The ozone layer, also called the stratosphere, is composed of the ozone gas (90% of the total ozone in the atmosphere). The ozone has three oxygen atoms, and it is the result of the action of Ultra Violet (UV) radiation on oxygen molecules, composed of two oxygen atoms. In the upper regions of the atmosphere, UV light breaks apart oxygen molecules into two oxygen atoms, one of which then combines with a second oxygen molecule to form ozone. The stratosphere is about 15-30 kilometers above the Earths surface.