Oldest known asteroid impact may have played role in ending ancient ice age

Outcrops in Western Australia mark the remains of the world’s oldest known impact crater, a heavily eroded structure known as Yarrabubba. Image: NASA

Isotopic analysis of minerals at the base of a heavily-eroded 70-kilometre-wide crater in Western Australia show the subsurface remnants date back 2.229 billion years, making it the oldest of roughly 190 known major impact structures.

The analysis shows the Yarrabubba crater is some 200 million years older than the previous record holder – the over 200-kilometre-wide Vredefort Dome in South Africa – and may have played a role in helping pull Earth out of a glacial deep freeze.

“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 Chris Kirkland, a professor in the School of Earth and Planetary Sciences at Curtin University.

“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 condition.”

The Yarrabubba crater has been mostly eroded away, leaving only rocky outcrops, but zircon and monazite taken from the base of what’s left of the crater’s rim were “shock recrystallised” by the impacting asteroid. By measuring the ratio of naturally occurring uranium and lead in the crystals, the researchers were able to calculate their age.

A zircon crystal that was used to date the Yarrabubba impact crater. Image: Curtin University

“The age of the Yarrabubba impact matches the demise of a series of ancient glaciations,” said Nicholas Timms, an associate professor at Curtin. “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 modelling 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 vapour, an important greenhouse gas, into the atmosphere. This finding raises the question whether this impact may have tipped the scales enough to end glacial conditions.”

In a paper published in the journal Nature Communications, lead author Timmons Erickson and the research team wrote that “many studies have described the atmospheric effects of the end-Cretaceous Chicxulub impact structure in Mexico, which resulted in global cooling of oceans and production of widespread acidic rains.

“While the Yarrabubba structure dated at 2229 ± 5 Ma represents the Earth’s oldest dated impact crater, its coincidence with termination of Palaeoproterozoic glacial conditions prompts further consideration of the ability of meteorite impacts to trigger climate change.”