Coal & Petroleum
Dig past the kitchen stove, the school bus, and the plastic ruler in your bag — and you'll find the same thing waiting underground: forests and sea-creatures that died millions of years ago, and never really left.
Fig 1 — a simplified cross-section: forest above, a coal seam below the topsoil, and an oil-and-gas trap sealed under non-porous rock, reached by a drill.
Natural Resources: Nature's Storeroom
Everything we use that we did not manufacture — air, water, soil, sunlight, forests, minerals, coal, and petroleum — comes from nature. We call these natural resources.
But not all resources are equally easy to "restock." Based on how quickly nature can replace them, we sort natural resources into two groups.
Renewable (inexhaustible) resources
These are resources that nature keeps producing or replenishing, often quite quickly — so using them does not really run them down. Sunlight, wind, and water are classic examples. Switch off the sun for a billion users and it still rises tomorrow.
Non-renewable (exhaustible) resources
These exist in a fixed, limited quantity in nature. Once used up, they cannot be replaced in any time frame that matters to us — some took millions of years to form in the first place. Coal, petroleum, natural gas, and minerals belong to this group, which is exactly why this chapter matters: we are spending a millions-of-years-old "savings account" within a couple of centuries.
Coal: A Forest That Never Decayed
Coal is a hard, black, combustible (burnable) rock-like substance. It looks lifeless, but it is — quite literally — an ancient forest in disguise.
How a forest becomes a fuel
Around 300 million years ago, large parts of the Earth were covered with dense, swampy forests. When these trees died, instead of rotting away in open air the way a fallen branch does in your garden, huge numbers of them got buried under layers of soil, sand, and water, cut off from oxygen.
Over millions of years, that buried plant matter was squeezed by enormous pressure and slowly cooked by the Earth's internal heat. With almost no oxygen around, the wood could not simply rot — instead it was gradually converted into carbon-rich coal. This slow transformation is called carbonisation.
Because coal formed from the remains of once-living plants, it is classified as a fossil fuel — and because the process took such an immense stretch of time, coal counts as a non-renewable resource.
Where coal is found in India
India has large coal reserves, most famously in the Damodar Valley region of Jharkhand and West Bengal, along with deposits in Chhattisgarh, Odisha, and Madhya Pradesh.
What coal is used for
- As a household and industrial fuel for heating.
- In thermal power plants to generate electricity — coal is still one of the world's largest sources of electrical power.
- In the steel and iron industry, where its derivative, coke, is essential.
- Historically, as fuel for steam locomotives and steamships.
When coal burns, it releases heat — but also carbon dioxide and, depending on its purity, sulphur dioxide. That heat is exactly why we mine it, and that gas is exactly why we need to be careful about how much of it we burn (more on this in the conservation section).
What We Get When We Process Coal
When coal is heated strongly in the absence of air — a process called destructive distillation of coal — it breaks down into several useful products instead of simply burning away.
Coke
Coke is a tough, porous, almost pure form of carbon, black in colour. It burns with very little smoke and gives intense, steady heat, which is exactly why it is prized in industry.
- Used in the extraction of metals from their ores (especially in blast furnaces for making iron and steel).
- Used in the manufacture of several other chemicals.
Coal tar
Coal tar is a thick, black liquid with a sharp, unpleasant smell. It might look like waste, but it is actually a treasure chest — it contains roughly 200 different substances, many of which are separated out and put to use.
- Naphthalene balls (used against moths and insects).
- Synthetic dyes, drugs, and explosives.
- Paints, photographic materials, and perfumes.
- Plastics and synthetic fibres.
- Roofing and road-surfacing materials.
Coal gas
Coal gas is produced alongside coke when coal is processed in industry. It is used as a fuel in factories situated near coal-processing plants, and historically it was famous for one particular job: lighting up the streets of cities such as London in the early days of gas lighting, long before electric bulbs took over.
Petroleum: "Rock Oil"
The word petroleum comes from the Latin petra (rock) and oleum (oil) — oil from rock. It is a dark, oily liquid made of a complex mixture of hydrocarbons (compounds of carbon and hydrogen), and it is so valuable to modern life that it has earned the nickname "black gold."
