Composition and Layers of the Atmosphere
Look up on a clear day: the sunshine, the clouds and the breeze all exist because of an invisible blanket of air around us, held to the Earth by gravity.
The atmosphere is a mixture of gases around the Earth. It shields us from harmful ultraviolet radiation and keeps the Earth warm by trapping some of the Sun's energy. It has five layers, defined by how temperature and density change with height.
Key idea 1: What the air is made of — Nitrogen (78%) and oxygen (21%) are the two main gases. Argon is 0.93% and carbon dioxide 0.04%. The rest are tiny amounts of neon, helium, krypton, xenon, ozone and hydrogen, plus water vapour (about 0.1–0.4%) and dust. Water vapour helps form clouds and rain.
- Easy: Nitrogen is the most abundant gas.
- Medium: Air density is highest near the ground and falls with height.
- Exam-type: The atmosphere also varies in composition with altitude.
In the figure: Five layers, from ground level to outer space.
Composition and Layers of the Atmosphere
In the app you can move this figure with your finger.
Open in the appKey idea 2: The five layers — Troposphere: weather, clouds, rain and the air we breathe. Stratosphere: cloud-free, good for aeroplanes, contains the ozone layer. Mesosphere: meteors burn up. Thermosphere: temperature rises rapidly as molecules absorb X-rays; reflects radio waves; auroras occur here. Exosphere: very thin air, helium and hydrogen drift into space. Temperature falls with height only in the troposphere and mesosphere.
- Easy: Tropopause separates the troposphere and stratosphere.
- Medium: Auroras form when solar wind particles reach the magnetic poles and gases glow.
- Exam-type: We do not feel air pressure because it acts from all sides and our body pushes back equally.
Weather happens only in the troposphere.
Thinking temperature drops steadily all the way up. It rises in the thermosphere.
Layer order. Memory clue: Tom Sat Munching The Egg = Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.
Spot the difference
| Layer | Key feature |
|---|---|
| Troposphere | Weather, breathable air |
| Stratosphere | Ozone, aeroplanes |
| Mesosphere | Meteors burn |
| Thermosphere | Aurora, radio reflection |
| Exosphere | Thinnest, gases escape |
Practice questions
- 1Name the two most abundant gases in the atmosphere.
- 2In which layer does rain occur?
- 3Which layer contains the ozone layer?
- 4What happens to temperature with height in the troposphere?
- 5Why do aeroplanes fly in the stratosphere?
- 6What causes auroras?
- 7A student says temperature always falls with height. How would you correct this?
- 8Why do we not feel the weight of the air above us?
Show answers (try them yourself first)
- 1Nitrogen and oxygen.
- 2The troposphere.
- 3The stratosphere.
- 4It decreases.
- 5It is free of clouds and weather disturbances.
- 6Solar wind particles directed to the magnetic poles make atmospheric gases glow.
- 7It falls only in the troposphere and mesosphere; it rises in the thermosphere.
- 8Air presses from all sides and our body exerts equal pressure outward.
Weather, Climate and Their Elements
You check whether it will rain this evening before going out to play. That is weather. Knowing that your town is hot every May is climate.
Weather is the hour-to-hour, day-to-day state of the atmosphere. Climate is the average of weather over a large area for a long time, usually 30 years or more.
Key idea 1: Five elements — Temperature, humidity, precipitation, atmospheric pressure and wind. Insolation (incoming solar energy) decreases from the equator to the poles, so temperature does too. Humidity is water vapour in the air; warm air holds more of it. Precipitation (drizzle, rain, snow, sleet, hail) depends on prevailing winds, mountains and seasons.
- Easy: Rain lowers the temperature of a place.
- Medium: On humid days sweat and clothes dry slowly.
- Exam-type: Sunlight strikes at a low angle near the poles, so they stay colder.
In the figure: Five elements together describe weather and climate.
Key idea 2: Pressure and wind — Pressure is highest at sea level and falls with height. Warm air rises and makes a low-pressure area, usually cloudy and wet. Cold air sinks and makes a high-pressure area, usually clear and sunny. Wind is air moving from high pressure to low pressure, and is named after the direction it blows from: a west wind is a westerly.
- Easy: Wind flows from high to low pressure.
- Medium: Low pressure often means clouds and rain.
- Exam-type: Light breeze 6–11 km/h rustles leaves; storm 103–117 km/h causes widespread damage.
Weather changes daily; climate is the long-term average.
Calling one hot day 'the climate'. That is weather.
Five elements. Memory clue: T-H-P-P-W = Temperature, Humidity, Precipitation, Pressure, Wind.
Spot the difference
| Term | Meaning |
|---|---|
| Weather | Short-term condition |
| Climate | Long-term average (30+ years) |
| Low pressure | Warm rising air, clouds |
| High pressure | Cold sinking air, clear sky |
Practice questions
- 1Define weather.
