The most abundant gas in the Earth’s atmosphere is nitrogen, which makes up about 78% of the atmospheric composition. This inert gas plays a crucial role in various biological processes and is vital for life on Earth. Nitrogen is not directly usable by most organisms in its gaseous form, but it can be converted into a bioavailable form through processes like nitrogen fixation. This conversion allows plants to absorb it as a nutrient, which then enters the food chain. Oxygen is the second most abundant gas, constituting approximately 21% of the atmosphere.