The moon may have been battered by a massive asteroid storm about 800 million years ago, in which 2 million billion kilograms of rock rained down. These would also have pummelled Earth and could have kickstarted one of the most brutal ice ages in the planet’s history.
It is difficult to measure the history of Earth’s surface because erosion and the effects of life tend to cover any craters, but we can look to the moon for clues. “It is a witness to the history of the solar system,” says Kentaro Terada at Osaka University in Japan. Any swarm of objects that gets close enough to hit the moon will probably hit Earth as well, so it can give us hints about our planet’s past.
“The moon’s surface has no erosion, so it preserves the impact history of the Earth-moon system,” says Terada. He and his colleagues used images from Japan’s Selenological and Engineering Explorer (SELENE), a lunar orbiter often known by its nickname Kaguya, to examine craters on the moon.
They analysed images of 59 craters to determine their ages and found that eight of them, including the huge Copernicus crater, appear to have formed at around the same time – about 800 million years ago. Considering the sizes of the craters, the researchers calculated that about two million billion kilograms of rock probably smashed into the moon at around that time.
Based on the relative sizes of Earth and the moon and how close they are together, they calculated that if this amount of rock did indeed hit the moon, about 23 times as much probably bombarded Earth from the same cloud of rocky space debris. That is between 30 and 60 times as much mass as the Chicxulub impactor that scientists think killed the dinosaurs hundreds of millions of years later.
This would have been dramatic, but no complex life forms would have been around yet to witness it. “From a geological standpoint, this happened quickly, but in reality it was probably spaced out over tens of millions of years or even longer,” says Bill Bottke at the Southwest Research Institute in Boulder, Colorado. “Watching it happen would be boring, punctuated by terror.”
Those moments of terror may have plunged Earth into the most intense ice ages the planet has ever experienced during what is known as the Cryogenian period, says Terada. However, so much is still unknown about this colossal asteroid storm that, while we know it marked the face of the moon, we can’t say for sure what its effects on Earth may have been.
“It seems like things should have been happening on Earth at the same time, so I’m interested to see it tested against geological data,” says Bottke. “This is not the end of the story, it’s the opening shot.”
Journal reference: Nature Communications, DOI: 10.1038/s41467-020-17115-6
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