Which gas is most abundant in Earth's atmosphere?

Nitrogen is the most abundant gas in Earth's atmosphere, comprising about 78% of the atmosphere by volume. This nitrogen is primarily in a molecular form (N₂), which is a stable and inert gas. Its abundance plays a crucial role in various biological and ecological processes, such as serving as a nitrogen source for plants through the nitrogen cycle, although plants primarily utilize it in fixed forms like ammonia or nitrates.

Oxygen, while vital for the respiration of many living organisms, constitutes around 21% of the atmosphere. Argon, a noble gas, makes up about 0.93%, and carbon dioxide, although essential for photosynthesis and a significant greenhouse gas, is present in trace amounts, accounting for approximately 0.04% of the atmosphere. Thus, nitrogen's prevalence reflects its fundamental role in maintaining atmospheric pressure and supporting life on Earth.