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Question
Give reasons for the following:
Earth as a whole does not expand.
Solution 1
About six important Convection Current Cells with over-riding six large plates have been identified below the Lithosphere. The Mid-Oceanic ridges from edges of the plates. For example, the Mid-Atlantic ridge is such a ridge. The molten matter from below adds new crust along such’ ridges. Taking the earth as a whole it has resulted in the spreading of the ocean floor at the rate of 1 cm to about 10 cm every year. It is called the constructive plate movement. At the same time, the crust at the other edges of the plates in oceanic trenches gets destroyed. It is called the destructive plate movement Consequently a balance exists and the Earth as a whole does not expand.
Solution 2
Inspite of various changes occurring within the earth it does not expand as it is affected by the centripital force of gravity working towards the centre of the earth
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