What is the primary gas that makes up Earth's atmosphere?

The primary gas that makes up Earth's atmosphere is nitrogen. In fact, nitrogen constitutes about 78% of the atmosphere by volume. It is an inert gas, meaning it does not readily react with other substances under standard conditions. This high concentration of nitrogen is essential for maintaining atmospheric stability and supports various life processes.

In contrast, oxygen, which is crucial for respiration in many living organisms, makes up approximately 21% of the atmosphere. Carbon dioxide and hydrogen are present in much smaller quantities, with carbon dioxide being vital for plant photosynthesis but accounting for only about 0.04% of the atmosphere. Hydrogen is the least prevalent of the common atmospheric gases, contributing to less than 0.00005% of the atmosphere. Thus, nitrogen's predominance is key to understanding the composition and behavior of Earth's atmosphere.