Hydrosphere refers to that part of the earth which is covered with water. This forms about 3/4 of the total surface area of the earth. In contract to hydrosphere, the part of the earth consisting of land mass is called lithosphere.
The hydrosphere includes the area covered by oceans, seas lakes, and rivers.
In hydrosphere the temperature and pressure of water varies considerably with depth. In this respect it resembles the earth's atmosphere. The average depth of oceans is about 3730 meters, and the deepest point of the oceans is more than 11 kilometers deep below the surface. The average sea level is about 840 meters less than average land level.
Hydrosphere is divided in two categories base on whether the body of water is fresh water or salt water. In general fresh water contains very small amount of other dissolved substances. In comparison salt water contains many chemicals in higher concentrations. Salt water has very high content of sodium chloride, that is common salt. It also contains appreciable quantities of magnesium, sulphates, calcium, carbonates, bromides and potassium. It also contains traces of other elements such silver, gold, and radium.
In nature water occurs on the land, below its surface, in atmosphere and in the biomass. Of the total volume of water available, 97% is in the vast oceans, 2% stored in the form of ice-sheets and less than 1% is available as fresh water.
The origin of terrestrial water is a controversial issue. It is stated that water existed in the early formation of Earth, but not in liquid form or as vapor in the atmosphere, but tied to rocks.
Gradually, water was released in the form of steam by the hot rocks, together with carbon dioxide, forming a second atmosphere. When crust cooling has widened,water has condensed , rain has appeared and formed seas, and water intake from depths,continued through emanations of volcanoes.
Thus,it was formed as a shell of the earth, consisting of oceans, seas, lakes, glaciers, rivers, groundwater, snow and ice, called the hydrosphere.
Earth is the only place known where the water is clear and liquid, the result of convergence of several natural and climatic factors.
All of these components of the hydrosphere, are the water source available on the planet Earth, regarded as national entities, by virtue of their sovereign rights over a territory, legally recognized.