Ozone (O3) is a relatively unstable molecule, and although it represents only a tiny fraction of the atmosphere, it is crucial for life on Earth. Depending on its location, ozone can protect or harm life on Earth. Most ozone resides in the stratosphere, where it acts as a shield to protect the surface from the Sun’s harmful ultraviolet radiation. In the troposphere, ozone is a harmful pollutant which causes damage to lung tissue and plants.