Why did dinosaurs go extinct?
About 66 million years ago, a huge asteroid slammed into Earth. Dust and debris filled the sky and dimmed the sunlight, and the planet turned cold. Plants struggled to grow, so the animals that depended on them went hungry. All the dinosaurs that were not birds died out. Some birds made it through, though, and their descendants are all around us today.
Where did the asteroid hit?
The asteroid left a scar: the Chicxulub crater, on the Yucatán Peninsula in Mexico. It is almost 200 kilometres across and today lies hidden, partly under land and partly under the sea. The asteroid that made it was more than ten kilometres across.
How do scientists tie the crater to the extinction? All around the world they find the same thin layer of material, and it is unusually rich in iridium. That metal is rare in Earth’s crust but much more common in asteroids.
What happened to the climate and the food?
The trouble did not stay near the crater. Less sunlight reached the ground, it grew colder, and plants and algae struggled to grow. The animals that ate them ran short of food. Then the predators that hunted those animals went hungry too.
Small animals generally need less food than big ones. Some could take shelter, or get by on seeds and insects. That helps to explain who survived, though scientists are still working out the details.
Which dinosaurs were alive then?
Tyrannosaurus and Triceratops lived near the end of the Cretaceous Period, so they were among the dinosaurs caught up in the disaster. Brachiosaurus and Stegosaurus weren’t. They had lived in the Jurassic, tens of millions of years earlier.
So the asteroid tells us how the Cretaceous ended. It can’t tell us what became of every dinosaur species that ever lived, because plenty had come and gone long before.
Why are birds still here?
Birds are part of the dinosaur family. The ancestors of today’s birds came through the catastrophe, while all the other dinosaurs died out. Crocodiles, turtles and many other animals survived as well.
Exactly why some birds made it and others didn’t is still being worked out. Size may have mattered, and so may diet. Our guide “Are birds dinosaurs?” explains the family connection.
What about volcanoes?
Huge volcanoes were also erupting in what is now India. The gases they poured out changed the environment too.
Researchers study both the eruptions and the asteroid. But the crater and the layer found all over the world are strong evidence that the asteroid played the main part in the extinction.
Questions kids ask
- Why did dinosaurs go extinct?
- About 66 million years ago an asteroid struck Earth and upset the climate and the food chains. All the dinosaurs died out except the ancestors of modern birds.
- Where did the asteroid hit?
- Close to the Yucatán Peninsula in Mexico. It left behind the Chicxulub crater, which is almost 200 kilometres across.
- Did every dinosaur die out?
- No. Birds survived, and birds are dinosaurs. All the other dinosaurs became extinct.
- Did volcanoes play a part?
- The eruptions changed the environment too. Scientists are still studying how much they added to the effects of the asteroid.
- Did T. rex and Stegosaurus die out together?
- No. Stegosaurus lived tens of millions of years before T. rex.
- Can we bring T. rex back?
- Nobody has found the DNA you would need to clone a T. rex. But one branch of the dinosaurs is still alive: the birds.
Remember this
- Check the dates on each animal’s card. The dinosaurs did not all live at the same time.
- If you draw the impact, show the dust in the sky as well as the crater.
- The birds you see today are descended from dinosaurs that survived.