Ozone is an invisible gas, a form of oxygen. A thin layer of ozone exists between 12 and 30 miles (20 to 50 kilometers) above the Earth and forms a protective shield that is vital to our survival. Without it, the sun would burn us, a few things would grow.

The ozone layer shields us from one particular kind of sunlight: ultraviolet (UV) light. Some UV light is important--it helps plants to grow, for example. UV light also gives people a suntan. But if much more UV light were allowed to filter through the ozone layer, it would cause some big problems. Millions of people could get eye and skin diseases, farmers' crops could become damaged, and fish could run out of food.

What is destroying the ozone layer? One of the biggest culprits is a family of chemicals called chlorofluorocarbons (pronounced KLOR-o-floor-o-CAR-bons), or CFCs. These are used in manufacturing hundreds of different products, including many that you and your parents buy regularly. Some kinds of plastics and foam packaging materials are made with CFCs. They are also used to keep refrigerators and air conditioners cool.

Why are CFCs so bad? When they are released into the atmosphere and interact with sunlight, CFCs release chlorine atoms. As they rise into the atmosphere, these chlorine atoms attack and destroy parts of the ozone layer. A single chlorine atom can destroy thousands of ozone molecules.

In 1985, scientists noticed that the ozone layer was not just thinning, but that there was actually a big hole in it over Antarctica. A very big hole. By 1987 it had stretched to cover an area the size of the United States. In 1988, scientists found another hole, this time over the arctic. The holes constantly change shape and size, depending on the time of year.

In 1990, many countries agreed to cut the use of CFCs substantially by the year 2000. Enviornmentalists hope that we can make a complete switch from CFCs even sooner. Several companies around the world are researching substances that can replaces CFCs in air conditioners, refrigerators, plastics, and in many manufacturing process.

The fact is, even if we were to stop using CFCs today, the existing chemicals would ensure the continued destruction of the ozone layer for at least a century! So, the sooner we stop, the less destruction of the ozone layer we will cause in the future.