Our living planet Earth is the only place where human habitations are taken place and it is possible due to the present of the atmosphere which makes it unique from the other planets or we can also say others heavenly bodies. This entire phenomenon is proved by the scientists under their keen interest using different advanced technological tools. But have we thought about what’s going on inside of the earth? As we know that there are very little knowledge about the inside of the earth if we compared it to the earth’s atmosphere and the knowledge acquired by the scientists through different sources or we can say assumptions because there is no possible of direct observation. Now this article give you some basic idea and knowledge about the interior of the earth.

Prediction/Sources of the study

The prediction of the study of the interior of the earth divided into two parts- 

     A) Direct Prediction

         a) Surface rocks

         b) Volcanic eruptions

         c) Mining etc.


     B) Indirect Prediction

        a)  Earth’s temperature and pressure

        b)  Fossil Fuel

        c)  Earth’s gravity

        d)  Magnetic sources

        e)  Meteors

        f)  Earthquake waves etc.




The interior of the earth is made up with the following important elements. They are-

        a) Iron(Fe)

        b) Magnesium (mg)

        c) Aluminium(Al)

        d) Oxygen (O)

        e) Silicon (Si)

        f) Silicate Compounds

Structure of the interior of the earth

The interior of the earth further split up into three parts i.e.-

         1) CRUST

         2) MANTLE 

         3) CORE

Fig: Crust, Mantle, Core.



  • The outer most layer of Earth is the crust or skin and brittle in nature.

Followings are the important characteristics of Earth crust i.e.-



  • The crust is the thinnest and outermost part of the part where human habitations are taken place. It’s thickness is not constant and is varies from ocean to land from 5 to 60 km. But on an average thickness of earth crust is 30 km.
  • Oceanic crust is thinner as compared to the Continental crust, average thickness of oceanic crust is 5 km and thickness of continental crust is 60 km.


  • The crust is further divided into two parts i.e. continental crust and oceanic crust (both have are further divided into two parts upper and lower crust). Continental crust is thicker as compared to the oceanic crust.
  • The Continental crust is composed mainly of Silicon and Aluminium and called as SIAL. 
  • Granites are predominantly found in the Sial layer (continental crust) which floats on the Sima (oceanic crust) that is rich in Silica and Magnesium
  • The continental crust is also called as Felsic because it composed of Iron and Silica
  • The Oceanic Crust is composed mainly of Silicon and Magnesium and popularly known as  SIMA. 
  •  Basalts are predominantly found in the Sima layer (oceanic crust).
Fig: SIAL floats on the denser SIMA


Forming Elements:

  • The Continental Crust made of two minerals i.e- Silica and Aluminium; known as SIAL.
  • And the Oceanic Crust is also made of two minerals i.e- Silica and Aluminium; known as SIMA.


  • The density of Sial is about 2.7 g/cm3 and desnity of Sima is about 2.95 g/cm3 or 3.0 g/cm3.
  • The average density of the crust is about  2.7 g/cm3.


  • The crust temperature is not fixed and is varies from depth. The temperature is increased with the increasing with depth and ranges from 5000to 10000C.


  • Pressure also increases with the increases with depth it’s due to the overburden of the underlying rocks.


  • Seismic discontinuities or discontinuties are the boundaries between the different layers of the Earth where seismic waves show markable change in their characteristics like speed etc.
  • Connard Discontinuity divides the earth’s upper crust (SIAL) and lower crust (SIMA) and Mohorovicic Discontinuity divide the entire crust from mantle. 
  • Andrija Mohorovicic, Croatian Geophysicist firth discovered the seismic or Moho Discontinuity in 1909.


In Short

The Crust

  1. Uppermost thin layer.
  2. Its continental  part – SIAL has average density of 2.7.
  3. Beneath the Sail and the bottom of oceans SIMA average density – 3.0
  4. SIAL – SIMA thickness 40-50 kilometers
  5. Volume- 1%




  •        The portion of the interior beyond the crust is called the mantle.

Followings are the important characteristics of Mantle i.e.-



  • If we see in terms of location and density then it is the intermediate layer of the earth. The thickness of this layer is about 2900 km (Moho discontinuity to the outer core).


  • The mantle is divided into two parts upper mantle and lower mantle. The upper mantle is also called as Asthenosphere, which thickness is about 250 km.
  • Asthenosphere is a Greek word which means weak. The substances in this layer are soft and molted.

Forming Elements:

  • Main forming elements of this layer is Iron, Nickel, Chromium, Magnesium and Silicon.
  • In upper part of Mantle, 30-700 km this region is composed of Chromium (Cr), Iron (Fe), Silicon (Fe) and Magnesium (Mg); and known as CROFESIMA (Cro+Fe+Si+Ma).
  • Lower part of Mantle is composed of Nicke (Ni), Iron (Fe), Silicon (Si),  and Magnesium (Mg); known as NIFESIMA (Ni+Fe+Si+Ma)


  • In mantle temperature ranges from 2000 to 30000C.


  • The average Density of the earth’s mantle  3.4 – 5.6 g/cm3

Low velocity zone:

  • The mantle’s asthenosphere is considered as low velocity zone it’s due to the velocity of the earthquake waves decreases (s-waves, 100 to 200 km depth).

