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Geologists have discovered the world's oldest impact crater; it's located in the heart of Western Australia's ancient Pilbara region. Analysis of rock layers in the region shows that the crater, at least 62 miles (100 kilometers) wide, was carved out after a large space rock slammed into Earth about 3,47 billion years ago, when our planet was almost entirely covered in water. The discovery pushes back the record for the oldest impact crater on Earth by more than 1 billion years — the previous record holder, the Yarrabubba impact structure, also in Western Australia.
"Given how rare this kind of evidence is due to geological reworking processes [on Earth], this is a major breakthrough in understanding the early Earth," Chris Kirkland of Curtin University in Australia, who led the discovery, told Space.com.
Researchers estimate that the space rock responsible for the crater was traveling at 36 miles per hour, with the impact scattering debris across the planet. But despite its global impact, Kirkland says the event wasn't just a destructive force. The crater it left behind could have played a crucial role in the development of early life, he says, and therefore provide insight into how life might have originated on our planet.
The high pressure resulting from the shock waves generated by meteorite impacts is known to alter the minerals in rocks, sometimes turning them into translucent glass. In principle, this allows more sunlight to penetrate the cracks that break apart the rocks, creating the physical and chemical conditions necessary for early life to flourish. As Kirkland explains, the meteorite impacts also led to the formation of hot, mineral-rich pools of water that could have served as cradles for early microbial life, fostering the conditions necessary for the emergence of life as we know it.
In May 2021, just over an hour after arriving around an area in the Pilbara region called the North Pole Dome, Kirkland and his colleagues discovered evidence of a crater: distinctive rocks that resembled inverted badminton shuttlecocks with their tops knocked off, known to scientists as “shattering cones.” The presence of these remarkably well-preserved structures, which span several hundred meters, “is direct and frankly incontrovertible evidence of an ancient collision,” Kirkland said. “The identification of [these] shattering cones was a truly remarkable moment.”
The researchers returned to the region for more detailed field studies in May last year, after which the Geological Survey of Western Australia dated rock layers above and below the identified debris cones. The layers are estimated to be about 3,47 billion years old, confirming that the crater is the oldest in the world. If future field studies confirm that these cones are present across the entire diameter of the 40-45-kilometer (25-28-mile) North Pole dome, this would match the 62-mile (100-kilometer) crater size suggested by the new study.
"Their discovery on the North Pole dome confirmed what we had long suspected based on isotopic evidence," Kirkland told Space.com.
“Serendipity is a remarkable thing,” he and his team wrote in an article on The Conversation. “To our knowledge, apart from the traditional owners, the Nyamal people, no geologists have seen these stunning features since they were formed.”
However, not everyone is convinced about the approximate size of the newly discovered ancient impact crater and its significance for advancing our understanding of early life on Earth. Mark Norman, an honorary fellow at the Australian National University's Research School of Earth Sciences, told the Australian Broadcasting Corporation that the study lacks conclusive evidence on the size of this particular crater and how it relates to the role of collisions on the early Earth.
"While the discovery of this ancient impact crater is interesting, it doesn't really advance our understanding of how impacts may have influenced the formation and evolution of the Earth over billions of years," he said.
In addition to its implications for early life on our planet, the newfound crater hints at a previously undiscovered population of similarly ancient impact craters, Kirkland said. The discovery “underscores the importance of re-examining ancient geological sites for evidence of early impacts.”
The best chance of finding older craters like the newfound one would be to look for debris cones and similar features that would survive our planet's geological landscape-recycling activity.
“The challenge is finding them, because most of them are destroyed or deeply buried,” Kirkland said. The discovery is described in a paper published Thursday (March 6) in Nature Communications.
