(a) Draw a well-labelled diagram to show the intreral structure of the earth (b) Describe the main features of any two of the parts shown in (a) above.

(a) Internal structure of the Earth

(b) Main features of the parts

1. Crust

• This is the thin, outermost, solid layer of the Earth.
• It varies in thickness: about 5 to 10 km beneath oceans and about 30 to 70 km beneath continents.
• It consists mainly of granitic rocks in the continental part, called sial because it is rich in silica and aluminium, and basaltic rocks in the oceanic part, called sima because it is rich in silica and magnesium.
• It forms the land and ocean floor, provides the soil, and supports life.

2. Mantle

• This is the middle layer lying immediately below the crust and surrounding the core.
• It is about 2,900 km thick and is made up of very dense silicate rocks, rich in minerals such as olivine and basaltic materials.
• It is very hot; although largely solid, parts of it behave plastically and contain molten material.
• Convection currents in the mantle help to move tectonic plates and are associated with volcanic and earthquake activity.

3. Core

• This is the innermost layer of the Earth, extending from below the mantle to the centre.
• It has a radius of about 3,476 km and consists mainly of iron and nickel, hence it is often called nife.
• It is divided into a liquid outer core and a solid inner core. The inner core remains solid because of the extremely high pressure.
• It is the hottest and densest part of the Earth, and movement in the liquid outer core produces the Earth's magnetic field.