Asteroids May Have Caused Rash of Craters

A team of scientists trying to understand a bombardment of space debris that resurfaced the Earth 3.9 billion years ago suggests that the cataclysmic event was caused by asteroids and not by comets.

Scientists have been trying to determine what caused the event, which was far more violent than the upheavals that contributed to the demise of the dinosaurs 65 million years ago. The earlier occurrence left Earth marred by tens of thousands of impact craters and scarred Mercury, Venus, the moon and Mars with thousands of craters. The objects that created the craters left almost no trace, so it has been difficult to determine what they were.

A new analysis of chemical traces left on samples of cratered moon rock suggests that the objects were stony and more like asteroids, not carbon-rich objects like comets, said Barbara Cohen, a planetary scientist at the University of Hawaii. It’s possible, she said, that a large asteroid broke up in the asteroid belt and showered the inner solar system with debris.

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Compiled by Times staff writer Usha Lee McFarling