GA Study Notes On Inside our Earth : SSC CGL Tier-1 2017

Inside Our Earth

The earth is made up of several concentric layers with one inside another. The structure of the earth’s interior is fundamentally divided into three layers – crust, mantle, and core. The crust forms only 1 percent of the volume of the earth, 84 percent consists of the mantle and 15 percent makes the core.The radius of the earth is 6371 km.

Crust

The uppermost layer over the earth’s surface is called the crust.
It is the thinnest of all the layers. It is about 35 km. on the continental masses and only 5 km. on the ocean floors.
The main mineral constituents of the continental mass are silica and alumina. It is thus called sial (si-silica and al-alumina).

The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium).
The discontinuity between the hydrosphere and crust is termed as the Conrad Discontinuity.

Manlte

Just beneath the crust is the mantle which extends up to a depth of 2900 km below the crust.
The discontinuity between the crust and mantle is called as the Mohorovich Discontinuity or Moho discontinuity.
The uppermost solid part of the mantle and the entire crust constitute the Lithosphere.
The asthenosphere (in between 80-200km) is a highly viscous, mechanically weak and ductile, deforming region of the upper mantle which lies just below the lithosphere.
The asthenosphere is the main source of magma and it is the layer over which the lithospheric plates/ continental plates move (plate tectonics).
The discontinuity between the upper mantle and the lower mantle is known as Repetti Discontinuity.
The portion of the mantle which is just below the lithosphere and asthenosphere, but above the core is called as Mesosphere.

Core

The innermost layer is the core with a radius of about 3500 km.
It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron).
The central core has very high temperature and pressure.
The core is separated from the mantle by Guttenberg’s Discontinuity.
The core is the densest layer of the earth.
The discontinuity between the upper core and the lower core is called as Lehmann Discontinuity.
Barysphere is sometimes used to refer the core of the earth or sometimes the whole interior.