The main gas in the Earth's atmosphere is nitrogen, which constitutes approximately 78% of the atmosphere by volume. Nitrogen is an inert gas that plays a crucial role in the environment, primarily as a component of proteins and nucleic acids in living organisms. It is essential for the growth and development of plants, as they absorb nitrogen from the soil in various forms, such as nitrates. Although nitrogen itself doesn't actively participate in vital atmospheric processes like respiration or photosynthesis, it provides stability and helps dilute oxygen and other reactive gases in the atmosphere.