Take a deep breath. Roughly four out of every five molecules you just breathed in were nitrogen — a gas your body does not even use. The air is a mixture, and knowing what is in it explains everything from why fires need oxygen to why the planet is warming.
What the air is made of
The atmosphere is a mixture of gases in roughly fixed proportions:
- Nitrogen — about 78%, by far the most common. It is unreactive, so it mostly just sits there.
- Oxygen — about 21%. The gas we (and fires) need.
- Other gases — about 1%, including argon, water vapour and carbon dioxide.
An easy way to remember it: for every 100 breaths of air, 78 are nitrogen, 21 are oxygen, and just 1 is everything else combined.
| Gas | Approx. amount | Note |
|---|---|---|
| Nitrogen | 78% | Most abundant, unreactive |
| Oxygen | 21% | Needed for burning & breathing |
| Other (incl. CO₂) | ~1% | Small but powerful |
The greenhouse effect
Some gases — mainly carbon dioxide and methane — are called greenhouse gases because they trap heat in the atmosphere. Sunlight warms the Earth's surface; the surface radiates heat back out; greenhouse gases absorb some of that heat instead of letting it escape to space. This is the greenhouse effect, and a natural amount of it is a good thing — without it, Earth would be frozen.
Picture a car left in the sun with the windows shut. Light gets in and warms the seats, but the heat cannot easily get back out, so the car turns into an oven. Greenhouse gases act like those closed windows for the whole planet.
Human activity and climate change
The trouble is that humans are adding extra greenhouse gases. Burning fossil fuels (coal, oil, gas) releases carbon dioxide; cutting down forests (deforestation) removes trees that would soak CO₂ up. More greenhouse gas means more heat trapped, which causes global warming and wider climate change.
Memory hook: air is "78-21-1" — Nitrogen big, Oxygen medium, other tiny. And greenhouse gases are the planet's blanket: a thin one keeps us cosy, too thick and we overheat.