The most abundant gas in the Earth’s atmosphere is nitrogen. The second most abundant gas is oxygen. Both of these gases occur as diatomic molecules. The Earth’s atmosphere is composed of approximately 78 percent nitrogen, 21 percent oxygen, 1 percent argon and trace amounts of other gases that include carbon dioxide and neon. Nitrogen is an important component of amino acids, protein, DNA and RNA. All living organisms depend on nitrogen for growth, metabolic processes and reproduction. Animals then acquire the nitrogen by eating plants and other animals. Other bacteria in the soil will convert the ammonium and nitrate into di-nitrogen.
Oxygen gas (O2) is required by all living organisms for respiration and is a component of DNA molecules. Ozone (O3) is a form of oxygen that is present in the Earth’s atmosphere. Ozone protects the Earth’s surface from ultraviolet radiation by both absorbing and reflecting harmful rays.