Scientists first noticed them a decade ago. A strange field of glass fragments scattered across Chile's Atacama Desert and aligned in a large corridor that stretches 75 km (almost 50 miles).
These odd pieces of glass are scattered along the desert corridor in many different locations. They take many forms, including large slabs measuring up to 50 cm (20 inches) in size.
Scientists say they have rough and smooth features and appear to be twisted or folded into their current form.
Researchers have discovered that many glass morphologies are indicative of sliding and shearing, twisting and rolling before being fully quenched. This is according to Peter Schultz (emeritus professor at Brown University in Rhode Island).
We don't know what caused these chaotic, violent transformations around 12,000 years ago.
Exemplaires of desert glass in situ (Schultz et al., Geology, 2021)
One early theory suggested that they might be caused by a meteor striking the atmosphere. This would have created a huge airburst, launching pieces of fiery space rock into the desert surface. The extra-terrestrial shrapnel then melted the soil and sand.
This is not as impossible as it seems. These mysterious glass remnants have been discovered in many locations around the globe. In many cases, meteoric impacts or explosions are the most probable explanations for how the glass got there.
Space rocks are not the only argument worth considering. Scientists have suggested that Atacama's glass fragments could have been formed in the furnace natural surface fires. This would have occurred in a different climate and age than when the desert was covered with more vegetation.
Five desert sites featuring glass deposits. (Schultz et al., Geology, 2021)
Which explanation is it? Schultz and his colleagues believe that the extra-terrestrial, space rock hypothesis is the most likely explanation.
The researchers took 300 desert glass samples and examined them under an electron microscope. They also analysed their chemical composition using spectroscopy.
According to the team, the results clearly indicate that the glass is not entirely of this planet.
Schultz states that this is the first time that we have any evidence of glasses being formed by thermal radiation or winds from an exploding fireball just above the surface.
Researchers believe that minerals found in glass called zircons have decomposed to create the mineral baddeleyite. This would have required extreme heat of over 1,670 C which is much hotter than a wildfire.
Get a close look at desert glass samples. (Schultz et al., Geology, 2021)
This is not all. These glass fragments contained thousands of rare mineral grains that are rarely found on Earth. They were also found in meteorites and other extraterrestrial rock.
These strange minerals include extraterrestrial cubanite. They were identified previously by NASA's Stardust mission in 2004, which took samples from Comet Wild 2 in 2004.
Although it's too soon to know for certain, whatever the object that created the strange glass fields in the Atacama desert, it may have had some connection to Wild 2, at the very least in terms its composition.
A second coincidence worth further investigation is the fact that this airburst's timing coincides with the disappearance in South America of Quaternary megafauna. This was also the time of the arrival of the ancient hunter-gatherers and climate changes.
Glass contains extraterrestrial minerals. (Schultz et al., Geology, 2021)
It's still not clear if the meteoric aeroburst played any role in that extinction.
Schultz states that it is too early to determine if there was any causality. "But we can confirm that the event occurred around the same time we believe the megafauna vanished, which is quite intriguing."
These findings were published in Geology.
