Geologists have discovered the world's oldest known impact crater; it sits in the heart of Western Australia's ancient Pilbara region.
An analysis of rock layers in the region suggests a crater at least 62 miles (100 kilometers) wide was carved after a large space rock struck Earth roughly 3.47 billion years ago, when our planet was almost completely 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 is in Western Australia.
"Given how rare such evidence is due to [Earth's] geological recycling processes, this is a major breakthrough in understanding early Earth," Chris Kirkland of Curtin University in Australia, who led the discovery, told Space.com.
The researchers estimate the space rock responsible for the crater was traveling at 36,000 kilometers per hour, with the collision scattering debris across the planet. Despite its global impact, however, the event was not merely a destructive force, according to Kirkland. The crater it left behind may have played a crucial role in fostering early life and therefore provide insights into how life on our planet might have originated, he said.
High pressures resulting from shock waves released in the aftermath of meteorite impacts are known to alter minerals within rocks, sometimes transforming them into translucent glass. In principle, this allows for more sunlight to penetrate into the cracks fracturing the rocks, creating the physical and chemical conditions necessary for early life to thrive. As Kirkland explains, meteorite impacts also lead 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 life as we know it to emerge.
In May 2021, little more than an hour after arriving around an area in the Pilbara region called the North Pole Dome, Kirkland and his colleagues identified evidence for the crater: distinctive rocks that resembled inverted badminton shuttlecocks, with the tops knocked off, known to scientists as "shatter cones." The presence of these hut-like structures, which are exceptionally well-preserved and span several hundred meters, "is direct and frankly indisputable evidence of an ancient impact event," Kirkland said. "Identifying [these] shatter cones was a truly remarkable moment."
The researchers returned to the region for more detailed fieldwork in May of last year, after which the Geological Survey of Western Australia dated the rock layers above and below the discovered shatter cones. The layers were estimated to be about 3.47 billion years old, confirming the crater as the world's oldest. If future fieldwork confirms that these cones are present throughout the 40- to 45-kilometer (25- to 28-mile) diameter of the North Pole Dome, this lines up with the 62-mile (100-km) crater size suggested by the new study.
"Their discovery at the North Pole Dome confirmed what we had long suspected based on isotopic evidence," Kirkland told Space.com.
"Serendipity is a marvelous thing," he and his team wrote in an article on The Conversation. "As far as we knew, other than the Traditional Owners, the Nyamal people, no geologist had laid eyes on these stunning features since they formed."
Not everyone is convinced, however, of the newfound ancient impact crater's estimated size and its significance in advancing our understanding of early life on Earth. Marc Norman, an Emeritus Fellow in the Research School of Earth Sciences of the Australian National University, told the Australian Broadcasting Corporation that the study lacks solid evidence regarding the size of this particular crater and how it relates to the role of impacts on early Earth.
"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," he said.
Beyond implications for early life on our planet, the newfound crater hints at an as-yet-undiscovered population of similarly ancient impact craters, said Kirkland. This discovery "highlights the importance of re-examining ancient geological terrains for evidence of early impact events."
The best chance of locating more ancient craters like the newfound one would be to search for shatter cones and similar features that would have survived our planet's landscape-recycling geologic activities.
"The challenge lies in finding them, as most have been destroyed or deeply buried," said Kirkland.
This discovery is outlined in a paper published Thursday (March 6) in Nature Communications.
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