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Inert gas. 78 percent of the Earth's atmosphere by volume and about 77 percent by weight is nitrogen. Colorless, odorless, tasteless, and non-toxic, it maintains at these levels by the nitrogen cycle. Nitrogen is an essential tissue component as amino acids and nucleic acids in all animals and plants. Plants derive it from the soil, fertilizers, or through the nitrogen cycle, and animals derive it from plants. Mainly for manufacturing ammonia, dyes, explosives, and fertilizers, air's liquefaction and fractional distillation is industry's nitrogen source.