Activity 1: Carbon Cycle

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Concepts
Learning Objectives
Set-Up
How To Demonstrate
Questions To Ask
Sample Dialogue
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Concepts
  • Natural phenomenon stores carbon in the atmosphere, ocean, terrestrial biosphere and rock, and over the course of a year carbon transfers between these sinks, creating a natural balance. Burning fossil fuels releases carbon into the atmosphere that cannot be balanced out by natural phenomenon.
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Learning Objectives
  • The visitor will use rice to represent carbon, moving carbon between the atmosphere, ocean and terrestrial biosphere to represent carbon moving between sinks. Then visitors will take rice from the rock sink, demonstrating that burning fossil fuels puts extra carbon into the atmosphere that cannot be taken in by the other sinks.
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Set-Up
  1. Turn on the carbon meter and make sure it is working.
  2. Open the atmosphere box and make sure it has two little boxes: "Flux to Biosphere" and "Flux to Ocean".
  3. Open the terrestrial biosphere box and make sure it has one little box: "Flux to Atmosphere".
  4. Open the ocean box and make sure it has one little box: "Flux to Atmosphere".
  5. Close all the boxes and have the fossil fuel box ready.

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How To Demonstrate
  • Attract visitors by asking them questions like, “What do you think air, water, rock and living things have in common?” or “What do you think is in the air?”
  • Give the visitor the carbon meter and ask them what they think it's measuring. Explain that carbon is an element that can take different forms, including a gas. Have them breathe on the meter and let them know they are breathing out carbon dioxide, or CO2. Take the meter back and be sure to turn it off.
  • Ask the visitors where they think the carbon they breathe out goes, and bring out the atmosphere box. Explain that each grain of rice represents a gigaton of carbon. This is a different way to measure carbon than the carbon meter uses, but the 800 grains of rice in the box are 800 gigatons which is about equivalent to around 350 parts per million. The carbon in the air is carbon dioxide and trace amounts of other gases such as methane.
  • Ask the visitors if they have ever heard of carbon-based life forms. DNA is carbon-based—all organisms on Earth have carbon in them and all living things have DNA. Give them the terrestrial biosphere box, letting them know that this represents all the carbon contained in living things on land. "Biosphere" is a word for all the life on Earth, and "terrestrial" means land. The terrestrial biosphere holds about 2,850 gigatons of carbon.
  • Give them the box representing the ocean, asking them where we can find life forms besides land. The ocean holds many life forms, all of which have carbon. Shells, such as those built by clams and snails, also contain carbon. Even the water itself holds carbon, and the ocean is denser than the atmosphere, so it can hold more. The ocean contains about 44,000 gigatons of carbon.
  • Ask the visitors where else there might be carbon, encouraging them to think about what happens when living things get buried. The Earth holds 65 million gigatons of carbon in rock as a result of living things, known as "organic" material, getting buried and because minerals like diamonds and graphite are made of carbon. We would need a little under 1,500 of the bigger boxes to hold 65 million grains of rice. Ask the visitors if they know what happens to organic material in the Earth after millions of years. Explain that Earth's process compress organic material into coal, oil, and natural gas, which are known as fossil fuels. The Earth holds about 10,000 gigatons of fossil fuels.
  • Have the visitor open the atmosphere box and take out the two smaller boxes inside. Ask them how they think carbon gets from the atmosphere into the terrestrial biosphere, explaining that plants make their own food in a process known as photosynthesis. Photosynthesis is a process in which plants use carbon dioxide and sunlight to sustain themselves. Plants take about 120 gigatons of carbon stored in the atmosphere per year. Have them move the little box from the atmosphere to the terrestrial biosphere.
  • Ask them how they think carbon gets from the atmosphere into the ocean. Explain that the ocean has a lot of plants algae, which take in carbon using photosynthesis. Water also chemically reacts with carbon dioxide, combining to store the carbon in the ocean. The ocean takes in 90 gigatons of carbon per year. Have them move the little box from the atmosphere to the ocean.
  • Have them look in the terrestrial biosphere box, asking them how they think carbon gets from the terrestrial biosphere to the atmosphere. Remind them what happened when they breathed into the CO2 meter. All organisms respirate, which means they take in oxygen and release carbon dioxide. Furthermore, when living things die they decompose, meaning they break down. The carbon that isn't buried is released into the atmosphere by tiny microorganisms. The terrestrial biosphere releases 120 gigatons of carbon back into the atmosphere every year. Have them move the box from the terrestrial biosphere to the atmosphere.
