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Human Energy Systems | Activity 4.2

Activity 4.2: Carbon Pools and Fossil Fuels (60 min)

Students learn about the Three Questions at the Large Scale and begin with the Carbon Pools Question to identify four pools of carbon: biomass (plants and animals), atmosphere, soil, and fossil fuels. Then they zoom into one particular pool—fossil fuels—to examine fossil fuels at an atomic-molecular scale and discuss how they were formed.

Resources Provided


Print enough copies of the 4.2 Fossil Fuels Worksheet and Three Questions Large Scale Handout so that each student has one copy of each. Prepare a computer and projector for the 4.2 Carbon Pools PPT You may want to print and post the Three Questions Large Scale 11 x 17 Poster for the rest of the unit.


1. Discuss scale of this unit.

Tell students that this unit is different from other Carbon TIME units because of the scale. Instead of looking at how carbon and energy move through an animal or a plant or a decomposer or an ecosystem, we are looking at how carbon and energy move around the entire world (i.e., at a large scale). By world, we mean the Earth and atmosphere for matter, and the sun and space for energy.


Students will not have complete accounts of where the energy in fossil fuels comes from and where it goes after fossil fuels are burned. Check during this activity to see where their ideas are as you begin to discuss fossil fuels. Use 4.2 Assessing The Fossil Fuels Worksheet to check for student understanding.


  • Have students draw pictures of the different things that are in soil instead of writing the words. Make a display on the wall with all of their artwork as a reminder of which types of things are in each pool.
  • Have students investigate the greenhouse effect with the Three Questions in mind. Where does the CO2 in the atmosphere come from? Where does the energy in the atmosphere come from? Where do they go next?


  • You may want to revisit the Powers of Ten 11 x 17 Poster (from the Systems and Scale unit) to refresh students’ memories about what we mean by “scale” when we zoom into fossil fuels.
  • Student responses to the energy questions at this point in the unit are most likely to be incomplete. At this point, encourage them to record their ideas, even if they are incomplete or inaccurate.
  • Students may have questions at this point about the difference in the way we define “organic” in the Carbon TIME units, and other meanings of this word. Remind them that in the Carbon TIME units, “organic” things contain C-C and C-H bonds. “Inorganic” things do not contain C-C and C-H bonds. Fossil fuels contain C-C and C-H bonds that make them a rich source of energy for people—this means that fossil fuels are organic, even though they are not living. If students raise these questions, point out that our definition of organic is also not the same as the definition they might see in a grocery store to refer to food produced without using pesticides, fertilizers, antibiotics, or growth hormones.

Extending the Learning

  • Have students bring in a bag of soil from their neighborhood and examine where the carbon might be in the bag: Do they see any dead plant material (roots, leaves, etc)? Any live animals? Any decomposers? Point out that a lot of the biomass in soil is made of decomposers that they can’t see, like bacteria.
  • Have students record different ways they use fossil fuels in one day of their lives and bring their journals to class. Check to see if they make the connection that using electricity uses fossil fuels (assuming the electricity comes from a coal-fired power plant). At this point in the unit, they may not be able to make this connection, but it could serve as a way to introduce the idea for later discussion.
  • Have students research things that are made using fossil fuels and make a list of products. They might be surprised how many things they use every day are made from oil and petroleum!
  • The overview of fossil fuel formation is very short in this Lesson. As an extension activity, have students research in more detail how different fossil fuels are formed, how they are extracted from the Earth, and how we use them.