What is the main substance found in Earth's atmosphere?

The primary substance in Earth's atmosphere is nitrogen, which makes up about 78% of the total atmospheric composition. Nitrogen is a colorless, odorless gas that plays a crucial role in various biological and chemical processes on Earth, including the nitrogen cycle, which is essential for plant growth. The high concentration of nitrogen helps dilute oxygen, reducing the risk of combustion and supporting life on the planet. While oxygen is also a significant component, accounting for roughly 21% of the atmosphere, nitrogen remains the predominant gas by a substantial margin. Understanding the composition of the atmosphere is vital for various fields, including meteorology, environmental science, and biology.