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Two Asteroids Collided, Showered Earth with Debris
By Robert Roy Britt
Senior Science Writer
posted: 02:36 pm ET
08 May 2003
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Scientists have found evidence on Earth for an ancient asteroid collision in space that appears to have generated a modest rain of fire on the planet for a few million years Scientists have found evidence on Earth for an ancient asteroid collision in space that appears to have generated a modest rain of fire on the planet for a few million years. The explosive collision might have been one of the largest in the solar system's recent history, the researchers say, involving two space rocks each up to 620 miles wide (1,000 kilometers). Asteroid collisions were once common in the solar system. They are less frequent now, but still occur in a region between Mars and Jupiter known as the asteroid belt, where most of these leftovers from planet formation orbit the Sun. In ancient marine sediments across a large swath of southern Sweden, researchers found sand-sized grains of the mineral chromite that are low in iron, a sign of extraterrestrial origin. The stuff appears to have fallen from the sky about 480 million years ago. Based on the number and size of the grains, the scientists determined that bright fireballs would have graced Earth's skies about 100 times more often than occurs today, said lead researcher Birger Schmitz at Göteborg University in Sweden. A small fraction of the fragments fell to the ground over a period of 5 million to 10 million years, Schmitz told SPACE.com via e-mail. When large asteroids strike Earth directly, mass extinctions can result, experts believe. But that's probably not what happened with this slow shower of debris. "We see prominent changes in the biota in the sections that we study," Schmitz said, "but there is no mass extinction." The biological shifts evident in the soil are due to environmental change, he said, but it's not clear if the asteroid collision was behind the environmental change or not. Another Recent Asteroid Collision More Asteroid News Space Photo Galleries & Wallpaper
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