The most common gas in the Earth's atmosphere is nitrogen. Comprising about 78% of the atmosphere, nitrogen is a colorless, odorless gas that plays a crucial role in the nitrogen cycle, which is essential for life. While nitrogen itself is inert and does not readily react with other substances, it is a fundamental ingredient in amino acids and nucleic acids, which are vital for all living organisms. Oxygen is the second most abundant gas, making up about 21% of the atmosphere. The composition of the atmosphere is crucial for maintaining life and regulating the Earth's climate.