The largest impact zone from a meteorite ever discovered on Earth has been found in central Australia.
But the exact ecological impact of the meteorite - which broke in two before slamming into the planet over 300 million years ago - remains a mystery.
A team of geophysicists found the "twin scars" during drilling for geothermal research in the Warburton Basin, near the borders of Queensland, South Australia and the Northern Territory.
While the crater from the impact has long since disappeared, evidence of the 400 kilometre-wide impact zone was hidden deep within the earth's crust.
The two asteroids would have been more than 10km wide, said Dr Andrew Glikson from the Australian National University's School of Archaeology and Anthropology.
"Large impacts like these may have had a far more significant role in the Earth's evolution than previously thought," he said.
While the exact date of the strike is unclear, Dr Glikson said it was likely to have signalled the end for many species of the time.
The surrounding rocks are between 300 and 600 million years old.
Researchers have previously been able to estimate the time of meteor strikes based on other evidence such as sediment in rock - the result of a huge plume of ash.
One such plume in Mexico, estimated to have been made 66 million years ago, is believed to have wiped out many species, including dinosaurs.
But Dr Glikson said there was no such evidence associated with the Warburton Basin site.
"It's a mystery - we can't find an extinction event that matches these collisions," he said.
"I have a suspicion the impact could be older than 300 million years."
The discovery could fuel new theories about the Earth's history, academics say.
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