The stratosphere is a layer of the atmosphere extending between 11 and 30 miles from the surface of the earth. The lower part of the stratosphere contains ozone. The ozone layer absorbs much of the incoming ultraviolet radiation from the sun. This protects land organisms from radiation's damaging mutagenic effects. Ozone is formed by the interaction of ultraviolet light and oxygen, a molecule consisting of 2 oxygen atoms. Ozone is a molecule consisting of 3 oxygen atoms. The ozone layer has begun to break down as a result of the presence in the stratosphere of chlorofluorocarbons, referred to as CFCs. CFCs were manufactured for their use in refrigeration and styrofoam production. When a molecule of CFC is exposed to ultraviolet light a chlorine atom breaks away. This chlorine strips away an oxygen atom from ozone, reducing the ozone to a molecule of oxygen. Then the oxygen atom in the resulting chlorine compound is pulled off by an oxygen atom. The chlorine is now free to start the cycle of ozone destruction all over again. One molecule of CFC can destroy 100,000 ozone molecules.