Question

A Geologic History of Earth



The Earth and its continents have not always looked the way they do now. There used to be only one continent. Earth’s climate has also changed a lot. The shape and climate of our planet will keep changing in the future.

Pangaea: The Supercontinent
Earth used to be covered in molten rock. As water formed, Earth’s outer layer cooled down. It became a solid crust. This crust is always changing shape. It makes up the continents we see today.

A long time ago, all the continents were together in a supercontinent. This was called Pangaea.

About 200 million years ago, the continents split apart. They slowly moved to the places they are in now.’


A diagram showing how Pangaea likely looked
We have lots of evidence that Pangaea existed. You can see the evidence by looking at a map of Earth. You can see that the continents are like puzzle pieces. It looks like they once fit together.

There is also evidence for Pangaea in rocks. The same kinds of rocks are found on different continents. This means they may have been closer together a long time ago.

Fossils also shows that the same plants and animals lived on different continents. Those continents are very far apart today. Scientists think it is because the continents all used to be close together in Pangaea.


Earth’s continents
Plate tectonics is an idea that scientists came up with. It explains how continents move. They move very slowly over long periods of time. We cannot see the movement. It is too slow. But it still happens.

Earth’s Changing Climate
Earth’s climate is always changing. We call this climate change. The planet goes through really cold and in-between periods. We call the very cold periods “ice ages.”


An image of what the Earth’s ice caps might have looked like during the last ice age
Scientists use lots of evidence and clues to study ice ages. They take ice cores from glaciers. They also look at rocks and fossils all over the world. This tells them the types of life that lived in parts of the world.


A scientist taking an ice sample from a glacier
Today, learning about our Earth’s history is very important. It can help us understand what is to come and how we need to be ready for it.

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Questions
Do you believe Pangaea existed? Why or why not?
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Answer 1

Yes — I believe Pangaea existed. Multiple, independent lines of evidence support it: the continents look like puzzle pieces that fit together; identical rock types and mountain chains are found on continents now far apart; the same fossils of plants and animals (for example Glossopteris and Mesosaurus) occur on different continents; and signs of ancient glaciers appear in places that are now tropical. Modern measurements of plate motions and paleomagnetic data also show continents have moved over time. Together, these facts make a strong scientific case that the continents were once joined in a supercontinent.