What is the primary component of Earth's atmosphere?

The primary component of Earth's atmosphere is nitrogen (N₂), which makes up approximately 78% of the atmosphere by volume. This gas is essential for various biological processes, including the nitrogen cycle, which is crucial for the growth of plants. Nitrogen is an inert gas under standard conditions, meaning it does not readily react with other elements, which helps maintain the stability of the atmosphere.

In contrast, substances like oxygen, carbon dioxide, and argon are present in much smaller quantities. Oxygen makes up about 21% of the atmosphere and is vital for respiration in living organisms. Carbon dioxide, while important for photosynthesis and as a greenhouse gas, constitutes only about 0.04% of the atmosphere. Argon is the third most abundant gas, accounting for about 0.93%, but its role in the atmosphere is negligible compared to that of nitrogen. Thus, the dominance of nitrogen in the atmosphere is what makes it the primary component.