Oxygen
From RationalWiki
Oxygen is an element that forms a diatomic gas (O2) under earth surface conditions. It also readily forms a triatomic molecule known as ozone under some conditions such as electrical discharges. Ozone is more stable in the upper atmosphere and forms a barrier to ultraviolet energy, the ozone layer, which is very important to current life forms on the planet.
It is a highly reactive chemical, so much so that most chemical reactions are classed as "oxidation" or "reduction" reactions depending on the relative exchange of electrons involved. The process of oxidation is fascinating, with its results varying from forming a protective, non-oxidizing surface coating on aluminum, through slowly destroying artifacts made of iron ("rust"), to rapid processes we call combustion, which release large amounts of energy in short periods of time.
Oxygen in its pure form is a useful industrial and medical commodity, and is often cooled and compressed into its liquid state for storage and transportation.
Earth's atmosphere is roughly 18% oxygen, which is created and replenished by plants using photosynthesis to capture energy from the sun, and consumed by most animal life and used in chemical reactions to obtain energy from food.
Oxygen-deprived regions are called "anoxic". Anaerobic bacteria are those which can survive only in environments in which there is no oxygen, and for which oxygen is toxic.
- Love Is Like Oxygen -- Sweet
