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article imageHuge Australian asteroid impact ‘Curtains for many life species'

By Robert Myles     Mar 24, 2015 in Science
Canberra - Geophysicists have discovered evidence of what may be the world’s largest asteroid impact in central Australia. The impact zone from what would have been a huge meteorite stretches over 400 kilometers.
A team of scientists, based at the Australian National University (ANU) in Canberra, made the discovery. They suggest the massive meteor must have broken in two moments before impact. ABC News reports that material from both impact sites appears to be identical leading researchers to conclude they emanate from the same meteorite.
Unlike Arizona’s well defined Barringer Crater, evidence that Australia was once the scene of a cataclysmic event has long since been wiped from the surface.
The asteroid impact occurred millions of years ago but geophysicists located twin scars of the dual impacts, in what they say constitutes the largest impact zone ever found on Earth, concealed far below Earth’s crust.
The impact zone, near where the borders of the Australian states South Australia, Queensland and Northern Territory intersect, was found during drilling as part of geothermal research.
"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," commented lead researcher Dr Andrew Glikson, based at the ANU’s School of Archaeology and Anthropology.
The Australian find of such a violent, ancient encounter with an asteroid could force scientists to revisit how life has evolved on Earth and the history of Earth itself.
"Large impacts like these may have had a far more significant role in the Earth's evolution than previously thought," Dr Glikson explained.
Precisely when Australia experienced what would likely have been a devastating event remains unclear. According to ANU, rocks surrounding the impact zone are between 300 and 600 million years old, however evidence of the type left by other meteorite strikes is lacking.
For example, the large meteor that crashed to Earth around 66 million years ago, giving rise to the Cretaceous–Paleogene extinction event that put paid to the dinosaurs, sent up clouds of ash and dust that subsequently settled to form a distinct sedimentary layer in rocks.
But the Australian event doesn’t seem to have left a similar layer in sediments dating from around 300 million years, according to Dr Glikson.
That may point to the Australian impact being significantly older, as Dr Glikson explained, “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."
The first clues that something major had taken place in central Australia eons ago were found quite by chance during drilling more than two kilometers beneath Earth’s crust as part of a geothermal project. When the drill core was examine it was found to contain traces of rocks that had been turned to glass, a common ‘symptom’ of meteoric impacts caused by the extreme temperatures and pressures typical of such impacts.
Subsequent magnetic modelling of the deep crust of the impact area revealed bulges hidden deep below the surface. These bulges were rich in iron and magnesium, corresponding to the composition of the Earth mantle. These bulges were caused as a result of the Earth attempting to resume its original shape after the impacts in much the same way as a rubber ball returns to the spherical after being squeezed.
As Dr Glikson explained, “There are two huge deep domes in the crust, formed by the Earth's crust rebounding after the huge impacts, and bringing up rock from the mantle below."
At 400 kilometers across, the two impact zones, located in the Warburton Basin in central Australia, are almost 250 times the size of the mile-wide Barringer Crater. The zones extend through the Earth's crust, which is about 30 kilometers (18.6 miles) thick in this area.
More about meteorite impacts, Meteors, Meteorites, Barringer crater, Extinction event
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