A band of ozone in the upper atmosphere. Ozone is a molecule made of three atoms of oxygen instead of the usual two.
- The ozone layer absorbs harmful ultraviolet radiation from the sun and is thus very important to the health of human beings and other life forms on Earth. The Earth's ozone layer could be at risk because of the action of chlorofluorocarbons, but international treaties have banned the production of these chemicals. The ozone layer is expected to return to normal in a few decades. (See ozone hole.)