What is the primary gas that constitutes the majority of the Earth's atmosphere?

The primary gas that constitutes the majority of the Earth's atmosphere is nitrogen. Approximately 78% of the Earth's atmosphere is made up of nitrogen, making it the most abundant gas. Nitrogen plays a crucial role in many biological processes, including the nitrogen cycle, which is essential for life on Earth.

Oxygen, while vital for most living organisms and making up roughly 21% of the atmosphere, is not the most abundant gas. Carbon dioxide exists in much smaller amounts, typically around 0.04%, and is significant primarily due to its role in climate regulation and the carbon cycle. Helium, though present in trace amounts, is not a significant component of the atmosphere compared to nitrogen.

This understanding of atmospheric composition is fundamental in disciplines such as environmental science, meteorology, and biology, highlighting the importance of nitrogen as a dominant gas essential for various life forms and ecological processes.