Remains of giant asteroid found in outback Australia


Scientists say asteroid could have been 40 kilometres across and would have left a crater hundreds of kilometres wide. Viviane Richter reports.


Chert in Marble Bar, Australia. The remains of the asteroid was found between two volcanic layers of this rock.
DIRK WIERSMA/GETTY IMAGES

The remains of a giant asteroid that smashed into Earth 3.46 billion years ago have been discovered in north-western Australia.

Scientists say the asteroid was up to 40 kilometres wide – amongst the largest to have collided with our planet – and its impact could have significantly changed how the Earth’s crust evolved during its youth.

The remnants of this asteroid come in the shape of tiny glass beads called spherules, which the scientists say formed from material vaporised by the impact.

These spherules were discovered in Western Australia’s Marble Bar, in samples of sedimentary rock which once formed a sea floor. Because the rock layer in which they were found was wedged between two volcanic layers, the team was able to date the glass beads to 3.46 billion years ago.

And when the scientists analysed the chemical composition of the rims of the spherules, they discovered elements such as iron, magnesium and nickel matched the levels found in asteroids.

A microscopy image of the tiny glass beads called spherules that are all that is left of the asteroid.
ANDREW GLIKSON

As the second oldest known to have plummeted into Earth in its youth, this asteroid “is just the tip of the iceberg,” said author Andrew Glikson from the Australian National University. “We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds.”

Glikson said the crater this asteroid created would have been wiped out by tectonic movement and volcanic activity, which leaves the location of where it impacted unknown.

But the scientists estimated the size of the asteroid based on a previously published model – a linear relationship between spherule size and the size of an impacting object.

The authors state the two-millimetre spherules, each barely larger than a pinhead, was likely formed by an impacting asteroid as large as 40 kilometres in diameter.

The crater left behind by such an asteroid would in turn have spanned hundreds of kilometres, Glikson said.

“The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble,” he said.

“Asteroid strikes this big result in major tectonic shifts and extensive magma flows,” Glikson added. “They could have significantly affected the way the Earth evolved.”

The discovery was published in the journal Precambrian Research.