Ancient Impact in Brazil: Newly Found Tektites Reveal 6.3 Million-Year-Old Cosmic Collision

Hundreds of pebble-like glass fragments discovered in Brazil are compelling evidence of an ancient cosmic collision that occurred roughly 6 million years ago. These objects, dubbed “geraisites” after the Brazilian state of Minas Gerais where they were first identified, represent spray from rock melted by the impact of a meteorite. While the discovery adds to our understanding of Earth’s impact history, the location of the actual impact crater remains a mystery.

The unusual finds began with a local resident of Minas Gerais who noticed the strange glass beads and contacted meteorite expert Gabriel Silva at the University of São Paulo. Initial skepticism – due to the availability of similar-looking materials for sale online – quickly gave way to investigation when a second report came from a resident 60 kilometers away. Subsequent fieldwork and analysis confirmed the objects were, in fact, tektites, formed from terrestrial material ejected during a high-energy impact event. More than 600 of these tektites have now been found, spanning a region that has since expanded to over 900 kilometers across Minas Gerais, Bahia, and Piauí.

What are Tektites and Why are They Rare?

Tektites are naturally occurring glass objects formed from terrestrial debris ejected during meteorite impacts. As explained by the Australian Museum, they are created when a meteorite strikes Earth with enough force to melt rock. This molten material is thrown into the atmosphere, cools rapidly, and solidifies into pebble-like shapes. The resulting spread of tektites is known as a strewn field.

Geologist Álvaro Penteado Crósta of the University of Campinas, Brazil, expressed his surprise at the discovery, noting to ScienceAlert, “Tektites are a very rare material on Earth.” Their rarity stems from two primary factors: the infrequency of large impact events and the relatively short lifespan of tektites themselves. These glassy objects degrade over geological timescales, lasting only a few tens of millions of years at most.

Unlocking the Past: Composition and Age

Confirming the impact origin of the geraisites involved a detailed analysis of their composition, particularly their water content. Volcanic glasses, like obsidian, typically contain a significant amount of water – between 700 parts per million and 2 percent. However, the geraisites contained a remarkably low water concentration, ranging from 71 to 107 parts per million. This near-total absence of water is a key indicator of an impact origin, as the extreme heat generated during an impact effectively boils off almost all moisture from the melted rock.

Dating the tektites using argon isotope analysis revealed a maximum age of approximately 6.3 million years. This dating provides a timeframe for the impact event. Further chemical and isotopic analysis revealed that the source material for the melted rock was ancient continental crust, specifically granitic rocks from the São Francisco Craton, one of the oldest and most stable geological regions in South America. Remarkably, the rocks that were vaporized by the impact were already around 3 billion years ancient when the meteorite struck, dating back to the Mesoarchean era – a time when Earth was less than half its current age.

The Missing Crater: A Common Challenge

Despite the compelling evidence of an impact event, the corresponding crater has yet to be identified. This isn’t unusual. Only three of the known tektite strewn fields have a clearly identified crater associated with them. The largest, the Australasian strewn field, is believed to have originated from a crater buried deep under the ocean.

Earth’s dynamic geological processes – including plate tectonics, erosion, and sedimentation – gradually wear away or obscure evidence of past impacts. As ScienceAlert reported in February 2026, even identifying ancient craters can be a challenge, as demonstrated by the recent discovery of a 1.6 billion-year-old impact crater in Australia.

Implications for Earth’s Impact Record

The discovery of the geraisite strewn field fills a significant gap in Brazil’s impact record and suggests that tektites may be more common than previously thought, but are often misidentified as other types of glass. Researchers are now working to refine their understanding of the impact event by reverse-engineering its properties, taking into account the expanding size of the strewn field. This data will aid to calculate the energy, velocity, and volume of molten rock involved.

The research team believes this discovery has broader implications for understanding Earth’s overall impact history. As Crósta and his team write in their paper published in Geology, the findings “hint that there might be other still undiscovered tektite occurrences with distinct origins, chemical compositions, and ages.”

Future Research and Ongoing Investigation

The search for the impact crater continues, guided by the characteristics of the geraisite strewn field and the ancient source rock. Researchers are employing geophysical techniques and remote sensing data to identify potential subsurface structures that could represent the buried crater. Further analysis of the tektites themselves, including detailed geochemical and isotopic studies, will provide additional clues about the nature of the impactor and the conditions at the impact site. The team too plans to continue surveying the surrounding regions in Brazil, hoping to uncover additional tektites and further delineate the extent of the strewn field.