Lab 2-Carbon Cycle

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West Chester University of Pennsylvania *

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101

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Chemistry

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Feb 20, 2024

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SCI 101 -- THE CARBON CYCLE Lab 2: The Carbon Cycle (37 pts.) Objectives (taken from the Pennsylvania Department of Education Academic Standards for Science and Technology and Ecology and Environment, 4 th grade and 7 th grade):  Describe the purpose of analyzing systems (3.1.4A) and define a system by distinguishing between inputs, outputs, closed loops and open loops (3.1.7A).  Identify different types of models, apply models as tools for prediction and insight, and identify theories that serve as models [3.1.4B], and describe their use as applications of scientific or technological concepts (3.1.7B).  Provide clear explanations that account for observations and results, distinguishing between a scientific fact and a belief (3.2.4A) and answer “what if “ questions based on observation, inference or prior knowledge or experience (3.2.7A).  Examine and explain change by using time and measurement (3.1.4E) and describe the effect of making a change in one part of a system on the system as a whole (3.1.7E). Materials:  For each table: large sheet of clean paper, bag of different colored beads, markers, separate handouts, scientific calculator, pencil or pen. Names of group members: Checklist for completing lab: Make sure all components listed below are turned in for your group _____ One copy of this lab handout per group, with answers to the questions. Background The Carbon Cycle is a way of describing how carbon, in different forms, is transferred among the biosphere, atmosphere, hydrosphere, and geosphere. Why is this important? First of all, carbon is the essential chemical element that makes up all living things in the Earth System, including humans. Second, carbon exists in the atmosphere in the form of carbon dioxide, where it plays an important role in maintaining the warm temperatures on the Earth’s surface that make life possible. Third, carbon stored in fossil fuels in the geosphere – coal, oil, and natural gas – is the major energy source used by humans since the Industrial Revolution. 1

SCI 101 -- THE CARBON CYCLE Questions for Review (13 points) Question 1. Define the term reservoir when talking about the Carbon Cycle and give an example of a reservoir of carbon in the Carbon Cycle. (2 pts.) Question 2. Define the term flow when talking about the Carbon Cycle, and give an example of a flow of carbon in the Carbon Cycle. (2 pts.) Question 3. Circle the correct choice (underlined term ) in the sentences below: (4 pts.) a. A reservoir always refers to an amount a rate (amount/unit time) b. The unit for flow is always an amount, an amount/unit time, such as Gigatons such as Gt/year c. The unit for a reservoir is always an amount, an amount/unit time, such as Gigatons such as Gt/year d. A flow always refers to an amount a rate (amount/unit time) Question 4. Define the term steady state when talking about the Carbon Cycle. How can you recognize if part of a system is at a steady state? (2 pts.) Question 5. Define the term residence time when talking about the Carbon Cycle. State the equation used to calculate the residence time. What is the unit of measurement for residence time? (3 pts.) 2

SCI 101 -- THE CARBON CYCLE Making a model of the Carbon Cycle Question 6a. Fill in the first 2 columns of the table below using information from Figure 1. DO NOT INCLUDE the Geosphere; DO NOT INCLUDE any flows related to the Geosphere. (2 pts.) Reservoir Amount of Carbon in Reservoir (in Metric Gigatons) Number of beads in Reservoir Flow (or Flux) Rate of flow, (in metric Gigatons/year) Number of beads AND direction of flow (which reservoir to which reservoir) Question 6b. Now we’re going to pretend that the carbon in each reservoir is represented by one of the colored beads in the plastic bag and that 1 bead = 50 Gt C. Using that ratio, figure out how many beads would be used to represent the carbon in each reservoir and fill in the third column of the table. (2 pts.) Using a large piece of paper and markers, draw a model of the Carbon Cycle with the Reservoirs and Flows listed in the table above. Your model should look similar to FIGURE 1, excluding the Geosphere. (Leave space to add in the Geosphere later in the lab.) After drawing your model, place the colored beads in the appropriate reservoirs. Question 7. What is a scale model and explain how we are making a scale model of the Carbon Cycle? (2 pts.) 3

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SCI 101 -- THE CARBON CYCLE 4

SCI 101 -- THE CARBON CYCLE Question 8. Move the beads around to physically model the flows of carbon in the Carbon Cycle. What is the minimum number of years required to completely change the carbon in one reservoir? Which reservoir is the first to change and why? (3 pts.) Question 9. Calculate the residence times for carbon in each of the three reservoirs we are using in this model. Show ALL your work and include the units . (3 pts.) Question 10. Considering ONLY the reservoirs and flows that we are using in this model, is this system at a steady state ? Explain your answer – how do you know? (2 pts.) Modify your model of the Carbon Cycle by drawing in the Geosphere and its associated flows. (See FIGURE 1). Question 11. How do the rates of rock weathering and rock formation compare with the rates of photosynthesis, respiration, and decomposition? (1 pt.) 5

SCI 101 -- THE CARBON CYCLE Question 12. Calculate the residence time (using inputs only) for the Geosphere – IGNORE fossil fuel burning. Show ALL your work and include the units . Compare the residence time for the Geosphere with the residence times for the Atmosphere, Land Vegetation, and Soil and Sediments. (2 pts.) Question 13. The Carbon Cycle is sometimes divided into a short-term cycle and a long-term cycle. Which reservoirs and processes from Figure 1 would you put in the short-term cycle and which reservoirs and processes would you put in the long- term cycle? Explain your reasoning . (3 pts.) Question 14. With your modified model, move the beads around on your model to simulate the Carbon Cycle for 10 years. (Hint: If the flow is too small to be represented by a bead for one year, what is the total flow for 10 years?) Which reservoir accumulates carbon from human use of fossil fuels? Is this reservoir in a steady state? (2 pts.) Question 15. Look at FIGURE 2 (handout), a graph showing the CO 2 abundance in the atmosphere compared with emissions to atmosphere from human activities, from 1750 to 2000. Are these graphs consistent with your answer to question 14? Explain your reasoning. (2 pts.) 6

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SCI 101 -- THE CARBON CYCLE FIGURE 1: Short-term and Long-term Terrestrial Organic Carbon Cycle , (updated numbers from CDIAC website) 7 Atmosphere 775 Land vegetation (primary producers) 550 Soil and sediments 1500 Geosphere: 50,005,000 total Respiration, 50 Photosynthesis, 100 Death and Deposition, 50 Rock weathering 0.05 Rock formation (sedimentation and burial), 0.05 Coal, oil and gas: 10,000,000 Carbonate rocks: 40,000,000 Long-term (inactive) Coal, oil, gas, and carbonate rocks available to people: 5000 Short-term (active) Decomposition, 50 Fossil fuel burning, asphalt, cement, 6