When you take a breath, you’re not inhaling mostly oxygen. In fact, nearly 78% of Earth’s atmosphere is nitrogen gas (N₂), while oxygen makes up only about 21%.

Why So Much Nitrogen?

Billions of years ago, volcanoes released vast amounts of nitrogen into the air. Unlike carbon dioxide or water vapor, nitrogen is chemically stubborn. It doesn’t easily react or dissolve, so instead of vanishing into oceans or rocks, it lingered and built up over time until it became the main ingredient in the sky.

What Happens When We Breathe It?

Even though nitrogen fills your lungs with every breath, your body doesn’t use it. Oxygen is the part your cells need, while nitrogen mostly passes through unchanged. That makes it a stable “filler gas,” balancing oxygen in the air and preventing our atmosphere from being dangerously reactive.

The Big Picture

Nitrogen may be invisible and ignored, but without it Earth’s atmosphere would be unstable, fires would burn out of control, and breathing would feel very different. The next time you inhale, remember: most of what’s in your lungs is nitrogen, quietly holding the sky steady.