Almost all the dinosaurs—and many other animals—died out 66 million years ago. This happened as the result of one very terrible day, when a huge asteroid (ASS-ter-oyd) struck Earth.

An asteroid is a rocky object in space. It orbits, or goes around, the sun. Most of the time asteroids don’t cause any trouble. But long ago, a huge asteroid came streaking through the sky and crashed into the sea.

This asteroid was about six miles long. That’s as long as Mount Everest is tall! But don’t worry. Scientists tell us that such a disaster likely won’t happen to our planet again for a long, long time.

The crash caused giant waves and earthquakes, and made volcanoes erupt. The heat from it caused fires. Worst of all, it made dust clouds. These clouds blocked out the sun, so plants could not grow well. With few plants to eat, most animals died out.