Australian researchers discover world’s largest asteroid impacts

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Researchers at Australian National University have discovered what they claim is world’s largest impact zone – a 400-km wide impact zone resulting from a meteor that slammed into Earth in Central Australia.

Though the crater has disappeared, a team of researchers led Dr Andrew Glikson from the ANU School of Archaeology and Anthropology has found twin scars of the impacts hidden deep in the earth’s crust. The impact zone was discovered when the researchers were carrying out drilling in an area near the borders of South Australia, Queensland and the Northern Territory as a part of geothermal research.

“The two asteroids must each have been over 10 kilometres across – it would have been curtains for many life species on the planet at the time,” said Dr Glikson in a press release. “Large impacts like these may have had a far more significant role in the Earth’s evolution than previously thought.”

Researchers haven’t been able to establish the exact date of the impact. The surrounding rocks are 300 to 600 million years old, but evidence of the type left by other meteorite strikes is lacking.

For example, a large meteorite strike 66 million years ago sent up a plume of ash which is found as a layer of sediment in rocks around the world. The plume is thought to have led to the extinction of a large proportion of the life on the planet, including many dinosaur species.

However, a similar layer has not been found in sediments around 300 million years old, Dr Glikson said.

“It’s a mystery – we can’t find an extinction event that matches these collisions. I have a suspicion the impact could be older than 300 million years,” he said.

A geothermal research project chanced on clues to the impacts while drilling more than two kilometres into the earth’s crust.

The drill core contained traces of rocks that had been turned to glass by the extreme temperature and pressure caused by a major impact.

Magnetic modelling of the deep crust in the area traced out bulges hidden deep in the Earth, rich in iron and magnesium, corresponding to the composition of the Earth mantle.

“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,” Dr Glikson said.

The two impact zones total more than 400 kilometres across, in the Warburton Basin in Central Australia. They extend through the Earth’s crust, which is about 30 kilometres thick in this area.

The research has been published in journal Tectonophysics.