Structure of the Earth – Geography

1. The Crust

• It is the outermost solid pan of the earth. It is brittle in nature.
• The thickness of the crust varies under the oceanic and continental areas. Oceanic crust is thinner as compared to the continental crust.
• The mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km. It is as much as 70 km thick in the Himalayan region.
• This type of rock found in the oceanic crust is basalt. The mean density of material in oceanic crust is 2.7 g/cm3.

2. The Mantle

• The portion of the interior beyond the crust is called the mantle.
• The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
• The upper portion of the mantle is called asthenosphere.
• It is the main source of magma that finds its way to the surface during volcanic eruptions. It has a density higher than the crust’s (3.4 g/cm3).
• The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km.

3. The Core

• The core- mantle boundary is located at the depth of 2,900 km.
• The outer core is in liquid state while the inner core is in solid state.
• The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the knife layer.