Earth's oldest-known crater discovered in outback WA is 3.47 billion years old, study finds
By environment reporter Peter de Kruijff
ABC Science
Topic:Geology
17m ago17 minutes agoThu 6 Mar 2025 at 10:10am
Rocky hills surrounding a flattish plain. The rocks and dirt are red. Small shrubs are scattered around.
The crater is in the Pilbara in Western Australia, where some of the oldest rocks on Earth are found. (Supplied: Chris Kirkland/Curtin University)
In short:
Geologists claim to have found the planet's oldest impact crater in Western Australia's ancient Pilbara region.
The crater, estimated to be 3.47 billion years old, could have been 100 kilometres wide.
What's next?
The authors say findings could provide a new line of study into Earth's history and the early origins of life on the planet.
What could be the world's oldest-known impact crater has been discovered in the remote north-west of Australia.
The crater, located near the Pilbara town of Marble Bar, is thought to have been created 3.47 billion years ago.
The site, detailed in the journal Nature Communications, has been dubbed North Pole Crater by geologists from Curtin University.
Such an impact eclipses a previous claim for oldest crater, Yarrabubba in WA's Mid-West, discovered by the same team, by more than 1 billion years.
At the time it was created, the researchers estimated the crater would have been about 100 kilometres wide.
Today, we can still see a raised area about 35km in diameter in the middle, called the North Pole Dome.
Geologist and study co-author Tim Johnson said the dome was likely to be uplifted by the impact of the meteor smashing into Earth.
"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," he said.
"We think those [sort of] domes are possibly the likely places where life would have taken a foothold in the Pilbara and elsewhere."
The North Pole Dome has long been studied as a site that might show the earliest signs of life forming on the planet.
How do we know a meteor hit?
The Earth formed an estimated 4.5 billion years ago but there has been little evidence of meteor strikes in the first half of its existence.
Our planet was mostly a water world during the Archaean eon, a time period covering about 4 billion to 2.5 billion years ago.
But so much change has happened since there are few geological relicts from so long ago.
There's a theory the Moon was bombarded by meteors billions of years ago, which suggests the same thing was happening simultaneously to Earth.
Three years ago, Professor Johnson and his colleagues suggested contentiously there had been a massive impact 3.6 billion years ago that formed a 250,000 square-kilometre region in WA known as the Pilbara Craton.
Seeking on-the-ground evidence of old craters, they headed to North Pole Dome, which sits in the craton.
After only an hour on-site the team discovered shatter cones.
Red and grayish rocks pointing upwards, a finger points at them.
WA geologists say the presence of shatter cones provides unequivocal evidence of an impact crater. (Supplied: Tim Johnson/Curtin University)
"They're these beautiful, delicate little structures that look a little bit like an inverted badminton shuttle cock with the top knocked off," Professor Johnson said.
"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."
Dating of rock layers above and below the cones by the Geological Survey of WA placed the formation at 3.47 billion years of age.
UNSW earth scientist Tim Barrows, who was not part of the study, said the presence of shatter cones was an unambiguous sign of an impact and an "exciting discovery".
"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," he said.
"So, it is likely to have had a global impact."
Professor Barrows said the study also noted the presence of spherules, cooled molten droplets, which were probably thrown into the air on impact.
"Possibly falling as far away as South Africa," he said
Planetary scientist Marc Norman, from Australian National University, agreed the shatter cones are compelling evidence for a large impact crater.
"However, the study lacks solid evidence for the size of this particular crater or how it relates to the role of impacts on the early Earth," Dr Norman said.
"While the discovery of this ancient impact crater is interesting, it doesn't really advance our understanding of how impacts might have influenced how Earth formed and evolved over billions of years."
Could there be older sites?
There have been challengers for oldest impact crater in places like Greenland.
A study from two years ago suggested there was a 3-billion-year-old impact crater, but the evidence was deemed by many to be inconclusive.
Two hands point to a circular formation on reddish rock.
Pillow basalts, which could have formed under water from lave flows after an impact event, overlying shatter cones in the Pilbara. (Supplied: Tim Johnson/Curtin University)
Professor Johnson said that didn't mean the Greenland site wasn't formed by a meteor.
"There are absolutely some impact craters in Greenland," he said.
"But we just haven't recognised them, I think we need to accept the fact the means we have of identifying impact craters are not sufficient to identify things that definitely are impact craters."
Further studies will be undertaken into the Pilbara looking into early signs of craters, including at North Pole Dome.
Professor Johnson said the next step would be to map out the shatter cones and take samples for further analysis.
"We'll do the various horrific things we do to rocks … in our labs to analyse them for all sorts of elements and isotopes and microstructures," he said.
"And really pick this unique discovery to bits.
"Of course, we hope others will be able to go up and look at them themselves and make up their own minds."
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Posted17m ago17 minutes agoThu 6 Mar 2025 at 10:10am
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