According to How Stuff Works, the ozone layer works by ultraviolet light breaking apart oxygen molecules and then reforming them as ozone. Ozone converts the dangerous ultraviolet rays into harmless heat. With an adequate supply of ozone and oxygen, the ozone layer will absorb approximately 98 percent of incoming ultraviolet rays.
Oxygen molecules consist of a pair of oxygen atoms, while ozone molecules consist of three oxygen atoms bonded together. Ozone molecules are less stable, allowing them to break apart when struck by ultraviolet energy. The molecules absorb the energy and convert it to heat, severing the molecular bond and producing three individual oxygen atoms. These freed oxygen atoms are then able to bond with each other, creating either oxygen or ozone molecules.
The remaining ultraviolet energy in the stratosphere can then be absorbed by the oxygen molecules, in turn severing their bond and allowing freed oxygen atoms back into the system. While many of these atoms will reform into oxygen molecules, some will find pre-existing oxygen molecules and join them to create ozone. Every step in this process consumes ultraviolet energy and releases heat, protecting the plants and animals on the surface, while also raising the temperature of the atmosphere slightly.