They first came to the attention of scientists about a decade ago: a mysterious field of glass fragments, scattered across Chile’s Atacama Desert, and located in a large corridor that stretches 75 kilometers long (almost 50 miles).
These strange pieces of glass, which are too numerous to count, are collected in a number of places along the desert corridor, and they assume a number of shapes, some occurring in large plates up to 50 centimeters (20 inches) across.
They have both rough and smooth features and look as if they have somehow been folded and twisted to their current shapes, scientists say.
“Many have morphologies that indicate slipping, displacement, twisting, rolling and folding (in some cases more than twice) before they are completely extinguished,” explains researchers in a new study analyzing the glass, led by first author and planetary geologist Peter Schultz, Professor Emeritus at Brown University, Rhode Island.
Whatever it was that triggered these violent, messy transformations about 12,000 years ago has never been fully understood.
An early hypothesis suggested that they could be the result of a large meteor that exploded in the atmosphere – a giant eruption that throws fragments of hot, burning space rock onto the desert surface, where the extraterrestrial shrapnel melts the sand and earth on the spot.
It’s not as far out as it immediately sounds. Mysterious glass remnants like this have been found in several places across the planet, and in many cases meteoric explosions or impacts are taken as the most likely explanations for how the glass got there.
Not that space stone is the only hypothetical argument to consider. In the case of Atacama’s shards of glass, scientists have also suggested that they could have been formed in the furnace by natural surface fires in another age and climate, where the desert was covered in more abundant vegetation.
So what is it? According to Schultz and colleagues, the extraterrestrial space stone hypothesis is actually the more likely explanation here.
In the new study, the researchers collected and studied over 300 samples of the desert glass, examined them under an electron microscope and analyzed their chemical composition through spectroscopy.
The results, the team says, unequivocally suggest that the glass is not entirely of this planet.
“This is the first time we have clear evidence of glasses on Earth created by the thermal radiation and wind from a fireball that explodes just above the surface,” says Schultz.
According to the researchers, minerals in the glass called zircons were decomposed and formed the mineral baddeleyit, which would have required extremely hot temperatures above 1,670 ° C, which is far hotter than a natural fire.
But that’s not all. The glass fragments also contained thousands of exotic mineral grains, of a kind rarely seen on Earth; so rare in fact that they are only known to occur in meteorites and other extraterrestrial rocks.
Some of these strange minerals, including extraterrestrial cubanite, were previously identified by NASA’s Stardust mission, which collected samples from comet Wild 2 in 2004.
It’s too early to say for sure, but whatever the long-lost object was that created these strange glass fields in the Atacama Desert, it could have had some sort of relation to Wild 2, at least in terms of its composition.
Another coincidence that should be investigated further is that the timing of this air eruption largely overlaps with the disappearance of Quaternary megafauna in South America, which in itself coincided with both the arrival of ancient hunter-gatherers in the area and changes in the climate.
As to whether the meteoric air eruption may have had anything to do with that extinction, it is not yet clear.
“It’s too early to say whether there was a causal link or not,” Schultz says. “But what we can say is that this event took place around the same time as when we think the megafauna disappeared, which is exciting.”
The results are reported in Geology.