The primary gas in the Earth's atmosphere is nitrogen, which makes up about 78% of the atmosphere by volume. Oxygen, which is essential for most life forms on Earth, accounts for about 21%. The remaining 1% consists of trace gases, including argon, carbon dioxide, and several others. Nitrogen plays a crucial role in maintaining the balance of the atmosphere, as it is relatively inert and does not readily react with other atmospheric components. This stability allows it to help in diluting oxygen and prevents combustion in the atmosphere, creating a conducive environment for life on Earth.