The primary gas found in the air we breathe is nitrogen, making up about 78% of Earth's atmosphere. This gas is essential for numerous biological processes, though it is not directly usable by most living organisms. Nitrogen must first be converted into a usable form through processes such as nitrogen fixation, facilitated by certain bacteria. Oxygen, another vital gas, comprises approximately 21% of the atmosphere and is crucial for respiration in most living organisms. The remaining 1% includes trace gases like carbon dioxide, which plays a significant role in climate and plant life.