|Appearance||colorless gas, very pale blue liquid|
Oxygen is a chemical element with the chemical symbol O and atomic number 8. On Earth it is usually bonded to other elements in compounds. Examples of common oxygen-containing compounds include water (H2O), sand (silica SiO2) and rust (iron oxide Fe2O3).
Diatomic oxygen (O2) is one of the two major components of air. It is produced by plants during photosynthesis and is necessary for aerobic respiration in animals. However, it is toxic to anaerobic lifeforms.
Triatomic oxygen (ozone O3) forms through radiation in the upper layers of the atmosphere. The ozone layer acts as a shield against UV radiation.