Pieces of 'cosmic glass' found only in Australia hint at a giant asteroid impact

Tiny pieces of natural glass found in South Australia carry the signature of an ancient asteroid impact. They are small, tough, and unassuming, yet they point to a violent event that reshaped a patch of Earth about 11 million years ago.

Researchers say these glasses are not part of any known deposit of similar material. They sit in their own category, formed from melted surface rock that cooled in flight and later fell across a long swath of land roughly 560 miles wide.

What scientists found

The work centers on a rare set of tektites, a kind of impact formed glass that scatters far from the impact site. These glasses show unusual chemistry, very low water content, and tiny grains of nearly pure silica inside them.

“These tektites are unique because of their unusual chemistry and their age, which is about 11 million years,” said Anna Musolino, PhD student at Aix-Marseille University (amU), working with collaborators at Curtin University and several French labs.

The team reports a precise age of about 10.76 million years, and they argue the glass marks a separate impact from the better known Australasian deposit.

Their peer reviewed paper sets out the age, texture, and composition that define this new group.

What are tektites?

Impact blasts can melt surface sediments and bedrock, then throw droplets of melt into the air at high speed.

Those droplets cool into glass as they arc through the atmosphere, land far from the crater, and build a large strewn field.

Tektites are clean glasses, usually with few bubbles and almost no crystals. Many include traces of lechatelierite, a pure silica glass that forms when quartz melts at very high temperature.

The new Australian glasses match that pattern, but their chemistry stands apart. The composition trends toward andesitic to dacitic rock, which hints at a volcanic arc target rather than typical continental crust.

Dating the cosmic impact glass

The team dated the glasses using 40Ar/39Ar geochronology, a method that heats a sample in steps and measures argon isotopes to build a plateau age.

The 40Ar/39Ar method is widely used for volcanic rocks and impact glasses because it can detect partial resetting and contamination.

Their reported age clusters tightly around 10.76 million years with small analytical errors. That timing places the event long before the youngest large tektite deposit in the region.

“Understanding when and how often large asteroids have struck Earth also helps us assess the risk of future impacts, which is important for planetary defense,” said Fred Jourdan, professor at Curtin University’s School of Earth and Planetary Sciences.

Clues to the missing crater

No crater has been located. The size of the strewn field, the chemistry, and isotopes point toward a volcanic arc target that was struck by a stony asteroid.

A rise in nickel, cobalt, and chromium in such glasses often signals contamination from a chondritic impactor.

The new samples show that pattern strongly, which is consistent with a stony asteroid mixing into molten surface rock.

The authors note isotope values for strontium and neodymium that match materials from several arcs around northern Australia.

They highlight sectors near Luzon, Sulawesi, and the Bismarck region as plausible sources, which would fit a long flight path and a wide landing ellipse.

Space glass in Earth history

Scientists recognize only a few large tektite fields on land. A 2021 study tied peculiar glasses in Belize to the Pantasma crater in Nicaragua, formally adding Central America to the short list.

Closer to Australia, the biggest and youngest field is the Australasian deposit, which blankets parts of Asia and Australia.

High precision estimates put its age at about 788,000 years, far younger than the South Australian glasses.

The comparison matters because it rules out a link to the Australasian event. It also shows that large, far flung impacts have happened multiple times in the recent geologic past, each with its own geochemical fingerprint.

Rock target evidence

The new glasses are low in water and show very few bubbles, a sign of rapid melting and violent ejection.

Their trace elements include a pattern often seen in volcanic arcs, with certain elements suppressed and others slightly elevated.

These features support an andesitic target rock rather than granite rich continental crust. They also align with the isotope story and the high nickel levels that flag incoming meteor material.

The researchers even see subtle differences along the width of the field.

Samples from the western end contain more bubbles and tiny silica inclusions, while eastern pieces look denser and cleaner, which may reflect temperature differences during flight.

Cosmic glass and asteroid threats

Tektites record impact conditions in a way that craters alone do not. Each glass sample is a small archive of temperature, chemistry, and even the mixing ratio between projectile and target.

Finding a new space glass field in Australia adds an extra episode to Earth’s late Miocene impact record.

It shows that large space impacts sometimes leave scattered glass without a clearly preserved crater, especially in active or remote regions.

“These glasses are unique to Australia and have recorded an ancient impact event we did not even know about,” said Jourdan.

That point brings the search back to the ground, where field teams can look for more pieces and, hopefully, the hidden scar that started it all.

The study is published in Earth and Planetary Science Letters.

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