The ozone layer contains about 90 percent of Earth's ozone. It is part of Earth's stratosphere and lies between 6 and 30 miles above the planet's surface, according to the Environmental Protection Agency. The highest concentration of ozone is found between 12 and 19 miles above the surface, notes Wikipedia.
The ozone layer absorbs from 97 to 99 percent of medium-length ultraviolet radiation from the sun, protecting life on Earth from UV radiation's harmful effects, according to Wikipedia. It is normally thinnest at the equator and thickest at the poles. It also varies with the seasons, and it is thicker in the spring than in the autumn. Ozone is depleted by free-radical catalysts from natural sources and man-made chemicals, such as chlorofluorocarbons and bromofluorocarbons.