The largest known asteroid impact crater has been found in the Australian outback. The extinction level impact zone is nearly 250 miles wide and is thought to have been caused by an asteroid which split in half just before crashing to Earth.

“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, from the ANU School of Archaeology and Anthropology, in a statement.

Although the event occurred many millions of years ago, researchers will not have an exact date until more testing is done.

The crater was discovered while drilling as part of a geothermal research mission in Central Australia near the borders of the Northern Territory, Queensland and South Australia. Geophysicists found the twin scars from the impact hidden in the Earth’s crust.

“The next step will be more research, hopefully deep crust seismic traverses. Under the Cooper Basin and Warburton Basin we don’t have that information and our seismic information covers up to five kilometres and some other data such as seismic tomography and magnetic data. The mantle underneath has been up-domed which is a very promising indication of a major event,” Dr Glickson told the Australian Broadcasting Corporation.

Although research on the site has only just begun, has led to new theories and speculation about the early history of the Earth.

“Large impacts like these may have had a far more significant role in the Earth’s evolution than previously thought,” Dr Glikson said.

A large impact 66 million years ago caused the mass extinction which claimed most dinosaur species. A plume of ash from that impact has been found in sediment around the world.

However, there is no mysterious layer of sediment from 300 million years ago which would match the impact found in Australia.

“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,” said Dr Gliksoin.

In addition to the Cretaceous-Tertiary mass extinction, which claimed the dinosaurs, scientists know of four others. The Triassic-Jurassic mass extinction occurred about 200 million years ago, is thought to have been caused by a variety of factors including volcanic activity and climate change.

The Permian mass extinction, also called ‘the Great Dying’ happened about 248 million years ago. A variety of factors are thought to have been involved in this event, which killed 96 percent of all species, but there is no single cause which can be blamed at this point.

Late Devonian mass extinction killed 75 percent of all species about 359 million years ago. Again there is no single event which appears to have caused it. Asteroid impacts, climate change and changes in sea level may have all been involved.

The Ordovician-Silurian mass extinction killed 85 percent of all species 443 million years ago and is thought to have been caused by an ice age.

“When we know more about the age of the impact, then we will know whether it correlates with one of the large mass extinctions [at the end of specific eras]. At this stage we do not have all the answers, but there has been a lot of interest and people are certainly interested in any impact on the dinosaurs,” said Dr Glickson.

The preliminary research has been published in the journal Tectonophysics.