Energy is essential for everything we do — for cooking, transport, running industries and generating electricity. Most of this energy comes from fuels, and among the most important fuels are coal and petroleum. These materials are called fossil fuels because they were formed from the remains of living organisms (plants and animals) that lived millions of years ago. Along with natural gas, coal and petroleum supply most of the energy used by modern civilisation.
Fossil fuels were formed over millions of years under the earth's surface through heat, pressure and the action of microorganisms. Because they take such a long time to form, they are exhaustible natural resources — once used up, they cannot be replenished within a human lifetime. This chapter explains how coal and petroleum are formed, what useful products we get from them, and why we must conserve them for the future.
The resources available in nature that we use for our survival are called natural resources. These include air, water, soil, forests, minerals and fuels. On the basis of exhaustibility, natural resources are of two types:
Coal, petroleum and natural gas are exhaustible resources, and they are also called fossil fuels because they are the fossilised remains of ancient life.
Coal is formed from the remains of vegetation. About 300 million years ago, huge forests grew in low-lying wetlands. When these plants and trees died, they sank into the swampy water and got buried under layers of soil and rock. Over millions of years, the increasing pressure and heat, along with the action of bacteria, slowly converted the dead plant matter into a dark, hard, combustible substance — coal.
The slow conversion of dead vegetation into coal is called carbonisation. Because this process produced a substance rich in carbon, coal is also called black gold and is one of the most important solid fossil fuels. Coal is used as a fuel in industries, thermal power plants and for cooking; it is also used to produce coke, coal tar and coal gas.
When coal is heated in the absence of air, it undergoes destructive distillation and gives three important products:
Coal is also used to generate electricity in thermal power plants, and to run steam engines.
Petroleum and natural gas were formed from the remains of tiny marine organisms. Millions of years ago, the bodies of countless microscopic sea plants and animals settled at the bottom of the sea and were covered by layers of sand and clay. Over millions of years, heat, pressure and the action of bacteria converted this organic matter into petroleum (crude oil) and natural gas. Because these formed deep inside the earth, petroleum is extracted by drilling deep wells. Since it is found trapped between layers of rock in the earth, petroleum is also called mineral oil.
The word petroleum comes from the Latin words petra (rock) and oleum (oil), meaning "rock oil". Natural gas is often found above the petroleum layer in oil fields, and it is also found separately in natural gas reservoirs. Natural gas is a clean fossil fuel and is stored and transported under pressure in cylinders.
Crude petroleum taken out of the earth is a dark, thick liquid, but it is a mixture of many substances that are not directly useful. The process of separating petroleum into its various useful components is called refining of petroleum, and it is done in a petroleum refinery by fractional distillation.
The various fractions obtained and their uses are:
Natural gas is a fossil fuel found above petroleum in oil fields. It is lighter than air and is a clean fuel. When natural gas is compressed by cooling to a very low temperature, it is stored as CNG (Compressed Natural Gas) in cylinders. Natural gas is also stored as LNG (Liquefied Natural Gas) in special tanks.
CNG is a very clean fuel because it produces fewer pollutants when burned. It is used to run vehicles (the Great Indian Bustard in Rajasthan and the city buses of Delhi use CNG), to generate electricity, and as fuel in homes and industries. CNG reduces air pollution compared to petrol and diesel, which is why the government encourages its use.
Fossil fuels took millions of years to form, but we are using them at a very fast rate. Coal, petroleum and natural gas are exhaustible resources that cannot be replenished quickly. If we continue using them at the present rate, the world's petroleum reserves may last only a few decades, and coal may last a few centuries. This is why these resources are precious, and why conserving them is urgent.
The conservation of resources does not mean not using them at all; it means using them carefully and wisely. Wasting fuel in traffic jams, leaving lights and appliances on, and using fuel-inefficient machines all waste precious energy. Steps such as carpooling, using public transport, switching to cleaner fuels like CNG, using energy-efficient appliances and promoting renewable energy sources (solar, wind, hydropower) all help conserve fossil fuels.
| Product | Nature | Uses |
|---|---|---|
| Coke | Hard, porous, almost pure carbon | Manufacture of steel, extraction of metals |
| Coal tar | Thick black liquid, mixture of ~200 substances | Dyes, drugs, perfumes, plastics, paints, explosives |
| Coal gas | Gaseous fuel | Fuel in industries, street lighting (earlier) |
| Fraction | Uses |
|---|---|
| Petroleum gas (LPG) | Domestic fuel |
| Petrol | Fuel for motor vehicles, aeroplanes |
| Kerosene | Fuel for stoves and lamps, jet engines |
| Diesel | Fuel for heavy vehicles, generators |
| Lubricating oil | Lubrication of machines and engines |
| Paraffin wax | Ointments, candles, cosmetics |
| Bitumen | Paints, surfacing of roads |
| Feature | Exhaustible | Inexhaustible |
|---|---|---|
| Availability | Limited, will get exhausted | Unlimited, not exhausted by use |
| Examples | Coal, petroleum, natural gas, forests, minerals | Air, sunlight, water |
Coal and petroleum are exhaustible fossil fuels formed over millions of years from dead plants and tiny marine organisms. Through processes like carbonisation (for coal) and refining by fractional distillation (for petroleum), we obtain essential products — coke, coal tar, coal gas, petrol, kerosene, diesel, LPG, lubricating oil, paraffin wax and bitumen — that power our homes, vehicles and industries. Natural gas, especially in the form of CNG, offers a cleaner-burning alternative. Because these resources are limited and non-renewable, every unit of energy we save matters. Adopting habits like using public transport, carpooling, conserving electricity and shifting to renewable sources ensures that future generations will still have the energy they need.