Major asteroid site found in Aussie outback

The impact crater was caused by an asteroid slamming into Earth between 298 and 360 million years ago, which places it in the same epoch as the Late Devonian mass extinction(Source: Fredrik/WikiMedia)

Stuart Gary
ABC

One of the largest ancient asteroid impact zones on Earth has been discovered in outback Australia.
The impact zone, which centres on the East Warburton Basin in north-eastern South Australia, was caused by an asteroid up to 20 kilometres-wide that slammed into the planet between 298 and 360 million years ago, report scientists from the Australian National University and University of Queensland.

Terrain around the impact site shows evidence of changes caused by shock-wave related deformation and heating of the ground by an impact event, says study co-author, Dr Andrew Glikson from the Australian National University.

"This shock metamorphic terrain covers an area of over 30,000 square kilometres making it the third-largest site of its kind ever discovered on Earth," says Glikson.

The team report their discovery in the journal Tectonophysics.

To confirm the area was an impact zone, Glikson and colleagues studied quartz grains retrieved from drill holes.

Optical and electron microscopic examination revealed tiny fractures, which indicate the quartz grains had been shocked by an asteroid or meteor impact.

"This is the only way these features are formed," says Glikson.

Follow up observations detected deep seismic anomalies below the terrain where the samples were taken.

"This allowed us to determine the scale of the impact site which is buried under four kilometers of younger sediments," he says.

Multiple hits

Glikson believes there is a link between this impact site and three or four other large impact sites of the same age scattered around Australia.

"Asteroid impacts commonly occur in clusters of two or more projectiles," he says.

"Where impacts are near-contemporaneous they're usually fragments of a larger body broken apart by the gravitational effect of the Earth-Moon system."

"This new discovery is a twin for one we reported on last year in the Eromanga Basin in south-western Queensland called the Tookoonooka Crater.

"It looks like both impacted at the same time."

He also believes there is a link between this site and a nearby potential impact site on the South Australian/Northern Territory border known as the West Warburton geophysical anomaly, and another site at Woodleigh in Western Australia.

Past and future

Glikson says the discovery shows that research into past asteroid impacts is essential if we are to prepare for future asteroid encounters and their effects.

"The 280 to 360 million years old impact window places this in the same epoch as the late Devonian mass extinction event".

The late Devonian mass extinction was one of five major extinction events in Earth's history, wiping out large groups of marine species.

"There are indications of mass extinction at this time caused by an impact winter, with the huge flash of the asteroid, major fires and seismic events with magnitudes of 10, 11 and 12, which would have disrupted habitats," says Glikson.