Australian scientists have found evidence of a huge asteroid they say slammed into Earth some 3.46 billion years ago - making it the second oldest known to have hit the planet and larger than the one blamed for wiping out the dinosaurs.
Andrew Glikson, from the Australian National University's Planetary Institute, said that while the asteroid would have been massive, the exact location of where it hit was not known.
"The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," he said in a statement.
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"Material from the impact would have spread worldwide."
Speaking to AFP on Wednesday, Glikson said he and Arthur Hickman from the Geological Survey of Western Australia had found tiny glass beads called spherules, which are formed by vaporized material from an asteroid's impact, in Australia's remote northwest.
They were discovered in a sediment layer originally on the ocean floor and which had been preserved between two volcanic layers. It dates from 3.46 billion years ago.
"It is the second oldest known," Glikson said of the asteroid, which was estimated to have been at least 20 kilometers (12 miles) across and to have created a crater hundreds of kilometers wide.
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This makes it larger than the giant asteroid that collided with Earth some 66 million years ago and is widely blamed for the demise of the dinosaurs. That asteroid is estimated to have measured around 15 kilometers wide.
Tests on the beads found in Western Australia found levels of elements such as platinum, nickel and chromium corresponding with those found in asteroids, according to the scientists' paper in Precambrian Research.
Glikson said while the find was evidence of the second oldest asteroid to hit Earth, there may have been other similar impacts that have yet to be discovered because asteroid craters from the period have been obliterated by volcanic activity and tectonic movements.
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"This is just the tip of the iceberg. We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds," he said in the statement.
"Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved."