Which gas composes the largest portion of the Earth’s atmosphere?

Nitrogen composes the largest portion of the Earth's atmosphere, making up about 78% of it. This gas plays a crucial role in the atmosphere as it helps dilute oxygen and other gases, thus contributing to the stability of the atmosphere. Nitrogen is relatively inert, meaning it does not readily react with other elements or compounds, which allows it to exist abundantly without contributing to combustion or other chemical reactions that could alter the makeup of the atmosphere. The prevalence of nitrogen is significant for various processes, including the nitrogen cycle, which is essential for life on Earth, as it is a key component of proteins and nucleic acids. In contrast, while oxygen, carbon dioxide, and argon are important components of the atmosphere, their concentrations are much lower than that of nitrogen.