What is the primary gas found in the Earth's atmosphere?

The primary gas found in the Earth's atmosphere is nitrogen. It makes up about 78% of the atmosphere by volume, playing a crucial role in maintaining the Earth's air pressure and supporting life. Nitrogen is an essential element for all living organisms as it is a major component of amino acids, proteins, and nucleic acids, but it is also inert and does not readily react with other substances under normal conditions.

Oxygen, while vital for respiration in most living organisms, constitutes about 21% of the atmosphere. Carbon dioxide is present in much smaller amounts, typically around 0.04%, but is significant due to its role in the greenhouse effect and in photosynthesis. Hydrogen is the least abundant gas in the atmosphere, as it mostly escapes into space due to its lightness. Thus, nitrogen is the dominant gas and plays a foundational role in the composition of the atmosphere.