Mystery surrounds evidence of two massive asteroids each more than 10 kilometres wide smashing into the centre of Australia hundreds of millions of years ago.
Such a violent double impact should have wiped out much of life on earth − yet there is no record of a mass extinction linked to the event.
Nor can scientists find any sign of an ash layer similar to the one left by the similar-sized meteor believed to have killed off the dinosaurs 65 million years ago.
A team of geophysicists discovered ancient scars of the twin impact deep beneath the earth’s crust in the Warburton Basin, a geological region of sandstone and volcanic rock in Central Australia.
Drill cores contained traces of rocks that had been turned to glass by the extreme temperature and pressure of the cataclysm.
Evidence was also found of the earth’s crust rebounding after the impacts, bringing up rock from the mantle below.
It’s a mystery − we can’t find an extinction event that matches these collisions
Although no sign of a crater still remains, together the impact zones covered an area more than 400 kilometres across. It is believed a monster meteor broke in two moments before slamming into the earth.
Lead researcher Andrew Glikson, from The Australian National University (ANU) School of Archaeology and Anthropology, said: “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.
“Large impacts like these may have had a far more significant role in the earth’s evolution than previously thought.”
Rocks surrounding the site are between 300 and 600 million years old, but the exact date of the impacts remains unclear.
“It’s a mystery − we can’t find an extinction event that matches these collisions,” said Glikson. “I have a suspicion the impact could be older than 300 million years.”
The discovery was made by accident after scientists drilled more than two kilometres into the earth’s crust as part of a project investigating ways of extracting heat energy from the earth.
Their findings are published in the journal Tectonophysics.
A 10-kilometre-wide meteor that struck the earth off the coast of Yucatan, Mexico, is widely believed to have caused the extinction of the dinosaurs after dust blocking out the sun produced an ‘impact winter’ the warmth-loving reptiles could not survive. That object threw up a plume of ash which left a tell-tale layer of rare iridium associated with a particular kind of asteroid around the world.
The explosion of the impact would have released as much energy as 100 trillion tons of TNT, more than a billion times the power unleashed by the atom bombs that destroyed Hiroshima and Nagasaki.