Sydney: Scientists have discovered a 200-kilometre-wide impact zone in the Australian outback they believe was caused by a massive asteroid smashing into Earth more than 300 million years ago.

Andrew Glikson, a visiting fellow at the Australian National University, said the asteroid measuring 10 to 20 kilometres in diameter was a giant compared to the plunging meteor that exploded above Russia a week ago.

While that event set off a shockwave that shattered windows and hurt almost 1,000 people in the Urals city of Chelyabinsk, Glikson said the consequences of the Australian event would have been global.

“This is a new discovery,” Glikson told AFP on Wednesday, describing the impact zone in South Australia’s East Warburton Basin.

“And what really was amazing was the size of the terrain that has been shocked. It’s now a minimum of 200 kilometres [in diameter], this makes it about the third biggest anywhere in the world.”

The basin has evidence of some 30,000-square kilometres of terrain that has been altered by some kind of shock, which Glikson first began studying after another scientist showed him rock samples that displayed structural anomalies.

“Following that I spent many months in the lab doing a number of tests under the microscope to measure the crystal orientations... and determined that these rocks underwent an extraterrestrial impact or shock,” he said.

“We are dealing with an asteroid which is least 10 kilometres in size.

“It would have had a global impact, not just regional.”

Besides leaving a vast crater, now buried under more than three kilometres of sediment, it would have released huge amounts of dust and vapour that would have blanketed the Earth.

“We think it was part of a cluster. We think it could be... about 360 million years ago. There were a number of other very large impacts at that time. That cluster we know has caused mass extinction,” Glikson said.

Glikson, from ANU’s Planetary Science Institute and School of Archaeology and Anthropology, said despite the recent Russian meteor and the 45-metre wide asteroid dubbed 2012 DA 14 that whizzed past Earth last week, events of the scale of the Australian asteroid were extremely rare.

“They fall once in every several tens of millions of years,” he said comparing it to once a century for the meteor shower.

“I don’t think we have to worry about it, not as much as we have to worry about nuclear accidents or about climate change.”