Word: cometted
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...town of Chicxulub, on the northern tip of Mexico's Yucatan Peninsula, and extending out under the Gulf of Mexico. The nature of the basin, its location and a preliminary estimate of its age suggest that it is the Crater, the one gouged into the earth by the comet or asteroid that killed the dinosaurs...
...Alvarezes analyzed this clay in the late 1970s and showed it had a far higher content of the rare element iridium than ordinarily found in the earth's crust. It was this discovery that led Luis Alvarez to his momentous - insight. Comets and asteroids have high iridium content, he reasoned, and the clay layer could have been formed by the worldwide fallout of the material vaporized when an errant asteroid or, as most scientists now suspect, a giant comet smacked into the earth...
...evidence mounts, more researchers are convinced that the Chicxulub crater marks the impact point of the killer comet. Says Boynton: "This is nearly as close to a certainty as one can get in science." Some scientists disagree. David Archibald, a biologist at San Diego State University, believes the extinctions took place more gradually and in a complex pattern. "There is zero evidence that dinosaurs became extinct virtually overnight...
...Shoemaker and his colleagues see it, a giant comet broke apart as it whipped around the sun. Over time, chunks of the comet separated but remained strung out in the same orbit. Then 65 million years ago, as the earth passed through the comet's orbit, it collided with the largest chunk, causing the Great Extinction. Perhaps only a year or two later, as the earth again entered the trail of cometary debris, it met a second, smaller chunk. Where did the second impact occur? This time no search is necessary. Shoemaker points to a well-known crater...
...What are the chances that much of life could once again be snuffed out by a collision with an icy comet? Rather small, but there are plenty of asteroids in the heavens capable of causing devastation. Astronomers have identified more than 130 asteroids whose paths could intersect earth's orbit. Consisting largely of rock or iron, some are over a mile wide and could ram the earth at 65,000 km (40,000 miles) per hour. The odds of a strike within the next 50 years are probably less than one in 10,000. But whenever it does happen...