  • Have them look in the ocean box, asking them how they think carbon gets from the ocean to the atmosphere. Explain that the life in the ocean respirates, releasing carbon. Furthermore deep ocean water has more carbon; when it rises and warms it can release carbon into the atmosphere. The ocean releases 90 gigatons of carbon back into the atmosphere every year. Have them move the box from the ocean to the atmosphere.
  • Explain that they have just demonstrated the fast carbon cycle--all the carbon exchange that happens on Earth within a year. Ask them if carbon is ever released from rock. Explain that over millions and millions of years, rock can take up or release carbon, but it takes a long time for this carbon to change places. Ask if there is a faster way to release carbon from the Earth. Encourage them to think about how we use fuels such as coal and oil. Tell the visitors to take out nine grains of rice from the fossil fuel box, representing the nine gigatons of carbon humans release from fossil fuels by burning them.
  • Have the visitor put the nine grains of rice where they think it would go. The atmosphere initially takes up this extra carbon, but encourage the visitors to think about what could use extra carbon. Have them put three grains of rice on top of the terrestrial biosphere box, representing plants that could use extra carbon. Have them add two grains of rice on top of the ocean, representing carbon taken up by water and ocean plants. Ask them what they think happens to the four extra gigatons of carbon in the atmosphere, encouraging them to think about how many extra gigatons that would be over two years, ten years, or one hundred years.
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Questions To Ask
  • What is a gas? A liquid? A solid?
  • What gas do you breathe out?
  • Have you ever heard of carbon based life forms?
  • Do you and I have carbon in us?
  • Have you heard of fossil fuels?
  • Are the carbon cycles of the Earth balanced?
  • What do you think happens to carbon in the atmosphere that isn't balanced out by a natural process?
  • How do we know how much carbon is in the air?
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Sample Dialogue

Key:
  • P    Presenter
  • G    Guest
  • Bold italics indicate action.
  • Italics indicate a note to the presenter.
  •    □ indicates a cue


P   Hi there! Want to see something cool?
G   Sure.
P   What are you breathing right now?
G   Air.
P   But what are you breathing out?
G   More air.
P   Want to see if it's a particular kind of air?
G   Sure.
P   This thing measures carbon. How much carbon is in the air right now?
G   500.
P   Yeah. That's 500 parts per million. That means if we split the air into a million pieces, 500 of those pieces would be carbon. Okay, now breathe out here. Did it go up at all?
G   Yeah.
P   Definitely. That's because you're breathing out something called carbon dioxide. Where do you think that carbon dioxide goes?
G   Into the air.
P   Yeah. I've got a box full of air right here! I'm going to turn this meter off now and have you hold the atmosphere. What's in the atmosphere?
G   Rice and little boxes.
P   You're right. Each grain of rice represents a gigaton of carbon. Gigatons are a different measurement than parts per million, but the number of grains in this box is about the same as what you measured using that meter. Do you know where else on Earth we can find carbon?
G   No.
P   Maybe you've heard the term 'carbon based life'. Do you know what life is carbon-based?
G   All of it?
P   Yeah! Carbon is in our DNA, and all life has DNA. Can you read the words on this box?
G   Terrestrial biosphere.
P   Yeah! The biosphere refers to all life on Earth, and terrestrial just means land. Okay, is there more rice in the terrestrial biosphere?
G   Yeah.
P   Right. The terrestrial biosphere holds about three times as much carbon as the atmosphere. Is land the only place we can find life?
G   No.
P   Great! Where else do we find it?
G   The ocean.
P   Cool! Here's the ocean. It can hold 44,000 gigatons of carbon, which is a lot more than the atmosphere or terrestrial biosphere put together! The ocean doesn't just hold carbon in life forms, but also in shells like you see on clams. The water can also combine with carbon to form other chemicals. Where else do you think we can find carbon?
G   I don't know.
P   What do you think happens to the carbon in a life form when the life form dies?
G   Um it decomposes.
P   Sure. And where do you think that carbon goes?
G   I don't know. The air?
P   Awesome! Some of it goes into the air, and some of it gets buried in the ground. How much carbon do you think is in the ground?
