Why did the dinosaurs disappear?

How do we know?

↻ One of the pages with a moving picture

A thin layer of clay, found all around the world, holds a clue.

1. Scientists think a giant space rock, an asteroid, slammed into Earth about 66 million years ago.
2. The blast threw dust and gases high into the sky.
3. Dust may have dimmed the sunlight, so plants grew less and Earth cooled.
4. With less food, more than 70% of living kinds died out, including the big dinosaurs.

In 1980, Luis and Walter Alvarez proposed the asteroid idea. One clue: a thin clay layer found around the world, full of iridium, a rare metal.

Then came the crater. It is 112 miles wide and is now hidden under younger rock, so no one found it for decades! It is near Chicxulub in Mexico, where the asteroid, nearly 6 miles across, hit.

Scientists still debate how much giant volcanoes in the Deccan Traps of India, erupting around the same time, helped.

Wow number

112 miles wide: the crater the asteroid left. It is now hidden under younger rock, so no one found it for decades!

Myth or fact?

Early people hunted dinosaurs. Myth. Our species is only about 300,000 years old.

Birds are living dinosaurs. Fact. Scientists found birds come from dinosaurs.

Think about it

If the asteroid had missed, what animals might live near you today?

Where in the world?

Chicxulub, Mexico where the asteroid, nearly 6 miles across, hit nearby. The Deccan Traps in India had giant volcanoes erupt around the same time — 21.4° N, 89.5° W.

Where these facts come from

Every number on page 25, and who measured it

Has this changed?

Parts of this story may change. Scientists still debate how much the volcanoes helped.

What does not change is that dinosaurs lived long before people did.

Words from this page

asteroid

A rocky object, much smaller than a planet, that travels around the Sun.

iridium

A rare metal.

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