You may have heard the term fossil fuels before, but do you know what it means? People talking about fossil fuels are likely talking about coal, crude oil, or natural gas. These are called fossil fuels because, like fossils, they were formed over millions of years by decomposition, heat, and the pressure of the earth. You will learn more about fossil fuels in this activity.

 Remember in an earlier lesson, you learned that all energy comes from the sun and that plants are able to store energy from the sun. That is an important part of the formation of fossil fuels.

Millions of years ago, the earth was covered with swamps and seas full of algae, plants, animals, and trees. When these plants died, they sank to the bottom of the swamps and were gradually covered by sand, clay, minerals, and rocks. Over the years, depending on the combination of plants, animals, and minerals buried under layers of earth, various fossil fuels were formed.

Coal

When this decomposition process results in a substance that has a fairly high carbon content, coal is formed. There are various stages of coal formation, from peat (partially carbonized decaying plant matter) to anthracite (hard coal with a high carbon content). From softest to hardest, the stages of coal formation are the following:

• peat

•  lignite

• sub-bituminous coal

• bituminous coal

•  anthracite

 

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Natural gas is also sometimes found with coal deposits.

Crude Oil and Natural Gas

Crude oil (sometimes called petroleum) and natural gas are formed as plants and bacteria decompose under layers of shale (clay compressed into stone). The oil and gas made of hydrogen and carbon also fill holes in rocks. These substances are light enough to move up through some of the earth's layers until they hit a layer of rock they cannot pass through.

Another fossil fuel you may know about from the deposits in Alberta is tar sand. In the distant past, crude oil also made of hydrogen and carbon moved up into sand.

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Advances in technology may develop more ways to use other fossil fuels in the earth's crust.

Fossil fuels are considered nonrenewable resources because of the length of time they take to form. In other words, amounts of fossil fuel available to us are limited. Once they are used, they are gone!