Air explores the Earth’s atmosphere—its composition, structure, and significance to life on our planet. This chapter provides an in-depth understanding of the various gases that make up the atmosphere, including nitrogen, oxygen, and trace gases like carbon dioxide and argon. It explains structure of the atmosphere, comprising the troposphere, stratosphere, mesosphere, thermosphere, and exosphere, each with distinct characteristics and functions. Additionally, the chapter examines essential atmospheric phenomena such as weather and climate, highlighting their roles in shaping the Earth’s environment.
1. Atmosphere
- Definition: A huge blanket of air surrounding the Earth.
- Importance:
- Provides air for breathing.
- Protects from harmful sun rays.
- Keeps Earth’s temperature livable (not too hot during day, not too cold at night).
- Facts:
- Without atmosphere, we’d burn in the day and freeze at night.
2. Composition of the Atmosphere
- Mixture of Gases:
- Nitrogen: Most plentiful gas
- We breathe it in and out, but plants need it for survival.
- Bacteria in soil/roots change nitrogen so plants can use it.
- Oxygen: Second most plentiful gas.
- Humans and animals breathe it.
- Plants make it during photosynthesis (keeps oxygen levels steady).
- Cutting trees disturbs this balance.
- Carbon Dioxide:
- Plants use it to make food and release oxygen.
- Humans/animals release it when breathing.
- Burning fuels (coal, oil) adds tons of it, upsetting the balance.
- Other Gases: Helium, ozone, argon, hydrogen (small amounts).
- Dust Particles: Tiny bits mixed in the air.
- Note: Pie chart shows percentages of air’s parts.
3. Greenhouse Effect and Global Warming
- Greenhouse Effect:
- Carbon dioxide traps heat from Earth, keeping it warm (like a greenhouse).
- Without it, Earth would be too cold to live on.
- Global Warming:
- Too much carbon dioxide (from factory smoke, car fumes) traps extra heat.
- Causes temperature to rise.
- Effects:
- Melts snow in cold places (e.g., poles).
- Raises sea levels, flooding coastal areas.
- Changes climate, may wipe out plants/animals.
- Headlines:
- “Warming unstoppable.”
- “Global warming can bring back Jurassic era.”
4. Air Movement
- How It Works:
- Hot air expands, gets light, and rises.
- Cold air is dense, heavy, and sinks.
- Cold air fills gaps left by rising hot air (creates circulation).
5. Structure of the Atmosphere
- Layers:
- Troposphere:
- Height: Up to 13 km.
- Importance: Where we breathe air; weather happens here (rain, fog, hail).
- Stratosphere:
- Height: Up to 50 km.
- Features: Few clouds, great for flying planes.
- Ozone Layer: Protects from harmful sun rays.
- Mesosphere:
- Height: Up to 80 km.
- Feature: Meteorites burn up here.
- Thermosphere:
- Height: 80-400 km.
- Feature: Temperature rises fast; includes Ionosphere.
- Ionosphere: Reflects radio waves for communication.
- Exosphere:
- Height: Topmost layer.
- Feature: Very thin air; light gases (helium, hydrogen) float into space.
6. Weather and Climate
- Weather:
- Definition: Hour-to-hour, day-to-day condition of the atmosphere.
- Examples: Hot, humid, breezy; affects mood (irritable or cheerful).
- Changes daily (e.g., cricket fans check forecasts).
- Climate:
- Definition: Average weather of a place over a long time.
- Activity: Note weather reports for 10 days to see changes.
7. Temperature
- Definition: Degree of hotness or coldness of air.
- Changes:
- Varies day to night, season to season (summers hotter than winters).
- Insolation:
- Definition: Solar energy reaching Earth.
- Fact: Earth gets only 1 in 2 billion parts of sun’s energy.
- Pattern: Decreases from equator to poles (why poles are snowy).
- Cities vs. Villages:
- Cities hotter due to concrete, metal, and roads heating up.
- High-rise buildings trap warm air.
- Note: Weather instruments help measure temperature.
8. Air Pressure
- Definition: Force of air’s weight on Earth’s surface.
- Facts:
- We don’t feel it because our body pushes back.
- Highest at sea level, drops with height.
- Temperature Effect:
- Hot air rises → Low pressure (cloudy, wet weather).
