Today, oxygen therapy is a commonplace part of trauma care, anesthesiology, management of respiratory diseases, and treatment of a wide variety of other acute and chronic medical conditions. The many medical benefits of oxygen usage are now taken for granted. It was not always so.
The colorless, odorless, medical gas commonly called “oxygen” is actually the diatomic atmospheric gas dioxygen or O2 , the most stable molecular form of elemental oxygen, which is by mass the third most abundant element in the universe after hydrogen and helium.
When Earth was formed some 4.55 billion years ago, oxygen was not a major constituent of its atmosphere. Thanks to plant photosynthesis, today the average composition of the atmosphere by volume is 78.08 percent nitrogen, 20.95 percent oxygen, 0.93 percent argon, 0.038 percent carbon dioxide, and traces of other gases.
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