawaii in Honolulu.

Impact Fingerprints

The fiery passage of asteroids and comets through Earth's atmosphere leaves chemical traces in the land, sea, and air.

The most common types of meteorites to hit Earth are chondrites, stony objects that originate in the asteroid belt.

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