Curtin University scientists have discovered Earth’s oldest asteroid
strike occurred at Yarrabubba, in outback Western Australia, and coincided with
the end of a global deep freeze known as a Snowball Earth.
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 Senior Research Fellow Dr
Aaron 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,
vaporised a large volume of ice into the atmosphere, and produced a 70km
diameter crater in the rocks beneath.
Professor
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 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.”
Dr Aaron Cavosie
said the Yarrabubba study may have potentially significant implications for
future impact crater discoveries.
“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 realised.
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,” Dr Cavosie said.
Journal article: https://www.nature.com/articles/s41467-019-13985-7
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