Some 12,000 years ago, something seared a vast swath of Chile's Atacama Desert with heat so intense it turned the sandy soil into vast plates of silicate glass. Now, a research team studying the distribution and composition of these glasses has reached a conclusion about the cause of hell.
In a study published in the journal Geology , the researchers show that the desert glass structures contain small fragments with minerals that are usually found in rocks of non-terrestrial origin. Those minerals closely match the composition of the material returned to Earth by the Stardust mission. NASA, which sampled particles from a comet called Wild 2 . The team concludes that these mineral assemblages are likely the remains of an object from space - most likely a comet with a composition similar to that of Wild 2. – which descended after the explosion melted the sandy surface below.
This is the first time we have clear evidence of glass on Earth that was created by thermal radiation and winds from a fireball that exploded just above the surface said Pete Schultz, professor emeritus in the Department of Earth, Environmental and Planetary Sciences at Brown University. To have such a dramatic effect over such a large area, this was a truly massive explosion. Many of us have seen fireballs streaking across the sky, but those are tiny flashes compared to this .
The glasses are concentrated in patches throughout the Atacama Desert, east of the Pampa del Tamarugal, a plateau in northern Chile nestled between the Andes Mountains to the east and the Chilean Coastal Range to the west. Dark green or black glass fields appear in a corridor that stretches about 75 kilometers. According to Schultz, there is no evidence that the glass was created by volcanic activity, so its origin has been a mystery.
Some researchers have posited that the glass originated from ancient grass fires, as the region was not always desert-like. During the Pleistocene, there were oases with trees and grassy wetlands created by rivers spreading from the mountains to the east, and it has been suggested that widespread fires may have burned hot enough to melt the sandy soil into large plates of glass. .
But the amount of glass present along with several key physical characteristics make simple fires an impossible formation mechanism, according to the new research. The glasses show evidence of being twisted, bent, rolled, and even thrown while still molten. This is consistent with the arrival of a large meteor and an airburst, which would have been accompanied by tornado-force winds. The mineralogy of glass casts serious doubt on the fire idea, says Schultz. Together with researchers from Georgia's Fernbank Scientific Center, Chile's Santo Tomás University, and Chile's Geology and Mining Service, Schultz and colleagues conducted a detailed chemical analysis of dozens of samples taken from glass deposits throughout the region. /P>
The analysis found minerals called zircons that had thermally decomposed to form baddeleyite. That mineral transition typically occurs at temperatures above 3,000 degrees Fahrenheit, much hotter than wildfires could generate, says Schultz.
According to the researchers, the analysis also revealed exotic mineral assemblages found only in meteorites and other extraterrestrial rocks. Specific minerals such as cubanite, troilite, and calcium- and aluminum-rich inclusions matched the mineral signatures of cometary samples recovered from the Stardust mission. from NASA.
Those minerals are what tell us that this object has all the markings of a comet said Scott Harris, a planetary geologist at the Fernbank Science Center and a co-author of the study. Having the same mineralogy that we saw in the Stardust samples embedded in these glasses is really powerful evidence that what we're seeing is the result of a cometary explosion in the air.
More work needs to be done to establish the exact ages of the glasses, which would determine exactly when the event took place, says Schultz. But the provisional dating places the impact right at the time when large mammals disappeared from the region.
It's too early to say if there was a causal connection or not, but what we can say is that this event occurred around the same time we think the megafauna disappeared, which is intriguing Schultz said. There is also the possibility that this was witnessed by the first inhabitants, who had just arrived in the region. It would have been quite a show .
Schultz and his team hope that further research can help narrow down the timing and shed light on the comet's size. For now, Schultz hopes this study can help researchers identify similar blast sites elsewhere and reveal the potential risk these events pose.
There may be a lot of these blast scars out there, but so far we haven't had enough evidence to believe they were actually related to airburst events Schultz said. I think this site provides a template to help refine our impact models and will help identify similar sites elsewhere .