Crust: The outer most layer or shell of the earth is known as earth’s crust. On an average it is
30km deep. It can be up to 70km under high mountains and up to 8km under ocean. It
represents less than 1% of earth’s total volume and its average density is 2.7 gm/cm3. It is
known as ‘sial’ because of abundance of silicon and aluminium. It is also divided into upper and
lower crust divided by Connarddiscontinuity.a
Mantle: The second layer of earth is called mantle. It is separated from crust by Mohorovicic
discontinuity. Its density ranges from 3.3 to 5.7. It is made of dense and rigid rocks which have
the predominance of magnesium and silicon, known as ‘sima’. It is also separated as upper
mantle up to 700km and lower mantle from 700 to 2900 km. The upper and lower mantle is
separated by Repetti discontinuity.
Core: The innermost layer is called core. It is separated from mantle by Gutenberg
discontinuity. It lies from 2900 km to 6371 km. The density of core varies from 9.5 to
14.5gm/cm3. It is called ‘nife’ as it probably contains alloy of Nickle and iron. It also has two
parts – a liquid outer core separated by inner solid core at 5150km by Lehman discontinuity.
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