What Are Fossil Fuels? - Definition, Advantages & Disadvantages

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  • 0:07 Fossil Fuels
  • 1:29 Fossil Fuel Creation
  • 2:52 Fossil Fuel as Energy
  • 4:21 Advantages of Fossil Fuels
  • 5:10 Disadvantages of Fossil Fuels
  • 6:35 Lesson Summary
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Lesson Transcript
Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

Fossil fuels are sources of energy that have developed within the earth over millions of years. Because fossil fuels - oil, natural gas, and coal - take so long to form, they are considered nonrenewable. Learn more about these fuels, including the pros and cons of using them.

Fossil Fuels

What comes to your mind when you think of fuel? You might think of gasoline for your car, or maybe food, which is fuel for your body, possibly firewood, which may provide heat for your home. The bottom line is that fuel is an absolutely necessary part of everyone's daily life. And, deep within our Earth, there are stores of fuel that our world has become totally dependent on. They are called fossil fuels, and in this lesson, we will explore how they came about and how they affect our lives.

You have undoubtedly heard of fuels such as coal, oil and natural gas. These are the three main types of fossil fuels. You rely on fossil fuels every day for such tasks as fueling your car and heating your home. And, it's very likely that the electricity in your home comes from a power plant that uses fossil fuels. But, did you know that these fuels were once plant and animal life? That's right; fossil fuels are actually the accumulated remains of living organisms that were buried millions of years ago. In fact, it may help you to recall this term by remembering that a 'fossil' is a naturally preserved remnant of a living thing from long ago. Let's take a closer look at these energy-rich substances and how they were created.

Fossil Fuel Creation

As we mentioned, the story of fossil fuels began millions of years ago, even before the dinosaurs first appeared on Earth. At that time, there were tiny plants and animals living in the oceans of the world. As these plants and animals died, they would sink down and settle on the ocean floor. This organic matter was eventually covered by layers of sand, rock and mud that later turned into sedimentary rock.

As these layers of rock grew thicker and thicker, the organic matter ended up being placed under a great amount of pressure. Over the millions of years that passed, this high pressure transformed the partially decomposed plant and animal matter into the major energy source that we know as oil and natural gas.

Coal is formed through the same type of process. However, coal originates mainly from dead tree and plant matter. Millions of years ago, leafy plants and trees died and sank into swamps and bogs that covered much of the Earth. This created a soupy plant-filled stew called peat. The peat became buried under layers of sediment, and water was squeezed out. Over the course of millions of years, compounds within the peat were subjected to heat and pressure, transforming them into the carbon-rich substance we know as coal.

Fossil Fuel as Energy

Fossil fuels are a great source of energy because they originate from living things. We know that plants and trees use sunlight to make food from carbon dioxide and water, using the process called photosynthesis. This is an easy term to recall when you remember that the prefix 'photo' is Greek for light, and the suffix 'synthesis' means to make, so photosynthesis is using the energy of sunlight to make food. This energy from the sun gets stored in the plants and transferred to any animal that eats the plants.

Now keep in mind, the dead plant and animal matter that made up these fossil fuels didn't have much time to decay. They sank into the water and were buried with much of their substance intact. This allowed the energy within them to remain as they were transformed.

You can imagine how concentrated the energy is within fossil fuels. The plant and animal matter has sunk into the water and has been greatly compressed. To try and visualize this, picture a bag of raw spinach. It takes up quite a bit of space, just like a plant would. Now put the spinach into a pot with a little bit of water, and cook it up. Suddenly, your pan only has a couple of inches of spinach at the bottom, all compressed into a dense layer of mush. All of the nutrients in the spinach leaves are now concentrated, just like the energy in fossil fuels.

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Additional Activities

Evaluating the Options

In this lesson, students were able to learn about the advantages and disadvantages of fossil fuels. In this activity, they will expand on that knowledge to find alternative fuel sources that address the disadvantages discussed about fossil fuels and present their information in a digital presentation such as Google Slides or Prezi. Students should take on the role of a scientist presenting options for alternative fuel sources for a government. For example, to address the concerns about the contribution of fossil fuels to global warming, students might suggest solar or wind power, which do not produce greenhouse gases.


Now that you're familiar with the advantages and disadvantages of fossil fuels, you're going to be furthering your knowledge to address those disadvantages. In this activity you're going to be a scientist presenting additional options to the government to address the problems with fossil fuels. This activity will require you to review the problems with fossil fuels described in the lesson, then research alternative fuels that could address these problems. Your final product will be a professional presentation which you should present to an audience. Don't forget the professional dress, you want to be taken seriously!

Criteria for Success:

  • Presentation is professionally designed and is colorful, attractive and easy to read
  • Presentation includes an explanation of what fossil fuels are and three problems that will be addressed
  • Presentation includes at least two alternative fuel sources that can address the problems with fossil fuels
  • Presenter does not read from slides and is knowledgeable and engaged

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