SYDNEY (AFP) - Scientists have discovered a massive 200-kilometre impact zone in the Australian outback they believe was caused by an asteroid which smashed 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 which exploded above Russia a week ago.
That event set off a shockwave that shattered windows and hurt almost 1,000 people in the Urals city of Chelyabinsk, but Dr Glikson said the consequences of the Australian event would have been global.
"This is a new discovery," Dr Glikson told AFP on Wednesday of 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 East Warburton Basin has evidence of some 30,000-square kilometres of shock-metamorphosed terrain which Glikson first began studying after another scientist showed him samples which displayed microstructural 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 a vast crater, now buried under more than three kilometres of sediments, it would have released huge amounts of dust and vapour which would have literally blanketed the Earth.
Dr 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 which whizzed safely past Earth last week, events of the scale of the Australian asteroid were extremely rare.