Structure of the Earth
Introduction

Everyone knows what the outside of the Earth looks like, but this is only a small part of it. The inside of the Earth has intrigued scientists for many years and has turned out to be very different from the outside.
Layers in the Earth
Move the cursor over the image of the Earth in Fig.1 below to find out about the different layers which make it up.

 Figure 1. Layers in the Earth.

Which layer of the Earth is the hottest?
Select the correct words to complete the sentence below.

• The crust floats on top of the crust because it is less dense.
Classify each of these layers as either solid, molten or both:
•  Inner core both molten solid Outer core both molten solid The mantle both molten solid Oceanic crust both molten solid Continental crust both molten solid
Shifting plates
The countries and continents on Earth have not always been in the same position. Click the button to watch the map of the world in Fig.2 below change.

 Figure 2. Drifting continents.
Roughly how fast is the continent of America moving away from Europe?
•  cm per year
When were the Alpine and Himalayan mountain ranges formed?
•  million years ago

There are certain areas on Earth, such as south-east Asia and the west coast of the USA, where many earthquakes and volcanoes occur. Scientists believe that active areas such as these lie on the edge of two plates. The plates in these active areas are moving together and creating mountain regions, volcanoes, and earthquakes.

In other areas of the world, such as in the middle of the Atlantic Ocean, the plates are moving apart. Molten volcanic material from the mantle flows up to fill the gap and then solidifies.

Summary

The Earth is made up of many different layers. Some of these layers are molten and some are solid.

The Earth's outermost layer is composed of plates in relative motion.

The motion of these plates is responsible for the creation of mountains, volcanoes, and earthquakes.

Exercises
 Figure 3.
1. Fig.3 above shows a cross-section through the earth. Select the correct letters that labels each of the layers of the earth below.
•  Inner core A B C D Outer core A B C D Mantle A B C D Crust A B C D
2. Match the descriptions below with the correct layer of the earth.
•  This is the hottest layer of the earth, containing solid metal. Continental crust Inner core Mantle Oceanic crust Outer core The huge solid plates in this layer drift about very slowly. Continental crust Inner core Mantle Oceanic crust Outer core When volcanoes erupt, it is the material from this layer that shoots into the sky. Continental crust Inner core Mantle Oceanic crust Outer core This layer is composed of molten metals. Continental crust Inner core Mantle Oceanic crust Outer core This dark, solid layer is composed mainly of basalt. Continental crust Inner core Mantle Oceanic crust Outer core
3. What causes continental drift?
4. Around 200 million years ago, scientists think all the land on earth was in a super-continent. What do they call this super-continent?
5. Currently, India and Asia are touching. If 100 million years ago, the distance between India and Asia was approximately 8000 km, what was the
average speed
The average speed of an object is the distance travelled in a relatively long time interval divided by that time.
average speed
at which they approached each other?
• mm/year
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