Ancient Comet May Have Turned Chilean Desert Into Glass

Ancient Comet May Have Turned Chilean Desert Into Glass
Clods of glass in the Atacama Desert, site of an ancient fireball airburst. (Photo: R. Scott Harris)

Nearly 80 kilometres of the Chilean coast are covered with oblong fragments of desert glass that researchers who recently studied them say came from a comet’s explosion over the Atacama Desert about 12,000 years ago.

The explosion was what’s called an airburst, which can happen when an object like a meteor or comet falls to Earth. These objects heat up due to friction with our planet’s atmosphere. While some burn up entirely in the atmosphere, other objects explode when they come in contact with thicker parts of the atmosphere. They can cause ground temperatures to be as hot as the Sun, with beyond-hurricane-force winds.

Such was the case for a comet that fell to Earth during the late Pleistocene, according to the team of researchers who studied the composition of the silicate glasses littered about Chile’s Atacama. They found the fireball’s explosion caused bits of space rock to fuse with the molten soils below, forming glasses. Their results were published this week in Geology.

“The Atacama is perfect for preserving the record,” Peter Schultz, a planetary geologist at Brown University, told Gizmodo in an email. “The difference between other glasses across the Atacama and these glasses is that our glasses are really large and indicate complex interactions between the airburst, heating, and winds.

“In other words, it teaches us about the details of the event for the first time,” Schultz added. “We actually have more glasses in Argentina of much older ages but can show that these were produced by actual collisions.”

Previously, a different team thought that the glasses came from ancient grass fires, long before the area became desert, that burned hot enough to transform the soil. But the recent team suspects an extraterrestrial object is the source of the geological oddity because of the unique mineral constitution and structure of the glasses, which showed evidence of being bent and transformed while still liquid. Those details have been observed in other airburst remnants and wouldn’t look so violent in grassfire glasses.

Furthermore, the team found minerals that come from other space rocks, like troilite and cubanite. Such inclusions are similar to those collected by NASA during the Stardust mission, from dust of the Wild-2 comet in 2004.

​​“Those minerals are what tell us that this object has all the markings of a comet,” said Scott Harris, a planetary geologist at the Fernbank Science Centre and a co-author of the study, in a Brown University release. “To have the same mineralogy we saw in the Stardust samples entrained in these glasses is really powerful evidence that what we’re seeing is the result of a cometary airburst.”

The current age estimate of the airburst remains a work in progress on the testing front. The youngest date estimate, made by another co-author, was about 11,500 years ago. “There’s also a chance that this was actually witnessed by early inhabitants, who had just arrived in the region,” Schultz said in the same release. “It would have been quite a show.”

If not for humans, depending on the timing, one has to pity the doomed giant ground sloths and other megafauna in the area. They would’ve been burned to a crisp in an instant.