Encyclopedia of Environmental Science and Engineering, Volume I and II

WATER: PROPERTIES, STRUCTURE, AND OCCURRENCE IN NATURE

THE CYCLE OF WATER

The Origin of the Hydrosphere

The assumption that the elemental composition originally

present in all regions of the solar system was similar to that

currently present in the sun furnishes a paradox in the marked

deficiency of the unreactive noble gases, such as neon and

argon, on the planet earth. Thus it is assumed that these gases,

as well as those of comparable molecular weight such as

water, nitrogen, oxygen, and carbon dioxide, escaped from

the earth’s surface before the planet cooled down. Thus the

accumulation of the water necessary to form the hydrosphere

by condensation of any primordial envelope of steam is incon-

sistent with the conditions of the primitive earth.

Rather, degassing, after the formation of the earth, is

considered to be the mechanism through which the “excess

volatiles” of water, nitrogen, chlorine, and so on accumu-

lated on the earth’s surface. According to Rubey, if only 1%

of the water emerging from hot springs and related phenom-

ena is truly juvenile water, then this process would have been

sufficient to produce the oceans and hence the hydrosphere.

The Hydrologic Cycle and Solar Energy

The dynamic equilibrium or steady state existing between

evaporation, precipitation, percolation, and runoff comprises

the hydrologic cycle.

Except for the small amount of radioactive energy and heat

transfer from within the earth, the sun provides the energy to

run this complex cycle by evaporating surface water and heat-

ing the humid air, which then results in stirring of the weather

systems. Four-fifths of the solar energy radiating toward the

earth actually reaches the earth’s surface. This incoming energy

totals 1.6 
 10 18 watts, about one-third of which recharges the

hydrologic cycle by vaporization. Under normal conditions it

requires about 540 calories per gram to evaporate water.

Evaporation

Of the 3.61 
 10 20 grams per year evaporated from the sea,

approximately 90% is returned directly to the ocean in the

various forms of precipitation. The remaining 10% is trans-

ported in the atmosphere and eventually released on the land

masses, as illustrated in Figure 1.

Sun

Atmosphere: 34.1 X 10^15 gallons

16.4 X 10^15 gallons/yr

26.1 X 10^15 gallons/yr

95.3 X 10^15

gallons/yr

85.5 X 10^15 gallons/yr

+ 60m

140m

Oceans:

748,700 X 10^15

gallons

9.8 X 10

15 gallons/yr

Probable range of sea level

controlled by growth and

shrinkage of glaciers

Ground water

Vadose water = 17.6 X 10^15 gallons

Ground water = 2200 X 10^15 gallons

Total ground water = 2217.6 X 10^15 gallons

Lakes and rivers:

60.8 X 10^15 gallons

Glaciers:

7700 X 10^15 gallons

9.8 X 10

(^15) gallons/yr
FIGURE 1 The hydrosphere and the hydrological cycle. From Skinner (1969).
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