Natural Resources
Contents
- Introduction to Natural Resources
- Types of Natural Resources
- Air – Composition, Importance & Pollution
- Water – Necessity & Pollution
- Soil – Formation, Types & Erosion
- Biogeochemical Cycles
- Greenhouse Effect & Global Warming
- Ozone Layer & Its Depletion
Introduction
Life on Earth depends on many factors. The energy from the sun and the resources available on the Earth are necessary to meet the basic requirements of all life-forms.
The outer crust of the Earth is called the lithosphere. Water covering 75% of the Earth's surface and found underground comprises the hydrosphere. The air forming a blanket around the Earth is called the atmosphere. The life-supporting zone where the atmosphere, hydrosphere, and lithosphere interact and make life possible is known as the biosphere.
The conditions surrounding an organism and regularly interacting with it form its environment. Physical (non-living) factors like air, water, soil, light, and temperature are called abiotic components. Living things such as humans, plants, animals, and microbes are the biotic components.
The materials useful to living organisms that are present in the natural environment are called natural resources. They may be physical (e.g., air, water, minerals, coal) or biological (e.g., microbes, plants, animals).
2.1 Types of Natural Resources
Depending on abundance and availability, natural resources are of two types:
2.1.1 Inexhaustible Resources
Resources which are unlimited in quantity and are not likely to be exhausted by human use. Examples: solar energy, air, tidal energy.
2.1.2 Exhaustible Resources
Resources which are limited and likely to be finished by human use. These are further divided into:
- Renewable resources: Resources that can maintain themselves or be replaced if managed wisely — water, soil, crops, forests. However, they may be lost by excessive and unwise use.
- Non-renewable resources: Resources that are not restored once used — metallic minerals, fossil fuels (coal, petroleum).
Check Out- CBSE Class 9 Science Notes
3. Air
Air is an inexhaustible natural resource consisting of a mixture of gases: nitrogen, oxygen, carbon dioxide, and others, along with water vapour and dust particles.
Composition of Air
| Component | Volume |
|---|---|
| Nitrogen (N₂) | 78.08% |
| Oxygen (O₂) | 20.92% |
| Carbon dioxide (CO₂) | 0.03% |
| Argon | 0.93% |
| Trace components | 0.04% |
3.1 Importance of Air
3.1.1 Role of Gases
- Respiration: Oxygen oxidises sugar molecules to produce CO₂, water, and energy.
- Burning: Oxygen is essential for combustion of wood, fuels, and organic wastes.
- Forest fire: Consumes large amounts of oxygen.
- Photosynthesis: Green plants convert CO₂ to glucose in sunlight.
- Formation of shells: Marine animals use dissolved carbonates to form shells.
3.1.2 Role in Climate Control
Air is a poor conductor of heat. The atmosphere acts as a protective blanket in the following ways:
- It keeps the Earth's temperature fairly steady through the greenhouse effect.
- Greenhouse gases like CO₂ and methane prevent sudden temperature increases during the day and slow heat escape at night. By contrast, the Moon (with no atmosphere) experiences temperatures ranging from −190°C to +110°C.
3.2 The Movement of Air: Wind
Unequal heating of the Earth's surface causes warm air to rise (creating low pressure) and cooler air to flow in. This horizontal movement of air is called wind. Convection currents, Earth's rotation, and mountain ranges also influence wind patterns.
3.2.1 Sea Breeze and Land Breeze
Sea breeze (daytime): Land heats faster → low pressure over land → air moves from sea to land.
Land breeze (night-time): Sea cools slower → low pressure over sea → air moves from land to sea.
3.2.2 Clouds and Rain
When air temperature falls below the dew point, water vapour condenses around dust particles (nuclei) forming tiny droplets. Millions of droplets form clouds. When droplets grow heavy enough they fall as rain.
3.3 Air Pollution
Any undesirable change in the physical, chemical, or biological characteristics of air, making it harmful to living organisms, is called air pollution.
Sources
- Natural: Volcanic eruptions, forest fires, dust storms.
- Man-made: Burning fossil fuels, urbanisation, industrialisation, deforestation, mining.
Harmful Effects
- Respiratory problems: Oxides of nitrogen and sulphur cause bronchitis, asthma, lung cancer, TB.
- Carbon monoxide poisoning: CO from vehicles and cigarettes affects the central nervous system.
- Acid rain: Rain containing H₂SO₄ and HNO₃ (pH < 5) makes soil and water bodies acidic.
