Story at a glance:
- The Atacama Desert was once a grassland where horses, sloths, and humans coexisted.
- In new research planetary scientist Peter Schultz disproves a theory from 2012 – that intense wildfires created the glassy material discovered in 2012.
- A grass fire could not have burned down sandy soil into a glassy boil, and if it did, the surface of the glass would be smooth.
Some 12,000 years ago, at the end of the Pleistocene era, the now dried-out Atacama Desert was once a grassland where horses, sloths, and humans coexisted — until a comet exploded overhead.
A new paper published in Geology by Brown University professor and planetary scientist Peter Schultz disproves a theory from 2012 – intense wildfires torched the Andes Mountains region land, even melting the underlying soil into the glassy surface on the corridor.
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A team of scientists and Schultz began exploring the possibility of a wildfire that would turn sand into glass, analyzing samples of glass from multiple sites separated by 30 km.
There was not a chance that a grass fire could have burned down the soil into a glassy boil, the team found, and if it did, the surface of the glass would be smooth, not the glass present that “showed signs of shearing, folding, tearing, and rolling.”
The glass looks like it was made because of an explosion that flung molten material from great distances.
“There was a dynamic force that formed them,” Schultz told TIME.
The glassy material also has embedded materials such as iron sulfides known as cubanite and troilite, and a phosphate mineral called chlorapatite.
These materials are often associated with asteroids and comets, and Schultz even found a similar sample of dust and mineral grains from a NASA voyage in 2006.
“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 a cometary airburst,” said co-author Scott Harris, of the Fernbank Science Center, in a statement that accompanied the research.
“There should be more examples,” Harris told TIME. “The difficulty is that such glasses can be easily destroyed with time. In addition, we found that only certain soils—fine dust—will form the glasses.”
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