The Core It is the innermost part of the earth. It is separated from the mantle by the Guttenberg-Weichert discontinuity and extends upto the very centre of the earth. It constitutes around 17 percent of the volume and 34 percent of the mass of the earth.

Since the S-waves do not pass through the outer core, no information about the inner core is provided by them. It only suggests that the core, at least in its outer part, is fluid-like in its character because it does not transmit the S.waves and because it retards the velocity of P-waves from 12.6 to 8.4 km/sec.

The pressure and temperature in the core are both very high. The pressure is assumed to be over three million atmosphere and the temperature is around 6000°C . There is a sharp change in the density from about 5.5 x lO’kgm-3 in the mantle to about 10.6 x 103kgm~3 in the core, while at the centre of the core the density increases to 12 or 13xl03 kg nv3.

The core consists of three parts:


(i) Outer-core

(ii) Middle-core and

(iii) Inner-core.

(i) Outer core


It extends from 2900 km to 4982 kms. It is considered to be in a state of homogeneous fluid. It does not transmit S-waves.

(ii) Middle core

It is a transition layer, that extends from 4982 kms to 5121 kms. The material is in a fluid to semi fluid state.

(iii) Inner core


It extends from 5121 kms upto the centre of the earth i.e. 6371 kms. The inner core is assumed to be in a solid state, with a density of about 13. It is believed to contain metallic nickel and iron and is called ‘Nife’. Its thickness is about 1250 kms.