Curtin University researchers have determined the most precise age yet for the oldest known impact crater on Earth, providing new insight into how meteorite strikes shaped the planet during its earliest history.
The team from Curtin's School of Earth and Planetary Sciences and the Geological Survey of Western Australia (GSWA) 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.
Using advanced mineral dating techniques, the researchers have now identified the clearest evidence yet that the impact occurred around 3 billion years ago.
Lead author Professor Chris Kirkland , from the Timescales of Minerals Systems Group within Curtin's School of Earth and Planetary Sciences , said the findings help 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," Professor 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."
Professor Kirkland said to confirm the result, the team analysed a second mineral, apatite, which formed as hot fluids moved through the shock-damaged rocks. This independent dating method produced the same age.
"The agreement between two different mineral systems gives us confidence that we are seeing the signature of a single major event — a meteorite impact," Professor 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.
"Ancient impact craters are incredibly difficult to date because over billions of years, rocks are altered by heat, pressure and fluids, which can obscure or reset the 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."
GSWA 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," Dr Johnson said.
The study 'How old is the North Pole Dome impact, Western Australia?' was published in Geology and can be found online here: https://doi.org/10.1130/G54866.1
