The end of the dinosaurs

About 66 million years ago an asteroid struck Earth and helped end the age of the dinosaurs. In this lesson you will find out how scientists worked this out from clues in rocks and fossils.

Clues in the rocks

Layers of rock build up over time, with the oldest at the bottom. Fossils of dinosaurs are found in layers older than 66 million years, but never in younger layers above them. Something made them die out.

In 1980 a team of scientists found a thin layer of clay, laid down at exactly that time, that contained unusually large amounts of a metal called iridium. Iridium is rare in Earth's crust but much more common in asteroids. They suggested that a giant asteroid had hit Earth and spread its dust around the world.

Finding the crater

Scientists then searched for a crater of the right age. They found it buried under the coast of Mexico, near the town of Chicxulub, which is said CHEEK-shoo-loob. The crater is about 180 kilometres wide and was made by an asteroid roughly 10 kilometres across.

The impact threw huge amounts of dust and gas high into the sky. Sunlight was blocked for months or years, the climate cooled and many plants stopped growing, so the animals that ate them starved. Around three quarters of all kinds of plants and animals died out.

The survivors

Not everything died. Small mammals, birds, crocodiles, turtles and many insects survived. With the big dinosaurs gone, mammals spread and changed over millions of years, which eventually led to animals such as elephants, whales and humans. Birds are the living descendants of one group of dinosaurs, so in a way, dinosaurs are still with us.

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