The main gas that makes up the air we breathe is nitrogen, which constitutes about 78% of Earth's atmosphere. Oxygen follows as the second most prevalent gas at around 21%. The remaining 1% is made up of trace gases, including argon, carbon dioxide, and others. The presence of nitrogen helps to dilute oxygen, making it less reactive and thus supporting life. This composition is crucial for maintaining the balance in ecosystems, allowing various biological processes to occur, including respiration and photosynthesis. Understanding the composition of air is vital for fields such as environmental science and healthcare.