DMPQ: Describe the interior of the earth and its composition.

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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