- Cold air sinks → High pressure (clear, sunny skies).
- Movement: Air flows from high to low pressure areas.
9. Wind
- Definition: Air moving from high to low pressure areas.
- Examples:
- Blows leaves, uproots trees in storms, moves smoke/dust.
- Hard to walk or hold an umbrella in strong wind.
- Types:
- Permanent Winds: Blow all year in one direction.
- Examples: Trade winds, westerlies, easterlies.
- Seasonal Winds: Change direction with seasons.
- Example: Monsoons in India.
- Local Winds: Blow in small areas at certain times.
- Examples: Land/sea breezes, Loo (hot, dry wind in North India).
- Note: Diagram shows pressure belts and wind systems.
10. Cyclones
- Definition: Nature’s fury with strong winds, rain, and tidal surges.
- Case Study: Odisha, 1999:
- Dates: 17-18 Oct (first cyclone), 29 Oct (supercyclone).
- Origin: Started as a depression near Port Blair, 25 Oct.
- Path: Moved northwest, hit Odisha coast (Erasama-Balikuda) at 10:30 a.m.
- Effects:
- Winds up to 260 km/hr for 36+ hours (uprooted trees, damaged houses).
- Heavy rain for 3 days (flooded rivers).
- Tidal waves (7-10 m high) swept 20 km inland (ruined crops).
- Damage: 13 million people affected, livestock killed, crops/forests destroyed, land turned infertile.
- Image: Shows destruction caused by a cyclone.
11. Moisture and Rainfall
- Moisture:
- Definition: Water vapor in the air (humidity).
- On humid days: Clothes dry slowly, sweat doesn’t evaporate.
- Rain Formation:
- Water vapor rises, cools, and condenses into droplets (clouds).
- Droplets get heavy and fall as precipitation (e.g., rain).
- Examples:
- Jet plane trails: Condensed moisture from engines.
- Cutting trees on hills causes rainwater to flood low areas.
- Types of Rainfall:
- Convectional: Hot air rises, cools, and rains.
- Orographic (Relief): Air hits mountains, rises, and rains.
- Cyclonic: Rain from cyclones.
- Importance:
- Brings fresh water; too little → drought, too much → floods.
12. Questions and Answers
12.1 Short Answer Questions
- What is atmosphere?
- A blanket of air around Earth for breathing and protection.
- Which two gases make the bulk of the atmosphere?
- Nitrogen and oxygen.
- Which gas creates greenhouse effect?
- Carbon dioxide.
- What is weather?
- Day-to-day condition of the atmosphere.
- Name three types of rainfall?
- Convectional, orographic, cyclonic.
- What is air pressure?
- Force of air’s weight on Earth’s surface.
12.2 Multiple Choice Questions
- Gas protecting from harmful sun rays?
- (c) Ozone.
- Most important layer of atmosphere?
- (a) Troposphere.
- Layer free from clouds?
- (b) Stratosphere.
- Pressure as we go up?
- (b) Decreases.
- Liquid precipitation?
- (b) Rain.
12.3 Matching
- (i) Trade Winds → (e) Permanent wind
- (ii) Loo → (f) Local wind
- (iii) Monsoon → (b) Seasonal wind
- (iv) Wind → (c) Horizontal movement of air
12.4 Give Reasons
- Wet clothes take longer to dry on humid day?
- Air is full of water vapor, so evaporation slows.
- Insolation decreases from equator to poles?
- Sun’s energy spreads less directly toward poles.
13. Activities
13.1 Crossword Puzzle
- Across:
- 6. Peepal (tree giving oxygen 24/7)
- 7. Carbon dioxide (0.03% of air)
- 8. Exosphere (outermost layer)
- 9. Air (mixture of gases)
- Oxygen (life-giving gas)
- Wind (air in motion)
- Neem (medicinal tree)
- Ozone (protects from sun rays)
- Cyclone (low pressure area)
- Down:
- Humidity (water vapor in air)
- Cloud (condensed vapor around dust)
- Loo (summer wind in North India)
- Weather (short-term changes)
- Rain (liquid precipitation)
- Atmosphere (air blanket)
- Barometer (measures pressure)
- Insolation (solar radiation)
- Fog (reduces visibility in winter)
- Noon (sun overhead)
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