Embedded in the crust 30 kilometers (19 miles) deep, in rock that is 300-600 million years old, the double impact crater has long gone, buried by geological processes, but its imprint in Earth’s crust remains. It covers a vast impact zone some 400 kilometers (250 miles) wide in the Warburton Basin in Central Australia.
“The two asteroids must each have been over 10 kilometers (6.2 miles) across — it would have been curtains for many life species on the planet at the time,” said Andrew Glikson from the Australian National University’s School of Archaeology and Anthropology.
Compared with the famous Chicxulub crater under the Yucatán Peninsula in Mexico, which is famous for causing the extinction of the dinosaurs some 66 million years ago, this Australian impact zone is a monster. The Chicxulub crater is 180 kilometers (110 miles) in diameter and was caused by a single 10 kilometer-wide asteroid; the Warburton Basin impact zone is over twice that size, caused by two Chicxulub-sized impactors.
The discovery came when a geothermal research project drilled out rock from South Australia and the Northern Territory that had been turned to glass; a tell-tail sign that an ancient impact had delivered a very energetic blow. But only on further investigation did the Glikson’s team realize the extent of the the impact.
Magnetic modeling of the crust throughout the region revealed bulges, rich in iron and magnesium, pushing upward into the Earth’s crust. These bulges originated from the Earth’s mantle — the tick layer of rock that separates the core from the crust — acting as ancient bruises left over by the cataclysmic impacts.
“There are two huge deep domes in the crust, formed by the Earth’s crust rebounding after the huge impacts, and bringing up rock from the mantle below,” Glikson said in a press release. The research was published in the journal Tectonophysics this month.
Although the evidence for a massive impact seems clear, some mysteries remain.
Read more at Discovery News
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