*Interior structure of the earth



Evidences suggest that life on Earth has existed for at least 3.6 billion years.In the initial stages of life evolution, there are simple forms of life ,like single cellular organisms for example 'Ameoba'.As the time passed, different complex forms of cells evolved.Like that in the formation of earth, first it was in gaseous form then it cooled down and various layers of earth formed.There are various phenomena that are responsible for it.Due to cooling of earth over a long period of time,dense material goes in the interior of the earth and lighter material floats upon it.Dense material forms the core of the earth whereas lighter forms the crust.






*Why is it important to know about earth's interior structure.



      Humans live on the surface of the earth, the factors like topography of landscape, climatic conditions have very great affect on all creatures living on it. But all these phenomena are interlinked with the interior of the earth.Earthwuakes, Tsunamis, volcanic eruptions all are associated with the interior structure of the earth.So their predictions are also associated with Earth's interior structure.Various types of unknown and rare material can be found with these studies.There is a greater possibility of finding new chemical composition which can be used for further exploration.


*Sources of information about the interior structure of the earth are given below:-

       (A)Direct Sources

(a). Volcanic eruptions (lava or magma)

(B).Deep earth drilling and rocks from mining areas.


       (B)Indirect Evidences


(a). Gravitation:- The value of gravitational force (Fg) is different for different latitudes of the earth.It is greater near the poles and less at the Equator which is basically due to differenceof length of centre of the earth at poles and Equator.


(b). Meteors:-They are also made of same material as earth is made of.


(c) Magnetism of earth:-It also helps the scientist to research on the interior of the earth.



*What is the cause behind the Magnetic field of Earth?



By the study of seismic waves (P and S waves) and their distribution over the globe when sudden earthquake outbreaks.Scientist observed that P-waves move faster and are the first to arrive at the surface.They can travel in all mediums.

Their velocity depends on shear strength of the material.S-waves cannot pas through liquids or gases.These waves extends halfway around the globe from the earthquake's focus.


        Source:-   Shadow Zone

                           P-waves.       S-Waves

Shadow.             103° -142°     103°-180° 
Zone

This observation led to the discovery of liquid other core.Since S-Waves cannot travel through liquids,so they don't pass through the liquid outer core.       

            

*Seismic Waves


When any earthquake occurred, earthquake waves are generated.These are generated from the focus or  'Epicentre'.They travel across the body of the earth and reached the surface.Where a new wave is generated which is known as  'Surface waves'.



          *Classification of earthquake's Waves:-
    

 - Body Waves :-.  Body waves are generated due to the release of energy at the focus and move in all directions going through the body of the earth.Because of that the name body waves.

(a). P-Waves :- . It is also called Longitudinal or Primary waves.These waves can pass through Solid, liquid and gases.

(b). S-Waves:- . It is also called transverse or Secondary waves.These waves can pass through solids only, not liquids or gases.

 -  Surface Waves :-.  These are the long waves that propagates on the surface of the earth.When P or S waves strikes the surface of earth then these waves are generated.


*Layers of Earth:-


(a).Crust:- It is the topmost layer of the earth ranging from 8 to 40 kms thick.The thickness depends upon many factors.
    For example :-
      (a). Oceanic crust:- about 5 kms
      (b). Continental crust:- about 30 kms
              It is basically made of silica(Si) and Aluminium (Al) by these terms, it is termed as SIAL , sometimes Lithosphere.Moho discontinuity forms boundary between crust and mantle.


(b).Mantle:-  This is the next layer beyond crust.It is about 2900 kms in thickness.It is made of silica (Si) and magnesium (Mg) ,so it is termed as 'SIMA' .The solid part of mantle is included in 'Lithosphere' .Behind that is liquid or mechanically weak mantle, where due to corolis force of earth, the magma moves inside 'Asthenosphere' which is responsible for 'Plate Tectonics'.

(c).Core :- It lies between 2800 kms to 6400 kms below the earth surface.It is basically composed of Nickel(No) and Iron(Fe) which is termed as NIFE.It is separated from the mesosphere by Guttenberg's discontinuity.



  • Parts of core :-
(1). Inner core.   -   Solid
(2). Outer core.  -    liquid
           Inner and outer core discontinuity:- Lehmann discontinuity


   Beno Guttenberg's (1889-1960) was a scientist who studied the interior structure of the earth.In 1913 ,he observed that there is a layer in the interior of the earth where P-waves slowed down and S- waves vanished completely. Because S-Waves is unable to pass through liquid medium.By this observation, he concluded that there is a liquid layer inside the earth.