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the interrupted water covering of the earth, which is distributed between the atmosphere and the solid crust of the earth (lithosphere) and makes up the totality of oceans, seas, and surface waters of the land masses. In a broader sense the hydrosphere also includes subterranean waters and the ice and snow of the arctic and antarctic regions, as well as atmospheric water and water contained in living organisms. The principal mass of water of the hydrosphere is concentrated in the seas and oceans. The second largest mass of water by volume is taken up by subterranean waters, and the third largest mass is the ice and snow of the arctic and antarctic regions. Surface waters of dry land and atmospheric and biologically bound waters make up a fraction of a percent of the general volume of water of the hydrosphere. The chemical composition of the hydrosphere is similar to the average composition of seawater.
Surface waters, which occupy a relatively small fraction of the general mass of the hydrosphere, nevertheless play an extremely important role in the life of our planet, since they are the basic source of water supply and irrigation. The waters of the hydrosphere constantly interact with the atmosphere, the earth’s crust, and the biosphere. The interaction of these waters and the mutual transformations from one type of water to another constitute the complex water cycle on the planet. The hydrosphere was the first part of earth to sustain life. Only at the beginning of the Paleozoic era did plant and animal organisms begin to move gradually to dry land.
A. A. SOKOLOV