You are here
The atmosphere is a thin, layered shell of air. It filters harmful rays coming in and traps just enough heat going out to keep the planet livable.
- The atmosphere is the air held around the Earth by gravity — mainly nitrogen (78%) and oxygen (21%) with small amounts of argon, CO₂ and water vapour.
- Nearly all weather occurs in the troposphere (about 0–12 km), where temperature falls with height (~6.5°C/km) as warm air rises to drive winds and storms.
- In the stratosphere (12–50 km) the ozone layer absorbs UV, so temperature rises with height; above lie the mesosphere, thermosphere and exosphere.
NCERT Question 6 — You have witnessed weather phenomena,
| Layer | Approximate altitudes | Features |
|---|---|---|
| Troposphere | 0 – 12 km | Weather formation; temperature decreases with height |
| Stratosphere | 12 – 50 km | Ozone layer absorbs UV; temperature increases with height |
K.R. Ramanathan , India’s atmospheric scientist, climbed to an altitude of 18,000 feet in the Himalayas in 1934 to measure ozone levels and found them lower than expected. His work laid the foundation for understanding how UV absorption varies with altitude and pollution, and he later led early monsoon forecasting efforts.
- First, it partly absorbs incoming solar radiation — the ozone layer blocks harmful UV, and clouds and gases absorb some sunlight.
- Second, it traps outgoing heat : the surface re-radiates infrared, and greenhouse gases (CO₂, CH₄, water vapour) absorb it, keeping the Earth warm enough for life.
- Excess CO₂ from human activity strengthens this greenhouse effect, causing global warming — as on Venus, whose thick atmosphere makes it hotter than Mercury.
NCERT Question 2 — Which of the following is
NCERT Question 11 — How is heat lost from
NCERT Question 14 — Explain how the Earth’s atmosphere
1. Visit the greenhouse-effect simulation and study how the concentration of greenhouse gas changes the surface temperature — more greenhouse gas traps more heat, so the surface grows warmer.
Why is the ozone layer so important? It acts as a protective shield, absorbing harmful UV radiation. Human-made chlorofluorocarbons (CFCs) once destroyed ozone faster than it formed, creating the ozone hole over Antarctica. The global Montreal Protocol reduced CFC use, and the ozone layer is now slowly recovering — a success of international cooperation.
- Insolation — the amount of the Sun’s radiation reaching the Earth’s surface.
- Solar constant — the average solar energy per unit area at the top of the atmosphere, about 1.4 kW m-2.
- Electromagnetic spectrum — the full range of EM radiation from gamma rays to radio waves.
- Albedo — the fraction of solar radiation reflected by a surface.
- Greenhouse effect — the trapping of outgoing infrared heat by atmospheric gases.
- Troposphere — the lowest atmospheric layer where weather occurs.
- Stratosphere — the layer above the troposphere that holds the ozone layer.
- Ozone layer — a layer of ozone in the stratosphere that absorbs harmful UV rays.
