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Geography Earth Geology

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Which of the following are true regarding the crust of the earth?

1. It is the outer thin layer with a total thickness of about 100 km

2. It forms around 10 per cent of the earth’s volume

3. The outer covering of the crust is of sedimentary material

4. The lower layer of the crust consists of basaltic and ultra-basic rocks

1 and 2

1, 2 and 3

1, 3 and 4

All of the above

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Explanation:

1. The outermost layer or cover of the earth is crust with an approximate thickness of 100 km.

2. It forms 0.5% of the earth’s crust volume.

3. The outer covering of the crust is of sedimentary materials and below that lie crystalline, igneous and metamorphic rocks which are acidic in nature.

4. The lower layer of the crust consists of basaltic and ultra-basic rocks. The continents are composed of lighter silicate= silica + aluminium (also called SIAL)- while the oceans have the heavier silicates- silica + magnesium (also called SIMA) which form the part of the mantle.