- Oxygen
- Nitrogen
- Carbon dioxide
- Hydrogen
Nitrogen (N₂) constitutes approximately 78% of Earth’s atmosphere by volume, making it the most abundant gas. This diatomic molecule is colorless, odorless, and relatively inert due to its strong triple bond, which requires substantial energy to break. Nitrogen’s abundance results from its stability and constant replenishment through biological and geological cycles. Oxygen follows at about 21%, with argon (0.93%), carbon dioxide (0.04%), and trace gases completing the composition. Despite its inertness, nitrogen is essential for life as a component of amino acids, proteins, and nucleic acids. However, atmospheric nitrogen must be “fixed” into reactive compounds (ammonia, nitrates) by bacteria, lightning, or industrial processes (Haber process) before organisms can utilize it. Nitrogen cycles through ecosystems via fixation, nitrification, assimilation, and denitrification. Human activities, particularly fertilizer production and fossil fuel combustion, have altered the nitrogen cycle, causing environmental concerns like eutrophication and greenhouse gas effects (nitrous oxide). Understanding atmospheric nitrogen is fundamental to climate science, agriculture, and environmental chemistry.
