The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is potentially damaging to life on Earth. It is mainly located in the lower portion of the stratosphere from approximately 13 km to 40 km above Earth, though the thickness varies seasonally and geographically. The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed the Dobson meter that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The 'Dobson unit', a convenient measure of the columnar density of ozone overhead, is named in his honor.

Ozone in the Earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O2), splitting them into individual oxygenatoms (atomic oxygen); the atomic oxygen then combines with unbroken O2 to create ozone, O3. The ozone molecule is also unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O2 and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle, thus creating an ozone layer in the stratosphere, the region from about 10 to 50 km (32,000 to 164,000 feet) above Earth's surface.

A chlorofluorocarbon (CFC ) is an organic compound that contains carbon, chlorine, and fluorine. Its chemical composition is CCl3F. Uses include refrigerants, blowing agents, propellants in medicinal applications, and degreasing solvents. These can deplete the amount of ozone in the stratosphere by making a separate chlorine atom start a chemical reaction that can destroy up to 100,000 ozone molecules per chlorine atom. That’s almost 300,000 ozone molecules per chlorofluorocarbon molecule! If CFCs weren’t banned in the late 1970s, in 50 years, our planet would have no ozone & everything would burn up.