Regen van Meteorieten in het Ordovicium, 480 Ma geleden. Wat zijn de gevolgen van deze regen voor de evolutie (if any)??
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Regen van Meteorieten in het Ordovicium, 480 Ma geleden. Wat zijn de gevolgen van deze regen voor de evolutie (if any)?? |
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METEORITES LINKED TO COLLISION Geologists have found new meteorite evidence to support the theory that a collision in the asteroid belt between Mars and Jupiter rained debris on Earth some 500 million years ago, according to a press release issued by Rice University. Meteorites encased in limestone deposits that formed about 480 million years ago in what now is southern Sweden provided the evidence, according to the scientists who conducted the study. Their study, based on samples collected from five quarries, found a 100-fold increase in meteorite activity during the period when the limestone was forming, and that the level of activity was consistent over a 250,000 square kilometer area. The meteorites contained a unique form of chromite that is associated with the breakup of a minor planet known as the L-Chromite parent body. The collision was previously theorized based on other meteorite evidence, but the new research significantly bolsters the hypothesis, according to Birger Schmitz, a visiting professor at Rice and a professor of marine geology at Goteborg University in Sweden. The previous evidence "was quite weak," Schmitz, the lead researcher on the project, said in an interview. About 20 percent of the meteorites found on Earth are from this asteroid, the geologists said. "What we are doing is astronomy, but instead of looking up at the stars, we are looking down into the Earth," Schmitz said in a statement. The research was sponsored by the National Geographic Society and the Swedish Research Council. The findings were first reported in the May 9 issue of Science magazine. |
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http://www.space.com/spacenews/archive03/splogsarch_052803.html |
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Signs Of Spectacular Asteroid Collision Unearthed
A new study of meteor fossils has revealed signs of a colossal asteroid collision that lit the night skies of ancient Earth with shooting stars. Marine geologist Birger Schmitz and colleagues at the Earth Sciences Center in Goteborg, Sweden, sampled ancient marine sediments in five Swedish quarries located in a 250,000-square-meter area. They then analyzed the sediments for traces of the mineral chromite. The presence of chromite indicates origins in a massive asteroid known as the L-chondrite parent body, which is thought to have exploded about 460 million years ago. The researchers identified 40 fossilized meteorites which likely originated from the explosion. Meteorites were present in every quarry, and were found in uniform concentrations, suggesting a constant impact rate over the entire area. The sediments in which the meteorites were found were laid down over a period of about two million years. The researchers report in the journal Science that meteorite bombardment during this period was about 100 times greater than is seen today. This spike in meteor activity coincides with evidence in similarly-aged sediments from the moon.http://www.calacademy.org/thisweek/archive/This%20Week%202003/20030514.html |
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http://www.geolsoc.org.uk/template.cfm?name=Schmitz387534 |
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