Earth's oldest meteorite crater found in Australia
The Archean Eon (4–2.5 million years ago) is the second of Earth's four major geologic eons, a time when the planet was mostly covered by oceans extending far deeper than those found today. Even so, its geology records can be accessed at excavation sites on modern continents like Australia. But researchers have long remained perplexed by what they found—or, rather, what they haven't found.
'We know large impacts were common in the early solar system from looking at the moon,' Tim Johnson, study co-lead and a professor at Curtin University's School of Earth and Planetary Sciences, said in a statement on Thursday.
It stands to reason, then, that a lack of 'truly ancient craters' documented on Earth isn't the result of sheer luck, but rather the nature of time. Early impact records are scarce thanks to billions of years of erosion, as well as the subduction of surface crust into the planet's convecting mantle. However, Archean Eon geology isn't completely erased, as evidenced by sites like the East Pilbara Terrane in northwest Australia. In 2021, Johnson and colleagues traveled to EPT to see what they could find.
What they discovered appears to be the first known Archean Eon crater, and is evidenced by formations known as shatter cones. These telltale geologic areas are only generated from the intense pressure following a meteorite striking Earth—and in this case, the shatter cones suggest a massive impact event. Researchers believe the space rock struck the planet around 3.5 billion years ago while travelling over 22,000 mph. The force subsequently generated a 62-mile-wide crater that ejected debris into the atmosphere and around the world.
It's not just the impact details that matter. According to study co-lead author Chris Kirkland, analyzing the nature of the first known Archean meteorite event can help researchers gain better insight into both continental evolution and the history of life's development on Earth.
'It… radically refines our understanding of crust formation,' he argued. 'The tremendous amount of energy from this impact could have played a role in shaping early Earth's crust by pushing one part of the Earth's crust under another, or by forcing magma to rise from deep within the Earth's mantle toward the surface.' There's even a chance the impact event eventually contributed to forming the giant precursors to continents known as cratons.
The study's authors believe this meteorite alone may have played an important role in Earth's geologic history, but it's almost certainly not the only one.
'Uncovering this impact and finding more from the same time period could explain a lot about how life may have got started, as impact craters created environments friendly to microbial life such as hot water pools,' said Kirkland.
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