Asteroid smash-up may have rained down on Earth 290 million years ago

By Leah Crane

Earth and the moon are two peas in a pod, at least when it comes to being pummelled by space rocks. A new analysis has found that impacts causing relatively large craters happen equally as often on both worlds, and there was a massive increase in these big hits about 290 million years ago.

On a cosmic scale, Earth and the moon are at essentially the same spot in space. That means that they should be hit by about the same number of meteorites, but a common assumption is that erosion on Earth – but not on the moon, which is not geologically active – would erase some of the resulting large craters, along with almost all of the small ones.

Sara Mazrouei at the University of Toronto in Canada and her colleagues used data from NASA’s Lunar Reconnaissance Orbiter to examine craters on the moon and determine if the frequency of craters more than 10 kilometres across is the same on Earth and the moon.

They found a striking match between the two, indicating that erosion might not be as destructive to large craters as we thought. They also found another surprise: about 290 million years ago, the rate of impacts causing these large craters increased by a factor of about 2.6 compared to the previous 700 million years.

“This work has some very interesting implications for the cause of this uptick in the cratering rate,” says Meenakshi Wadhwa at Arizona State University. It could indicate that one or more large asteroids in the asteroid belt broke up around that time, sending a rain of shrapnel towards the inner solar system, she says.

That shrapnel could have had a significant effect on life on Earth, and it may even be connected to the impact thought to have killed the dinosaurs 65 million years ago, says Mazrouei.

“We can’t say that impacts are a cause of an extinction feature for example a mass extinction event,” she says. “But if you are getting bombarded by asteroids at a global scale, that could cause global effects.”

Journal reference: Science, DOI: 10.1126/science.aar4058

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