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Activity

Carbon Cycle Demonstration

Background: Dr. Art's Guide to Science, pages 121-124.

Purpose:
The carbon cycle is perhaps the most important of Earth's matter cycles. Not only is it vital for life (photosynthesis and respiration), it plays a key role in Earth's global climate because atmospheric carbon dioxide contributes significantly to Earth's greenhouse effect. By participating in and viewing a physical simulation of the carbon cycle, a group can gain a deeper understanding of the reservoirs and flows of the carbon cycle.

Equipment and Supplies:
Demonstration Mode - At least 15 black balloons to represent carbon. Two other balloons, each of a different color (e.g., blue and white). These can be filled with helium or air. String and weights for balloons (especially if using helium!). Signs to identify the principal carbon reservoirs (Atmosphere; Land Biomass; Ocean; Fossil Fuel; Rock).

Safety Issues:
None

Duration:
20 minutes plus more time for extended discussion

Procedures:

  1. Introduce the carbon cycle. Discuss why it is important and why it is harder to understand than the water cycle. Reinforce that whenever we examine a cycle of matter, it is useful to investigate the different reservoirs and flow rates. Explain that you are representing the amounts of carbon in each reservoir using balloons.
  2. Assign 5 different locations within a room for the different carbon reservoirs. These should be close enough for visual comparison and to easily move balloons from one reservoir location to another. Place identifying signs in each location, and have a volunteer sit in that location. A physical or other graphic representation of that reservoir (e.g., a picture of the sky, a plant, a big rock, etc.) can enhance the presentation.
  3. Explain that one balloon represents all the carbon in the atmosphere. Elicit what form that carbon is in (carbon dioxide gas). Place one black balloon with the Atmosphere location volunteer.
  4. Have participants estimate how many balloons should be used to represent the carbon in the Land Biomass reservoir. Place 4 black balloons there. Discuss the form of the carbon (cellulose, starch, sugar, protein, etc.). Discuss how the carbon got there (photosynthesis).
  5. Have participants estimate how many balloons should be used to represent the carbon in the Ocean reservoir (answer - 50 balloons). Place 2 black balloons and one blue balloon there. State that of course everyone knows the scientific conversion that one blue balloon equals 48 black balloons. Discuss the form of the carbon (bicarbonate salt resulting from the absorption of carbon dioxide from the ocean to form carbonic acid which dissociates to H+ and bicarbonate).
  6. Have participants estimate how many balloons should be used to represent the carbon in the Fossil Fuel reservoir. Place 7 black balloons there. Discuss the form of the carbon (solid coal, liquid hydrocarbon petroleum, and gas hydrocarbon methane). Discuss how the carbon got there (photosynthesis hundreds of millions of years ago and subsequent burial). Note that fossil fuel carbon is not part of current carbon cycle flows unless people bring it to the surface.
  7. Have participants estimate how many balloons should be used to represent the carbon in the Rock reservoir. Place 1 white balloon there. State that of course everyone knows the scientific conversion that one white balloon equals 66,000 black balloons. Discuss the form of the carbon (solid carbonate as in limestone - e.g., white cliffs of Dover).
  8. Now change the focus from the amounts/kinds of carbon to how it flows from one reservoir to another. Take the atmosphere balloon and add it to the Land Biomass reservoir. Say that over the course of seven years, all the carbon in the atmosphere goes into land biomass via the process of photosynthesis. Ask and discuss why we still have carbon dioxide in the atmosphere (over a seven year period one balloon amount of carbon returns to the atmosphere from land biomass via the process of respiration). Bring a black balloon from the Land Biomass reservoir back to the Atmosphere reservoir.
  9. Take a black balloon from the Atmosphere reservoir and add it to the Ocean reservoir. Say that over the course of seven years, all the carbon in the atmosphere dissolves in the ocean. Ask and discuss why we still have carbon dioxide in the atmosphere (over a seven year period one balloon amount of carbon returns to the atmosphere from the ocean via evaporation of carbon dioxide). Bring a black balloon from the Ocean reservoir back to the Atmosphere reservoir.
  10. Inflate a black balloon by blowing into it and walk over to the Atmosphere volunteer. Discuss how humans have been un-burying fossil fuels and burning them, thereby releasing carbon dioxide into the atmosphere. Show that today's atmosphere has 25% more carbon dioxide than the pre-industrial atmosphere. Illustrate that the amount of carbon dioxide in the atmosphere is projected to double in about fifty years.
  11. Review the reservoirs of the carbon cycle and how carbon flows into and out of them. Discuss why people care about the increase in carbon dioxide in the atmosphere (enhanced greenhouse effect leading to global climate change).

Appendix/Further Explorations

  1. Explore the Greenhouse Effect on this web site, and why people care about the concentration of carbon dioxide in the atmosphere.
  2. Explore alternatives that will reduce emissions of carbon dioxide.

 



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