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What is a Fossil Fuel?

Coal, Oil and Natural Gas Formation - Fossil Fuels.

Just as coal has formed by the action of heat and pressure
on the remains of trees and plants on land over millions of years,
so oil and natural gas have formed
by the action of heat and pressure on the
remains of sea plants and animals over millions of years.

The remains were buried in sediments which
excluded the air (kept out oxygen) and stopped them decaying.
Further deposits of sediment buried the remains
deeper and deeper until the effects of pressure and heat
eventually turned the remains into coal, oil and natural gas.
They are called fossil fuels because they are buried underground
(from Latin fossilis - dug up).
Coal is mainly carbon. It is sometimes called a carboniferous rock.

The oil deposits are formed in porous rock sediments.
Porous rock has pores in it. Pores are small holes
(see for example sandstone). The small holes allow
the oil and natural gas to pass through the rock
and rise until they are stopped by a layer of non-porous rock.
Non-porous rock (for example shale) has no holes,
and acts as a barrier to prevent the oil and natural gas rising.
The oil and natural gas become trapped underground.

The oil is called crude oil (or petroleum, from Latin - rock oil),
and has natural gas in it or in a pocket above it
trapped by non-porous rock. Drilling through the rock
allows the oil and gas to escape to the surface.
Crude oil is a mixture of hydrocarbons and is used to make
fuels, polymers, chemicals, solvents, lubricants and roads.

Natural gas is mostly methane (CH4).

Fossil fuels are a finite resource and non-renewable.
Fossil fuels are burnt in power stations to generate electricity.

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