Oil, natural gas, and coal are the main sources of energy for modern use. All of these fuels are classified as fossil fuels. They are hydrocarbon deposits because they contain hydrogen and carbon

Formation

All of the three major types of fossil fuels were formed many millions of years ago in the Carboniferous period. The Carboniferous period occurred from about 360-286 million of years ago. Coal was one of these fossil fuels. At the time the land was covered with swamps filled with enormous trees and plants. As the trees and the plants died, they sank to the bottom of these swamps. They formed layers of a spongy material called peat. Over many hundreds of years, sand, clay and other minerals covered the peat that made it into sedimentary rock. More and more pressure was applied to the peat and also the heat built up making the water and gas squeeze out eventually forming coal!

What is coal?

Coal is a hard, black coloured substance. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur. The three main types of coal are anthracite, bituminous and lignite. Anthracite is the hardest and has the highest carbon content; this also gives it the highest energy content. Lignite is the softest and low in carbon but high in high in hydrogen and oxygen. Bituminous is in between. The earliest known use of coal was in china-about 3500 years ago.

What are fossil fuels?

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What are fossil fuels?

Oil, natural gas, and coal are the main sources of energy for modern use. All of these fuels are classified as fossil fuels. They are hydrocarbon deposits because they contain hydrogen and carbon. Hydrocarbon molecules come in a variety of shapes and sizes, this is one of the things that make them so valuable because it allows them to be used in so many different ways. The reason they are called fossil fuels is because they are all made from decayed plants and animals that have been preserved in the earth's crust by pressure, bacterial processes and heat. It takes millions of years for these organisms to chemically change into fossil fuels. Fossil fuels are usually found below ground. Coal is either mined or dug out while oil and natural gas are pumped out. Coal is widely distributed and is easier to locate than oil and gas.

Formation of oil and gas

Oil has formed throughout much of the Earth's history; in fact, oil is being formed in some parts of the Earth today. Almost all oil and gas comes from tiny decayed plants, algae, and bacteria. Oil from the North Sea is mainly found in rocks that formed during the Jurassic period - about 150 million years ago.

During this time the seas and swampy areas were rich in microscopic plants and animals. When these died they slowly sank to the bottom forming thick layers of organic material. This in turn became covered in layers of mud that trapped the organic material. Oil and gas were formed by the anaerobic decay of organic material in conditions of increased temperature and pressure. The layers of mud prevented air from reaching the organic material. Without air, the organic material couldn't rot in the same way as organic material rots away in a compost heap. As the layers of mud grew in thickness, they pushed down on the organic material with increasing pressure. The temperature of the organic material was also increased as other processes going on inside the Earth heated it. Very slowly, increasing temperature, pressure and anaerobic bacteria - micro organisms that can live without oxygen - started acting on the organic material. As this happened the material was slowly cooked and changed. In this was the energy first given to the plants by the sun is transferred and the organic matter is changed into crude oil and gas. Oil forms first, then as the temperature and pressure increase at greater depth gas begins to form. Increasing heat and pressure first cause the buried algae, bacteria, spores and cuticles (leaf skin) to join their wax, fat and oil to form dark specks called kerogen. As rock gets hotter, chains of hydrocarbon chemicals use this heat energy to break away from the kerogen to form waxy and viscous heavy oil. At greater depth, the temperature rises. At higher temperatures the chains of hydrocarbons become shorter and break away to give light oil and gas. Most North Sea Oil is the valuable light oil. Gas from the Southern North Sea is methane.