EARTH SCIENCE • GEOGRAPHY

Structure of the Atmosphere and All Its Layers

Earth is surrounded by a blanket of gases called the atmosphere. It gives us air to breathe, helps regulate temperature and protects life from many harmful effects coming from space.

The atmosphere does not have the same conditions at every height. As we move upward, air becomes thinner and temperature changes. Scientists divide it into five main layers.

What Is the Atmosphere?

The atmosphere is the mixture of gases held around Earth by gravity. Dry air near Earth's surface contains about 78% nitrogen and 21% oxygen, with small amounts of argon, carbon dioxide and other gases. Water vapour varies from place to place.

Most of the atmosphere's mass lies close to Earth's surface. There is no sharp outer edge: the air gradually becomes thinner and merges with space.

Earth surrounded by the atmosphere A cross-section illustration showing Earth at the bottom and a thin blue atmospheric envelope fading into dark space above it. SPACE Atmosphere A thin blanket of gases around Earth EARTH'S SURFACE Air gets thinner
The atmosphere is thickest near the ground and gradually becomes thinner with height. This illustration is conceptual, not to scale.

The Five Main Layers at a Glance

Learn the layers from the ground upward. The heights shown are approximate because the boundaries change with latitude, season and solar activity.

Labelled diagram of the five layers of Earth's atmosphere A vertical diagram from Earth's surface to space. It labels the troposphere from zero to about twelve kilometres, stratosphere from twelve to fifty kilometres, mesosphere from fifty to eighty-five kilometres, thermosphere from about eighty-five to six hundred kilometres, and exosphere above about six hundred kilometres. EXOSPHERE About 600 km and above THERMOSPHERE About 85–600 km MESOSPHERE About 50–85 km STRATOSPHERE About 12–50 km TROPOSPHERE Ground to about 12 km ALTITUDE Above sea level ~600 km ~85 km ~50 km ~12 km 0 km Satellites Some orbit in theupper atmosphere AurorasOften seen here Meteors burn upMostly in this layer Ozone layerMainly in this layer Weather happensin this layer
Five main atmospheric layers, arranged from Earth's surface upward. Altitude boundaries are approximate; the vertical drawing is not to scale.

Easy order to remember: Troposphere → Stratosphere → Mesosphere → Thermosphere → Exosphere.

1. Troposphere — The Weather Layer

Surface to about 8–18 km (often taken as ~12 km)

The troposphere is the lowest layer and the one in which we live. It contains most of the atmosphere's mass and nearly all of its water vapour.

  • Clouds, rain, snow, winds and most other weather events occur here.
  • Air pressure and air density decrease as altitude increases.
  • Temperature usually decreases with height, although local conditions can vary.

The troposphere is generally thinner near the poles and taller near the equator. That is why its upper boundary is given as a range rather than one fixed height.

2. Stratosphere — The Ozone Layer

About 12–50 km

The stratosphere lies above the troposphere. It contains the ozone layer, where ozone gas absorbs much of the Sun's harmful ultraviolet (UV) radiation.

  • The ozone layer protects living things from much of the Sun's harmful UV radiation.
  • Temperature generally increases with height in this layer because ozone absorbs ultraviolet energy.
  • Some aircraft fly in the lower stratosphere to avoid much of the weather below.

3. Mesosphere — The Coldest Layer

About 50–85 km

The mesosphere is above the stratosphere. It is usually the coldest atmospheric layer, especially near its upper boundary.

  • Many meteoroids heat up and break apart here, producing the streaks of light we call shooting stars.
  • Temperature generally falls as height increases through the mesosphere.
  • The air is extremely thin, so this region is difficult for ordinary aircraft to reach and for satellites to orbit in for long periods.

4. Thermosphere — Very High Temperatures

About 85–600 km (boundary varies)

In the thermosphere, gases absorb high-energy radiation from the Sun. The measured temperature can become very high, but the air is so thin that it would not transfer heat to a person in the same way that hot air near the ground does.

