Internal Struture of Earth : Layer of Crust, Mantle, Core & Rocks

Earth's Internal Structure : Crust, Mantle, Core

The earth as a whole is divided mainly into 3 Layers – Crust, Mantle and Core.

Crust

• The outer most solid cover or shell of the earth is known as Crust. Its thickness is 30km.
• It is thicker in the region of continents and thinner in the region of sea floor.
• The average density of upper crust is 2.8 and that of the lower crust is 3.0.
• Silica and Aluminum are the main constituting elements of the crust. Therefore, it is also known as the SIAL.

Mantle

• This layer lies below the crust. Silica and Magnesium are the major constituting elements of this layer; hence it is also called SIMA.
• Its thickness is about 2900km and the density of substances in the mantle ranges from 3.0 to 4.7.

Core

• The earth’s core lies below the mantle.
• Its thickness is around 347km.
• Its radius is 6371 km according to IUGG (International Union of Geodesy and Geophysics).
• It is divided into two parts, Outer core-liquid state, and        inner core-solid state.
• Its main constituents are Nickel and ferrous (NIFE).
• The temperature of the centre part of the earth is about 5000°ᶜ.

Rocks

• Outer hard layer of the earth’s crust is called rocks.
• On the basis of formation rocks are classified into Igneous Rocks, Sedimentary Rocks and Metamorphic Rocks

Igneous Rocks

• Formed by the solidification of molten magma from the interior of the earth.
• Igneous rocks are generally harder and granular. There are no layers in igneous rocks.
• Most of them are crystalline and do not contain fossils.
• All other types of rocks formed from these rocks, thus called primary rocks.
• These rocks contain silica from 40 to 80% others are feldspar, magnesium and iron etc.
• Granite, pumice stone, basalt and gabbros are the example of igneous rocks.

Sedimentary Rocks

• They are formed by the deposition, sedimentation and lithification of sediments over a long period of time.
• The remains of plants, dead animals etc. are found in the deposited material.
• Such fossil containing sedimentary rocks are useful for studying life on earth.
• Sandstone, limestone, shale are some examples of sedimentary rocks.

Metamorphic Rocks

• The nature of igneous and sedimentary rocks changes due to the effects of great pressure, intense temperature or the action of water and chemical activity and it transforms into another rocks called metamorphic rocks.

Example of Metamorphic Rocks formed from different rocks