The Hydrosphere: 

The hydrosphere, or water sphere, mostly covers the depressions of the lithosphere. Some  amount of water is also found in the rocks and much exists in the form of water vapour in  the atmosphere. The oceans represent about 71 per cent of the globe and therefore contain  the great bulk of the water. The average depth of the oceans is about 3,800 m. 

The total volume of the world oceans is about 1-4 billion cu. km. which comprises more  than 97 per cent of the world’s free water. Of the remaining 3 per cent, about 2 per cent is  locked up in the ice sheets of Arctic and Antarctica and about 1 per cent is being  represented by fresh water of the lands. 

Sea or ocean water is a solution of salt whose constituents have maintained more or less  fixed proportions over a considerable span of geologic time. In addition to their importance  in the chemical environment of marine life, these salts make up a vast store-house of  mineral matter. 

1. The earth’s water moves through an interesting cycle known as hydrological cycle.
2. It is  made up of two parts. In the first of atmospheric part, the horizontal movement of water  vapour predominates.
3. In the terrestrial, the second part, the movement of water in the  liquid and solid phase predominates. 
   

By evaporation, water enters the air as water vapour from the oceans and other water bodies as also from plants and animals by transpiration. As the water vapour moves up the  air it condenses and ultimately returns to the surface as precipitation.

From the land it returns back to the oceans or adds directly to the air through evaporation  and transpiration. This functional interrelation of hydrosphere, atmosphere and lithosphere  makes possible the continued existence of plant and animal life.