'Largest ever asteroid impact' found in Australia

The 400-kilometre (250-mile) wide area is buried deep in the earth's crust and consists of two separate impact scars.

The team behind the discovery, from the Australian National University (ANU), said the asteroid broke into two before it hit, with each fragment more than 10km across.

The impact is thought to have occurred at least 300 million years ago.

The surface crater has long since disappeared from central Australia's Warburton Basin but geophysical modelling below the surface found evidence of two massive impacts, said Dr Andrew Glikson, who led the ANU team.

"It would have been curtains for many life species on the planet at the time," said Dr Glikson.

But the team, which published its findings in the geology journal Tectonophysics, has not been able to connect the impact to any known extinction.

"It's a mystery - we can't find an extinction event that matches these collisions," said Dr Glikson. "I have a suspicion the impact could be older than 300 million years."