In chemistry, we represent elements with letters (for example “O” stands for the element “oxygen”), and the small numbers to the lower-right of the element indicate the number of atoms of that element in the molecule. For example, O₂ represents a molecule that consists of two oxygen atoms, which is the stable form of “regular” oxygen. O₃ represents a molecule that consists of three oxygen atoms, which is the unstable form of oxygen called ozone.

Ozone has existed on Earth for as long as oxygen has been here — about 500 million years. It has existed in our universe for billions of years. Wherever oxygen comes into contact with an electric arc, such as lightning and/or a particular wavelength of ultraviolet rays, like those from the sun around which the planet orbits, ozone will be created.