The Earth provides us with everything we need to survive - air to breathe, water to drink, soil to grow our food, forests for timber, and minerals and fossil fuels for energy. These things that nature provides are called natural resources. Life on Earth depends entirely on these resources, and the study of how they are formed, used and conserved is essential for our future.
The atmosphere, the lithosphere (the land and soil) and the hydrosphere (water bodies) together make up the biosphere - the region of the Earth where life exists. The biosphere is a self-contained system in which energy from the Sun drives the movement of matter in cycles, such as the water cycle, the carbon cycle and the nitrogen cycle.
In this chapter we study the role of the atmosphere, the water cycle, the composition of air, the different types of soil, the greenhouse effect, and the need to conserve our natural resources.
The biosphere is the part of the Earth where life exists. It is composed of three main realms:
Energy from the Sun drives the processes in the biosphere. The Sun's energy causes evaporation of water, drives the winds, and supports photosynthesis, which forms the basis of the food chain.
The atmosphere is a mixture of many gases. The major components are: - Nitrogen: about 78 percent - Oxygen: about 21 percent - Carbon dioxide: about 0.03 percent - Other gases: argon, neon, helium, methane and water vapour in small amounts.
Role of carbon dioxide: Carbon dioxide is an important gas in the atmosphere. Plants use it during photosynthesis to prepare food. Carbon dioxide is also released by respiration, combustion of fuels and the decay of organic matter. It helps trap heat in the atmosphere (the greenhouse effect), which keeps the Earth warm.
Role of oxygen: Oxygen supports combustion and respiration. Oxygen in the atmosphere is replenished by photosynthesis and is consumed by respiration and burning.
Role of nitrogen: Nitrogen is an inert gas that does not react easily. Nitrogen-fixing bacteria convert atmospheric nitrogen into compounds that plants can use. Nitrogen makes the air chemically less reactive.
Water exists on the Earth in three states - solid (ice), liquid (water) and gas (water vapour). The water cycle is the continuous movement of water between the atmosphere, land and oceans.
The main processes in the water cycle are: 1. Evaporation: The Sun's heat converts water from oceans, rivers and lakes into water vapour. 2. Transpiration: Plants release water vapour into the atmosphere through their leaves. 3. Condensation: Water vapour cools and changes into tiny droplets, forming clouds. 4. Precipitation: When the droplets grow large enough, they fall as rain, snow or hail.
The water cycle ensures the continuous supply of fresh water on the Earth. Human activities like deforestation and the pollution of water bodies disturb the water cycle.
Some gases in the atmosphere, like carbon dioxide, methane, nitrous oxide and water vapour, trap heat radiated from the Earth. These gases are called greenhouse gases, and this trapping of heat is called the greenhouse effect.
The greenhouse effect keeps the Earth warm enough for life to exist. Without it, the Earth would be too cold for living organisms. However, an increase in the concentration of greenhouse gases due to human activities - burning of fossil fuels, deforestation, and industrial processes - has led to an enhanced greenhouse effect, causing global warming.
Global warming: The rise in the average temperature of the Earth due to the increased greenhouse effect is called global warming. Global warming can lead to the melting of glaciers, rising sea levels, changes in rainfall patterns and the loss of biodiversity.
Soil is the uppermost layer of the Earth's crust, formed by the breaking down of rocks over millions of years. The formation of soil is called weathering, which involves physical, chemical and biological processes.
Types of soil: Depending on the size of the particles, soil can be sandy soil (large particles, poor water retention), clayey soil (fine particles, good water retention) and loamy soil (a mixture, the best for plant growth because it holds water and is well-aerated).
Soil profile: The soil profile has different layers called horizons - the topsoil (A horizon) which contains humus, the subsoil (B horizon), and the bedrock (C horizon).
Soil is important because it provides anchorage and nutrients to plants, which are the base of the food chain. Soil erosion, caused by wind and water, removes the topsoil and reduces the fertility of the land. Soil is conserved by afforestation, terrace farming, and the use of cover crops.
Nitrogen is essential for the formation of proteins and nucleic acids in living organisms, but most organisms cannot use atmospheric nitrogen directly. The nitrogen cycle converts atmospheric nitrogen into usable forms and returns it to the atmosphere.
The steps of the nitrogen cycle are: 1. Nitrogen fixation: Nitrogen-fixing bacteria, present in the roots of leguminous plants (rhizobium) and in the soil (azotobacter), and lightning convert atmospheric nitrogen into nitrogen compounds (nitrates) that plants can use. 2. Nitrification: Nitrifying bacteria convert ammonia into nitrites and then into nitrates. 3. Absorption: Plants absorb nitrates from the soil and use them to make proteins. 4. Consumption and decay: Animals get nitrogen by eating plants. When organisms die, decomposers break down the dead matter and release nitrogen compounds into the soil. 5. Denitrification: Denitrifying bacteria convert nitrates back into atmospheric nitrogen, completing the cycle.
Natural resources are limited, and many are being used faster than they can be replenished. It is therefore essential to conserve them.
Why conservation is needed: 1. Fossil fuels like coal and petroleum are non-renewable and will run out. 2. Forests are being cut down for timber and land, leading to soil erosion and loss of biodiversity. 3. Water resources are being polluted and depleted. 4. The increasing population is putting pressure on all resources.
Ways to conserve resources: 1. Using renewable sources of energy like solar and wind energy. 2. Reducing, reusing and recycling materials. 3. Planting trees (afforestation) and preventing deforestation. 4. Conserving water and preventing its pollution. 5. Reducing the burning of fossil fuels to control global warming.
| Gas in Air | Approx. Percentage | Importance |
|---|---|---|
| Nitrogen | 78% | Inert; nitrogen fixation |
| Oxygen | 21% | Respiration, combustion |
| Carbon dioxide | 0.03% | Photosynthesis, greenhouse effect |
| Sphere | What It Contains |
|---|---|
| Atmosphere | Blanket of air |
| Hydrosphere | Water bodies |
| Lithosphere | Land, soil, rocks |
| Biosphere | Region where life exists |
| Soil Type | Particle Size | Water Retention |
|---|---|---|
| Sandy | Large | Poor |
| Clayey | Fine | Good |
| Loamy | Mixed | Best (ideal for plants) |
In this chapter we learned that the Earth's natural resources - air, water, soil, forests, minerals and fossil fuels - are essential for life. The biosphere, consisting of the atmosphere, hydrosphere and lithosphere, supports all living organisms, and the Sun's energy drives the movement of matter through cycles. We studied the composition of the atmosphere, the water cycle, the greenhouse effect and global warming, and the formation and types of soil. The nitrogen cycle showed how nitrogen moves from the atmosphere into the soil and living organisms and back again. Finally, we understood why the conservation of natural resources is critical for sustainable living. Protecting our air, water and soil is not just a duty of governments - it is a responsibility of every individual.