The hydrosphere is the combined mass of water found on under and above the surface of a planet or minor planet or naturalsatellite. Hydrosphere on Earth has been around for about four billion years and it continues to change in shape. This is causedby seafloor spreading and continental drift which rearranges the land and ocean. The frozen part of hydrosphere is made of ice.The frozen part of the hydrosphere has its own name the cryosphere. The water cycle refers to the transfer of water from onestate or reservoir to another. Fresh water sources contain rivers or lakes and rain whereas saline water sources contain oceansand seas along with these two sources other reservoirs are groundwater and polar ice caps. Solar energy in the form of heatlight and gravity cause the transfer from one state to another over periods from hours to thousands of years. Most evaporationcomes from the oceans and is returned to Earth as snow or rain. Sublimation refers to evaporation from snow and ice.Transpiration refers to the expiration of water through the minute pores or stomata of trees. Marq de Villiers has described thehydrosphere as a closed system in which water exists. De Villiers claimed that on Earth the total amount of water has almostcertainly not changed since geological times so what we had then we still have now. Water can be polluted and abused ormisused but it is neither created nor destroyed it only migrates. There is no strong evidence that water vapour escapes intospace. Water is a basic necessity of life. Two third of the Earth is covered by water. The Earth is also called the blue planet andthe watery planet. The hydrosphere plays an important role in the existence of the atmosphere in its present form. Oceans areimportant in this regard. When the Earth was formed it had only a very thin atmosphere rich in hydrogen and helium similarto the present atmosphere of Mercury. Later the gases hydrogen and helium were expelled from the atmosphere. The gases andwater vapour released as the Earth cooled became its present atmosphere. Other gases and water vapour released by volcanoesalso entered the atmosphere. As the Earth cooled the water vapour in the atmosphere condensed and fell as rain.