In this video Paul Andersen explains how stratospheric ozone protects humans from ultraviolet light. He explains how stratospheric ozone is formed when diatomic oxygen absorbs an ultraviolet photon and is split into two free oxygen atoms. The free atoms bond with another oxygen molecule to form an ozone molecule creating a stable ozone layer. He then explains how chlorine atoms released from chlorofluorocarbon molecules act as an enzyme to breakdown up to 100,000 ozone molecules. The Montreal Protocol was a treaty signed by countries on the planet to reduce the amount of CFCs in the atmosphere to protect the ozone layer.