How petroleum forms
While forests were turning into coal on land, something similar was happening at sea. Tiny marine organisms died and settled on the sea floor, where they were gradually buried under layers of sand and clay. Cut off from air and squeezed under immense pressure and heat over millions of years, this organic matter slowly transformed into petroleum and natural gas.
Because petroleum, too, comes from the remains of once-living organisms, it is a fossil fuel — and a non-renewable one.
Trapped between the rocks
Petroleum and natural gas don't sit around in open underground "lakes." They get trapped between layers of rock that don't let liquid pass through (non-porous rock), with natural gas usually settling just above the petroleum, since gas is lighter.
Extraction
To reach this trapped petroleum, engineers drill holes through the layers of rock down to the rock trap. Once the drill reaches it, the pressure underground often pushes the oil up on its own; where it doesn't, pumps are used to force it out.
Where petroleum is found in India
- Digboi, Assam — India's oldest oil well, and one of the oldest in Asia.
- Ankleshwar, Gujarat.
- Mumbai High — an offshore field in the Arabian Sea.
- Krishna–Godavari basin, Andhra Pradesh.
Refining: sorting the mixture
Crude petroleum, as pumped out of the ground, is a jumbled mixture — not directly useful in that form. It is sent to a refinery, where it undergoes fractional distillation: it is heated, and its different components (called fractions) boil off and are collected separately at different temperatures, each fraction being a useful product in its own right.
Seven Things Hiding Inside Crude Oil
Picture the refinery's distillation tower as a tall column: lighter fractions rise and are drawn off near the top, heavier ones are collected lower down. Here is what comes out, top to bottom.
Notice the pattern: lighter, more "watery" fractions like LPG and petrol come off first; thick, sticky bitumen — practically tar — is left right at the bottom. Each fraction has its own boiling point, which is exactly what fractional distillation uses to separate them.
Natural Gas
Natural gas is often found trapped above petroleum deposits, though it also occurs independently in its own reservoirs. Its main component is methane.
Getting it to your kitchen
- For vehicles, it is compressed and stored as CNG (Compressed Natural Gas) — used as a cleaner-burning fuel for buses, autos, and cars in many Indian cities.
- For homes, it is supplied through pipelines as PNG (Piped Natural Gas), used directly for cooking.
- It is also burned in power plants to generate electricity, and used as a raw material in manufacturing fertilisers and various chemicals.
Why natural gas is a favourite
- It can be transported over long distances easily and cheaply through pipelines.
- It burns cleanly, leaving behind no ash or residue.
- It causes comparatively less air pollution than coal or petrol/diesel.
Fossil Fuels, In One Frame
Coal, petroleum, and natural gas are together called fossil fuels, because all three were formed from the buried, fossilised remains of plants and animals that lived millions of years ago.
Fossil fuels currently power most of the world — vehicles, factories, and power plants all rely on them. But they share two serious limitations: they took millions of years to form and exist in limited quantities, and burning them releases gases (mainly carbon dioxide, along with sulphur and nitrogen oxides) that contribute to global warming and acid rain.
Coal vs Petroleum vs Natural Gas, side by side
| Feature | Coal | Petroleum | Natural Gas |
|---|---|---|---|
| Physical state | Solid | Liquid | Gas |
| Formed from | Buried forests (land plants) | Buried marine organisms | Buried marine organisms |
| Main use | Power plants, steel industry | Transport fuel (petrol, diesel) | Cooking (PNG), vehicles (CNG) |
| Found in India at | Damodar Valley (Jharkhand, WB) | Digboi, Mumbai High, Ankleshwar | Often with petroleum deposits |
| Transport | Rail / trucks (bulky) | Pipeline or tanker | Pipeline (easiest) |
| Residue on burning | Ash, smoke | Smoke (varies by fraction) | Almost none |
Did You Know?
Why We Must Conserve Coal & Petroleum
We've travelled down through 300 million years of buried forests and ancient seas. The trip back up is where the responsibility begins.
Coal, petroleum, and natural gas are exhaustible — once the present reserves run out, no amount of waiting will refill them on any timescale useful to us. On top of that, burning fossil fuels pollutes the air: carbon dioxide build-up drives global warming, while sulphur and nitrogen oxides cause acid rain that damages soil, water, and buildings.
