🌎 Class 9 Science – Earth as a System: Energy, Matter, and Life Original Visual Revision Notes
Aligned with the Class 9 Science syllabus. Independently created study material. Not affiliated with or endorsed by NCERT.
💡 Think about this first! Think of Earth as a giant living machine with five overlapping parts all working together. The rocky ground beneath your feet, the oceans and rivers, the ice on mountains, the air you breathe, and all the living things — each of these is a separate "sphere" and they all talk to each other! Water evaporates into the air, falls as rain onto the land, flows into rivers, and freezes into glaciers. Gases from plants change the air composition. In this lesson, we see how these five spheres keep Earth working like a perfectly balanced system.
🌎 Topic 1: Earth’s Five Spheres
Earth has five big parts called spheres.
Geosphere means all the rocks and soil.
Hydrosphere means all the water on Earth.
Cryosphere means all the ice and snow.
Atmosphere is the blanket of air around Earth.
Biosphere is where all living things exist.
☀️ Topic 2: How the Sun Heats Earth
The Sun is Earth’s main source of energy.
Sunlight hits the ground and warms it up.
Places near the equator get the most heat.
Places near the poles get the least heat.
This uneven heating drives weather and wind.
🌡️ Topic 3: Greenhouse Effect
Sunlight passes through the atmosphere to Earth.
Earth sends heat back toward outer space.
Some gases trap this heat like a blanket.
These are called greenhouse gases.
Carbon dioxide and methane are greenhouse gases.
Without them, Earth would be very cold.
🌊 Topic 4: Land and Sea Breezes
Land heats up faster than water during day.
Hot air over land rises up quickly.
Cool air from the sea moves toward land.
This daytime wind is called sea breeze.
At night, land cools faster than water.
Wind blows from land to sea at night.
This nighttime wind is called land breeze.
🌀 Topic 5: Monsoon Winds
Monsoon is a large seasonal wind pattern.
In summer, land heats more than the ocean.
Moist ocean air rushes toward the hot land.
This brings heavy rain in summer months.
In winter, the wind reverses its direction.
🌊 Topic 6: Ocean Currents
Ocean water moves in big paths called currents.
Wind pushes the water on the ocean surface.
Warm currents flow from the equator toward poles.
Cold currents flow from the poles toward equator.
Ocean currents help control our climate.
💧 Topic 7: Water Cycle
The Sun heats water in rivers and oceans.
Water turns into vapour and rises up. This is evaporation.
Vapour cools high up and forms tiny droplets.
This cooling step is called condensation.
Droplets join to make clouds, then fall as rain.
Rain collects in rivers, lakes, and underground.
🌳 Topic 8: Carbon Cycle
Carbon is found in all living things.
Plants take in carbon dioxide from the air.
Plants use it to make food by photosynthesis.
Animals eat plants and get carbon from food.
When living things breathe out, carbon dioxide returns.
Dead things decay and release carbon into soil.
🧬 Topic 9: Nitrogen Cycle
Air is about 78 percent nitrogen gas.
Plants cannot use nitrogen gas directly from air.
Special bacteria fix nitrogen into usable forms.
These bacteria live in soil or plant roots.
Plants absorb fixed nitrogen through their roots.
When things die, nitrogen returns to the soil.
⚠️ Topic 10: Human Impact on Earth
Burning fuels adds extra carbon dioxide to air.
Extra greenhouse gases cause global warming.
Cutting forests means fewer trees to absorb carbon.
Factories and cars pollute the air and water.
We must use clean energy to protect Earth.
🎨 Section 2 — Easy Illustrations
Fig 1: Earth’s five spheres shown as nested layers
Fig 2: Sea breeze by day (left) and land breeze by night (right)
Fig 3: Four stages of the water cycle
Fig 4: Carbon moves between air, plants, animals, and decomposers
Fig 5: Greenhouse gases trap heat and keep Earth warm
🔬 Section 3 — Worked Examples
💡 Example 1: Composition of Air
A classroom has 5000 litres of air. About 78% of air is nitrogen. How many litres of nitrogen are in the room?
1
We know 78% of air is nitrogen gas.
2
Nitrogen = 78 ÷ 100 × 5000.
3
Nitrogen = 0.78 × 5000 = 3900 litres.
Part = Percentage ÷ 100 × Whole
Answer: The room has 3900 litres of nitrogen.
💡 Example 2: Water Cycle Rainfall
A town receives 120 mm of rain in June and 90 mm of rain in July. What is the total rainfall over these two months?
1
June rainfall = 120 mm.
2
July rainfall = 90 mm.
3
Total = 120 + 90 = 210 mm.
Total = Month 1 + Month 2
Answer: The total rainfall is 210 mm.
💡 Example 3: Carbon Dioxide and Trees
One tree absorbs about 22 kg of carbon dioxide per year. A park has 150 trees. How much CO2 does the park absorb in one year?
1
One tree absorbs 22 kg of CO2 per year.
2
The park has 150 trees in total.
3
Total CO2 absorbed = 22 × 150 = 3300 kg.
Total = per tree amount × number of trees
Answer: The park absorbs 3300 kg of CO2 per year.
📋 Section 4 — Cheat Sheet
Term
Meaning
Geosphere
All rocks, soil, and minerals on Earth.
Hydrosphere
All water on Earth: oceans, rivers, lakes.
Cryosphere
All frozen water: ice caps, glaciers, snow.
Atmosphere
The layer of gases surrounding the Earth.
Biosphere
All areas where living things are found.
Greenhouse Effect
Gases trap heat and keep Earth warm.
Evaporation
Liquid water turns into water vapour.
Condensation
Water vapour cools and forms tiny droplets.
Precipitation
Water falls from clouds as rain or snow.
Carbon Cycle
Carbon moves between air, life, and soil.
Nitrogen Fixation
Bacteria change nitrogen gas into usable forms.
Sea Breeze
Wind from sea to land during daytime.
Land Breeze
Wind from land to sea during nighttime.
Monsoon
Seasonal wind that brings heavy summer rain.
Global Warming
Earth getting hotter from extra greenhouse gases.
🏠 Section 5 — Take-Home Handout
Part A: Fill in the Blanks
1. All the water on Earth is called the _______.
2. The Sun heats the _______ more than the poles.
3. Greenhouse gases _______ heat near the surface.
4. During the day, wind blows from sea to land. This is a _______ breeze.
5. Plants take in _______ from the air for photosynthesis.
Part B: True or False
1. The geosphere includes all the oceans on Earth.
2. Land heats up faster than water during the day.
3. Condensation means water turns into vapour.
4. Nitrogen makes up about 78% of Earth’s air.
5. Cutting down forests helps reduce global warming.
Part C: Solve These
1. If air has 21% oxygen and a hall has 8000 litres of air, how many litres of oxygen are there?
2. A single tree absorbs 18 kg of CO2 per year. How much CO2 do 200 trees absorb in one year?
3. A town gets 85 mm rain in August and 110 mm rain in September. Find the total rainfall.
Part D: Match the Columns
Column A
Column B
Your Answer
1. Evaporation
A. Frozen water on Earth
2. Cryosphere
B. Bacteria change nitrogen for plants
3. Sea Breeze
C. Water becomes vapour from heat
4. Nitrogen Fixation
D. Wind from sea to land in daytime
5. Greenhouse Effect
E. Gases trap heat near Earth
Part E: Draw and Label
Draw the water cycle. Label these four stages: Evaporation, Condensation, Precipitation, Collection.
Fig 6: Mind map of Earth as a system and its key processes
⚠ This is independently created study material aligned with the Class 9 Science syllabus. Not affiliated with or endorsed by NCERT or any government body.