The mountains did not exist in their present place or form since the time of formation of the earth but were brought into existence later. Some mountains were formed due to volcanic action, some due to erosion of plateaus while others came into existence as a result of compression and elevation of sediments which had accumulated in seas and oceans, Himalayas being an example of this type of mountain ranges. These events took place during various periods in the earth’s, history and lasted for very long periods of time. It has been suggested that the relationship of land surface to ocean floors is comparable to the floatation of light and heavy blocks. The land is high because it is of light material, the ocean floor is depressed because it is of heavy material. These ideas are embodied in the “Theory of Isostacy” which suggests that, there are a set conditions of these floating blocks i.e. mountains and ocean basins, which give equilibrium to our rotating globe, but which, if disturbed, will lead to earth movements. This implies that in the absence of mountains, the earth could have been in a continuous state of disturbance. In other words, mountains in addition to serving other purposes (controlling wind, rain etc.), keep the earth’s crust in a balanced state.