  • Many auroras occur in this region when charged particles interact with gases in the upper atmosphere.
  • The ionosphere, an electrically charged region important for radio communication, overlaps parts of the mesosphere and thermosphere and can extend higher.
  • The International Space Station orbits Earth within the thermosphere.

5. Exosphere — The Outermost Layer

Roughly 600 km upward, gradually merging into space

The exosphere is the outermost part of Earth's atmosphere. Its gas particles are extremely far apart, and some can travel long distances without colliding with other particles.

  • Hydrogen and helium are among the gases found there.
  • There is no sharp line where the atmosphere suddenly ends; it gradually becomes thinner and blends into space.
  • Some high-altitude satellites orbit in or near this region, although satellites occupy a wide range of altitudes.

How Does Temperature Change in the Atmosphere?

Temperature does not simply keep falling as we move away from Earth. It changes direction from one layer to another.

Simplified temperature trend through the atmosphere A line graph with altitude increasing upward and temperature increasing to the right. Temperature generally falls in the troposphere, rises in the stratosphere, falls in the mesosphere, and rises strongly in the thermosphere. Altitude increases ↑ Temperature increases → Thermosphere Mesosphere Stratosphere Troposphere Ground Generally rises Falls Rises Falls Conceptual trend only — not measured data
A simplified pattern: temperature generally falls in the troposphere, rises in the stratosphere, falls in the mesosphere and rises in the thermosphere. Exact values vary with location, time and solar activity.

Quick Comparison of the Five Layers

LayerApproximate heightMain feature
TroposphereGround to 8–18 kmWeather, clouds and most water vapour
StratosphereAbout 12–50 kmOzone layer; temperature generally rises with height
MesosphereAbout 50–85 kmMany meteors burn up; very cold upper region
ThermosphereAbout 85–600 kmAuroras and the orbit of the International Space Station
ExosphereRoughly 600 km upwardOutermost, extremely thin region merging into space

Note: The altitude ranges are approximate. Different textbooks and scientific models may use slightly different boundaries.

Why Is the Atmosphere Important?

  • It supplies essential gases: oxygen for many living things and carbon dioxide for photosynthesis.
  • It supports weather and the water cycle: clouds and precipitation form mainly in the troposphere.
  • It helps regulate temperature: greenhouse gases help keep Earth warm enough for life.
  • It filters harmful radiation: ozone in the stratosphere absorbs much of the Sun's harmful UV radiation.
  • It provides protection: atmospheric gases cause many small meteoroids to heat up and break apart before reaching the ground.

Common Misunderstandings

  • “The ozone layer is a separate atmospheric layer.” It is a region with higher ozone concentration within the stratosphere, not a sixth main layer.
  • “All meteors burn up in the mesosphere.” Many do, but some begin to ablate at different heights and larger objects can survive to the ground.
  • “The atmosphere ends exactly at 600 km.” It has no sharp edge; the exosphere gradually merges with space.
  • “The thermosphere feels extremely hot.” Its particles can have very high temperatures, but the air is extremely thin.

Frequently Asked Questions

How many main layers does Earth's atmosphere have?

It is commonly divided into five main layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere.

Which layer do we live in?

We live at Earth's surface, within the troposphere, the lowest atmospheric layer.

Which layer contains the ozone layer?

The ozone layer is mainly in the stratosphere.

Which is the coldest atmospheric layer?

The mesosphere is generally the coldest layer, with temperatures near its upper boundary often dropping to around −90°C or lower depending on conditions.

Where do most weather events occur?

Most weather events occur in the troposphere, where most water vapour and clouds are found.

Quick Revision

Troposphere: weather and life near Earth's surface.

Stratosphere: ozone layer.

Mesosphere: many meteors burn up; very cold upper region.

Thermosphere: auroras and the International Space Station's orbit.

Exosphere: outermost, extremely thin region.