What is the dominant gas in Earth's atmosphere?

The dominant gas in Earth's atmosphere is nitrogen, which makes up about 78% of the atmosphere by volume. This abundance is significant as nitrogen plays a crucial role in several biological and chemical processes on Earth. For example, it is a key component of amino acids, proteins, and nucleic acids, which are fundamental to life. Additionally, nitrogen acts as a stabilizing agent in the atmosphere, diluting the concentration of oxygen and preventing rapid combustion.

Oxygen, while essential for respiration in many organisms, makes up only about 21% of the atmosphere. Carbon dioxide, though important for photosynthesis and as a greenhouse gas, occurs in much smaller quantities, roughly 0.04%. Helium is present in trace amounts and is not involved in the life processes on Earth. Understanding the composition of the atmosphere helps in grasping various environmental and biological concepts.