The gas that makes up most of the Earth's atmosphere is nitrogen, accounting for about 78% of the atmosphere by volume. Oxygen follows as the second most abundant gas, making up approximately 21%. The remaining components include trace gases such as argon, carbon dioxide, and others. Nitrogen is crucial for life, as it is an essential component of amino acids and nucleic acids, which are building blocks of proteins and genetic material. The balance of gases in the atmosphere is vital for sustaining life and regulating the planet's climate.