Page 124 - SST Class 07
P. 124
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
124
