CS_Ch9_Environment
2/28/05
4:41 PM
Page 586
A Vote for Ecology
Bio Words
water (hydrologic) cycle:
the cycle or network of
pathways taken by water
in all three of its forms
(solid, liquid, and vapor)
among the various places
where is it temporarily
stored on, below, and
above the Earth’s surface
evaporation: the process
of changing from a liquid
to a gas
condensation: the process
of changing from a gas to
a liquid
precipitation: water that
falls to the Earth’s surface
from the atmosphere as
liquid or solid material in
the form of rain, snow,
hail, or sleet
runoff: the part of the
precipitation appearing in
surface streams
groundwater: water
contained in pore spaces
in sediments and rocks
beneath the Earth’s
surface
infiltration: the
movement of water
through pores or small
openings into the soil and
porous rock
aquifer: any body of
sediment or rock that has
sufficient size and
sufficiently high porosity
and permeability to
provide an adequate
supply of water from
wells
long cycle
t
cycle
condensation
ens
ns
precipitation
THE WATER
CYCLE
cond
con
ondensation
atm
water vapor
life processes
precipitation
evaporation
evaporation
vap
va
runoff
infiltration
groundwater
The volume of water in the biosphere remains fairly constant through
time. In fact, the water that you used today has been around for
hundreds of millions of years. It has probably existed on the Earth’s
surface as a liquid, a solid, and a vapor. However, water is always
moving from place to place. It is forever changing from one state to
another.This complicated movement of the Earth’s water is called the
water cycle or hydrologic cycle. Some of the pathways of this
cycle are shown in the diagram above.
One of the largest reserves of water on Earth is found in the oceans.
The oceans contain about 97% of the Earth’s water. Other surface
water includes lakes, rivers, estuaries, marshes, and swamps. By
contrast, the atmosphere holds less than 0.001% of the Earth’s water.
This means that rapid recycling of water must take place between the
Earth’s surface and the atmosphere.
By absorbing heat energy from the Sun, some of the water on the
Earth’s surface changes to water vapor by evaporation. It rises
upward into the atmosphere until it reaches a point where the
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