Formation of coal:
The plants in large and dense forests in low lying wetlands got burried under the soil due to the natural processes like floods and earthquakes. As more soil deposited over them, the organic matter was compressed. The temperature also rose.
As the organic matter sank deeper and deeper, under high pressure and high temperature, these dead plants slowly converted to coal.As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called corbonisation. Since coal was formed from the remains of vegetation, it is also called fossil fuel.
Formation of petroleum:
Petroleum was formed from the remains of tiny organisms called plankton that were found in the bottom of seas and oceans. Plankton have tiny droplets of oil inside their bodies.As these organisms died, their bodies settled at the bottom of the see or ocean and covered with layers of sand and clay.Over millions of years, due to absence of air, high temperature and high pressure these dead organisms transformed into petroleum and natural gas. Like coal and petroleum natural gas were also formed from the dead remains (fossils) of living organisms, they too are known as fossil fuels.
Why are coal and petroleum so versatile?
Coal consists of mainly carbon whilepetroleum consists of a mixture of compounds called hydrocarbons (they contain mainly hydrogen and carbon).These compounds make good starting materials for other compounds based on carbon. Carbon is very versatile and is the basis for most of the materials. Therefore, coal and petroleum too are very important starting materials for synthesising variety of useful compounds.
Alternatives to natural gas:
The gas resources which are not conventional like natural gas are known as Non-conventional gas resources .Our country has enormous non-conventional gas resources like coal bed methane and gas hydrates. These are not in commercial production phase due to the lack in proper technology. In future, when the oilera is expected to end, the only way to meet the energy demands will be by producing this non-conventional gas.