Mantle transition zone:

  • The region between 400 to 670 km is known as Mantle transition zone.


  • Repetti Discontinuity divides the earth’s upper mantle (CROFESIMA) and lower mantle (NIFESIMA) and Gutenberg Discontinuity divide the entire mantle from the core and here the earth’s velocity and density of p-waves increases.

Important of Mantle:

  • The mantle plays an important role in all the happenings in the interior of the earth. It also gives rise to Convection Currents. These currents supply energy for happenings like Continental drift, earthquakes, volcanoes etc.


In Short


  1. Thickness 2900 km.
  2. Volume 83%
  3. Beginning from the Moho.
  4. Three parts- Moho, Upper and Lower Mantle.
  5. There arise convection currents in it.
  6. Supply of energy for Continental Drift, Volcanoes and Earthquakes.


Fig: Different parts of Earth


  • The inner most layer is called Core.


  • The mantle is divided into two parts outer core and inner core. The upper core is assumed to have the properties is in liquid state and the lower core is in solid state.
  • Outer Core ranges from 2900 km – 5100 km
  • Inner Core ranges from 5100 km – 6370km 



  • The core is the innermost layer of the earth and it’s thickness is about 3500 km in radius.


  • The average density of this layer is 9.1 g/cm3 to 13.1 g/cm3
  • The density of the inner core is about 14 g/cm3 where as is about 11  g/cm3 in outercore.

Forming Elements:

  • The earth’s mantle is formed from two minerals i.e- nickel and iron. Hence, this layer is also known as NIFE (nickel and iron).


  • The temperature of the core is ranges from 3000 to 50000C.
  • The average temperature of the core is 50000C.


  • Lehman Discontinuity divides the earth’s outer core from the earth’s inner core.
  • Gutenberg Discontinuity divides the mantle from the core.

                               Thus, the interior of the earth constitutes crust 1%, mantle 83% and core 16% respectively.

In Short

The Core

  1. Thickness: 2900 km to 6371 km.
  2. Outer Core: Semi Molten
  3. Inner Core: Solid.
  4. Whole Core (Volume): 16%
  5. Made of Iron and Nickel called NIFE.
Fig: Zones, Densities and Thickness of the Earth



Seismic discontinuities or discontinuties are the boundaries between the different layers of the Earth where seismic waves show markable change in their characteristics like speed etc.

These represents the difference in the physical and chemical properties of the Earth’s interior.

Location Discontinuity
Between upper crust and lower crust (Sial – Sima)-  Conard discontinuity


Between lower crust and upper mantle Mohrovicic Discontinuity
Between upper mantle and lower mantle Repetti Discontinuity
Between upper mantle and lower mantle Weichert Gutenberg  Discontinuity  
Between outer core and inner core Lehman discontinuity


Fig: Different layers and discontinuties inside the earth



1) Density of the core is highest because-

             a) due to heavy pressure of overlying rocks

             b) due to heavy temperature of overlying rocks

             c) due to heavy density of overlying rocks

             d) none of the above

 Ans- a


2) The average density of the earth is-

            a) 2.3 gm/cm3

            b) 5.5 gm/cm3

            c)  17.2 gm/cm3

            d)  6.5 gm/cm3

  Ans- b


3) Who discovered the core-

            a) Harold Jeffreys

            b) R.D Oldham

            c) Inge Lehman

            d) none of the above

 Ans- b


4) The inner core is solid first proved by-

            a) Inge Lehman

            b) Suess

            c) Cavendish

            d) R.D Oldham

Ans- a


5) The source of the Earth’s magnetic field is-

            a) outer mantle

            b) liquid outer core

            c) lower crust

            d) outer crust

 Ans- b


6) On the basis of the satellite data the average density of the core of the earth is-

   a) 13 g cm3

   b) 12 g cm3

   c) 11 g cm3

   d) 10 g cm3



7) The core of the earth is made of the mixture of-

   a) Silica and nickel 

   b) Nickel magnesium

   c) Silica and magnesium 

   d) Nickel and iron



8) In the tectonically active areas,  temperature remains ________at the depth of 43 km from the surface of the earth.

    a) 900° C

    b) 1000° C

    c) 1100 °C

    d) 1200° C



9) In the tectonically stable areas, temperature at the depth of 40 km from the surface remains at-

   a) 500° C

   b) 550° C

   c) 600° C

   d) 650° C

Ans- a


10) The asthenosphere is-

    a) Totally moltel

    b) Partially moltel

    c) Totally solid

    d) Partially solid



11) Which waves cannot pass through liquid materials?

    a) Primary waves

    b) Secondary waves

    c) Surface waves

    d) All of the above



12) Pg – SG waves were discovered by-

    a) Jeffrey’s

    b) Conard

    c) Wegener

    d) Daly



13) Lithosphere is mostly composed of-

     a) Amphibolite

     b) Granite

     c) Basalt

     d) Peridotite



14) Who has recognised two major layers in the earth?

      a) Daly

      b) Suess

      c) Harold Jaffrey

      d) Arthur Holmes

Ans- d


15) On the basis of velocity, seismic waves are divided into_______sets of waves-

       a) six

       b) five

       c) four

       d) three

Ans- d




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