The most abundant gas in the Earth's atmosphere is nitrogen, comprising about 78% of the atmosphere's total composition. Nitrogen is a colorless, odorless gas that is essential for life; it serves as a critical component of amino acids and nucleic acids, which are the building blocks of proteins and DNA, respectively. Although nitrogen is not directly usable by animals and plants, it is crucial in the nitrogen cycle, where it is converted into more reactive forms through processes like nitrogen fixation. This gas's high concentration contributes to the stability and overall balance of the atmosphere.