The hydrosphere is the combined mass of water found on under and above the surface of a planet or minor planet or natural satellite. Hydrosphere on Earth has been around for about four billion years and it continues to change in shape. This is caused by 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 one state or reservoir to another. Fresh water sources contain rivers or lakes and rain whereas saline water sources contain oceans and seas along with these two sources other reservoirs are groundwater and polar ice caps. Solar energy in the form of heat light and gravity cause the transfer from one state to another over periods from hours to thousands of years. Most evaporation comes 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 the hydrosphere as a closed system in which water exists. De Villiers claimed that on Earth the total amount of water has almost certainly not changed since geological times so what we had then we still have now. Water can be polluted and abused or misused but it is neither created nor destroyed it only migrates. There is no strong evidence that water vapour escapes into space. Water is a basic necessity of life. Two third of the Earth is covered by water. The Earth is also called the blue planet and the watery planet. The hydrosphere plays an important role in the existence of the atmosphere in its present form. Oceans are important in this regard. When the Earth was formed it had only a very thin atmosphere rich in hydrogen and helium similar to the present atmosphere of Mercury. Later the gases hydrogen and helium were expelled from the atmosphere. The gases and water vapour released as the Earth cooled became its present atmosphere. Other gases and water vapour released by volcanoes also entered the atmosphere. As the Earth cooled the water vapour in the atmosphere condensed and fell as rain. The atmosphere cooled further as atmospheric carbon dioxide dissolved into the rain water. In turn this further caused the water vapour to condense and fall as rain. This rain water filled the depressions on the Earth surface and formed the oceans. The first life forms began in the oceans. These organisms did not breathe oxygen. Later cyanobacteria evolved the process of conversion of carbon dioxide into food and oxygen. As a result Earth atmosphere has distinctly different composition from that of other planets and allowed for life to evolve on Earth. The activities of modern humans have drastic effects on the hydrosphere. For instance water diversion human development and pollution all affect the hydrosphere and natural processes within. Humans are withdrawing water from aquifers and diverting rivers at an unprecedented rate. The Ogallala Aquifer is used for agriculture in the United States and if the aquifer goes dry more than twenty dollar billion worth of food and fibre will vanish from the worlds markets.