Fossil fuels rule
An insight into how crude oil, coal and natural gas form
Coal is found throughout the world and unlike oil and gas, it is very plentiful, with reserves that will last at least another 200 years. Coal is the primary source of electrical energy world-wide.
Coal is formed from the remains of trees that lived in enormous forests when the Earth was hot, humid and lush. These forests were located near marsh areas, swamps or near the sea and this is where the initial stages of coal formation occurred. The trees were buried under water and mud and no longer were exposed to oxygen. As a result, decomposition was slowed to a point where more sediment layers were deposited on top of the organic layer before the trees were fully decomposed. This trapped the organic energy.
Over millions of years, more sediment layers built up, and pressure and heat were exerted on the organic layer, gradually breaking down and chemically changing the composition of the organic matter into elementary carbon. The older the coal, the more elemental carbon it contains and therefore the more efficient the fuel.
The best coal, anthracite, formed over 300 million years ago and it's very hard. It has the fewest impurities and the highest percent (90 percent +) of elemental carbon. It has been subjected to so much heat and pressure that anthracite is a metamorphic rock, unlike black coal.
Black coal is a sedimentary rock and contains more impurities. It is used in many power stations for the production of electricity and was produced 100 to 300 million years ago. It still contains a high level of elemental carbon and remains an efficient form of energy for the production of electricity.
A younger form of coal, produced about 65 million years ago, is known as brown coal or lignite. This contains many impurities and fibrous debris, which makes this a very 'dirty' coal which, when burnt, gives off a lot of pollution. The final form of coal, which is coal in its very early stages, is peat. This is not a good fuel and burns very inefficiently.
Coal is mined and sent to power stations. There it is burned and the heat turns water into steam. This steam turns turbines, which turn generators that produce electrical energy. This electrical energy is then transported via pylons to our homes or wherever else it is needed giving us electricity.
Crude oil and natural gas
Estimates of when crude oil and natural gas will run out vary, but they will probably be gone in the next 50 years given its high consumer consumption.
Like coal, oil and gas are made from the remains of living things but in this case it is sea creatures that died and sank to the bottom of the ocean. Again, it is the lack of biodegradation that is the key. So if massive amounts of dead organisms build up on the sea floor and are quickly covered by other sedimentary layers, they do not get decomposed, and eventually become compressed.
All living things are basically a combination of carbon, hydrogen, oxygen and nitrogen. When these sea creatures are compressed with more sediment layers building up, oxygen and nitrogen are eliminated, leaving the hydrogen and carbon behind. This combination of hydrogen and carbon are known as hydrocarbons and are contained in a source rock.
This is the layer of rock where crude oil and natural gas are formed. Being liquid and gas, they move around and rise through the rock and through any porous (meaning it has holes) rocks above the source rock. They keep rising, even above water as oil is less dense than water and gas is obviously less dense than oil, until they reach a non-porous rock layer known as a cap rock. Here, a layer of natural gas settles on top, with a crude oil layer underneath. It is in this situation that, when discovered, oil and gas can be collected.
Every nation uses oil daily for many purposes. But before it can be used, it first must be cracked.
Cracking is where long chained hydrocarbons are broken down into simpler hydrocarbons. Oil is an very long hydrocarbon, and it is cracked in oil refineries. Oil is cracked in a distillation column and the products are subdivided according to temperature. Longer chained hydrocarbons collect at the bottom of the distillation column where it is the hottest. These include diesel, bitumen and heavy residual oil.
The temperature drops the further up the column the fuel rises. The shorter chained hydrocarbons are collected in the upper regions. See graphic.
Twelve-carbon chained hydrocarbons represent kerosene, which is used for airplane fuel. An eight-carbon chained hydrocarbon is octane, which we know as gasoline. A substance called naptha is also produced during the process. Naptha can be subjected to chemical change and polymerized to produce plastics and certain drugs. Further gases can also be collected that are as short as one- to four-carbon chained hydrocarbons, which are used for cooking and heating.
Whenever fossil and other fuels are burnt they produce water and carbon dioxide. As fossil fuels are constantly used throughout the day worldwide, they are responsible for the increased carbon dioxide levels in the atmosphere which, in part, cause global warming. But that's story for another article.
David Canavan has an MSc in Behavioral Ecology and teaches science, math and ICT at Garden International School. David is fascinated by science and loves animals, especially the dangerous kind; the more dangerous the better. You may contact David at firstname.lastname@example.org .
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Last modified: October 19, 2007