Oldest known asteroid strike may have ended Snowball Earth

Katie Ramirez
January 22, 2020

Some 2.2 billion years ago, an asteroid slammed into the Earth, leaving behind a massive, 43-mile-wide crater in what's now Western Australia, scientists announced Tuesday. The timing of Yarrabubba's impact coincides with the formation of some of Earth's earliest icecaps and glaciers, shortly after the emergence of oxygen in the atmosphere.

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.

Timmons Erickson from NASA's Johnson Space Center said: "The age of the Yarrabubba impact matches the demise of a series of ancient glaciations".

In a statement, study co-author Aaron Cavosie of Curtin University said the 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 almost two decades before its significance was realized".

Till now, the oldest asteroid impact on Earth was the Vredefort Dome in South Africa. In those cases, they dated material created by the asteroid strikes, but couldn't find the impact craters.

Erickson and his colleagues identified that the meteorite which hit the earth and caused the crater had a diameter of around several miles.

At 2.2 billion years old, Yarrabubba is around half the age of Earth itself - 4.5 billion years.

And, it was around the same time that scientists believe Snowball Earth - or the global deep freeze - ended.

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"Without the precise age, we would have had no clue that Yarrabubba occurred at such an interesting time in Earth's history", he told ABC News.

The team realised that the new, more precise date of the impact meant that most of Earth, including Australia, was covered with thick ice sheets at the time. For instance, after the impact, glacial deposits are absent in the rock record for 400 million years.

'This finding raises the question whether this impact may have tipped the scales enough to end glacial conditions, ' said Professor Timms.

The Snowball Earth hypothesis speculates the planet's surface was covered in ice sheets between one and three miles thick.

The study supports its correlation between the asteroid impact and the glaciers melting using numerical modelling.

Yarrabubba has been named as one of the oldest craters in the world for years.

'Our findings highlight that acquiring precise ages of known impact craters is important - this one sat in plain sight for almost two decade before its significance was realised, ' said Dr Aaron Cavosie at Curtin University.

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