Clues to ancient 15-mile-wide asteroid impact found in Western Australia

Scientists have found evidence of a huge asteroid that struck the Earth early in its life with an impact larger than anything humans have experienced.

Tiny glass beads called spherules, found in northwestern Australia, were formed from vaporised material from the asteroid impact, said Dr. Andrew Glikson from The Australian National University (ANU).

“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,” said Dr. Glikson, from the ANU Planetary Institute and also Geoscience Australia.

“Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago.”

The asteroid is the second oldest known to have hit the Earth and one of the largest.

Dr. Glikson said the asteroid would have been 20 to 30 kilometres across and would have created a crater hundreds of kilometers wide.

About 3.8 to 3.9 billion years ago the Moon was struck by numerous asteroids, which formed the giant craters, called maria [singular: mare], that are still visible from Earth.

“Exactly where this asteroid struck the Earth remains a mystery,” Dr. Glikson said. “Any craters from this time on Earth’s surface have been obliterated by volcanic activity and tectonic movements.”

Dr. Glikson and Dr. Arthur Hickman from Geological Survey of Western Australia found the glass beads in a drill core from Marble Bar, in northwestern Australia, in some of the oldest known sediments on Earth.

The sediment layer, which was originally on the ocean floor, was preserved between two volcanic layers, which enabled very precise dating of its origin.

Dr. Glikson has been searching for evidence of ancient impacts for more than 20 years and immediately suspected the glass beads originated from an asteroid strike.

Subsequent testing found the levels of elements such as platinum, nickel and chromium matched those in asteroids. There may have been many more similar impacts, for which the evidence has not been found, said Dr. Glikson.

“This is just the tip of the iceberg. We’ve only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds.”

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

Dr. Glikson is lead author on a study published in the July 2016 issue of the journal Precambrian Research.