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The research published in Science 9 May, is based on analysis of fossil meteorites found in ancient limestone from five Swedish quarries located up to 500 kilometres apart. The limestone formed over two million years, 480 million years ago, sealing meteorites in to a geological time capsule. Investigations in to the fossils revealed trace minerals from disintegrated meteorites, resulting from a cosmic collision.
Meteorite activity on the Earth is relatively uniform at present with an average of about one meteorite falling every 12 500 square kilometres per year. The new research shows that during the formation of the limestone, meteorite activity would have been 100 times what it is today. Most of the meteorites originate from an asteroid that broke apart 500 million years ago in the largest collision that occurred in relatively recent solar system history.
Around 20 per cent of the meteorites that land on Earth come from this asteroid break up, these are called L-chondrites. The scientists from Rice University in Gothenburg, Sweden, looked for the mineral chromite, which is only found in L-chondrites. They found that the fossil meteorites came from this asteroid break up and meteorites from each quarry matched the concentration of chromite, indicating the activity rate was the same over the entire area.
The scientists were only alerted to the fossil meteorites when quarry workers found them on a regular basis. Until the scientist joined the workers the meteorites were discarded as they blemished the quality of the limestone. It is believed that similar meteorites will be present worldwide in limestone that formed during this period. The scientists have recently obtained funding to continue their study in Chinese and South American sites.
More info: Rice University
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