ozone layer

Region in the upper atmosphere, about 6–30 mi (10–50 km) high, with significant concentrations of ozone, formed by the effect of solar ultraviolet (UV) radiation on oxygen and also present in trace quantities elsewhere in earth's atmosphere. Ozone strongly absorbs solar UV radiation, causing atmospheric temperature to climb to about 30°F (0°C) at the top of the layer, and preventing much of this radiation from reaching earth's surface, where it would injure many living things. Chlorofluorocarbons, or CFCs, and some other air pollutants that diffuse into the ozone layer destroy ozone. In the mid-1980s, scientists discovered that a “hole”—an area where the ozone is up to 50% thinner than normal—develops periodically in the ozone layer above Antarctica. This severe regional depletion, explained as a natural seasonal depletion, appears to have been exacerbated by the effects of CFCs, and may have led to an increase in skin cancer caused by UV exposure. Restrictions on the manufacture and use of CFCs and other ozone-destroying pollutants were imposed in 1978.