2. HYDROSPHERE hydrosphere (from Greekὕδωρ - hydor, "water" and σφαῖρα - sphaira, "sphere") in physical geography describes the combined mass of water found on, under, and over the surface of a planet. The total mass of the Earth's hydrosphere is about 1.4 × 1018tonnes, which is about 0.023% of the Earth's total mass. About 20 × 1012tonnes of this is in the Earth's atmosphere (the volume of one tonne of water is approximately 1 cubic metre). Approximately 75% of the Earth's surface, an area of some 361 million square kilometres (139.5 million square miles), is covered by ocean. The average salinity of the Earth's oceans is about 35 grams of salt per kilogram of sea water (35 ‰).
3. Discontinuous layer of water at or near the Earth's surface. It includes all liquid and frozen surface waters, groundwater held in soil and rock, and atmospheric water vapour. Virtually all of these waters are in constant circulation through the hydrologic cycle. Although the components of the hydrosphere are undergoing continuous change of state and location, the total water budget remains in balance. The components of the hydrosphere have been seriously affected by the water-polluting activities of modern society.
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5. WATER POLLUTION One of the biggest problems facing our planet in this current century is the threat of water pollution. Water pollution happens on every continent, in every country, near nearly every city. It is the result of chemicals, garbage and other foreign items going into the water and contaminating the system. Sadly, water pollution is going to have a major impact on our future as more and more water is polluted and less and less drinking water is available. Rivers, lakes, seas and oceans are all being affected by water pollution that is slowly killing the major life source for the entire planet.
6. The water portion of the Earth as distinguished from the solid part and from the gaseous outer envelope (atmosphere). Approximately 74% of the Earth's surface is covered by water, in either the liquid or solid state. These waters, combined with minor contributions from ground waters, constitute the hydrosphere.
