Scientists have uncovered new evidence of a large asteroid impact on Earth approximately 6.3 million years ago. The remnants of this cosmic event were discovered in the form of naturally occurring glass fragments scattered across Brazil.
These glass fragments are known as tektites, materials created when an asteroid strikes the Earth’s surface with immense energy. The impact melts the rock at the point of collision, and the resulting molten material is ejected into the atmosphere before cooling and falling back to the surface.
Recent research has identified a new type of tektite, named geraisites, after the Minas Gerais region of Brazil where the fragments were first found. This discovery offers further insight into the history of asteroid impacts and their geological consequences.
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The research was led by Álvaro Penteado Crósta, a geology professor at the Institute of Geosciences at the State University of Campinas (UNICAMP) in Brazil. Crósta explained that the glass fragments are more widespread than previously thought.
Initially, geraisites were found in only three locations within Minas Gerais. However, further investigation revealed similar fragments in other states, including Bahia and Piauí. Researchers now estimate the dispersal area exceeds 900 kilometers.
“This growth in the dispersal area is fully consistent with what is observed in other tektite fields around the world. The size of the field is highly dependent on the energy of the impact,” Crósta stated, according to Science Daily.
Geraisites appear as opaque black glass, but become translucent with a greenish-gray hue when exposed to strong light. Their shapes vary, ranging from spherical and elongated to resembling liquid droplets. These forms provide clues about their formation.
As the molten rock material was ejected into the atmosphere during the asteroid impact, it moved rapidly while rotating in the air before cooling and solidifying. This process created the tektites’ characteristic aerodynamic shapes.
Crósta also noted the presence of small cavities on the surface of the fragments. These cavities formed as gases escaped from the molten material during rapid cooling in the atmosphere.
“These small cavities are traces of gas bubbles escaping as the molten material cooled quickly in the atmosphere,” he explained.
Laboratory analysis also indicates that geraisites have a high silica content and very low water levels – hallmarks of tektites formed by high-energy celestial impacts.
Despite strong evidence of the asteroid impact, scientists have yet to locate the impact crater that created the geraisites. This isn’t unusual; the source craters remain undiscovered for several tektite fields globally.
Researchers suspect the crater may be located within the São Francisco Craton, one of the oldest continental crust regions in South America. Isotope analysis of the tektite samples suggests the source rock was likely from very vintage continental granite.
“Isotopic signatures point to a source of very old continental granite rocks. This significantly narrows the potential area for the impact location,” Crósta said.
Future research will employ geophysical survey methods, such as magnetic and gravity analysis, to search for circular structures beneath the ground that could be remnants of the asteroid crater.
The discovery of geraisites adds to the growing body of evidence suggesting that the history of asteroid impacts on Earth may be more complex than previously understood. Many impact traces likely remain unidentified, particularly in vast and under-explored regions.
(rns/rns)