- Lowering visibility (Smog): Unburnt carbon particles reduce visibility, especially in cold weather.
4. Water
About 97% of Earth's water is saline (seas and oceans). Fresh water (~3%) is found in polar ice caps, snow-covered mountains, rivers, lakes, and underground. Availability of fresh water is a key factor in sustaining life.
4.1 Rain Water Harvesting
A technique to capture and store rain water using structures such as dug-out wells, percolation pits, check dams, and lagoons, to recharge underground water resources.
Advantages
- Reduces run-off loss of rain water.
- Helps control floods.
- Checks soil erosion.
- Raises the water table.
4.2 Necessity of Water
Importance in Human Life
- Dissolves salts and nutrients in food.
- Provides aqueous medium for metabolic reactions.
- Regulates body temperature.
- Required for removal of waste products.
Importance in Plant Life
- Essential for seed germination and plant growth.
- Required during photosynthesis.
- Medium for transport of minerals and food.
4.3 Water Pollution
An undesirable change in the physical, biological, or chemical qualities of water that adversely affects aquatic life and makes water less fit for use.
Sources
- Industrial waste: Acids, alkalies, heavy metals (e.g., mercury from paper industries).
- Fertilizers and pesticides: Washed by rain water into water bodies.
- Sewage: Organic wastes from towns and cities.
Effects
- Diseases: Typhoid, cholera, jaundice caused by pathogens in polluted water.
- Destruction of microorganisms: Industrial chemicals kill useful microbes that purify water naturally.
- Eutrophication: Excess nutrients → algae growth → reduced dissolved oxygen → harm to aquatic organisms.
- Imbalance in biodiversity: Thermal pollution (hot water from industries/dams) affects breeding cycles and life-forms.
5. Soil
Soil is an important natural resource that forms the top surface layer of the Earth's crust. Its composition: Mineral matter (45%), Organic matter (5%), Water (25%), Air (25%), and Living organisms.
5.1 Formation of Soil (Weathering)
Soil formation is slow — hence soil is regarded as a non-renewable resource. Over millions of years, rocks are broken down by:
5.1.1 Physical Weathering
- Sun: Unequal expansion/contraction of rocks causes cracks.
- Water: Freezing in crevices breaks rocks; fast-flowing rivers erode and transport particles.
- Wind: Continuously erodes rock surfaces.
5.1.2 Biological Weathering
- Lichens: Produce acids that corrode rock surfaces.
- Mosses: Grow on rock surfaces and break them further.
- Roots: Enter cracks, grow, and widen them.
5.1.3 Chemical Weathering
Rocks undergo hydrolysis, hydration, oxidation, and reduction, leading to soil formation.
5.2 Composition of Soil
| Particle Type | Size |
|---|---|
| Gravels | > 2 mm |
| Sand particles | 0.05 – 2 mm |
| Silt particles | 0.005 – 0.05 mm |
| Clay particles | < 0.005 mm |
5.3 Types of Soil
- Sandy soil: Large sand particles, cannot hold much water — found in deserts, unfit for plant growth.
- Clayey soil: Large clay proportion, holds water but not air — not suitable for plant growth.
- Loamy soil: Clay + silt + sand + humus — best for plant growth as it is porous and holds both water and air.
5.4 Soil Pollution
Contamination of soil with solid waste, chemicals, fertilizers, and pesticides that reduce its fertility.
Sources
- Solid wastes from residences, cattle sheds, and industries.
- Industrial chemicals dumped in vacant sites or deposited as acid rain.
- Excess fertilizers/pesticides — non-biodegradable chemicals (e.g., DDT) enter the food chain via biological magnification.
Harmful Effects
- Reduces soil fertility and crop yield.
- Emits foul smell due to decomposing solid waste.
- Kills earthworms and microorganisms that make humus.
5.5 Soil Erosion
Removal of the top layer of soil by agents such as strong winds and fast-flowing water is called soil erosion.
Causes
- Strong winds carrying away loose, uncovered topsoil.
- Heavy rains and floods washing away topsoil.
- Improper farming and abandoned cultivation.
- Large-scale deforestation.
Prevention
- Intensive cropping and sowing grasses on uncultivated land.
- Terrace farming on hilly slopes.
- Embankments along river banks.
6. Biogeochemical Cycles
The movement of nutrient elements through the living and non-living components of the biosphere is called a biogeochemical cycle. These nutrient elements — called biogeochemicals — are continuously recycled.