- 2What is climate?
- 3Name the five elements of weather and climate.
- 4What is insolation?
- 5What does a low-pressure area usually bring?
- 6Why does temperature fall from the equator to the poles?
- 7Explain why clothes dry slowly on a humid day.
- 8If place A has pressure 1012 and place B 996, which way does wind blow?
Show answers (try them yourself first)
- 1Hour-to-hour, day-to-day condition of the atmosphere.
- 2Average weather of a large area over 30 years or more.
- 3Temperature, humidity, precipitation, pressure and wind.
- 4Incoming solar energy intercepted by the Earth.
- 5Cloudy skies and wet weather.
- 6Insolation decreases towards the poles because sunlight strikes at a low angle.
- 7The air already holds a lot of water vapour, so moisture evaporates slowly.
- 8From A (1012) to B (996).
Local Winds and Seasons of India
At the beach in the afternoon a cool wind comes from the sea; at night it turns and blows out to sea. The year also turns through seasons you know well.
A sea breeze blows from sea to land by day; a land breeze blows from land to sea at night. India has four IMD seasons and, traditionally, six ṛtus.
Key idea 1: Land and sea breezes — By day land warms faster than the sea, so pressure over land is low and the sea breeze blows in. At night land cools faster, so a gentler land breeze blows towards the sea because the difference in temperature and pressure is small. These winds keep coastal climates moderate.
- Easy: Sea breeze = day, sea to land.
- Medium: Land breeze = night, land to sea.
- Exam-type: A land breeze is weaker since the temperature difference is small.
In the figure: IMD recognises four seasons in India.
Key idea 2: Seasons — Winter: December to early April, coldest in December–January. Summer: April to June; April hottest in west and south, May in north. Monsoon: June to September. Post-monsoon: October to December. Himalayan states add autumn and spring. Traditional ṛtus: Vasanta (Mar–Apr), Grīṣhma (May–Jun), Varṣhā (Jul–Aug), Śharad (Sep–Oct), Hemanta (Nov–Dec), Śhiśhira (Jan–Feb). Kauṭilya's Arthaśhāstra records rainfall measurements used for revenue and relief.
- Easy: IMD seasons are four; traditional ṛtus are six.
- Medium: Himalayan states have two extra seasons.
- Exam-type: Winter temperature rises from the north-west towards the south-east.
India's climate is broadly tropical monsoon.
Thinking India has only three seasons. IMD lists four and tradition lists six.
IMD seasons. Memory clue: W-S-M-P = Winter, Summer, Monsoon, Post-monsoon.
Spot the difference
| Season | Months |
|---|---|
| Winter | Dec–early Apr |
| Summer | Apr–Jun |
| Monsoon | Jun–Sep |
| Post-monsoon | Oct–Dec |
Practice questions
- 1Which wind blows from sea to land?
- 2When does a land breeze blow?
- 3How many seasons does the IMD recognise?
- 4Name the four IMD seasons.
- 5Which are the coldest months?
- 6Name the six traditional ṛtus.
- 7Why is a land breeze usually weaker than a sea breeze?
- 8What did the Arthaśhāstra record about rain, and what was it used for?
Show answers (try them yourself first)
- 1Sea breeze.
- 2At night.
- 3Four.
- 4Winter, summer, monsoon and post-monsoon.
- 5December and January.
- 6Vasanta, Grīṣhma, Varṣhā, Śharad, Hemanta and Śhiśhira.
- 7At night the temperature and pressure difference between land and sea is small.
- 8Scientific rainfall measurements, used in managing revenue and relief.
Monsoon
Farmers wait anxiously for the first rain every June. The wind that brings it changes direction with the season; that reversal is the monsoon.
Monsoon is the seasonal reversal of wind direction during a year. The word comes from the Arabic mausim, meaning season. There are two: the south-west and the north-east monsoon.
Key idea 1: South-west monsoon — In summer the Indian landmass heats faster than the surrounding ocean. This makes low pressure over the subcontinent, while the cooler Indian Ocean has high pressure. Moist winds blow from the ocean to land between June and September and bring most of India's rainfall.
- Easy: SW monsoon is the summer monsoon.
- Medium: Winds flow from high to low pressure.
- Exam-type: Unequal heating of land and sea causes it.
In the figure: Unequal heating drives the monsoon.
Key idea 2: North-east monsoon and importance — From October to February land cools faster than the sea, so cold dry winds blow from land to sea; after crossing the Bay of Bengal they bring rain to Tamil Nadu, Andhra Pradesh and parts of Karnataka. Monsoon decides agriculture, water supply, festivals and jobs; too much rain brings floods and too little brings drought. Ancient scholars like Kṛiṣhiparāśhara and Varāhamihira predicted rain using Moon and Sun positions and nakṣhatras; Kālidāsa described monsoon clouds in the Meghadūtam. Today the National Monsoon Mission and Mission Mausam improve forecasts.
