The main gas that composes the Earth's atmosphere is nitrogen, making up about 78% of the atmosphere by volume. This inert gas is crucial as it is a primary component of proteins and nucleic acids, essential for life on Earth. Oxygen follows as the second most abundant gas, constituting around 21%, vital for respiration in most living organisms. Other gases, including argon, carbon dioxide, and trace gases, make up the remaining percentage. The composition of the atmosphere is crucial for maintaining the planet’s climate and supporting diverse ecosystems through various biological and chemical processes.