theory. according to this theory, a huge asteroid struck the earth's surface about 65 million years ago. the exploding asteroid threw enormous amounts of dust into the air. the dust blocked out sunlight for more than a year. plants on the earth's surface died. dinosaurs who lived on those plants died out. so did the meat-eating dinosaurs who lived off the plant eaters.
but how is it possible to know if an asteroid really did hit the earth's surface 65 million years ago? scientists have now found an answer. in some parts of the earth, they have found a layer of the earth's crust that contains an unusually high level of 