Page 124 - SST Class 07
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The hydrosphere                     17












             q   Fresh and saline water                             q   Major water bodies
             q   Ocean waters and their circulation

            Introduction                                            use water, we pollute it. If we pollute it all, we
                                                                    will have no water for our use, so be careful and
            Water is present on the earth in large quantity.
                                                                    conserve water as much as you can.
            About 71 percent of the earth is covered with
            water. The water mass which covers the greater                  Just Think!
            parts of the surface of the earth, is called
            hydrosphere. It includes water bodies like oceans,
                                                                     We have so little freshwater despite 70% of the
            seas, lakes, rivers, ice caps and underground water.
                                                                     earth’s surface being covered with water. Why?
                         FRESH AND SALINE WATER                     How does the seawater become saline? By saline
                                                                    water is meant salty water. You have read that
            You may say that we have so much of water on
                                                                    evaporation takes place from water bodies. Since
            the earth, then why talk of conserving it all the       oceans and seas are the largest water bodies, the
            time. No doubt, 71 percent of the earth’s surface       quantity of evaporation from them is the greatest.
            is covered with water, yet the amount of water we
                                                                    But only fresh water is evaporated; that is, all that
            can use is only a little. Let us see the distribution   is dissolved in water remains back in the oceans
            of water on the earth in order to drive this point      and seas, while clean water is evaporated. The
            home :
                                                                    things that are dissolved in the seawater include
            Oceans and seas        :     97.30 percent              salt, minerals and other impurities. The rivers
                                                                    carry these impurities to the sea, which keep
            Ice-caps               :     0 2.00 percent
                                                                    accumulating there, thus making the seawater
            Groundwater            :     0 0.66 percent             very saline.
            Rivers, lakes etc.     :     0 0.02 percent             On an average, the seawater contains about 35
            Atmosphere             :     0 0.02 percent             gm    of    sodium    chloride    (common      salt),
                                                                    magnesium, calcium and potassium.
                  F ind Outind Out                                                    Calcium  Potassium
                                                                               Sulphate  1%
                                                                                                1%
            When is the World Water Day celebrated?                       Magnesium 8%
                                                                             4%
            The water in the oceans and seas is saline, so we
            cannot use it. Another 2 percent is in the form of
            ice-caps, that too is not available to us for use.
                                                                                                       Sodium
            That leaves only 0.70 percent which we can use.               Chloride                       55%
            This water is as much as about half a glass out of a           31%
            bucketful of water. This is precisely the reason that
            everybody talks of conserving water. When we
                                                                                    Composition of seawater
                     Contemporary Social Science-7
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