G   I don't know.
P   Awesome. There is in fact so much carbon in the ground that I would have to get 1,500 of these ocean boxes and fill them all up with rice--that's 65 million grains of rice! Instead, I just took the carbon in the ground that is in the form of fossil fuels and put them in this box. Do you know what fossil fuels are?
G   Like oil?
P   Right! Oil, coal and natural gas are formed from dead things in the ground being compressed over millions and millions of years. There are about 10,000 gigatons of fossil fuels in the Earth, so that's the last box. Okay, try opening the atmosphere box. What's inside?
G   Two little boxes.
P   Right! What's the picture on one of those little boxes?
G   It's an arrow pointing to trees.
P   Okay! Trees and other plants take carbon out of the air. Let's talk about how they do that. Do plants eat?
G   They make their own food.
P   Right! Plants make their own food in a process called photosynthesis. Photosynthesis uses carbon dioxide and sunlight to make sugar for the plant to eat. So where does this little box of carbon end up?
G   In the terrestrial biosphere.
P   Okay! Go ahead and put it in the terrestrial biosphere box. Now, what's on the picture in the little box in the terrestrial biosphere box?
G   An arrow from a bunny out to the sky.
P   Great! That bunny is releasing carbon back into the atmosphere. How does it do that?
G   I don't know.
P   Remember when you used that meter? How do you release carbon into the atmosphere?
G   I breathed it out!
P   Right! Bunnies breathe out too. All animals take in oxygen and breath out carbon dioxide. In fact, all life forms take in oxygen and release carbon dioxide. This is called respiration--even plants do it. So where do you think this little box should go?
G   Back into the atmosphere?
P   Fantastic! Great. So we just traded those little boxes. Do they look like they have about the same amount of rice in them?
G   Maybe.
P   Right. Each box has about 120 grains. Every year plants take in about 120 gigatons and all life forms respirate about 120 gigatons. What's on this other box in the atmsophere?
G   An arrow to the ocean.
P   Right! The ocean takes in carbon because it's full of plant life that uses carbon to make food. The water itself also combines with carbon to form new chemicals. So where should we put this box?
G   In the ocean?
P   Exactly. Go ahead and put it in. And what's on this box in the ocean?
G   An arrow back to the sky.
P   Yeah. What stuff in the ocean might release carbon dioxide?
G   All the animals. Otherwise known as sea-bunnies.
P   Right! Life in the ocean respirates, releasing carbon, and at certain temperatures the water itself can release carbon back into the atmosphere. Okay, did we trade about the same amount that time too?
G   Yes.
P   Right. The ocean takes up about 90 gigatons of carbon and releases about 90 gigatons every year. Okay, those are the fast carbon cycles! Was there any carbon we didn't use?
G   Fossil fuels?
P   Right. Remember, fossil fuels are things like coal and oil. How do humans use coal?
G   We burn it?
P   Absolutely. When we burn coal, where do you think the carbon in it goes?
G   Maybe into the air?
P   Definitely! I'm sure you've seen the smoke from when that happens. So, in order to account for that carbon, count out nine grains of rice from the fossil fuels box. That's nine gigatons of carbon that people burned--so where should we put that rice?
G   In the atmosphere.
P   Great. Go ahead and set it on top of the atmosphere box. Now, let's think about what the atmosphere can trade carbon with. Can anything else use some of this carbon?
G   Maybe trees?
P   Awesome. Take three of those grains of rice and put them on top of the terrestrial biosphere. Plants used that extra carbon to photosynthesize. What else can the atmosphere trade its carbon with?
G   The ocean?
P   Yep! Take another two grains and put them on top of the ocean box. Okay, how many extra grains of rice do you have?
G   Four.
P   Does that seem like very much?
G   No.
P   Yeah. Just four extra gigatons of carbon in the air a year--but nothing balances out those extra gigatons. How much carbon would there be after two years?
G   Eight?
P   What about after 100 years?
G   Um . . . 400?
P   Definitely. What about after 200 years?
G   Um . . . 800?.
P   Yeah! How much carbon did we start out with?
G   800.
P   Exactly. So in 200 years, we've doubled the amount of carbon in our atmosphere, and there's nothing in nature to trade it back. Thanks for looking at carbon cycles with me!
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