1. The Earth’s Crust (Lithosphere)

This is the outermost layer of the earth made up of solid hard rocks. Its thickness varies from 6km to 40km. It is divided into two layers. These layers are;

• Sial (Continental crust)
• Sima (Oceanic crust)

1. Sial

A sial is the continental crust that moves up the continents. It is made up of igneous, sedimentary and metamorphic rocks with minerals such as silica and aluminum. It is lighter with an average density of 1.7.

2. Sima

This is the oceanic crust that makes up the ocean floor. It is heavier with an average density of 3.0. It has mainly basaltic rocks with minerals such as silica and magnesium. The lighter continental crust seems to be floating on the denser oceanic crust.

2. The Mantle (Mesosphere)

The mantle is also called the mesosphere. It is much thicker and is about 2900km thick. It contains very dense rocks rich in magnesium and iron (Fe). The rocks are in a molten state and a temperature of about 5000°C. This is the layer where magma is formed.

3. The Core (Bryosphere)

The core is the center of the earth and the hottest zone. It is about 6700km thick. This layer is below the mantle. It is also rich in iron and Nickel (Ni). The core is subdivided in two parts.

1. The outer core,
2. The inner core.

The outer core is in the molten state and the inner core is in the solid state and consist mainly iron (Fe). These layers are separated from each other by boundaries called discontinuities.