NCERT Class 7 Geography Chapter 2: Inside our Earth Completes Notes Part 2

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Inside Our Earth

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Mantle

  • About 2900 km thick

  • 85% by volume

  • 64% by mass

  • Made of iron but mainly silicates

  • Asthenosphere – Upper mantle – Convection currents

    • Viscous, weak and ductile

    • Just below lithosphere

    • Main source of Magma

  • B/w Upper & lower mantle – Repetti Discontinuity

  • B/w Mantle & Core – Guttenberg Discontinuity

When we talk about mantle again first thing is layer between core and the mantle is known as Moho. Now again mantle can be further sub divided as upper metal and lower metal. The boundary between upper mantle and lower mantle is known as Repetti boundary. Similar to Conrad boundary that was present between the upper crust and lower crust between upper mantle and lower mantle you have Repetti boundary and between the crust and the mantle you have Moho discontinuity and between the mantle and core you have another boundary which is known us Guttenberg boundary. So between mantle and core you would have Guttenberg.

Now some basic characteristic of mantle. Mantle is around 2900 km thick. It is 85% by volume and 64% by mass it is manly made up of iron and silicates. So mainly components of mantle is iron and then you have Silicates. Again there is basic difference between Upper mantle and lower mantle. Upper mantle is liquid in its states as a result it is also known as Asthenosphere. However lower mantle is solid in states. Asthenosphere you have convection current that moves on it is much discuss ductile in nature and this is main source of Magma and Magma is what makes of the main volume of volcanic activates if I say. So you have Asthenosphere which is main source or main depository of Magma. So you have the basic structure of mantle. Now moving on the core.

Core

  • Radius of about 3500 km

  • Made of Iron & Nickel (NIFE)

  • High temperature & pressure

  • 15% of earth’s volume

  • 32.5% of earth’s mass

  • B/w Outer & Inner Core – Lehmann Discontinuity

  • Outer Core – Liquid (Slow Moving – Produces Earth’s Magnetic Field)

  • Pressure, Density increases towards center

Again we can divide the core into upper and lower core. The upper and lower core is again the differentiated by a discontinuity which is known as Lehmann discontinuity. You have upper crust and lower crust which is differenced by Lehmann discontinuity. Now upper crust or outer crust what we call those is liquids as compare to inner crust. Which is solid. So you have inner crust extremely solid but you have the upper crust is liquid in nature. Now this liquidity is main cause of the magnetic field that is seen in the earth. So you have the North Pole and north magnetic pole and the South Pole and south magnetic pole that is visible and this liquid nature leads to the earth magnetism. So this the upper core is important. Now core is compose of Ni, Fe so Ni stands for Nickel and Fe stands for Iron. So core is mainly compose of iron and Nickel. It occurs is very height temperatures and pressure. It contribute to 15% of the earth’s volume and 32.5% of the earth’s mass and as we move inside from crust to core you have the pressure and density that increases towards center of the earth. Now we have talked about earth and interior, let’s move on what are rocks? How they are forms?

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