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Fossil Fuels and the Carbon Cycle

Fossil Fuels and the Carbon Cycle

Coal seam in a cliff that is approximately 335 million years old.
© David Shand. Used with permission.

  • Grades:
  • Length: 45 Minutes


Physical Science

Using straws to extract "core samples" from a multi-layered model, students learn how geologists locate fossil fuels below the Earth's surface. Student sheets are provided in English and in Spanish.

This activity is from The Science of Global Atmospheric Change Teacher's Guide. Although it is most appropriate for use with students in grades 3–5, the lessons are easily adaptable for other grade levels. The guide is also available in print format.

Teacher Background

In the United States, more than 75% of the energy used in homes and businesses and for transportation comes from coal, oil, or natural gas. These fuels are known as “fossil” fuels because they are the remnants of ancient plants and other living things buried under intense heat and pressure over millions of years. They are very efficient sources of energy. However, it is important to keep in mind that the energy in fossil fuels originally came from the sun and was trapped by plants and similar organisms during photosynthesis. During this process, plants also consumed carbon dioxide (CO2) from the atmosphere. So when fossil fuels are burned, trapped carbon is released back into the atmosphere, principally as CO2.

  • Petroleum, or crude oil, is a thick, gooey liquid that can be found within Earth’s crust on land or beneath the sea floor. It was formed principally from tiny marine organisms that were buried in layers of sediment, such as sand. In addition to containing high-energy carbon compounds, petroleum contains varying amounts of substances such as oxygen, sulfur, and nitrogen. Crude oil must be heated and distilled to separate it into gasoline, heating oil, diesel oil, asphalt, and other materials. Some components of crude oil are used to manufacture industrial chemicals, fertilizers, pesticides, plastics, medicines, and other products.

  • Natural gas is a mixture of methane (CH4) and smaller amounts of related gases. It is often found above deposits of crude oil. Natural gas burns hotter and produces less air pollution than any other fossil fuel. When burned, it also releases less CO2 relative to the amount of energy produced.

  • Coal is a solid that is formed in several stages. It is a mixture of many different substances, with varying amounts of water, nitrogen, and sulphur. Coal is formed from peat—a moist soil substance made of partially decayed plant material. When peat is subjected to intense heat and pressure, it becomes lignite—a brown coal. Lignite will become bituminous coal if it is placed under more heat and pressure. Bituminous coal is often used as fuel because it produces high levels of heat and is abundant. The most desirable form of coal is anthracite, a hard mineral that results from the transformation of bituminous coal under more conditions of very high heat and pressure. Anthracite is a very attractive fuel because it burns cleanly and produces great quantities of heat.

When geologists look for fossil fuels, they often drill deep into Earth. They remove narrow cores of rock and sediments and examine them for clues about the presence of oil and other fuels. In the following activity, students explore the layers in a muffin representing Earth’s crust, using a straw to drill “cores.”

Objectives and Standards


  • Fossil fuels are found within Earth’s crust.

  • The presence of certain layers of soil and rock helps predict the presence of oil.

  • The supply of fossil fuels cannot be replenished.

Science, Health, and Math Skills

  • Predicting

  • Observing

  • Identifying patterns

  • Mapping

  • Drawing conclusions

Materials and Setup

Teacher Materials (see Setup)

  • 24 aluminum baking cups and a cookie sheet (see Setup)

  • 2 envelopes of bran muffin mix (plus ingredients)

  • 2 envelopes of corn muffin mix (plus ingredients)

  • Green and red food coloring

Materials per Student Team or per Student

  • prepared GeoMuffin (see Setup)

  • cotton swab

  • crayons or colored markers

  • plastic serrated knife

  • section of plastic straw about 8 cm (3 in.) in length

  • toothpick

  • copy of “GeoMuffin Observations” sheet


  1. Bake 24 GeoMuffins (see recipe, PDF) in advance, using two envelopes of prepared bran muffin mix and two envelopes of prepared corn muffin mix, plus ingredients listed on the packages. (Cake mixtures usually are less satisfactory because the baked texture is too soft. Other flavors may be substituted as long as they are different colors and contain no fruit or nuts.)

  2. Cut straws into 3-in. lengths for students to use.

  3. Students may work individually or in teams of two or more.

  4. As an alternative to baking, use different colors of clay or modeling dough to make the layered GeoMuffins.

Procedure and Extensions

  1. Show the muffins to the class. Point out that all of the muffins look the same on the surface. Tell students that the muffins are made of layers that look similar to those visible in a cross section of Earth’s crust. Explain that they will be exploring their muffins to discover whether or not the muffins hold petroleum deposits, and where those deposits might be located. Lead the class in a discussion of how fossil fuels were formed under the ground, how they are mined, and how they are used.

  2. Give a muffin and a “GeoMuffin Observations” sheet to each student or team of students. Ask, What do you think the inside of the muffin looks like? Without touching or removing the baking cup, instruct students to draw their predictions on their student sheets. They also should predict whether or not they will find oil (see “Geomuffin Legend,” PDF).

  3. Have students insert a toothpick near the edge of their muffins to represent “North.” Based on what they can observe on the top surface of the muffin, have students identify six places on the muffin to “drill.”

  4. Demonstrate the technique to be used. Show the students how to take a core sample by gently twisting a section of plastic drinking straw into a muffin and then pulling it back out. Use a cotton swab to dislodge the core by inserting it in the top of the straw and pushing the core out the bottom.

  5. Encourage students to take at least six samples, recording each sample’s location on their worksheets, then drawing and coloring the samples in order.

  6. Once they have finished sampling, recording, and coloring, students should evaluate their information, looking for a pattern. Based on their cores, students should draw an estimate of a side view of the muffin, showing all the layers.

  7. Now instruct students to cut through the center of the muffin. They should compare their predictions with their muffins. Ask, Did the core samples give you valuable information? Why or why not? Did you find anything that predicts the presence of oil? Mention that geologists frequently look for certain patterns of layers in the cores. Certain patterns predict or suggest that oil might be present. 

  8. Have students consider petroleum as a resource. Ask, What happens when we burn products made from oil? Does burning oil produce carbon dioxide? Do you think we could run out of oil? Help students understand that oil and coal are resources that cannot be replaced once they have been “used up.”

  9. Initiate a discussion about where oil and other fossil fuels come from. Use the “Carbon Dioxide and the Carbon Cycle” page as an overhead to help students understand how photosynthesis by ancient plants and similar organisms is responsible for the carbon now found in fossil fuels. Challenge students to figure out what happens to the carbon in fossil fuels when the fuels are burned (carbon returns to the atmosphere as carbon dioxide).


  • Instead of having students cut their muffins in half after making their predictions, challenge them to restore the “landscape” on the top of their muffins before proceeding with the rest of the activity.

  • Encourage students to use resources in the library or on the Internet to learn about other important cycles in ecosystems. Nitrogen is another example of an atmospheric gas that cycles through nonliving and living parts of ecosystems in many different forms.

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