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from Our World October 20, 2003
The Great Dinosaur Mystery
by Edward Leete
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In 1841 the British scientist Robert Owen introduced the word dinosaur into the English language by combining the Greek words for "terrible" and "lizard." He used it to describe large bone fossils that had been discovered in southern England. Before this discovery, scientists had no idea that enormous reptiles once existed. Since the nineteenth century, more than one thousand species of dinosaurs have been identified. Dinosaur fossils have been found on every continent. Yet scientists still do not know what made the dinosaurs disappear. How could such massive creatures have simply vanished from the planet?
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Dinosaurs are believed to have roamed Earth for about 160 million years. Various types and sizes of dinosaurs lived during this period. Then, an estimated 65 million years ago, dinosaurs and many other animals suddenly disappeared. Scientists have different theories about what caused this mass extinction. One group believes that a sudden extraterrestrial disaster, such as the impact of a meteor, may have caused the dinosaurs to vanish. Another group favors earthbound events, such as a gradual shift in climate.
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The most popular explanation is the "giant meteor impact" theory. In 1980 the physicist Luis Alvarez proposed that a six-mile-wide meteorite hit Earth about 65 million years ago. According to Alvarez’s theory, great dust clouds from the meteorite’s impact blocked sunlight for a long period of time. Many plants died, and as a result, the animals that fed on those plants died. Then the larger animals who fed on the plant-eating animals also died. The largest of these creatures, of course, was the dinosaur. Smaller animals, requiring less food, could survive by hibernating. Plants with root systems eventually could bloom again. Life gradually came back to Earth, but the dinosaurs did not return.
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