Massive meteor shower hit Earth and moon 800 million years ago, study says

Japan Times -- Jul 22
A giant meteor shower bombarded Earth and the moon 800 million years ago with more than 30 times the force of the asteroid strike that killed the dinosaurs, new research showed Tuesday.

Japanese scientists examined images taken by the Kaguya lunar orbiter and found that an enormous asteroid — at least 100 kilometers (60 miles) in diameter — broke up and plunged into the Earth-moon system, having a profound impact on life on our planet.

The probability of an asteroid that size hitting Earth is roughly once in 100 million years, and impact craters of meteor strikes created before 600 million years ago have been erased by aeons of erosion and other geological processes.

But there is virtually no erosion on the moon, allowing the team to reconstruct the history of nearly 60 large craters.

Researchers from Osaka University looked at the age the large craters were formed by examining the density of smaller craters within their ejecta range — where chunks of rocks would have landed after the main impact.

They used scaling laws and collision probabilities to calculate that the mass of meteors to strike Earth and the moon was 40-50 million billion tons — that’s 30-60 times greater than the Chicxulub impact event.

- Japan Times