Earth’s Oldest Known Meteorite Impact Structure Identified

The 70 km- (43.5-mile) diameter Yarrabubba impact structure in Western Australia is approximately 2.23 billion years old, according to new research led by Curtin University scientists.

Composite aeromagnetic anomaly map of the Yarrabubba impact structure within the Yilgarn Craton, Western Australia, showing the locations of key outcrops and samples used in this study. The image combines the total magnetic intensity (TMI, cool to warm colors) with the second vertical derivative of the total magnetic intensity (2VD, grayscale) data. The demagnetized anomaly centered on the outcrops of the Barlangi granophyre is considered to be the eroded remnant of the central uplift domain, which forms the basis of the crater diameter of 70 km. Prominent, narrow linear anomalies that cross-cut the demagnetized zone with broadly east-west orientations are mafic dykes that post-date the impact structure. Image credit: Erickson et al, doi: 10.1038/s41467-019-13985-7.

To determine the exact age of Yarrabubba, Dr. Timmons Erickson of Curtin University and NASA’s Johnson Space Center and colleagues analyzed the minerals zircon and monazite that were ‘shock recrystallized’ by the asteroid strike.

The researchers inferred that the impact may have occurred into an ice-covered landscape, vaporized a large volume of ice into the atmosphere, and produced a huge crater in the rocks beneath.

“The timing raised the possibility that the Earth’s oldest asteroid impact may have helped lift the planet out of a deep freeze,” said Curtin University’s Professor Chris Kirkland.

“Yarrabubba, which sits between Sandstone and Meekatharra in central Western Australia, had been recognized as an impact structure for many years, but its age wasn’t well determined.”

“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.”

The study authors noted the precise coincidence between the Yarrabubba impact and the disappearance of glacial deposits.

“The age of the Yarrabubba impact matches the demise of a series of ancient glaciations,” Dr. Erickson said.

“After the impact, glacial deposits are absent in the rock record for 400 million years.”

“This twist of fate suggests that the large meteorite impact may have influenced global climate.”

Numerical modeling further supports the connection between the effects of large impacts into ice and global climate change.

Calculations indicated that an impact into an ice-covered continent could have sent half a trillion tons of water vapor into the atmosphere.

This finding raises the question whether this impact may have tipped the scales enough to end glacial conditions.

“This study may have potentially significant implications for future impact crater discoveries,” said Dr. Aaron Cavosie, also from Curtin University.

“Our findings highlight that acquiring precise ages of known craters is important — this one sat in plain sight for nearly two decades before its significance was realized.”

“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 results were published in the journal Nature Communications.

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T.M. Erickson et al. 2020. Precise radiometric age establishes Yarrabubba, Western Australia, as Earth’s oldest recognised meteorite impact structure. Nat Commun 11, 300; doi: 10.1038/s41467-019-13985-7