The most common gas found in the Earth’s atmosphere is nitrogen, accounting for approximately 78% of the atmosphere's composition. This inert gas plays a vital role in sustaining life, although it is not directly usable by most organisms. Nitrogen must be converted into more accessible forms, like nitrates, through processes such as nitrogen fixation carried out by specific bacteria. The remaining components of the atmosphere include oxygen, carbon dioxide, and trace gases, all of which are essential for various biogeochemical cycles that support life on Earth.