The Atmosphere (Copy)
7.1 The Atmosphere – Cheat Sheet
Structure of the Atmosphere
| Layer | Altitude | Characteristics | Importance |
|---|---|---|---|
| Troposphere | 0–12 km | Weather occurs here, temperature decreases with altitude | Supports life, contains most water vapour |
| Stratosphere | 12–50 km | Contains ozone layer, temperature increases with altitude | Ozone absorbs harmful UV radiation |
| Mesosphere | 50–80 km | Coldest layer, meteors burn up here | Protects Earth from meteoroids |
| Thermosphere | 80–500 km+ | Very thin air, high temperatures, auroras occur here | Absorbs X-rays, satellites orbit here |
Composition of the Atmosphere
| Gas | Percentage | Role |
|---|---|---|
| Nitrogen (Nâ‚‚) | ~78% | Inert, essential for proteins (via nitrogen cycle) |
| Oxygen (Oâ‚‚) | ~21% | Supports respiration and combustion |
| Argon (Ar) | ~0.9% | Inert, no major role |
| Carbon Dioxide (COâ‚‚) | ~0.04% | Key greenhouse gas, photosynthesis |
| Water Vapour (H₂O) | Variable (0–4%) | Weather, greenhouse effect |
The Natural Greenhouse Effect
| Step | Process |
|---|---|
| 1 | Sunlight passes through atmosphere, warms Earth’s surface |
| 2 | Earth radiates heat as infrared radiation |
| 3 | Greenhouse gases (COâ‚‚, CHâ‚„, water vapour) absorb and trap some heat |
| 4 | Keeps Earth warm enough to support life (~15°C average) |
Ozone Layer
- Found in stratosphere.
- Absorbs UV radiation, protecting living organisms.
- Depletion caused by CFCs → ozone holes (Antarctica).
- Recovery improving due to Montreal Protocol banning CFCs.
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Environmental Management Full Scale Course