Without the ozone layer, the sun's ultraviolet radiation would negatively affect life on land and in the water, leading to mass extinction. The ozone layer is a protective area of the Earth's stratosphere that absorbs between 97 and 99 percent of the sun's UV radiation, allowing life to exist.
The ozone layer is not evenly distributed throughout the globe; it is thicker near the polar regions than around the equator. Seasonal changes also influence the ozone layer's thickness, with the highest levels of thickness found in the spring. Free radical catalysts are responsible for the worldwide depletion of the ozone. Such agents include nitric oxide, nitrous oxide, bromine, chlorine and hydroxl. The commercial production of chlorofluorocarbons and bromofluorocarbons utilizes bromine and chlorine in levels that are not found in nature. When chlorofluorocarbons and bromofluorocarbons, which are very stable, rise into the stratosphere, chlorine and bromine radicals are freed by UV light and begin to break down ozone molecules.
Ozone, or trioxygen, is an allotrope of oxygen that is known for its pale-blue color and strong smell, which is similar to chlorine. It results from the reaction between dioxygen and ultraviolet light or atmospheric electrical discharges. Not all ozone is relegated to the stratosphere; a minute amount is found throughout the atmosphere. When condensed at cryogenic temperatures, ozone becomes a dark-blue liquid before becoming a near-black solid.