What is the most abundant gas in Earth's atmosphere?

The most abundant gas in Earth's atmosphere is nitrogen. It constitutes about 78% of the atmosphere, making it the dominant component. Nitrogen's abundance is significant because it plays a crucial role in various environmental and biological processes. For example, it is essential for the synthesis of amino acids and nucleic acids, which are vital for life. Additionally, nitrogen serves as a non-reactive filler in the atmosphere, helping to dilute oxygen and other gases, which allows for a stable environment suitable for living organisms.

In contrast, oxygen, while essential for respiration in many life forms and about 21% of the atmosphere, is not nearly as abundant as nitrogen. Carbon dioxide and hydrogen make up even smaller percentages of the atmosphere, with carbon dioxide being important for the greenhouse effect and hydrogen being a trace gas. Therefore, nitrogen's role and prevalence underscore its importance in Earth's atmospheric composition.