3.1 Plate tectonics

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3.1 The earth's layers and plates

Learning objectives

After studying this section, you will be able to:

• Describe how the earth’s layers fit together
  
• Describe what tectonic plates and tectonic plate boundaries are

The layers of the earth

The Earth consists of different layers:

• Inner core (solid iron and nickel)
  
• Outer core (liquid rock)
  
• Mantle (liquid rock)
  
• Crust (solid rock)
  

Which part of the Earth consists of tectonic plates?

1. Inner core
2. Outer core
3. Mantle
4. Crust

The puzzle pieces of the crust

The crust is broken up into several pieces called tectonic plates.

These plates move around because of convection currents (= movement of liquid rock in the mantle, caused by heat of the inner core).

Plate tectonics = The movement of tectonic plates.

Plate boundaries = The places where two plates meet.

Tectonic plates of the world

The Netherlands lies on the Eurasian Plate.

This is the plate boundary between the South American Plate and the African Plate.

This is the plate boundary between the Pacific Plate and the North American Plate.

Look at the places where most earthquakes and volcanoes take place. What do you notice?

Where two plates move away from each other, pressure is released, resulting in gentle volcanic eruptions.

Where two plates move towards each other, pressure builds up, resulting in earthquakes and explosive volcanic eruptions.

What do we call the movement of liquid rock in the mantle, caused by heat of the inner core?

1. Plate tectonics
2. Plate boundaries
3. Convection currents
4. Tectonic plates

Tectonic plate types

Oceanic plate

• Tectonic plate underneath an ocean.
• Quite thin, only up to 10 kilometres. 
• Type of rock: basalt (heavy)

Continental plate

• Tectonic plate that makes up the continents.
• Much thicker than oceanic plates, between 35 and 40 kilometres. Underneath large mountains, such as the Himalayas, the crust can even be up to 75 kilometres thick. 
• Type of rock: granite (lighter than basalt)

What type of rock do oceanic plates consist of?

1. Basalt
2. Granite
3. Sandstone
4. Limestone

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Kilometres or kilometers? Centre or center?

The average distance to the centre of the earth is 6,371 kilometres. But the Americans would say: The average distance to the center of the earth is 6,371 kilometers. Spelling between British English and American English can vary. The ending –re or –er is just one example of the differences between the two types of English. Other differences include the ending –our or -or, such as in the British colour and the American color. Or –ise and –ize for the British organise and the American organize. BRICKS Geography uses British English.

Continental drift (geological theory)

The slow movement of the tectonic plates can cause a very different view of the world: if you could only wait long enough. Many scientists believe that 300 million years ago, all the continental plates were stuck together. They formed a supercontinent called Pangea. 175 million years ago, these plates started to move slowly apart.

One of the reasons scientists think there once was a supercontinent are the locations of the fossils of certain animals. Some fossils have been found in areas that are now separated by a large ocean. An example is the fossil of a freshwater reptile called the Mesosaurus. This reptile lived around 270 million years ago. Fossils of this reptile were found in both Africa and South America.

Talking point

The knowledge we have about the earth changes all the time. Can we be sure that what we know is true?

Essence

The earth is made up of four layers. From the inside to the outside the order is: inner core, outer core, mantle, crust. The outer layer of the earth is divided into different pieces: tectonic plates. At the plate boundaries, earthquakes can happen and volcanoes can be found. There are two types of tectonic plates: oceanic plates and continental plates.

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