The primary gas that makes up the Earth's atmosphere is nitrogen, accounting for about 78% of the total composition. Oxygen follows as the second most abundant gas, making up approximately 21%. Other components include argon, carbon dioxide, and trace gases. Nitrogen plays a crucial role in the atmosphere, being inert and thus facilitating the stability of conditions necessary for life. It is essential for forming amino acids and nucleic acids in living organisms through the nitrogen cycle, which makes it vital for ecological balance and growth processes.