A study led by researchers at Brown University found that the heat generated by a comet's explosion on the ground fused the sandy soil into 75 kilometers of glass fragments. About 12,000 years ago, something scorched a large swath of land in Chile's Atacama Desert with such heat that it turned sandy soil into a broad silicate glass form. Now, a team of researchers studying the distribution and composition of these glasses has come to a conclusion about what caused this "hellfire."
In a study published in the journal Geology, researchers showed that samples of desert glass contain tiny fragments that are often found in extraterrestrial rocks. The minerals dovetail well with the composition of the material returned to Earth by NASA's Stardust mission, which collected particles from a comet called Wild 2. The team concluded that the combination of minerals was most likely the remains of an extraterrestrial object — most likely a comet with a composition similar to Wild 2 — that flowed down after the explosion, melting the sandy surface below.
The 75-kilometer-long corridor of the Atacama Desert in northern Chile is littered with sediment of dark silicate glass. New research suggests that the glass may have formed from the heat of an ancient comet that exploded above the surface.
Pete Schultz, professor emeritus in Brown University's Department of Earth, Environment and Planetary Sciences, said: "This is the first time we have definitive evidence that glass on Earth is formed by thermal radiation and wind from fireballs that explode above the surface. To have such a huge impact on such a large area is a real mass explosion. Many of us have seen fireballs across the sky, but those fireballs are only a small bright spot compared to this. "
These vitreous bodies are concentrated in the Atacama Desert, east of Pampa del Tamarugal, a plateau in northern Chile, bordered by the Andes to the east and the Chilean Coast Mountains to the west. Dark green or black glass fields appear within a corridor that stretches for about 75 kilometers. Schultz said there is no evidence that the glass may have been produced by volcanic activity, so their origins have remained a mystery.
Some researchers believe that the glass was caused by ancient wildfires because the area wasn't always desert. During the Pleistocene period, there were oases, trees, and grassy wetlands formed by rivers extending from the eastern mountains, and it has been suggested that widespread fires might have burned hot enough to melt the sand into large pieces of glass.
Analysis of the glass samples showed that its mineralogy was consistent with the origin of the comet
But the new study found that the amount of glass, along with several key physical features, made simple fires an impossible formation mechanism. The glass shows evidence of being twisted, folded, rolled, and even thrown when still in a molten state. This is consistent with the arrival of large meteors and air explosions, which seem to accompany the power of tornadoes. Schultz said the mineralogy of the glass raises further doubts about the claim of wildfires. Together with researchers from the Fairbank Science Center in Georgia, the University of Santo Tomas in Chile, and the Chilean Geological and Mining Agency, Schultz and colleagues conducted detailed chemical analysis of dozens of samples extracted from glass deposits across the region.
The analysis uncovered minerals called zircons, which were thermally decomposed to form Badlaisite, a mineral transition that typically occurs at temperatures above 3,000 degrees Fahrenheit, far higher than those produced by wildfires.
The analysis also found a combination of exotic minerals found only in meteorites and other extraterrestrial rocks, the researchers said. Specific minerals, such as calcite, meteoric iron sulfide, and calcium-rich inclusions, match the mineral characteristics of comet samples taken from NASA's Stardust mission.
Scott Harris, a planetary geologist at the Fernbank Science Center and co-author of the study, said: "These minerals tell us that this object has all the hallmarks of a comet, and the same mineralogy we see in the stardust samples is interspersed in these glasses, really strong evidence that what we are seeing is the result of a comet gas burst." "
The researchers will need to do more work next to determine the exact age of these glasses, which will determine the exact time the event occurred. But the tentative age makes this impact exactly when large mammals disappeared from the area.
Schultz and his team hope that further research may help limit time and elucidate the size of the impactor. Hopefully, the study could help researchers identify similar blast sites elsewhere and uncover the potential risks posed by such events.