Earth is often called the water planet because
about 70 per cent of it is covered by water. Pictures from space
show it to be a beautiful blue jewel, veiled in trailing clouds.
It is a lovely home for living beings.
Not all of this water is
really available for our use, however. 97.3 % of the water is
in the oceans, and the oceans are salty. Over billions of years
rain has washed salts and other minerals into the seas. The water
has evaporated, leaving the minerals behind. Our bodies, and
the land plants around us, cannot make use of salty water for
The oceans do make our planet
habitable, however. The water that evaporates from the ocean
surface forms clouds that water the land area with rain and snow.
The huge volume of water tends to stabilize temperatures on the
The ocean is also rich in fisheries
and other sources of food.
As land dwellers, however, let
us look at the water situation more closely now.
Beside the huge cube that represents
the ocean water, we see the tiny portion of the water that is
fresh. However, this is not all available to us.
Where the Fresh Water Is
Volume in Thousands of Cubic Kilometers
Percentage of Total Water on Earth
||This is salty sea water.
||Much of this ice is in the Antarctic
||Underground aquifers, deep wells
||Provide drinking water, irrigation
water, fish and recreation
| Soil Moisture
||This is being used by our crops,
trees, and surface vegetation
| Water Vapor
in the Atmosphere
|| Clouds, fog, and dew
||Provide water for drinking,
irrigation, and recreation
from: Environment Canada
When we see how little of the earth's water sustains life on
the land, we cannot help but be concerned about preserving that
water. Right now our water supply is being contaminated with
biological and industrial wastes and poisons. Once groundwater
is contaminated, it is very difficult (perhaps impossible) to
restore its purity. We are also pumping water out of the deep
aquifers more quickly than rainfall can refill them. Our children
may come to regret our thoughtless misuse of the precious water
on our world.
As you design your planetary
system, consider the presence of salt among the minerals on your
planet. If you have very little land, your oceans may not be
as saline as the oceans on earth. If you have much less water,
you can expect more salty seas. We have some small, salty seas
on earth: the Dead Sea and the Great Salt Lake, for instance.
When water is saturated with dissolved salt, the excess salt
precipitates out as crystals.
Photographs from a Corel CD-ROM
: for viewing only, not for downloading.
Header from NASA Earth From Space
1999, 2003. Elizabeth Anne
Viau and her licensors. All rights reserved. This
material may be used by individuals for instructional purposes
but not sold. Please inform the author if you use it at firstname.lastname@example.org.