What is the Atmosphere?
- The atmosphere is a layer of gases surrounding the Earth, held by gravity.
- It protects life, regulates temperature, and provides oxygen for respiration.
Composition of the Atmosphere
| Gas | Percentage | Function |
|---|---|---|
| Nitrogen (N₂) | 78% | Essential for plants, maintains balance |
| Oxygen (O₂) | 21% | Supports life and combustion |
| Argon (Ar) | 0.93% | Inert gas |
| Carbon Dioxide (CO₂) | 0.04% | Absorbs heat, needed for photosynthesis |
| Water Vapor | 0-4% | Causes weather changes |
| Ozone (O₃) | Trace | Protects from UV rays |
Layers of the Atmosphere
| Layer | Altitude (km) | Features |
|---|---|---|
| Troposphere | 0-12 km | Weather, clouds, airplanes, life-supporting layer |
| Stratosphere | 12-50 km | Ozone layer, jet planes fly here |
| Mesosphere | 50-80 km | Coldest layer, meteors burn up here |
| Thermosphere | 80-700 km | Aurora formation, space stations orbit |
| Exosphere | 700+ km | Outer layer, merges into space |
Importance of the Atmosphere
✔ Provides Oxygen & Carbon Dioxide – Supports life and photosynthesis.
✔ Regulates Temperature – Greenhouse effect maintains Earth’s climate.
✔ Protects from UV Rays – Ozone layer prevents harmful radiation.
✔ Enables Weather & Rainfall – Water vapor forms clouds and precipitation.
✔ Burns Meteors – Protects Earth from space debris.
Weather vs. Climate
| Factor | Weather | Climate |
|---|---|---|
| Definition | Short-term atmospheric conditions | Long-term weather patterns |
| Duration | Hours to weeks | Decades to centuries |
| Examples | Rain today, storm tomorrow | Tropical, desert, polar climates |
Atmospheric Pressure
- Decreases with altitude (higher altitude = lower pressure).
- Measured by a barometer (in millibars or Pascals).
- High Pressure = Clear skies ☀️
- Low Pressure = Rain & storms ⛈️
Greenhouse Effect & Global Warming
- Greenhouse gases (CO₂, CH₄, N₂O, water vapor) trap heat and warm the Earth.
- Excess CO₂ from pollution increases temperature → Global Warming.
- Effects: Rising sea levels, extreme weather, ice melting.
- Solution: Reduce fossil fuels, plant trees, use renewable energy.
Ozone Layer & Depletion
- Ozone Layer (O₃) in the Stratosphere absorbs UV rays.
- Chlorofluorocarbons (CFCs) from refrigerators & ACs damage ozone.
- Ozone Hole detected over Antarctica.
- Solution: Ban CFCs, use eco-friendly chemicals.
MCQs on Atmosphere
1. Which gas is most abundant in the atmosphere?
a) Oxygen
b) Nitrogen
c) Carbon Dioxide
d) Hydrogen
Answer: b) Nitrogen
2. In which layer do airplanes fly?
a) Troposphere
b) Stratosphere
c) Mesosphere
d) Thermosphere
Answer: b) Stratosphere
3. Which layer protects us from UV radiation?
a) Troposphere
b) Stratosphere
c) Mesosphere
d) Exosphere
Answer: b) Stratosphere
4. The coldest atmospheric layer is:
a) Stratosphere
b) Troposphere
c) Mesosphere
d) Thermosphere
Answer: c) Mesosphere
5. Which gas causes global warming?
a) Oxygen
b) Nitrogen
c) Carbon Dioxide
d) Argon
Answer: c) Carbon Dioxide
Short Answer Questions
1. What are the major gases in the atmosphere?
- Nitrogen (78%)
- Oxygen (21%)
- Carbon Dioxide (0.04%)
- Argon & other gases
2. Name the layers of the atmosphere in order.
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
3. What is the greenhouse effect?
The greenhouse effect occurs when gases like CO₂, methane, and water vapor trap heat and keep the Earth warm.
4. How does the ozone layer protect us?
The ozone layer in the stratosphere absorbs harmful UV rays from the Sun, preventing skin cancer and environmental damage.
5. What is atmospheric pressure?
Atmospheric pressure is the weight of air above us, measured in millibars (mb) or Pascals (Pa).
Conclusion
The atmosphere is vital for life on Earth. It regulates climate, weather, and air composition, protecting us from harmful radiation.
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