Natural glass found only in Australia could be evidence of an unknown, ancient asteroid impact, researchers say.
A new analysis of impact-created “tektites” points to a powerful collision millions of years ago that hurled debris across southern Australia. Scientists are still looking for the impact crater.
Tektites are naturally formed glasses created when meteorites crash into Earth, throwing melted surface rock in all directions. Most tektites come from one of five major splash zones, including one that spread debris across Australia and southeast Asia nearly 800,000 years ago.
In 1969, researchers studied tektites from this Australasian field. Most of the glasses had similar compositions, but a few appeared older and chemically different from the rest. A 1999 study found that the odd tektites were several million years old — but there was considerable wiggle room in previous estimates, and there wasn’t enough information to determine whether the strange rocks had formed in a different major impact.
Now, in a new study published Aug. 29 in the journal Earth and Planetary Science Letters, scientists measured the densities and magnetic properties of several thousand tektites in the South Australian Museum’s collection, gathered from that region. They brought 417 unusual samples to France where, after further examination, they identified six tektites that had the same chemical makeup as the anomalous tektites that had been studied decades ago.
The team determined that the tektites were different enough in both age and composition from most of the other tektites in the region that they were most likely not formed in the impact that created the Australasian tektite field. Instead, they could be from a previously unidentified impact that occurred nearly 11 million years ago.
“These tiny pieces of glass are like little time capsules from deep in our planet’s history,” Jourdan said.
The team dubbed tektites from this ancient impact “ananguites.” Some of the tektites landed in areas home to the Pitjantjatjara and Yankunytjatjara people, who refer to themselves as Anangu, meaning “human being,” the researchers wrote in the study.
“What makes the discovery even more intriguing is that, although the impact must have been immense, scientists are yet to locate the crater,” Jourdan said. While there aren’t any known craters of the appropriate age nearby, the team proposed some possible sites in the Philippines, Indonesia and Papua New Guinea. In volcanically active areas like Papua New Guinea, the impact crater might have been mistaken for a volcanic feature, or it may have been obscured over the years.
The findings could give scientists a better idea of how often Earth undergoes extreme impacts and could indicate that impacts large enough to produce tektites are more common than previously thought.
“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,” Jourdan said.