Lab 4 Day 1 Part 2

Lab 4 Part 2

One of the key ideas you should have taken from the Carbon Cycle Prezi is that in any matter cycle, the substance at the heart of that cycle (e.g., water, nitrogen, and carbon) is converted to different physical and chemical forms and moved from one part of the Earth to another. As you move through the Carbon Cycle lab, you will see how carbon moves through the different ‘spheres’ into which scientists divide the planet: the biosphere (global set of ecosystems where living things are found), the lithosphere (the rocky upper layers of the Earth), the hydrosphere (combination of all sources of water on under and over the Earth’s surface), and the atmosphere (layers of gases above the Earth). In the biosphere, carbon is found in the form of organic compounds trapped in living organisms and in the soil; in the lithosphere, it is held in carbonate rocks and other materials like coal; and in the hydrosphere it dissolves in the water to form carbonic acid. Practically all the carbon in the Earth’s atmosphere exists in the form of carbon dioxide (CO₂) and methane (CH₄).

The picture below shows the global carbon budget for 2010. This is a way of tabulating the amount of carbon (in billions of tons) that is released by carbon sources and absorbed by carbon sinks. Ideally, the Earth would have a ‘balanced spreadsheet’ where those two amounts were equal; as you examine the picture you should consider whether this was the case in 2010.

Q1: Identify two sources of carbon in the picture. Identify two sinks.

Q2: Where did the 9 petagrams of carbon emitted into the atmosphere by anthropogenic activities in 2010 end up going?

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So let’s follow a carbon atom through one portion of the carbon cycle. Look at the picture below that focuses on that portion: the exchange of carbon between the atmosphere and the biosphere.

As noted above, most of the carbon atoms in the atmosphere are nestled in between two oxygen atoms in the form of CO₂. Green plants can take in that CO₂, combine it with water (H₂O) and make carbohydrates (literally, hydrated carbon) through the process of photosynthesis. It is through that process that plants grow and gain mass. While it may be hard to imagine that plants get their mass from water and an invisible gas in the air, the time-lapse photograph of wheat-grass growing may make that more believable.

Q3: If that wheatgrass were out in nature (instead of in a videographer’s studio), what would happen to the carbon captured in the wheatgrass once it died?

Now, there are a lot of ways that this carbon in the carbohydrates can be released back into the atmosphere. Both plants and the animals who eat them can break the carbohydrates (mostly the sugar glucose) back down into water and carbon dioxide, getting some useful energy out of the process, and releasing the CO₂ through respiration. Also, fungi and bacteria can break down the carbon compounds in dead plants and animals and convert the carbon to CO₂ if oxygen is present. Finally, combustion (which is really the same process as respiration, except that it involves burning fuels instead of foods) can oxidize the organic (carbon-containing) materials in plants back to CO₂. One form of combustion that you ran across in a previous lab (The Troposphere) was “slash and burn”, which is used to clear out large areas of forest for agriculture. The picture to the left below shows just how far-reaching the effect of this human activity can be.

Q4: Green plants both photosynthesize (causing them to act as a carbon sink) and respire (causing them to act as a carbon source); based on the carbon cycle picture to the right above, are these plants a net sink or source of carbon?

Q5: People have concerns about the use of slash and burn (http://geography.about.com/od/urbaneconomicgeography/a/slashburn.htm), partly because it affects the carbon cycle in two different ways. What are those two ways?

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Next, let’s focus on the other half of the larger carbon cycle: the exchange of carbon between the atmosphere and the hydrosphere. Take a look at the picture below that focuses on the processes involved in this exchange.

It should make sense that, since oceans cover 70% of the Earth’s surface, we would want to concentrate on how carbon moves between the atmosphere and the oceans. You can see from the picture above that some of the same processes – photosynthesis and respiration – are part of the exchange between these two parts of the global ecosystem. There is another mechanism by which the oceans can act as both a carbon sink and a carbon source: the water in the ocean can absorb carbon dioxide (leading to acidification of the ocean water) and, like a soda going flat, release it through the agitation caused by ocean currents.

Q6: Overall, is there a greater amount of carbon exchanged between the atmosphere and the biosphere, or between the atmosphere and the hydrosphere?

Q7: How did the amount of carbon absorbed by the hydrosphere compare to the amount carbon released by the hydrosphere in 2010?

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There is one last portion of the carbon cycle on which we want to focus. Before we do so, though, it is important for us to remember that the carbon cycle represents a global system, so even though we have looked at the cycle in manageable portions, we have to remember that the processes in each portion are interrelated and any change in one process produces changes in the others.

All right, so with that reminder in place, we can direct our attention to how carbon is exchanged between the lithosphere and the atmosphere. In the Prezi for this lab, we saw one video that talked about “young ‘fast’ carbon”. This is the ‘kind’ of carbon that is found in living plants among other things, and we call it that because it can easily move into and out of the carbon cycle. The video also talked about “old ‘slow’ carbon”, which is the ‘kind’ found in fossil fuels. It is labeled this way because this kind of carbon has been trapped in a form (natural gas, oil, and coal) that makes it more unlikely that the carbon will enter the carbon cycle. Well, more unlikely until man started to pull it out of the Earth and burn it for electricity production. When that combustion of fossil fuels takes place, carbon with hydrogen atoms attached to it (hydrocarbons) is transformed to carbon with oxygen attached to it (carbon monoxide and carbon dioxide). The image on the left below shows the percentage of carbon dioxide from the combustion of various fossil fuels. The image in the middle is of Plant Bowen, a coal-burning power plant near Cartersville, GA; it should be familiar to you as the background of the Prezi. Finally, the image on the right is a schematic of Plant Scherer which is southeast of Atlanta.

Q8: Which form of fossil fuel did you expect would have contributed the most to carbon dioxide production? Which form actually contributes the most?

Q9: In the Plant Bowen picture, the cooling towers are highlighted. Many people incorrectly link the presence of cooling towers to the presence of nuclear power plants, but all large-scale power plants have them. What is it that is coming out of the cooling towers? (Hint: This has an important relationship to the matter cycle you considered in the Troposphere lab.)

Humanity’s thirst for cheap sources of energy has led us to search for new places from which to obtain fossil fuels. One of those is shale formations which are found throughout the country. Watch the PBS video below about the extraction of oil and natural gas from these shale formations, then answer Q10 and Q11.

Q10: What is meant by ‘fracking’?

Q11: What are the benefits – and the risks – with getting natural gas and oil from shale through the fracking process?

Before moving on to the next section of this lab, it is important to put together the separate pieces of the carbon cycle that were discussed above. To that end, take a look at the picture of the 2010 global carbon budget that is found below and that also opened this section.