Scientists think they have identified the precise date a meteorite hit the Earth and created its oldest preserved impact structure.
The Yarrabubba crater in Western Australia appears to be 200 million years older than its closest challenger, the researchers write.
The site was hit by a meteorite 2.229 billion years ago.
The researchers dated the site with technological methods using shocked minerals that were found in the crater, they write in a newly published paper in Nature Communications.
Dating such craters can be difficult. The Earth's surface changes over time, as tectonics and erosion shift material around, making very old craters hard to identify.
In the past, pieces that have been thrown out of impacts that appear to be more than two billion years old have been found in parts of Australia and Africa. But the impact craters they would have come out of could not be identified.
Now scientists say they have precisely dated the Yarrabubba crater, giving a specific age for the impact structure long regarded as one of the world's oldest.
The meteorite hit the Earth 2.229 billion years ago, give or take five million years, the researchers said.
At that time, in the same region, glaciers would have been forming and the Earth was largely covered in ice. Simulations suggest that if the meteorite that formed the crater hit a continental ice sheet, it would have thrown as much as 5,000 trillion kilograms of water vapour up into the atmosphere
That could have fundamentally changed the Earth's climate, the scientists note. It might even have created a greenhouse effect that brought an end to the period known as "Snowball Earth" that covered our planet when the meteorite arrived.
“Yarrabubba, which sits between Sandstone and Meekatharra in central WA, had been recognised as an impact structure for many years, but its age wasn’t well determined,” said Curtin University's Chris Kirkland, one of the authors of the study.
“Now we know 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”.