Ancient and Asteroid: Unique Twin Meteorite Impacts Found in Sweden

Twin craters in a county in Sweden have been found to be the remnants of ancient simultaneous meteorite collisions that took place about 460 million years ago, say University of Gothenburg researchers. The impacts, one very large and the other about a tenth of the size, were found in the Swedish county of Jämtland. These were not the only meteorites that landed on Earth during this time.

"Around 470 million years ago, two large asteroids collided in the asteroid belt between Mars and Jupiter, and many fragments were thrown off in new orbits. Many of these crashed on Earth, such as these two in Jämtland," Erik Sturkell, professor in the University of Gothenburg's Department of Earth Sciences, said in a news release.

During this period, Jämtland was under about 500 meters of water in that area. The impact forced the surrounding water away for a short time, during which the craters were completely dry. Sturkell explained that when the water rushed back in, it brought meteorite fragments with it and caused large sea waves. Double impacts are very unusual, and this is the first one that has been proved to land on Earth.

"Information from drilling operations demonstrates that identical sequences are present in the two craters, and the sediment above the impact sequences is of the same age. In other words, these are simultaneous impacts," Sturkell explained in the release. 

According to this study, other locations in Sweden have also experienced meteorite impacts. Over the past 15 years, there have been roughly 90 meteorites from impacts found on Kinnekulle, which is a ridge in the province of Västergötland.

"In the 1940s, an unusual-looking red limestone slab was found in a quarry. A few years later, researchers understood that there was a meteorite in the slab. Large meteors explode and disintegrate almost completely, while small meteors fall as rocks, such as in this limestone," Sturkell said in a statement. "Small meteorites survive the fall, while large ones explode and disintegrate. In Jämtland we have only found minerals from the meteorites, small grains of chromite."

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