What is the most abundant gas in Earth's atmosphere?
Quick answer
Nitrogen (N₂) is the most abundant gas in Earth’s atmosphere, making up about 78% of dry air. Oxygen is second at about 21%, followed by argon at almost 1%. Carbon dioxide is only about 0.04%, but it has a big effect on climate.
What the air is made of
| Gas | Share of dry air |
|---|---|
| Nitrogen (N₂) | ~78.08% |
| Oxygen (O₂) | ~20.95% |
| Argon (Ar) | ~0.93% |
| Carbon dioxide (CO₂) | ~0.04% |
| Neon, helium, methane, krypton, hydrogen and others | Tiny traces |
Air also contains water vapor, usually from almost 0% to about 4%, depending on the weather and place. That’s why the table above refers to dry air.
Why so much nitrogen?
Early volcanoes released nitrogen, and it stayed because it’s very stable: two nitrogen atoms are held together by a strong triple bond, so the gas rarely reacts with anything. Oxygen, by contrast, was added much later, mostly by tiny ocean organisms through photosynthesis, starting more than 2 billion years ago.
Why nitrogen matters
- Proteins and DNA need nitrogen; it’s part of every amino acid.
- Plants can’t use nitrogen gas directly. Bacteria in soil and lightning convert it into forms plants can absorb, a process called nitrogen fixation.
- Farmers add nitrogen fertilizers to boost crops.
- Liquid nitrogen, at −196°C, is used to freeze food and preserve medical samples.
The atmosphere’s layers
Gases are held around Earth by gravity, thinning out with height. Most of the air, and almost all weather, is in the lowest layer, the troposphere. Above it, the stratosphere holds the ozone layer that shields us from ultraviolet light.
The atmosphere also explains why the sky is blue and how the northern lights glow green (oxygen) and purple (nitrogen).
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