2.2. Indirect Sources

The centre of the earth downward is 6,371 kilometers away from the surface of the earth. In comparison to this distance the depth of a deep well or a mine is insignificant. It is therefore, necessary to take help of indirect scientific evidences to know about the interior of the earth. These sources include temperature, pressure and density of earth, behaviour of seismic waves (the waves generated by Earthquakes), Meteors, the Moon etc. These sources may be classified into three groups

(a) Artificial sources such as temperature, pressure and density.

(b) Evidences from the theories of origin of earth

2.2.1. Temperature Fig 1: Temperature profile of the inner Earth 2.2.2. Density 2.2.3. Pressure 2.2.4. Gravitation force 2.2.5. Magnetic surveys 2.2.6. Meteorites 2.2.7. The Moon 2.2.8. Evidence from Theories 2.2.9. Earthquake Waves Fig 2: Particle motion in seismic waves Fig 3: Arrival time of seismic waves Fig4: Shadow Zones Fig 5: Earthquake Fig 6