Chile’s Atacama Desert is steeped in mysteries. It’s the home of enormous glyphs whose meaning has been lost to the mists of time, and tiny, alien-like skeletons whose stories have only recently been revealed. Its earth is as barren as the soil on Mars – yet simultaneously rich with gold, silver, and some of the most unique ecosystems on the planet.
That’s not the only puzzle strewn across the soil of the Atacama. For years, scientists have wondered about the origins of a vast corridor, about 75 kilometers (46.6 miles) long, filled with shards of black and green glass. Ranging up to 50 centimeters (19.7 inches) across in size, the shards seem oddly twisted into their various shapes by some unknown force. But now, in a new paper published in the journal Geology, researchers think they’ve found the explanation: an exploding cosmic fireball, burning the Atacama with such intensity that the ground was forged into glass.
“This is the first time we have clear evidence of glasses on Earth that were created by the thermal radiation and winds from a fireball exploding just above the surface,” said Pete Schultz, lead author of the paper. “To have such a dramatic effect on such a large area, this was a truly massive explosion.”
“Lots of us have seen bolide [explosive] fireballs streaking across the sky, but those are tiny blips compared to this,” he said.
This isn’t the first suggestion as to what could be responsible for the glass fragments: previous researchers have suggested the culprit might have been ancient grass fires from when the desert was filled with lush vegetation. However, in the new study, the team found a few pieces of evidence that made that impossible.
Firstly, the glass shards' position – plus how their shapes showed evidence of “sliding, shearing, twisting, rolling, and folding (in some cases, more than twice)” while in a molten state – is inconsistent with a grass fire, the paper explains. So too is the sheer volume of glass found: “it would require grass quantities that greatly exceed that available in these desert wetlands” to create such an abundance of glass, the authors write.
Perhaps the most intriguing piece of evidence for the new interplanetary explanation comes from the composition of the shards themselves. Instead of being made up of one type of material, as would be expected if created by a grass fire, the glass matches the makeup of the soil around it – with a few extraterrestrial additions.
“Every sample examined thus far […] contained thousands of exotic mineral grains and rock fragments [...] atypical of the local sediments,” the study notes. Specifically, the team found minerals like cubanite, troilite, and calcium-aluminum-rich inclusions in the glass fragments – a mixture that matches samples brought back by NASA’s comet research mission Stardust.
“Those minerals are what tell us that this object has all the markings of a comet,” said study co-author Scott Harris. “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.”
There’s still much research to be done to uncover more details of the explosion: the size and date of the explosion, for instance, have yet to be pinned down – and estimates the researchers are able to make in this direction only deepen the intrigue.
“It’s too soon to say if there was a causal connection or not, but what we can say is that this event did happen around the same time as when we think the megafauna disappeared, which is intriguing,” Schultz said. “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.”