High in the atmosphere is a layer of ozone that performs an
important job: It screens out much of the sun's harmful ultraviolet radiation.
Without protection from the radiation, life on Earth couldn't survive. And the
ozone layer is being destroyed by chemicals that people put in the air.
The ozone layer is thought to have formed billions of years
ago, through the interaction of sunlight and oxygen. Because this interaction
is still going on, the layer is constantly renewed. But since the 1970’s,
scientists have observed a thinning in the layer. The thinning is most serious
over the Earth's poles -- over Antarctica, the ozone level has dropped so much
that scientists talk about a "hole" in the layer. But it's occurring
worldwide.
Several pollutants are thought to be destroying the ozone.
The most important are chlorofluorocarbons, or CFC's. CFC's are used as
solvents, refrigerants, foaming agents in styrofoam and similar products, and
propellants in aerosol sprays. When they are released into the air, they rise
into the upper atmosphere and destroy the ozone.
The change in the ozone layer can't be seen or felt, but it
could have serious results. Even a small increase in ultraviolet radiation can
lead to higher rates of skin cancer and other health problems. The radiation can
harm crops. And it can kill the tiny plants and animals that are at the bottom
of the food chain. That might make survival impossible for larger animals.
Under an international treaty, 93 nations agreed in 1990 to
phase out the use of CFC's, using other chemicals in their place. But some
scientists fear that the chemicals used in place of CFC's will contribute to
another problem: global warming. (Grolier Book of Knowledge Encyclopedia)