Approximately $78\%$ of the Earth’s atmosphere is composed of nitrogen.

Nitrogen is the most abundant gas in the Earth’s atmosphere, constituting about $78\%$ of its total volume. This means that out of every $100$ molecules of gas in the atmosphere, $78$ are nitrogen. The remaining components of the atmosphere are primarily oxygen, which accounts for about $21\%$, along with trace amounts of other gases such as argon and carbon dioxide.

Nitrogen itself is a colorless, odorless, and tasteless gas that is relatively inert, indicating that it does not readily react with other elements. This inertness contributes to its stability as a major component of the atmosphere. Nitrogen is vital for life on Earth, as it is an essential building block of amino acids, proteins, and DNA. However, most organisms are unable to utilize atmospheric nitrogen directly. Instead, they depend on specific bacteria to convert it into a usable form through a process known as nitrogen fixation.

The high concentration of nitrogen in the atmosphere is the result of billions of years of volcanic activity, which released nitrogen and other gases from the Earth’s interior. Over time, lighter gases, such as hydrogen and helium, escaped into space, while heavier gases like nitrogen and oxygen remained, thus shaping the current composition of the atmosphere.

In summary, nitrogen is the most prevalent gas in the Earth’s atmosphere, making up approximately $78\%$ of its total volume. It is a stable, inert gas that plays a crucial role in supporting life on our planet.