Researchers in Western Australia have used advanced mineral dating methods to uncover evidence of the oldest known impact crater on Earth – formed about 3 billion years ago.
The team from Curtin’s School of Earth and Planetary Sciences and the Geological Survey of Western Australia investigated rock formations at the North Pole Dome in the Pilbara region of Western Australia, a site long debated as an ancient asteroid impact structure.
Lead author Professor Chris Kirkland said the findings helped to resolve a longstanding question about the timing of the impact.
"While the site had previously been identified as an ancient impact structure, its exact age remained uncertain," Kirkland said.
"The impact left a ‘mineral clock’ behind. By dating minerals that were remade or newly grown in the damaged rocks, we can now pin down when this extraordinary event happened.
"The key evidence comes from zircon, a tiny but extraordinarily resilient mineral that can keep geological time for billions of years. Some zircons at North Pole Dome have unusual branching, skeletal shapes. We interpret these as impact-modified crystals, formed when older zircon was disrupted, partly recrystallised, and in places regrown during the intense heating caused by the impact.
"These zircon crystals record an event at about 3 billion years ago, which we believe is the best estimate for the impact."
Kirkland said a second mineral, apatite, was also tested to confirm the result.
"The agreement between two different mineral systems gives us confidence that we are seeing the signature of a single major event — a meteorite impact," Kirkland said.
“The new age places the North Pole Dome structure as Earth’s oldest known impact crater and the only recognised example from the Archean eon, a time when the planet’s earliest continents were forming."
He said ancient impact craters were difficult to date because heat, pressure and fluids alter the rocks over billions of years, resetting original impact signals.
"What we’ve been able to do here is separate the moment of impact from its long geological history.
“This discovery pushes Earth’s impact record deeper into geological time than any previously well-dated crater, offering a rare glimpse of the violent processes that shaped the early Earth.”
Geological Survey of Western Australia Director of Geoscience Dr Simon Johnson said the results of the research were truly exceptional.
“Collaborations of this calibre are vital to unlocking the rich, complex geological story of our State and driving new scientific discovery,” Johnson said.
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