7 Geography

Inside Our Earth

Learning Goals:

  • Internal structure of earth
  • Types of rocks
  • Igneous Rocks
  • Metamorphic Rocks
  • Sedimentary Rocks

The earth is a dynamic planet i.e. it undergoes changes constantly. These changes are:

  • Inside the earth
  • Outside the earth

Interior of the earth

The earth is made up of several concentric layers. Concentric means having a common centre. The earth has one layer inside another.

interiors of earth

Broadly, there are three layers of the earth:

  • Crust
  • Mantle
  • Core

The Crust

It is the outermost layer over the earth’s surface. It is

  • The thinnest of all the layers.
  • About 35 km on the continental masses and only 5 km on the ocean floors.

The main minerals constituting the continental mass are:

  • Silica
  • Alumina

The continental mass is also called ‘sial’. The name sial is derived from letters ‘si’ of silicon and ‘al’ of alumina.

The main mineral constituents of the oceanic crust are:

  • Silicon
  • Magnesium

The oceanic crust is called ‘sima’. The root of the word sima is ‘si’ from silica and ‘ma’ from magnesium.


It is the layer just beneath the crust and extends up to a depth of 2900 km below the crust.


It is the innermost layer i.e. it is below the mantle. Its radius is about 3500 km. The core consists of outer core and inner core. It is mainly made up of:

  • Nickel
  • Iron

The innermost layer is also called ‘nife’. The name nife is derived from the word ‘ni’ from nickel and ‘fe’ from ferrous meaning iron. The temperature and pressure of the central core is very high.


Lesson Part 2



Short & Long Questions

NCERT Solution