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A mystery 300-mile wide formation lurking beneath Australia may be the largest asteroid impact crater on Earth

Marianne Guenot   

A mystery 300-mile wide formation lurking beneath Australia may be the largest asteroid impact crater on Earth
  • Scientists have uncovered traces of what they think could be the world's largest asteroid impact.
  • The structure, hidden in the ground in Australia, is thought to be about 300 miles across.

The world's largest asteroid impact, 300 miles across, could be hidden in the Australian ground.

Scientists have been tracing "magnetic" and "gravity" patterns spreading out in circles from a point about 10 miles from Deniliquin in New South Wales, Australia.

The structure, the scientists say, could be the remnants of an enormous asteroid impact that hit the Earth hundreds of millions of years ago.

If confirmed, it would be the largest asteroid impact on record.

The memory of the impact is hidden in the ground

One would think finding the world's largest asteroid impact should be fairly easy. But the reality is very different.

It is true that asteroid impacts create massive geological structures.

The force of the impact is so strong it can bend the Earth's crust, creating ripples similar to those a rock makes when hitting a pond, Andrew Glickson, a paleo-geophysicist from the Australian Geological Survey Organization, said in a post in The Conversation August 10.

But if this impact happened, hundreds of millions of years of erosions would have erased most of the visible features of the event.

Still, scientists can look for telltale signs left behind, with a little patience, Glickson said.

Five years of ground surveys around the area of Deniquilin have uncovered "radial faults," circular fractures that radiate from a central structure, Glickson and his colleague Tony Yeates said in a peer-reviewed paper published last year.

These are accompanied by "small magnetic anomalies" around the center point. These were likely caused by molten rock oozing into the peaks and troughs left behind by the impact.

Glickson said this so-called Deniliquin structure "spans up to 520 kilometers in diameter" or about 300 miles.

That would be an impact bigger than any other documented on Earth. That includes the Vredefort impact structure in South Africa, which is thought to have been between 100 and 200 miles wide, and the Chicxulub impact, about 90 miles across, which scientists believed triggered the mass extinction that wiped out the dinosaurs.

To confirm the finding, the scientists will aim to get physical evidence from the site itself.

"For proof of impact, we'll need to collect physical evidence of shock, which can only come from drilling deep into the structure," said Glickson in the post.

The asteroid may have caused one of Earth's mass extinctions

Before the scientists can drill into the site, it will be difficult to know when exactly this asteroid would have hit.

Glickson believes the impact happened when Australia was still part of Gondwana, a supercontinent that broke off from Pangea and later turned into South America, Africa, Arabia, Madagascar, India, Australia, and Antarctica.

That would mean it would be at least 180 million years old, probably more.

"Specifically, I think it may have triggered what's called the Hirnantian glaciation stage, which lasted between 445.2 and 443.8 million years ago," Glickson said in the post.

This mass extinction event was caused by an ice age that wiped out 85% of the planet's species, 350 million years before the dinosaurs were wiped out, Glickson said.

But the impact could be even older. Glickson said he could see it date back up to 514 million years.