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Dinos bite the dust.


Approximately 65 million years ago, dinosaurs and most other species suddenly became extinct. Some scientists have theorized that a single, large asteroid may have hit the Yucatan Peninsula in present-day Mexico, sparking the die-off. Another theory blames multiple asteroid impacts for the mass extinction mass extinction, the extinction of a large percentage of the earth's species, opening ecological niches for other species to fill. There have been at least ten such events. The five greatest were those of the final Ordovician period (approximately 435 million years ago), the late Devonian period (357 million years ago), the final Permian period (250 million years ago), the late Triassic period (198 million years ago), and the final Cretaceous. Which is correct? New evidence suggests it was indeed one hit that did in the dinos.

Ken MacLeod John James Rickard 1876-1935.
British physiologist. He shared a 1923 Nobel Prize for the discovery and successful clinical application of insulin.
, a geologist at the University of Missouri, was part of a drilling expedition in the Atlantic Ocean that collected the evidence. Roughly 4,500 kilometers (2,800 miles) from the Yucatan Peninsula, the team collected sediment samples from deep beneath the seafloor. If evidence of many asteroid impacts existed, it would be scattered throughout multiple sediment layers. Instead scientists found only one layer loaded with elements common in space rocks. The conclusion: a single impact.

How could one asteroid cause such widespread destruction? Upon slamming into Earth, the massive space rock could have sent dirt flying into the atmosphere. This would have blocked sunlight and killed off the food source of many dinosaurs--plants. "It sometimes seems harder to explain how anything survived [the impact] rather than how so much died," says MacLeod.

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Title Annotation:GRAPH IT/METEORITES
Author:Hennessey, Gail
Publication:Science World
Date:Feb 5, 2007
Words:196
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