A pungent-smelling, slightly bluish gas which is a close chemical cousin to molecular oxygen. About 90% of the earth's ozone is located in a natural layer far above the surface of the globe, in a frigid region of the atmosphere known as the stratosphere. Here in this outer region it protects the earth and its inhabitants from the harmful effects of ultraviolet radiation from the sun.

Last modifed Monday, December 18, 2006.