6.1 The Water Cycle (Hydrological Cycle)
Global water cycle: Water evaporates from oceans/rivers → forms clouds → precipitates as rain/snow → some soaks into ground, some flows into rivers → eventually evaporates again.
Biological water cycle: Animals drink water and release it as urine/sweat; plants absorb water and lose it through transpiration; death and decay also add water back to the environment.
6.2 Nitrogen Cycle
Nitrogen (78% of atmosphere) is essential for proteins, DNA, RNA, vitamins, and urea. The cyclic pathway by which nitrogen is circulated through living and non-living components is the nitrogen cycle.
6.2.1 Nitrogen Fixation
Conversion of free atmospheric nitrogen into nitrogen compounds:
- Atmospheric fixation: Lightning combines N₂ with O₂ → oxides of nitrogen → dissolves in rain → nitrates in soil.
- Biological fixation: Rhizobium bacteria in root nodules of leguminous plants fix atmospheric nitrogen.
- Industrial fixation: N₂ + H₂ → NH₃ (ammonia) → converted into nitrates or ammonium salts for use as fertilizers.
6.2.2 Ammonification
Conversion of complex organic compounds (proteins from dead plants/animals) into ammonia by soil bacteria.
6.2.3 Nitrification
Conversion of ammonia into nitrites and nitrates by nitrifying bacteria (Nitrosomonas & Nitrobacter).
6.2.4 Denitrification
Conversion of nitrate salts back to free nitrogen by denitrifying bacteria (Pseudomonas) present in soil.
6.3 Carbon Cycle
Carbon is the basic constituent of all living beings. Three main reservoirs: atmosphere (CO₂), oceans (dissolved CO₂), and minerals/fossil fuels.
- Enters life: Photosynthesis converts CO₂ → glucose.
- Returns to atmosphere: Respiration, decomposition, volcanic eruptions, combustion of fossil fuels.
6.4 Oxygen Cycle
Oxygen is found in elemental form (21% in atmosphere) and in combined forms (oxides, carbonates, sulphates). The cycle involves:
- Respiration: consumes O₂, releases CO₂.
- Photosynthesis: consumes CO₂, releases O₂.
- Combustion: consumes O₂, releases CO₂.
7. Greenhouse Effect & Global Warming
A greenhouse is a glass building that traps heat by reflecting long-wavelength infrared radiation while allowing short-wavelength solar radiation to enter.
Similarly, gases like CO₂, methane (CH₄), and nitrous oxide in the atmosphere trap heat that the Earth's surface radiates back. This is the greenhouse effect, which keeps the Earth warm.
Human activities (burning fossil fuels, deforestation) add excessive CO₂ and CH₄ to the atmosphere, causing abnormal warming known as global warming.
8. Ozone Layer & Its Depletion
In the upper atmosphere (stratosphere), UV radiations cause O₂ molecules to form ozone (O₃). This thick ozone blanket is called the ozone shield. It absorbs harmful UV radiation, protecting life on Earth.
8.1 Depletion of the Ozone Layer
Chlorofluorocarbons (CFCs) — used in air-conditioners, refrigerators, and aerosol sprays — rise to the upper atmosphere and release chlorine atoms, which react with ozone:
- CFC → chlorine atoms
- Cl + O₃ → ClO (chlorine monoxide) + O₂
This creates an ozone hole, most prominent over Antarctica.
8.2 Effects of the Ozone Hole
- Without the ozone shield, UV rays reach Earth causing skin cancer and cataracts.
- UV rays adversely affect plant life as well.
Quick Q & A
Exercise: Air, Water & Soil
- Name three physical agents which cause weathering of rocks.
- Name any three water pollutants.
- What is soil erosion?
- What is eutrophication?
- Why is air called the breath of life?
- What causes winds?
- Why is life on Venus and Mars not possible?
- Write about the sources of soil pollution.
- How are clouds formed?
- Describe the sources and harmful effects of air pollution.
Exercise: Biogeochemical Cycles
- Name the different biogeochemical cycles operating in nature.
- What are the two forms of oxygen found in the atmosphere?
- Name some greenhouse gases.
- What are the different states in which water is found during the water cycle?
- What is denitrification?
- How is the ozone layer useful to us?
- What are CFCs?
- What is nitrogen fixation? Explain the various ways by which it is fixed.
- Explain the biological water cycle.
- With the help of a diagram, explain the oxygen cycle.