Planet and moon have been hit by more asteroids in the past 290m years than at any time in previous billion
The rate at which asteroids are slamming into Earth has nearly tripled since the dinosaurs first roamed, according to a survey of the scars left behind. Researchers worked out the rate of asteroid strikes on the moon and the Earth and found that in the past 290m years the number of collisions had increased dramatically.
Before that time, the planet suffered an asteroid strike about once every 3m years, but since then the rate has risen to once nearly every 1m years. The figures are based on collisions that left craters at least 10km (6.2 miles) wide.
Writing in the journal Science, the researchers describe how they turned to the moon to examine the violent history of Earth. The Earth and moon are hit by asteroids with similar frequency, but impact craters on Earth are often erased or obscured by erosion and the shifting continents which churn up the crust. On the geologically inactive moon, impact craters are preserved almost indefinitely, making them easier to examine.
Using images from Nasa’s Lunar Reconnaissance Orbiter, the scientists studied the “rockiness” of the debris surrounding craters on the moon. Rocks thrown up by asteroid impacts are steadily ground down by the constant rain of micrometeorites that pours down on the moon. This means the state of the rocks around a crater can be used to date it.
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