C.2. Structure Of The Earth
[Title: Interior of the Earth]
The Crust
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- It is the outermost solid part of the earth.
- It is brittle in nature.
- The thickness of the crust varies under the oceanic and continental areas.
- Oceanic crust is thinner as compared to the continental crust.
- The mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km.
- It is as much as 70 km thick in the Himalayan region.
- It is made up of heavier rocks having density of 3 g/cm3.
- This type of rock found in the oceanic crust is basalt.
- The mean density of material in oceanic crust is 2.7 g/cm3.
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The Mantle
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- The portion of the interior beyond the crust is called the mantle.
- The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
- The upper portion of the mantle is called asthenosphere.
- The word astheno means weak. It is considered to be extending upto 400 km.
- It is the main source of magma that finds its way to the surface during volcanic eruptions.
- It has a density higher than the crust’s (3.4 g/cm3).
- The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 km.
- The lower mantle extends beyond the asthenosphere. It is in solid state
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The Core
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- The core- mantle boundary is located at the depth of 2,900 km.
- The outer core is in liquid state while the inner core is in solid state.
- The density of material at the mantle core boundary is around 5 g/cm3 and at the centre of the earth at 6,300 km, the density value is around 13g/cm3.
- The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the nife layer.
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[Title: Structure of earth]