A corridor of 75 kilometers in the Atacama Desert, northern Chile, is littered with deposits of dark silicate glass. New research has shown that these glasses were probably formed by the heat from an ancient comet exploding over the surface. Credit: P.H. Schultz/Brown University
A large area of the Atacama Desert, Chile, was scorched by heat around 12,000 years ago. This intense heat transformed the sandy soil into massive slabs of silicate glasses. A research team has now come to an agreement about the cause of the inferno by studying the distribution and composition these glasses.
Researchers published their findings in the journal Geology. They found that desert glass samples contain small fragments of minerals commonly found in rocks from extraterrestrial origin. These minerals are very similar to the material collected by NASA's Stardust mission from Wild 2, which samples particles from the comet. They believe that these mineral assemblages may be remnants of an extraterrestrial object, most likely a comet that streamed down from the explosion that destroyed the sandy surface below.
"This is the first evidence that we have of glasses created by thermal radiation and winds from an exploding fireball just above the surface," stated Pete Schultz, a Brown University professor emeritus. This was a massive explosion that had such an impact on such a vast area. Many of us have seen fireballs from bolides streaking across the sky. But those are small blips in comparison to this.
These glasses are found in scattered areas in the Atacama Desert east from Pampa del Tamarugal. This plateau is located in northern Chile, between the Andes Mountains and the Chilean Coastal Range. Within a corridor of approximately 75 km, there are fields of black or dark green glass. Schultz claims that there is no evidence that these glasses were created by volcanic activity. This leaves the question of their origin.
Researchers have suggested that the glass was formed by ancient grass fires as the area wasn't always deserted. There were many oases of trees and grassy wetlands in the Pleistocene period. It is possible that large fires could have melted the sandy soil to make large glassy slabs.
A corridor of 75 kilometers in northern Chile's Atacama Desert is littered with deposits of dark silicate glass. New research has shown that these glasses were probably formed by the heat from an ancient comet exploding over the surface. Credit: P.H. Schultz/Brown University
The new research revealed that simple fires are impossible to form due to the glass content and other key characteristics. These glasses are evidence that they were twisted, folded and rolled while still in their molten state. This is consistent with an incoming meteor or airburst explosion that would have been accompanied tornado-force winds. Schultz states that the mineralogy of this glass casts doubt on the grassfire theory. Schultz and his colleagues conducted a chemical analysis on dozens of samples from different glass deposits in the region, along with researchers from Chile's Universidad Santo Toms and Georgia's Fernbank Science Center.
An analysis revealed that minerals called zircons had been thermally decomposed and formed baddeleyite. Schultz states that this mineral transition occurs at temperatures exceeding 3,000 F.
Researchers also discovered assemblages that are only found in meteorites or other extraterrestrial rock, according to the analysis. Specific minerals like cubanite, troilite and calcium-aluminum-rich inclusions matched mineral signatures from comet samples retrieved from NASA's Stardust mission.
Scott Harris, a co-author of the study and a Fernbank Science Center planetary geologist, said that those minerals tell us that the object bears all the hallmarks of a Comet. "Seeing the same mineralogy in these glasses that we saw in Stardust samples is strong evidence that we are seeing the result of a cometary explosion is very powerful."
Schultz states that more research is needed to determine the exact age of the glass. This would help to pinpoint the time and date. The tentative dating shows that the impact occurred around the time large mammals vanished from the area.
Analyses of the glass samples showed that there was a consistent mineralogy with cometary origin. Credit: P.H. Schultz/Brown University
Schultz stated that although it was too early to determine if there was any causality, we can confirm that the event occurred around the same time we believe the megafauna vanished. There is also the possibility that early inhabitants of the area witnessed this. It would have been quite the spectacle.
Schultz and his colleagues hope further research will help to determine the timing of the event and reveal the impactor's size. Schultz hopes that this study will help researchers find similar blast sites and expose the risk associated with such events.
Schultz stated that although there may be many blast scars, we don't have enough evidence to prove they are related to airburst events. "I believe this site will serve as a template for improving our impact models and help us to identify similar sites in other places."
Sebastian Perroud and Nicolas Blanco were also authors.
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More information: Peter H. Schultz and colleagues, Widespread glasses created by cometary fireworks during the late Pleistocene at the Atacama desert, Chile, Geology (2021). Information from the Journal: Geology Peter H. Schultz and colleagues, Widespread glasses created by cometary fireballs in the Atacama Desert (Chile),(2021). DOI: 10.130/G49426.1