The main gas in the air we breathe is nitrogen, which constitutes approximately 78% of the Earth's atmosphere. While nitrogen is essential for plant growth and is a key component of amino acids and nucleic acids, it is largely inert in its molecular form (N2) and does not readily react with other substances. The second most abundant gas is oxygen, making up about 21% of the atmosphere, which is vital for the survival of aerobic organisms. Other gases, such as carbon dioxide, argon, and trace gases, comprise the remaining percentage. The balance of these gases supports life, climate, and atmospheric processes.