The Layers of the Atmosphere

A blanket of air around our world

Earth is wrapped in a thin shell of gases we call the atmosphere. It gives us air to breathe, shields us from the Sun's harmful rays, burns up most incoming space rocks, and is the stage on which all our weather plays out. Compared with the size of the planet, the atmosphere is incredibly thin — a bit like the skin on an apple.

But the atmosphere is not the same all the way up. Scientists divide it into five main layers, based on how the temperature changes as you rise. Let's travel upward from the ground and meet each one.

Layer 1: The troposphere — where weather lives

The troposphere is the layer you are standing in right now. It stretches from the ground up to about 8-15 km high (higher over the warm equator, lower over the cold poles).

This layer is special for two reasons:

• It holds about three-quarters of all the air in the atmosphere and almost all of its water vapour.
• Almost all weather happens here — clouds, rain, snow, wind and storms.

In the troposphere, the air gets colder as you go up, dropping by roughly 6.5°C per kilometre. This is why mountain tops are snowy even in summer, and why tall storm clouds spread out into a flat "anvil" shape when they reach the top of this layer and can rise no further. If you want to see how those clouds form, read Types of Clouds.

Layer 2: The stratosphere — home of the ozone layer

Above the troposphere sits the stratosphere, reaching up to about 50 km. Here something surprising happens: the air gets warmer as you climb, the opposite of the troposphere.

The reason is the ozone layer, a region rich in a gas called ozone. Ozone absorbs most of the Sun's harmful ultraviolet (UV) radiation, and in doing so it heats the surrounding air. This shield is vital — without it, UV rays would damage living cells and make life on land very difficult.

Because the stratosphere is calm and free of weather, passenger jets often cruise at its lower edge. The air is so stable here that pollution and ash from large volcanic eruptions can linger for months.

Layer 3: The mesosphere — where meteors burn up

The mesosphere runs from about 50 km to 85 km. Temperatures fall again, making this the coldest layer, dropping below -90°C near the top.

The mesosphere is Earth's natural shield against space debris. When small rocks and dust from space plunge into it, they smash into air molecules, heat up and glow — the streaks of light we call meteors or "shooting stars". Almost all of them burn up completely before reaching the ground.

Layer 4: The thermosphere — hot but empty

Next is the thermosphere, stretching from 85 km up to several hundred kilometres. Here temperatures soar, sometimes above 1,500°C, because the few molecules present absorb intense solar energy.

Yet an astronaut here would not feel hot. The air is so thin — the molecules so far apart — that there are simply too few of them to pass on much heat. This is a great example of the difference between temperature (how fast molecules move) and heat (how much energy actually transfers).

The thermosphere is also where the glowing auroras (the Northern and Southern Lights) appear, and where the International Space Station orbits.

Layer 5: The exosphere — fading into space

The outermost layer is the exosphere. Here the atmosphere becomes incredibly sparse, just a scattering of fast-moving hydrogen and helium molecules. They are so spread out they can travel hundreds of kilometres without bumping into one another. Slowly, the exosphere fades into the emptiness of space, with no clear edge.

Why the layers matter

These layers are not just labels — each one protects us or shapes our lives:

• The troposphere gives us breathable air and our weather.
• The stratosphere's ozone blocks dangerous UV rays.
• The mesosphere burns up meteors.
• The thermosphere hosts satellites and the auroras.

Together they explain why air pressure drops as you climb a mountain, why planes fly where they do, and why the sky is the engine room of our weather. To explore how moving air becomes wind, read Air Pressure and Wind.

Activity: feel the troposphere shrink

You can experience the thinning atmosphere with a simple weather-watch observation.

1. Find a sealed, empty plastic water bottle. Squeeze it flat and seal the lid at ground level (or, even better, at the top of a tall hill).
2. Carry it to a place at a very different height — down to sea level, or up a tall building or hill.
3. Watch the bottle. As you go up, the lower outside pressure lets the trapped air push the bottle outward, making it firm or bulge. As you go down, higher pressure squashes it inward.

This shows that the "ocean of air" really does press on everything, and that its push weakens with height. Keep a log of how the bottle behaves at different altitudes — you are measuring the atmosphere itself.