What is the primary gas found in the Earth's atmosphere?

The primary gas found in the Earth's atmosphere is nitrogen, which makes up approximately 78% of the atmosphere by volume. Nitrogen is crucial for various biological processes, including being a key component of amino acids and nucleic acids, which are the building blocks of life. This abundance of nitrogen helps to maintain stable environmental conditions for living organisms and is essential for the balance of the atmosphere.

Oxygen, while vital for life as it is required for respiration by many organisms, constitutes only about 21% of the atmosphere. Carbon dioxide is present in even smaller amounts, around 0.04%, and is significant primarily in its role in photosynthesis and as a greenhouse gas. Hydrogen, although it is the most abundant element in the universe, is rare in the Earth's atmosphere due to its lightness; it tends to escape into space because it cannot be held by Earth's gravity in significant amounts. Thus, nitrogen's dominance in the atmosphere establishes its role as the primary gas present.