ABSTRACT
The dependence of life on water is absolute on Earth. Plants, animals and humans depend all upon the availability of water to sustain life. Water constitutes the primary constituent of the oceans, rivers and subterraneous fluids on our planet. In its various forms, water occupies about 1.4 × 1018 m3 on Earth (Berner and Berner 1987). The water cycle on the planet includes the evaporation of water, atmospheric circulation of vapour, precipitations and flowing streams both above and below ground. Through this cycle, air and water constantly interact: in the atmosphere, at the sea surfaces and on the mainland. These continuous exchanges are most important for the biological and chemical equilibrium of the planet including the balance between nitrogen, oxygen and carbon dioxide in the atmosphere.
