The most common gas in Earth's atmosphere is nitrogen, which makes up approximately 78% of the atmosphere by volume. This inert gas plays a crucial role in supporting life on Earth, although it is not directly usable by most organisms. Nitrogen is essential for the synthesis of amino acids, proteins, and nucleic acids, making it vital for biological processes. Atmospheric nitrogen cycles through various systems in nature, including the nitrogen cycle, where it is converted into usable forms by certain bacteria, thereby supporting plant growth and, in turn, the entire food web.