coal, petroleum and natural gas

Coal-
It is a hard, black coloured substance made up of carbon, hydrogen, nitrogen, oxygen and sulphur.
Coal is processed industrially to obtain derivatives like coke, coal tar and coal gas.

Formation of Coal
The process of formation of coal is known as coalification.
The dense forest present in the low-lying wetland got buried in the earth, millions of years ago.
Soil kept depositing over them and they got compressed.
As they went deeper and deeper, they faced high temperature and pressure.
As a result, the substances slowly got converted into coal.

Uses of Coal
Coal was used to produce steam in the railway engines initially.
It is used to cook food.
It is used to generate electricity in thermal plants.
It is used in industries as fuel.

Petroleum
It is a clear, oily liquid, usually green or black in colour.
It has a very strange smell and is a mixture of petroleum gas, diesel, paraffin wax, petrol, lubricating oil, etc.
It is also termed as “Black Gold” because of its wide range of uses in many industries.

Formation of Petroleum
The sea animals and plants died and their bodies settled at the bottom of the sea.
They got compressed by the layers of sand and clay.
Their encounter with high temperature and pressure converts them into petroleum.
The petroleum is separated from the crude oil by a series of processes in a refinery. This is known as petroleum refining.

Uses of Petroleum
Petroleum is used as a transportation fuel.
Petroleum is used in lubricants to reduce friction in vehicles and industrial machines. 
Petroleum is used for industrial power, heating and lighting, and the petro-chemical industry
Petroleum is also used in agriculture, road construction, and pharmaceuticals.
Petroleum is a raw material for many fertilizers, pesticides, synthetic fragrances, and plastics.

Natural gas
It is a clean and non-toxic fossil fuel.
It is colourless and odourless and can be easily transferred through pipelines.
It is stored as compressed natural gas (CNG) under high pressure.
It is a less polluting and less expensive fossil fuel.
Methane is the most important natural gas.

Formation of Natural Gas
The phytoplankton and zooplankton sink to the bottom of the ocean and mix with organic materials to form an organic-rich mud.
The mud buried under more sediments and lithifies to form an organic shale. This prevents its exposure to oxygen. This is done to protect the organic materials from being decomposed by bacteria.
The increasing pressure and temperature transform the shale into a waxy material known as the kerogen.
At temperatures between 90-160°C kerogen is transformed into natural gas.

Uses of Natural gas
Compressed Natural Gas is used for generating power.
It is used as fuels in automobiles.
It can be used at homes for cooking.
It is used as a starting material in chemicals and fertilizers.