Scientists have found a fascinating discovery in Brazil—a huge field of tektites, a rare form of natural glass formed from meteorite impacts. This field measures about 560 miles (900 kilometers) and dates back to an enormous impact that happened around 6.3 million years ago. An international team collected around 500 of these new specimens, dubbing them “geraisites,” after the Minas Gerais state where they were found. Before this, only a handful of tektite fields existed on Earth.
The findings were detailed in a recent study published in Geology. These new discoveries help us understand the ancient impact history of South America. However, researchers are still in search of the impact crater that created these tektites.
Understanding Tektites
Tektites are born when large meteorites hit Earth, melting rocks and sending molten material into the atmosphere. As these blobs cool, they take on unique shapes like spheres or droplets before landing back on Earth. Currently, known tektite fields exist across several regions, including the large Australasian field and sites in Central Europe and North America.
Discovery Process
The research began in three municipalities in northern Minas Gerais: Taiobeiras, Curral de Dentro, and São João do Paraíso. Initially, they focused on a 55-mile stretch but later found tektites in Bahia and Piauí, significantly expanding the area. Álvaro Crósta, lead author of the study and a geologist, noted that the size of the field corresponds to the impact energy, which is common in other tektite fields worldwide.
The collected tektites vary in size, ranging from tiny fragments to larger pieces weighing up to 3 ounces (about 85 grams). At first glance, they look black but reveal a grayish-green color when exposed to light. Each tektite type is named based on its discovery location, which is why these are called geraisites.
What Makes Geraisites Unique?
Geraisites are primarily made of silica but have higher concentrations of sodium and potassium oxides compared to other tektites. Researchers also found lechatelierite, a special glassy silica formed by intense heat. One critical feature of tektites is their low water content. While volcanic glass can contain up to 2% water, tektites have significantly lower levels, around 71 to 107 parts per million.
The event that led to the creation of geraisites happened during the Miocene epoch, a time that saw significant biological changes, including the divergence of early hominins from chimpanzees. Despite the clues pointing to a meteorite impact, the actual crater remains elusive. Only three known tektite fields have been linked to confirmed craters, making this a challenging area of study.
Experts suggest that the crater could be in the São Francisco Craton, a geological region in eastern South America. Researchers plan further surveys to explore this area for signs of the ancient impact site.
This new understanding of geraisites not only enriches our knowledge of Earth’s impact history but also opens up questions about the geological processes that shape our planet. As scientists continue their work, each finding adds to the intriguing story of Earth’s interactions with the cosmos.
For further reading, you can access the original study here.
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