- The atmosphere is a multilayered, dynamic envelope of gases, liquids, and suspended solids that surrounds Earth.
- It forms the outer limit of the biosphere, acting as a protective barrier that separates Earth from outer space.
- Its composition, structure, and physical processes make life possible by regulating temperature, filtering radiation, enabling weather, and redistributing energy and gases across the planet.
- The atmosphere interacts continuously with the lithosphere, hydrosphere, and biosphere, creating interconnected Earth system processes.
The atmosphere acts like Earth’s “life-support system,” regulating temperature, shielding from radiation, and circulating essential gases, similar to how a greenhouse maintains stable conditions for plants.
Composition of the Atmosphere
- The atmosphere contains a relatively stable mixture of gases up to about 80 km above Earth’s surface.
- These gases are vital for climate regulation, respiration, and ecological balance.
| Gas | Percentage | Importance |
|---|---|---|
| Nitrogen (N₂) | ~78% | Maintains atmospheric pressure, essential for nitrogen cycle |
| Oxygen (O₂) | ~21% | Supports respiration, combustion, and metabolic processes |
| Argon (Ar) | ~0.9% | Inert gas; does not react but contributes to total atmospheric mass |
Trace Gases (<0.1%)
- Carbon dioxide (CO₂) (~0.04%): vital for photosynthesis and regulating Earth’s temperature through the greenhouse effect.
- Water vapour (H₂O): influences weather, cloud formation, and precipitation.
- Ozone (O₃): concentrated in the stratosphere; absorbs harmful UV radiation.
- Methane (CH₄) & Nitrous oxide (N₂O): potent greenhouse gases affecting climate dynamics.
Suspended particles
- Dust
- Ash
- Soot
- Sea salt
- Aerosols
Even though CO₂ and other greenhouse gases make up a tiny percentage of the atmosphere, they have a massive influence on global climate.
Structure of the Atmosphere
The atmosphere is divided into distinct layers based on temperature variations.
Troposphere (0–12 km)
- The troposphere is the lowest atmospheric layer, where almost all weather processes occur.
- Air temperature decreases with increasing altitude.
- This layer contains most of the atmosphere’s water vapour and greenhouse gases.
- Human activities, including pollution and fossil fuel combustion, primarily affect this layer.
2. Stratosphere (12–50 km)
Ozone layer
The ozone layer is a concentration of ozone molecules located in the stratosphere that protects living organisms from harmful ultraviolet radiation.
- The stratosphere contains the ozone layer, which absorbs most of the harmful ultraviolet radiation from the Sun.
- Unlike the troposphere, temperature increases with altitude due to ozone absorbing solar radiation.
- This layer is relatively stable and experiences limited vertical mixing.
3. Mesosphere (50–80 km)
- The mesosphere is the coldest atmospheric layer.
- Meteors burn up in this layer due to increasing atmospheric friction.
4. Thermosphere (80–700 km)
- The thermosphere has very low gas density but extremely high temperatures because the few particles present absorb large amounts of solar radiation.
- Auroras appear in this layer, and satellites and space stations orbit within it.


