This page contains a short description of the fossil fuels and their origins. There is also a diagram of waht can be derived from a barrel of oil and there are some conversion factors relating to the fossil fuels' energy and carbon content.
Where Fossil Fuels Come From
There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs - hence the name fossil fuels. The age they were formed is called the Carboniferous Period. It was part of the Paleozoic Era. "Carboniferous" gets its name from carbon, the basic element in coal and other fossil fuels.
The Carboniferous Period occurred from about 360 to 286 million years ago. At the time, the land was covered with swamps filled with huge trees, ferns and other large leafy plants. The water and seas were filled with algae - the green stuff that forms on a stagnant pool of water. Algae are actually millions of very small plants.
Some deposits of coal can be found during the time of the dinosaurs. For example, thin carbon layers can be found during the late Cretaceous Period (65 million years ago) - the time of Tyrannosaurus Rex. But the main deposits of fossil fuels are from the Carboniferous Period. For more about the various geologic eras, go to www.ucmp.berkeley.edu/help/timeform.html
As the trees and plants died, they sank to the bottom of the swamps of oceans. They formed layers of a spongy material called peat. Over many hundreds of years, the peat was covered by sand and clay and other minerals, which turned into a type of sedimentary rock.
More and more rock piled on top of more rock, and it weighed more and more. It began to press down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over millions of years; it turned into coal, oil or petroleum, and natural gas.
Coal is a hard, black colored rock-like substance. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulfur. There are three main types of coal - anthracite, bituminous and lignite. Anthracite coal is the hardest and has more carbon, which gives it higher energy content. Lignite is the softest and is low in carbon but high in hydrogen and oxygen content. Bituminous is in between. Today, the precursor to coal - peat - is still found in many countries and is also used as an energy source.
The earliest known use of coal was in
Oil or Petroleum
Oil is another fossil fuel. It was also formed more than 300 million years ago. Some scientists say that tiny diatoms are the source of oil. Diatoms are sea creatures the size of a pin head. They do one thing just like plants; they can convert sunlight directly into stored energy.
As the diatoms died they fell to the sea floor. Here they were buried under sediment and other rock. The rock squeezed the diatoms and the energy in their bodies could not escape. The carbon eventually turned into oil under great pressure and heat. As the earth changed and moved and folded pockets where oil and natural gas can be found were formed.
Oil has been used for more than 5,000-6,000 years. The ancient Sumerians, Assyrians and Babylonians used crude oil and asphalt ("pitch") collected from large seeps on the
Over time the demand for oil continued to increase as a fuel for lamps. Petroleum oil began to replace whale oil in lamps because the price for whale oil was very high. During this time, most petroleum oil came from distilling coal into a liquid or by skimming it off of lakes.
Oil and natural gas are found under ground between folds of rock and in areas of rock that are porous and contain the oils within the rock itself. The folds of rock were formed as the earth shifts and moves. To find oil and natural gas, companies drill through the earth to the deposits deep below the surface. The oil and natural gas are then pumped from below the ground by oil platforms. They then usually travel through pipelines or by ship.
The diagram shows what can be derived from a barrel of crude oil. Oils from different regions have contain slightly different amounts of the various hydrocarbons.
One barrel contains 42
The ~2.8% of the content labelled 'feedstocks' are the basis of the organic chemical industry. As the reserves of oil diminish as they must do, sufficient stocks of oil-for-chemistry need to be ensured.
Oil is stored in large tanks until it is sent to various places to be used. At oil refineries, crude oil is split into various types of products by heating the thick black oil.
Oil is made into many different products - fertilizers for farms, the clothes you wear, the toothbrush you use, the plastic bottle that holds your milk, the plastic pen that you write with. They all came from oil. There are thousands of other products that come from oil. Almost all plastic comes originally from oil.
The products include gasoline, diesel fuel, aviation or jet fuel, home heating oil, oil for ships and oil to burn in power plants to make electricity. Here's what a barrel of crude oil can make.
Sometime between 6,000 to 2,000 years BCE (Before the Common Era), the first discoveries of natural gas seeps were made in
Natural gas is less dense than air. Natural gas is mostly made up of methane, CH4. Natural gas is usually found near petroleum underground. It is pumped from below ground and travels in pipelines to storage areas.
Natural gas usually has no odour and is colourless. Before it is sent to the pipelines and storage tanks, it is mixed with organic sulfides that give it a strong odour. The odour makes it easy to smell if there is a leak.
Some conversion factors
Natural gas quantities are usually quoted as cubic feet at one atmosphere pressure. One cubic foot = 0.283 cubic metres and contains 53.5 grams of carbon.
Oil supplies are usually quoted as barrels. One barrel has a volume of oil of 159 litres [cubic decimetres]. 7.3 barrels contain one metric tonne [1000 kg] of oil.
Coal supplies are usually quoted in tonnes.
The carbon [tonnes] and energy content [gigaJoules, giga = 109] of one tonne of each of the fossil fuels are given in the table below.
|Values for one tonne of fuel||Carbon/t||Energy/GJ|