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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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