Everything we use to survive — the air we breathe, the water we drink, the soil that grows our food — comes from nature for free. These are natural resources, and the way they keep cycling round and round is what keeps our living planet alive.
🌍 Resources
The Sun, air, water, soil and minerals support all life on Earth.
🌬️ Atmosphere
The blanket of air that gives us oxygen, warmth and protection.
💧 Hydrosphere
All the water — oceans, rivers, ice and groundwater.
♻️ Cycles
Water, carbon, oxygen and nitrogen keep moving in endless loops.
1. What are natural resources?
The resources available on Earth and the energy from the Sun are needed to meet the basic requirements of all life-forms. These resources are the land, the water and the air. The outer crust of the Earth is called the lithosphere. The water covering 75% of the Earth's surface — in oceans, rivers, lakes and underground — is the hydrosphere. The air that covers the whole Earth like a blanket is the atmosphere. The life-supporting zone of the Earth where the atmosphere, hydrosphere and lithosphere interact and make life possible is called the biosphere. Living things in the biosphere are the biotic components, while air, water and soil are the abiotic components.
2. The breath of life — Air
Air is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour. On planets such as Venus and Mars, where there is no life, the air contains 95–97% carbon dioxide. On Earth, living things have shaped the air: nitrogen makes up about 78%, oxygen about 21%, and carbon dioxide only a tiny fraction. Oxygen is used by living things for respiration and by fuels for combustion; it is put back by plants during photosynthesis. Carbon dioxide is kept in balance because plants fix it back into glucose.
3. The role of the atmosphere in climate control
Air is a bad conductor of heat. The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the whole year. It prevents a sudden increase in temperature during daylight hours and slows down the escape of heat into outer space during the night. On the Moon, which has no atmosphere, the temperature ranges from −190°C to 110°C. The atmosphere acts like a protective cover and a thermostat.
4. How do winds blow?
When sunlight heats up land and water bodies, the air above them gets warm, becomes lighter and rises up, creating a region of low pressure. Cooler air from a high-pressure region rushes in to take its place — this moving air is what we call wind. Because land heats up and cools down faster than water, the speed and direction of these convection currents change between day and night and across seasons. Other factors such as the rotation of the Earth and the presence of mountain ranges also affect wind patterns.
5. How do clouds form and how does rain happen?
During the day, water from water bodies, plants and soil evaporates due to the Sun's heat and rises with the hot air as water vapour. As this air rises higher, it expands and cools. The cooling causes the water vapour to condense into tiny droplets around dust and other particles, forming clouds. When these droplets grow big and heavy enough, they fall down as rain, hail or snow. Rainfall patterns decide what kind of vegetation grows in a region.
6. Air pollution
Burning fossil fuels like coal and petroleum releases oxides of nitrogen and sulphur. These dissolve in rain to make acid rain, which damages plants, buildings and water bodies. The burning of fuels also adds suspended particles and smoke to the air. A combination of smoke and fog is called smog, which is a visible sign of pollution and causes breathing problems and allergies. Reducing the burning of fossil fuels helps keep the air clean.
7. Water — a wonder liquid
All cellular processes take place in a water medium, and all the substances dissolved in water are transported inside the body using water. Living things need a steady supply of fresh water. The availability of water decides the diversity of plants and animals that can live in an area. Water pollution happens when undesirable substances (sewage, factory waste, fertilisers, pesticides) are added to water bodies, when harmful substances are removed, or when the temperature of the water changes. Even a change in temperature can be dangerous for the breeding of aquatic animals.
8. Soil — the thin skin of the Earth
Soil is formed over thousands of years by the breaking down of rocks. The Sun, water, wind and living organisms all act on rocks. The Sun heats rocks during the day so they expand, and at night they cool and contract, causing cracks that break the rock into smaller pieces. Water gets into cracks and freezes, widening them; flowing water also wears rocks down. Wind erodes rocks just like water. Lichens and mosses grow on rock surfaces and release substances that powder the rock. This long process produces soil. The mixture of small rock particles, decomposed dead remains (called humus), minerals and microbes makes soil fertile. The topmost layer that contains humus and living organisms is the topsoil.
9. Soil erosion and its prevention
The removal of topsoil by fast-moving wind and water is called soil erosion. The roots of plants hold the soil firmly and prevent erosion, so cutting down trees and overgrazing speed up erosion. Once the fertile topsoil is gone, the land becomes barren. Planting trees and grass and avoiding deforestation help protect the soil.
- Atmosphere of Earth: ~78% nitrogen, ~21% oxygen, traces of CO2, argon and water vapour.
- Venus and Mars air: 95–97% carbon dioxide (no life).
