“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,” said Senior Research Fellow Dr Aaron Cavosie at Curtin University about the discovery of Earth’s oldest asteroid strike that occurred at Yarrabubba, in outback Western Australia, and coincided with the big thaw that marked the end of global deep freeze known as a Snowball Earth, vaporizing a large volume of ice into the atmosphere, creating a 70 kilometer diameter crater.
The ice of Snowball Earth , which built up over several thousand years, “melted in no more than 1 million years,” said Shuhai Xiao, a paleobiologist at Virginia Polytechnic Institute and State University in Blacksburg in an April 2019 Science report, Ancient ‘Snowball Earth’ thawed out in a flash. “That’s the blink of an eye in our planet’s 4.56-billion-year history, suggesting the globe reached a sudden tipping point”
The research, published in the leading journal Nature Communications, used isotopic analysis of minerals to calculate the precise age of the Yarrabubba crater for the first time, putting it at 2.229 billion years old – making it 200 million years older than the next oldest impact.
Lead author Dr Timmons Erickson, from Curtin’s School of Earth and Planetary Sciences and NASA’s Johnson Space Center, together with a team including Professor Chris Kirkland, Associate Professor Nicholas Timms and Cavosie, all from Curtin’s School of Earth and Planetary Sciences, 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.
The team inferred that the impact may have occurred into an ice-covered landscape, vaporized a large volume of ice into the atmosphere, and produced a 70km diameter crater in the rocks beneath. Kirkland said the timing raised the possibility that the Earth’s oldest asteroid impact may have helped lift the planet out of a 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,” Professor Kirkland said.
“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”.
Associate Professor Nicholas Timms 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. 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,” Associate Professor Timms said.
“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 vapor – 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.”
The Daily Galaxy, Andy Johnson, via Curtin University
Image credit: NASA