Earth’s oldest asteroid strike was at Yarrabubba, in Western Australia’s outback, around 2.229 billion years ago, Aussie scientists have confirmed.
The team from Curtin University in Perth used isotopic analysis of minerals to calculate the precise age of the 43-mile-wide impact crater for the first time.
The asteroid strike that created the crater occurred 200 million years before the next oldest impact at Vredefort in South Africa.
The Yarrabubba impact structure is regarded as one of Earth’s oldest, but until now lacked a precise age.
‘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 Professor Chris Kirkland at Curtin University.
The Earth has a continually changing surface due to tectonics and erosion, which means that very old impact craters are difficult to identify.
The team analysed the minerals zircon and monazite that were ‘shock recrystallized’ by the asteroid strike, at the base of the eroded crater to determine the exact age of Yarrabubba.
At 2.2 billion years old, Yarrabubba is around half the age of Earth itself – 4.5 billion years.
The timing of the impact that created the crater may even have helped lift planet Earth out of a deep freeze, the researchers say.
‘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,’ said Professor Kirkland.
The Yarrabubba impact also coincided with the disappearance of glacial deposits, which are absent in the rock record for 400 million years since the impact.
‘This twist of fate suggests that the large meteorite impact may have influenced global climate,’ said Associate Professor Nicholas Timms.
The team’s calculations indicated that an impact into an ice-covered continent could have sent half a trillion tones of water vapour into the atmosphere, potentially playing a role in modifying Earth’s climate.
‘This finding raises the question whether this impact may have tipped the scales enough to end glacial conditions,’ said Professor Timms.
The asteroid may have landed on an ice-covered landscape, vaporising a large volume of ice into the atmosphere and producing the 43-mile crater in the rocks beneath that we see today.
The study could have significance for future impact crater discoveries – some of which may even be older than Yarrabubba, which was first reported in 2003.
‘Our findings highlight that acquiring precise ages of known impact craters is important – this one sat in plain sight for nearly two decade before its significance was realised,’ said Dr Aaron Cavosie at Curtin University.
‘Yarrabubba is about half the age of the Earth and it raises the question of whether all older impact craters have been eroded or if they are still out there waiting to be discovered.’
The team say that while material thrown out from an impact crater found in parts of Australia and Africa has previously been identified as older than 2 billion years, their corresponding craters could not be identified.
The research team, which also included Timmons Erickson from the Astromaterials Research and Exploration Science division at NASA, published their study in Nature Communications.