Unit 123 How the Dinosaurs Disappeared

G : The death of the dinosaurs is a great mystery.

About 65 million years ago, dinosaurs lived all over the Earth. They had existed for nearly 200 million years. Suddenly, they all became extinct. Many scientists believe that the dinosaurs were killed by a large meteor. They think that this meteor was about six to twelve miles wide. It crashed into southern Mexico and made a hole about 130 miles wide. The crash threw dust and dirt into the sky. Dust clouds darkened the Earth's atmosphere. The crash caused fires, earthquakes, and tidal waves. The plants were killed. The oceans were poisoned. Very soon, there was no food left for the plant-eating dinosaurs. When they died, there was no food for the meat-eating dinosaurs. The meteor killed almost 70 percent of all plants and animals on Earth. The only animals that could survive were small ones that could eat many different kinds of food. Some scientists say the meteor alone did not cause dinosaurs to become extinct. They think that dinosaurs were already getting weaker. They are not sure why. One reason might be disease. Another might be climate change. A big part of the mystery is why some types of animals survived. If climate change killed dinosaurs, it should also have killed frogs. If the meteor killed most sea reptiles, it should have killed crocodiles. Yet frogs and crocodiles still exist in the world today.