Scientists Discover Rare Tektite Field Dating Back 6.3 Million Years
For the first time, scientists have found a vast field of tektites in Brazil. These glassy fragments formed when a massive asteroid struck Earth about 6.3 million years ago. Researchers named them “geraisites” after Minas Gerais, where they first appeared.The discovery fills a major gap in South America’s impact record. Previously, only five major tektite fields existed worldwide. Now Brazil joins this exclusive group.
What Are Geraisites?
Geraisites are dark, aerodynamic glass droplets. They stretch across more than 900 kilometers of Brazilian terrain. Under strong light, they turn translucent with a grayish-green color.Their surfaces have tiny pits and cavities. “These small cavities are traces of gas bubbles that escaped during rapid cooling,” explains geologist Álvaro Penteado Crósta from the State University of Campinas.The fragments vary greatly in size. Some weigh less than 1 gram, while others reach 85 grams. They form shapes like spheres, ellipsoids, droplets, and even dumbbells.
How Scientists Confirmed Their Origin
Laboratory tests provided crucial evidence. The glass contains high silica levels between 70% and 73%. It also has very low water content—only 71 to 107 parts per million.For comparison, volcanic glass like obsidian holds 700 to 20,000 ppm water. This extreme dryness confirms an impact origin rather than a volcanic one.Researchers also found lechatelierite, a glass that forms only under intense heat. This finding further supports the asteroid impact theory.
Dating the Ancient Event
Using argon isotope dating, scientists pinpointed the impact around 6.3 million years ago. This period falls near the end of the Miocene epoch. Three separate age tests produced closely grouped results, confirming a single event.Interestingly, no crater has surfaced yet. However, this isn’t unusual. Only three of the six major tektite fields have confirmed craters. The Australasia field’s crater likely lies beneath the ocean.Isotope evidence points to the São Francisco craton as the impact zone. This region ranks among South America’s oldest and most stable crust areas. Future magnetic surveys might reveal buried crater structures underground.
