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.
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Using Fig.1, answer these questions about the structure of the Earth.

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

  • The crust floats on top of the crust because it is less dense.
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Classify each of these layers as either solid, molten or both:
  • Inner core
    Outer core
    The mantle
    Oceanic crust
    Continental crust
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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.
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Roughly how fast is the continent of America moving away from Europe?
  •  cm per year
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When were the Alpine and Himalayan mountain ranges formed?
  •  million years ago
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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.  
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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
    Outer core
    Mantle
    Crust
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2. Match the descriptions below with the correct layer of the earth.
  • This is the hottest layer of the earth, containing solid metal.
    The huge solid plates in this layer drift about very slowly.
    When volcanoes erupt, it is the material from this layer that shoots into the sky.
    This layer is composed of molten metals.
    This dark, solid layer is composed mainly of basalt.
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3. What causes continental drift?
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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?
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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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