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A. So here the story begins. B. The earth got colder and colder gradually. C. The idea was first suggested by some scientists. D. Were there any strange happenings in the world? E. Changes in the natural environment play an important role in the process. F. The idea is very possible because we know there have been similar events. |
Dinosaurs used to be quite common on the earth. Then about 65 million years ago, most of them disappeared at nearly the same time. Although the mystery is still with us, there are many possible guesses. Here is one of them.
They were studying old layers (层) of rocks, which are about 65 million years old, when they suddenly found a kind of rare metal (稀有金属) in them. The metal has already been found in meteorites (陨石). And the scientists believe that it can be found in asteroids (小行星), too.
65 million years ago, a huge asteroid might hit the earth. Then wildfires broke out because of the hit. After the fires burned out, there was so much dust in the air that the sun could not shine through. For this reason, many plants could not grow. Plant-eating dinosaurs died too because they could not find enough food. Then meat-eating dinosaurs died, too.
The dust cloud may have hung over the earth for many months or even a year. Slowly it covered the ground, making the rock layers.
In 1908, something hit the earth in the forest of Siberia, a part of Russia. It broke millions of trees and caused fires. The object might be an asteroid.
