Starter

Draw a diagram to show what you know about the structure of Earth?

TASK 1:

Look at Hodder textbook pages 189-190 (4th edition) to find out more about the structure of the Earth. Define the following terms:

• Inner Core
• Outer Core
• Mantle
• Crust
• Lithosphere
• Asthenosphere

Core

is made up of dense rocks containing iron and nickel alloys and is divided into:

• a solid inner core and
• a molten outer one, with a temperature of over 5000 °C.

This heat is produced mainly as the result of two processes:

• primordial heat left over from the Earth’s formation and
• radiogenic heat produced by the radioactive decay of isotopes, particularly Uranium-238, Thorium-232 and Potassium-40.

Mantle

The mantle is made up of molten and semi-molten rocks containing lighter elements such as silicon and oxygen.

Crust

The crust is even lighter because of the elements that are present, the most abundant being silicon, oxygen, aluminium, potassium and sodium. The crust varies in thickness – beneath the oceans it is only 6–10 km thick but below the continents this increases to 30–40 km and under the highest mountain ranges this can be as high as 70 km.

Lithosphere

The lithosphere consists of the crust and the rigid upper section of the mantle and is approximately 80–90 km thick. This is the section of the Earth that is divided into seven very large plates and a number of smaller ones (Figure 5.6). Plates are divided into two categories, oceanic and continental, depending on the type of material from which they are made (see Table 5.1)

Asthenosphere

The asthenosphere lies beneath lithosphere and is semi-molten on which the plates float and move.

TASK 2:

How do we know that tectonic plates are moving?

What is the theory of plate tectonics?

What evidence did Alfred Wegener use to support his ideas about plate movement?

TASK 3:

There are two types of plate – oceanic and continental.

Where two plates meet it is known as a boundary or a margin.