Across a 75 kilometer stretch of the Atacama Desert in Chile, huge rocks of black and green glass can be found lying around. Researchers picked up on this unusual phenomenon around a decade ago, but they were stumped by this mystery with no reasonable explanation to be found, until now.

A team from Brown University finally has a reasonable hypothesis for the spew of glass: the explosion of a comet that entered Earth’s atmosphere around 12,000 years ago. Analysis of the space dust entangled in the glass allowed this estimation to be made, as extraterrestrial particles were being identified in its midst. Thanks to NASA’s Stardust mission, we know minerals like cubanite, troilite, and calcium-aluminum-rich inclusions are signs of a comet. The glass actually formed around these particles due to the high temperature and pressure of the sand which occurred on impact.

This realization has scientists excited, as it is the best evidence of a comet impact site that is known so far on Earth. There are other indentations on the planet from falling space rocks. However, contact with a comet is much rarer due to the fact they are made from mainly rock and ice which usually explodes before reaching the ground.

The lack of crater at this site means an ‘airburst’ occurred here. This is basically a huge explosion where its contents are scattered over a long distance due to the violent impact, hence the long patch of glassy desert. An airburst also gives an explanation to the twisted state of the glass, with the co-author of the paper, Peter Schultz, describing its shape as “kneaded bread.”

At the time of this explosion, archeological evidence shows humans would have lived in the area. “There’s also a chance that this was actually witnessed by early inhabitants, who had just arrived in the region. It would have been quite a show. It would have seemed like the entire horizon was on fire,” said Schultz.

This study published in Geology confirming the comet impact site could open up the door to understanding other airbursts over the globe. “There may be lots of these blast scars out there, but until now we haven’t had enough evidence to make us believe they were truly related to airburst events,” Schultz stated. “I think this site provides a template to help refine our impact models and will help to identify similar sites elsewhere.”

Source study: Geology – Widespread glasses generated by cometary fireballs during the late Pleistocene in the Atacama Desert, Chile