Nov 23, 2012

The Ozone Layer

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)