THE world’s oldest-known crater from an asteroid smash 3.5 billion years ago has been discovered in the Australian outback.
The ancient hole, near the town of Marble Bar, north-west Australia, was 60 miles wide when first blasted into Earth’s crust.
The meteor blasted a 100km crater in Earth’s crust – similar to this hole in the Arizonan desert[/caption]
Scientists found evidence of the impact in the outback of the Pilbara region, western Australia[/caption]
Scientists said it had a “global impact”, with debris strewn as far as South Africa.
Until now, a crater called Yarrabubba held the title of the world’s oldest meteor strike site.
But the Pilbara site – dubbed the “North Pole Crater” – has steamed to the top spot, beating the competition by more than a billion years.
Today, there is still a 35km scar in the land, but – interestingly – the ground is raise rather than dipped.
Tim Johnson, a geologist and co-author of the new study, explained why.
He said: “So, when you form a really big crater, the middle bit forces it’s way back to the surface so you get a dome structure.”
Professor Johnson and his team have held for years that there was a massive meteor impact around 3.6 billion years ago in the area.
They called the region in north-west Australia the Pilbara Craton – and visited to try and back up their theory.
After just an hour on site, they came across rock structures called “shatter cones” – proving them right.
Johnson said: “They’re these beautiful, delicate little structures that look a little bit like an inverted badminton shuttle cock with the top knocked off.
“So, upward facing cones with delicate feathery-like features.
“The only way you can form those in natural rocks is from a large meteorite impact.”
Research by the Geological Survey of Western Australia dated the rock around the shatter cones as 3.47 billion years old.
Tim Barrows, a scientist at the University of New South Wales, said the “exciting discovery” of shatter cones proved beyond doubt that a meteor had struck.
Geologists proved it was an impact site after finding structures called ‘shatter cones’ in the dusty ground[/caption]
Pilbara took the title of Earth’s oldest crater from Yarrabubba, beating it by a billion years[/caption]
He said: “It would be near the diameter of the impact that resulted in the extinction of the dinosaurs, Chicxulub crater, which is the second-largest impact structure on Earth.
“So, it is likely to have had a global impact.”
The scientist also said that solidified molten droplets – known as spherules – would have showered the air, possibly falling as far as South Africa.
Earth was formed around 4.5 billion years ago, and the meteor smashed into Pilbara around a million years later.
There is very little evidence of meteor impacts in the first half of Earth’s life time – making Pilbara a rare find.
This impact happened during the Archaean eon – the time period from 4 billion to 2.5 billion years ago.
During that time, our planet was mostly water.
Evidence of the meteor strike was found in the Pilbara region, just where Johnson and his team predicted[/caption]
