The Earth

Geography Study Material

THE EARTH

Structure of the earth

The main layers of earth are following :

The Crust

It is the topmost layer of the earth.

This layer has the least density and thickness.

A zone, Mohorovicic discontinuity, separates it from the intermediate layer, the mantle,

This later is also called Sial (Silica and Aluminum).

The Mantle

It is the intermediate layer of earth.

It is separated by Gutenberg discontinuity from the core.

It is also known as Sima ( Silica and Magnesium).

The Core

It is the innermost layer.

It is about 3475 km in radius and its temperature is between 2200 and 2750 degrees Centigrade.

Density of this part is many times greater than average density of earth.

It is also known as Nife ( Nickel and Iron ).


EARTH’S MOVEMENTS

ROTATION : The earth spin on its own imaginary axis from west to east once in 24 hours ( in precisely 23 hours 56 minutes and 4.091 seconds ). The axis always remains inclined at an angle of 66 1/2 degrees to the plane of Earth’s orbit.

REVOLUTION : The earth is rotating round the Sun. It takes 365 1/4 days to complete one round.

Longest day or Shortest night : June 22 ( Northern Hemisphere ), December 22 ( Southern hemisphere ).

Shortest day of Longest night : December 21 ( Northern hemisphere ), June 21 ( Southern Hemisphere ).