The ozone layer is a strip of physically, biologically occurring ozone gas that is situated 9.3 to 15 to 30 kilometers above the Earth and is considered to be a natural shield from the harmful ultraviolet B radiation produced by the sun. Currently, there is widespread concern that the ozone layer is being systematically destroyed because of the large-scale release of greenhouse gasses containing the chemicals chlorine and bromine. This destruction allows large amounts of ultraviolet B rays to reach Earth, which are the main causes of skin cancer and cataracts in humans and very harmful to animals as well.
Extra ultraviolet B radiation that reaches Earth also restricts the reproductive cycle of phytoplankton, single-celled organisms such as algae that make up the bottom rung of the food chain. Biologists fear that reductions in phytoplankton populations will in turn lower the populations of other animals. Researchers also have documented changes in the reproductive rates of young fish, shrimp, and crabs, as well as frogs and salamanders exposed to excess ultraviolet B. Ozone, is a highly reactive molecule that consisting of three oxygen atoms. It is continuously being formed and broken down in the high atmosphere, 6.2 to 31 miles (10 to 50 kilometers) above Earth, in the region called the stratosphere.
Chlorofluorocarbons (CFCs), chemicals found mainly in spray aerosols heavily used by industrialized nations for much of the past 50 years, are the primary culprits in ozone layer breakdown. When CFCs reach the upper atmosphere, they are exposed to ultraviolet rays, which causes them to break down into substances that include chlorine. The chlorine reacts with the oxygen atoms in ozone and rips apart the ozone molecule. One atom of chlorine can destroy more than a hundred thousand ozone molecules, according to the U.S. Environmental Protection Agency. About 90 percent of CFCs currently in the atmosphere were emitted by industrialized countries in the Northern Hemisphere, including the United State.
The ozone layer above the Antarctic has been especially destroyed by pollution since the mid-1980s. This region’s low temperatures speed up the conversion of CFCs to chlorine. In the southern spring and summer, when the sun shines for long periods of the day, chlorine reacts with ultraviolet rays, destroying ozone on a massive scale, up to 65 percent. This is what some people erroneously refer to as the “ozone hole.” In other regions, the ozone layer has deteriorated by about 20 percent and will continue to deteriorate unless the current rate of pollution is stopped