What you can actually do
- Switch off vehicle engines at long red lights instead of idling.
- Choose public transport, carpooling, cycling, or walking for short distances.
- Get vehicles serviced and "tuned" regularly — a well-maintained engine burns less fuel.
- Switch off lights, fans, and appliances when not in use, and prefer energy-efficient LED bulbs.
- Use CNG/PNG where available — it burns cleaner than petrol or diesel.
- Support and use renewable alternatives — solar water heaters, solar cookers, wind energy — wherever possible, to ease the load on fossil fuels.
None of these are dramatic acts. They are small, repeatable habits — and habits, multiplied across millions of people, are exactly how a "countdown" resource gets a longer countdown.
Glossary — Quick Reference
Exam-Oriented Q&A
What are fossil fuels? Give three examples.
Fossil fuels are fuels formed from the buried, fossilised remains of dead plants and animals over millions of years, under heat, pressure, and the absence of air. Coal, petroleum, and natural gas are the three main fossil fuels.
Differentiate between renewable and non-renewable resources.
Renewable resources, like sunlight, wind, and water, are continuously replenished by nature and do not get exhausted by use. Non-renewable resources, like coal and petroleum, exist in limited quantities, took millions of years to form, and cannot be replaced once used up at the present rate.
How is coal formed? Name the process.
Around 300 million years ago, dense forests got buried under layers of soil due to natural changes. Cut off from oxygen and subjected to high pressure and heat over millions of years, this plant matter slowly turned into coal. This slow transformation is called carbonisation.
What is coke? State two of its uses.
Coke is a tough, porous, nearly pure form of carbon obtained by processing coal. It is used in the extraction of metals from their ores, such as in blast furnaces for making iron and steel, and in manufacturing several other chemicals.
Why is petroleum called "black gold"?
Petroleum is called "black gold" because of its dark colour and its enormous economic value — it is refined into a wide range of essential products, from petrol and diesel to LPG and lubricants, making it one of the most valuable natural resources in the world.
Name any four products obtained by refining petroleum, with one use each.
Petroleum gas (LPG) is used as cooking fuel; petrol is used as fuel for vehicles; kerosene is used in stoves, lamps, and jet aircraft; diesel is used as fuel for trucks, buses, and generators. (Other valid fractions: lubricating oil, paraffin wax, bitumen.)
What is the difference between coal gas and natural gas?
Coal gas is manufactured by processing coal in industry and is obtained alongside coke. Natural gas occurs naturally underground, often trapped above petroleum deposits, and consists mainly of methane. They are produced and sourced differently, even though both are used as fuels.
Why is it necessary to conserve fossil fuels?
Fossil fuels are non-renewable — their known reserves are limited and took millions of years to form, so they cannot be replaced within a useful timeframe. Burning them also pollutes the air and contributes to global warming and acid rain, making careful, reduced use essential for the future.
Suggest any three ways students can help conserve fossil fuels.
Switching off vehicle engines at long red lights, preferring cycling, walking, or public transport over private vehicles for short distances, and switching off lights and appliances when not in use are all simple, effective habits that reduce fossil fuel consumption.
Chapter Summary
- ✓Natural resources are materials provided by nature; they are classed as renewable (sunlight, wind, water) or non-renewable (coal, petroleum, natural gas, minerals).
- ✓Coal formed from buried forests over ~300 million years through carbonisation, under heat, pressure, and absence of air.
- ✓Destructive distillation of coal gives coke, coal tar, and coal gas — each with distinct industrial uses.
- ✓Petroleum ("rock oil") formed from buried marine organisms and is trapped between layers of non-porous rock, often with natural gas above it.
- ✓Crude petroleum is refined by fractional distillation into LPG, petrol, kerosene, diesel, lubricating oil, paraffin wax, and bitumen.
- ✓Natural gas (mainly methane) is used as CNG for vehicles and PNG for homes, and is valued for being clean-burning and easy to transport.
- ✓Coal, petroleum, and natural gas are together called fossil fuels — important but limited, and polluting when burned.
- ✓Conservation matters: simple daily habits, careful vehicle use, and shifting towards cleaner or renewable alternatives all help stretch these limited resources.
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