- Easy: NE monsoon blows October–February.
- Medium: Retreating monsoon leaves north India in October.
- Exam-type: Nakṣhatras divide the Moon's path into 27 equal parts.
A good monsoon means good crops and water; a bad one means drought.
Thinking the winter monsoon is rainy everywhere. It mainly rains on the south-east coast.
Which monsoon, when. Memory clue: SW = Summer-Wet (June–Sept); NE = Nov-ish east coast rain (Oct–Feb).
Spot the difference
| Feature | SW monsoon | NE monsoon |
|---|---|---|
| Season | Jun–Sep | Oct–Feb |
| Land vs sea | Land hotter | Land cooler |
| Wind | Sea to land | Land to sea |
| Rain | Most of India | South-east coast |
Practice questions
- 1What does the word 'monsoon' mean?
- 2Who named the monsoon?
- 3When does the SW monsoon blow?
- 4What causes the SW monsoon?
- 5What is the NE monsoon?
- 6Which states get rain from the NE monsoon?
- 7Why is the monsoon important to India?
- 8How can cold, dry winter winds still bring rain to the east coast?
Show answers (try them yourself first)
- 1Seasonal reversal of wind direction; from Arabic mausim, 'season'.
- 2Arab traders.
- 3June to September.
- 4Unequal heating of land and sea.
- 5Cold, dry winds blowing from land to sea from October to February.
- 6Tamil Nadu, Andhra Pradesh and parts of Karnataka.
- 7Agriculture, water supply, festivals and jobs depend on it.
- 8They pick up moisture crossing the Bay of Bengal.
Climate Change, Carbon Footprint and Punjab Floods 2025
Burning fuel for cars, cutting trees for roads and heavy factory smoke all add gases to the air. Over years, those gases change how hot or wet our world becomes.
Climate change is long-term change in weather patterns mainly caused by human activities. A carbon footprint is the total greenhouse gases released by a person's activities: energy use, transport, goods and services.
Key idea 1: Causes and effects — Burning fossil fuels, deforestation and industrial pollution raise greenhouse gases (carbon dioxide, methane, nitrous oxide, water vapour). They trap heat and warm the Earth. Effects: more floods and droughts, melting glaciers, rising sea level, loss of biodiversity, and harm to health, farming and livelihoods, including for women and children.
- Easy: Greenhouse gases trap heat.
- Medium: Fossil fuels, deforestation and industry raise carbon dioxide.
- Exam-type: Effects reach health, agriculture and livelihoods.
In the figure: How human actions lead to climate change.
Climate Change, Carbon Footprint and Punjab Floods 2025
In the app you can move this figure with your finger.
Open in the appKey idea 2: What we can do, and the Punjab floods — Reduce carbon footprint by saving energy and water, using renewable energy, protecting forests and avoiding single-use plastic. In the footprint activity, low = 1, medium = 2, high = 3, very high = 4 points. In 2025, heavy monsoon rain with western disturbances made the Satluj, Beas, Ravi and Ghaggar overflow in Punjab. Human factors: weak old embankments (dhūsī bāndh), houses and farms near rivers, silt reducing capacity, and late warnings. Effects: deaths, relief camps, paddy damage, farm animal losses, damaged roads and bridges, and waterborne diseases.
- Easy: Plant trees and save energy.
- Medium: Flood causes were both natural and human-made.
- Exam-type: Better planning, embankments and early warnings reduce damage.
Every small step counts in reducing carbon footprint.
Thinking floods are purely natural. Human choices increased the damage.
Footprint scoring. Memory clue: 1-2-3-4 = Low, Medium, High, Very high.
Spot the difference
| Natural cause | Human cause |
|---|---|
| Heavy monsoon rain | Weak embankments |
| Western disturbances | Building near rivers |
| Rivers already high | Silt build-up, late warnings |
Practice questions
- 1Define climate change.
- 2Name two greenhouse gases.
- 3What is a carbon footprint?
- 4Give two ways to reduce your carbon footprint.
- 5Name the rivers that overflowed in Punjab in 2025.
- 6Name one natural and one human cause of the floods.
- 7A student ticks: private car (3), lights sometimes left on (2), one-bucket bath (1), disposable plastics sometimes (2). Total?
- 8How can youth help in disaster preparedness?
Show answers (try them yourself first)
- 1Long-term change in weather patterns caused mainly by human activity.
- 2Carbon dioxide and methane.
- 3Total greenhouse gases released by human activities.
- 4Save energy and plant trees (or use renewable energy).
- 5Satluj, Beas, Ravi and Ghaggar.
- 6Heavy monsoon rain with western disturbances; weak embankments.
- 73 + 2 + 1 + 2 = 8.
- 8By spreading warnings, helping relief work and learning safe practices.