The ozone layer is a region in Earth’s stratosphere that contains high concentrations of a bluish gas called ozone. Although ozone constitutes only about one millionth of the atmosphere’s gas es , it absorbs most of the sun’s ultra violet radiation. Without the ozone layer , this radiation would destroy all life on the surface of the planet. Ultraviolet radiation creates and perpetuates ozone. When an ozone molecule is struck by an ultraviolet ray, it falls apart, yielding free oxygen and an oxygen atom that combines with an other free oxygen to form more ozone . This cycle absorbs most UV radiation.
Some manufactured chemicals interfere with this cycle, thus reducing the amount of ozone in the stratosphere. Among the worst offenders are chlorofluorocarbons (CFCs), usually found in refrigerants and aerosol sprays and now generally banned.
Falling ozone levels have caused a thinning of the ozone layer above Antarctica, known as the ozone hole . The Antarctic ozone hole has increased dramatically in size over the past two decades. A smaller hole over the Arctic is now developing.