- Moon temperature range: −190°C to 110°C (no atmosphere).
- Biosphere = atmosphere + hydrosphere + lithosphere where life exists.
- Biotic = living components; Abiotic = air, water, soil.
- Acid rain comes from oxides of nitrogen and sulphur.
- Humus = decomposed organic matter that makes soil fertile.
Trace, step by step, how a drop of sea water travels through the water cycle and returns to the sea.
- Evaporation: The Sun heats the sea; liquid water turns into water vapour and rises into the air.
- Transpiration: Plants also release water vapour from their leaves, adding to the moisture in the air.
- Condensation: As the vapour rises and cools, it condenses around dust particles into tiny droplets, forming clouds.
- Precipitation: The droplets join, grow heavy, and fall as rain, snow or hail.
- Collection & run-off: Rain water flows over land into rivers and lakes, and seeps underground as groundwater.
- Return: Rivers carry the water (along with dissolved minerals) back to the sea, and the cycle starts again.
Explain how nitrogen from the air becomes part of a plant and finally returns to the air.
- Nitrogen fixation: Atmospheric N2 is converted into nitrates/nitrites by Rhizobium bacteria in the root nodules of legumes, by lightning, and by free-living soil bacteria.
- Assimilation: Plants absorb these nitrates from the soil and use them to make proteins and other compounds.
- Transfer to animals: Animals eat the plants and get the nitrogen-containing compounds.
- Ammonification: When plants and animals die, decomposers break down their proteins and release ammonia.
- Nitrification: Bacteria convert ammonia into nitrites and then nitrates, which plants can use again.
- Denitrification: Other bacteria convert nitrates back into free nitrogen gas, returning N2 to the atmosphere.
Remember the four cycles with "W-O-C-N" — Water, Oxygen, Carbon, Nitrogen. For the spheres think "BLAH": Biosphere holds the Lithosphere, Atmosphere and Hydrosphere together.
Do not mix up the spheres. Lithosphere is the solid crust, hydrosphere is the water, atmosphere is the air, and the biosphere is only the thin zone where all three meet and life survives. Also, ozone (O3) is a part of the atmosphere that protects us, but it is not the same as oxygen (O2) that we breathe.
Q1. How is the atmosphere of Earth different from that of Venus and Mars, and why?
Answer: The atmospheres of Venus and Mars contain 95–97% carbon dioxide and have no oxygen, because there is no life on them. Earth's atmosphere contains about 78% nitrogen, 21% oxygen and only a small amount of carbon dioxide. This is because living organisms on Earth constantly use and recycle these gases — plants release oxygen during photosynthesis and absorb carbon dioxide, keeping the atmosphere balanced and suitable for life.
Q2. How does the atmosphere act as a blanket that regulates temperature?
Answer: Air is a bad conductor of heat. During the day the atmosphere prevents a sudden rise in temperature by reflecting and absorbing some of the Sun's heat, and at night it slows down the escape of heat into outer space. This keeps Earth's temperature fairly steady. The Moon, which has no atmosphere, swings from −190°C at night to 110°C during the day, showing how important the atmospheric blanket is.
Q3. Describe how soil is formed and why topsoil is so important.
Answer: Soil is formed over thousands of years by the weathering of rocks. The Sun heats rocks so they expand by day and contract at night, forming cracks; water freezing in cracks widens them; flowing water and wind erode the rock; and lichens and mosses chemically break it down into fine particles. Mixed with humus (decomposed organic matter), minerals and microbes, this forms soil. The topmost layer, the topsoil, is rich in humus and living organisms, making it fertile and able to support plant growth. If topsoil is eroded, the land becomes barren.
Q4. What is the role of bacteria in the nitrogen cycle?
Answer: Bacteria play a central role at almost every step. Nitrogen-fixing bacteria such as Rhizobium (in the root nodules of legumes) and free-living soil bacteria convert atmospheric nitrogen into nitrates and nitrites that plants can absorb. After organisms die, decomposer bacteria carry out ammonification, releasing ammonia; nitrifying bacteria then convert ammonia into nitrites and nitrates. Finally, denitrifying bacteria convert nitrates back into free nitrogen gas, returning it to the atmosphere. Thus bacteria keep nitrogen cycling between air, soil and living things.
- ✅ Natural resources = land (lithosphere), water (hydrosphere) and air (atmosphere); the biosphere is where they meet life.
- ✅ The atmosphere regulates temperature, causes winds and brings rain through evaporation and condensation.
- ✅ Air, water and soil pollution harm living things; reducing fuel burning and planting trees help.
- ✅ Water, oxygen, carbon and nitrogen cycle endlessly, recycling resources so life can continue.
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