From ground to space
The atmosphere is divided into five layers based on temperature gradients. Each layer has distinct properties and plays a specific role in protecting and sustaining life on Earth.
| Layer | Altitude | Temperature | Key Feature |
|---|---|---|---|
| Troposphere | 0–12 km | Decreases with altitude | All weather occurs here; 75–80% of atmospheric mass; heated from Earth's surface |
| Stratosphere | 12–50 km | Increases with altitude | Contains the ozone layer (15–35 km); absorbs UV radiation; commercial aircraft fly here |
| Mesosphere | 50–85 km | Decreases (coldest: −90°C) | Most meteors burn up here due to friction; coldest atmospheric layer |
| Thermosphere | 85–700 km | Increases (up to 2000°C) | ISS orbits here; auroras (Northern/Southern Lights) form here; very thin air |
| Exosphere | 700+ km | Merges with space | Outermost layer; satellites orbit here; gradually merges into outer space |
Memory trick: The Sky Meets The Expanse — Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.
Earth's UV shield
The ozone layer sits within the stratosphere at 15–35 km altitude. It absorbs most of the Sun's harmful UV-B and UV-C radiation, preventing it from reaching Earth's surface. Without it, life as we know it could not exist on land.
🛡️ How it works
Ozone (O₃) molecules absorb UV radiation and break apart into O₂ and a free oxygen atom. These recombine to reform O₃, creating a continuous cycle that converts UV energy into heat — warming the stratosphere.
⚠️ The Ozone Hole
Chlorofluorocarbons (CFCs) from refrigerators and aerosol sprays destroy ozone molecules. A significant "hole" formed over Antarctica. The Montreal Protocol (1987) phased out CFCs globally — the ozone layer is now slowly recovering.
How Earth stays warm
The greenhouse effect is a natural process that keeps Earth's average temperature at ~15°C instead of −18°C. Greenhouse gases (CO₂, water vapour, methane, nitrous oxide) absorb outgoing infrared radiation from Earth's surface and re-emit it in all directions, trapping heat in the lower atmosphere.
Sunlight (shortwave radiation) passes through the atmosphere and warms Earth's surface.
Earth's surface emits longwave infrared (heat) radiation upward.
Greenhouse gases absorb this infrared radiation instead of letting it escape to space.
Greenhouse gases re-emit heat in all directions — including back toward Earth's surface.
Earth's surface warms further. Human emissions amplify this natural process, causing global warming.
Venus example: Venus has a thick CO₂ atmosphere creating an extreme greenhouse effect, making its surface ~465°C — hotter than Mercury despite being farther from the Sun. This shows how powerful greenhouse gases can be.
🇮🇳 K.R. Ramanathan — India's Pioneer
Indian scientist Kalpathi Ramakrishna Ramanathan was among the first to study the greenhouse effect and atmospheric radiation in the early 20th century. His work on ozone and atmospheric physics laid the foundation for modern climate science in India.