Briefly explain the indirect sources of information of the interior of the earth other than the seismic activity. 

The indirect sources of information of the interior are :

(i)Density - The density of the sedimentary rocks is 2.7 and beneath the sedimentary rocks the density of igneous rocks is 3.5. This means that the density inside the earth is much higher. It is estimated that the core of the earth has the density of 11 to 12.

(ii)Temperature - There is a gradual increase in the temperature as depth increases. The rate of increase is 12°C per km at a depth of 100km. It is 2°C/km at a depth of 300 km and 1°C per km, below it.

(iii)Pressure- Like density and temperature, pressure also increases with the increase in depth inside the earth. It is due to overlying layers or depressions of the heavier material. It is estimated that the pressure at the centre of the earth is about 3500 kilobars.

(iv)The other indirect sources include gravitational magnetic field and the seismic activity. The gravitational force is greater near the poles and lesser at the equator.

(v)The gravity values also differ according to the mass of the material. Uneven distribution of the mass of material within the earth influences this value.