Australia's Yarrabubba crater is the oldest known hole on Earth, scientists concluded in a report published in the journal Nature Communications on Tuesday.
An asteroid smashed into what is now Western Australia about 2.2 billion years ago, when Earth was about half as old as it is today. The collision left a pit 70 kilometers in diameter.
An international team of geo- and planetary scientists, including NASA experts, examined the crater for chemical evidence of the impact. They analyzed minerals called monazite and zircon, whose inner structures had been rejiggered — the technical term for this is a "shock" — by the force of the blow.
Uranium isotopes measured in the shocked minerals gave the researchers a relatively precise value for the extreme date. It's the oldest crater on Earth by 200 million years, the scientists say.
What's remarkable about the crater is that it still exists. The moon's pockmarks are visible reminders of the many space rocks that have smacked into heavenly bodies over the lifetime of our solar system. But tectonic activity, weathering and other factors smooth or erase the evidence of ancient collisions on Earth.
The study authors suggest that this impact knocked the young Earth out of an early icy phase. "The Yarrabubba crater was made right at the end of what's commonly referred to as the early Snowball Earth — a time when the atmosphere and oceans were evolving and becoming more oxygenated and when rocks deposited on many continents recorded glacial conditions," said study author Chris Kirkland, an expert in geochronology at Curtin University in Australia, in a statement. The impact might have warmed up the planet by vaporizing glacial ice, filling the atmosphere with water vapor — a greenhouse gas that, like carbon dioxide, traps heat.
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