Scientists Identify Crater Associated with Dinosaur Extinction (Great Events: 1900-2001)
Article abstract: Geologists discovered a huge crater, probably formed by the collision of an asteroid or comet, that may have played a key part in the extinction of the dinosaurs.
Death of the Dinosaurs
The extinction of dinosaurs about sixty-five million years ago has intrigued and challenged scientists ever since the first dinosaur fossils were discovered. Several hypotheses have been proposed to explain their disappearance. In 1980, Walter Alvarez and his coauthors suggested a new, interesting, and somewhat worrisome hypothesis—that the dinosaur extinction occurred as a result of a collision between the earth and an asteroid approximately six miles (ten kilometers) in diameter.
Models suggested that such an impact should have blasted out a crater at least 120 miles (200 kilometers) in diameter. According to the theory, the dust thrown into the atmosphere surrounded the earth for months, reflecting large amounts of sunlight. The earth cooled, and photosynthesis by plants was reduced. All animals depend on the food produced by photosynthesis, because they either eat plants or eat plant-eating animals. As a result of these and other disturbances caused by the impact, dinosaurs became extinct.
Evidence for the hypothesis centered on the Alvarez team’s discovery of a sixty-five-million-year-old layer of clay that was rich in iridium. Iridium is rare in the earth’s crust but is common in...
(The entire section is 988 words.)
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