The ozone layer is a region of atmosphere 12-30 mi (19-48 km) above Earth's surface that consists of ozone concentrations of as much as 10 parts per million. Ozone is an allotropic form of oxygen composed of three atoms of oxygen in each molecule, O. The main function of the ozone layer is protection of Earth's surface from harmful ultraviolet rays from the Sun. Although this atmospheric layer filters ultraviolet rays, the ozone layer does allow enough ultraviolet rays to pass through to support the activation of vitamin D in humans.

The word ozone is derived from the Greek oxein meaning to smell. It is a pale blue gas with a strong odor. Ozone boils at -169.5°F (111.9°C) and melts at -314.5°F (-192.5°C). In the liquid form ozone appears bluish-black, but when frozen it becomes a violet-black color. Liquid ozone...