Carbon is stored in every one of Earth's spheres: as carbon dioxide in the air, dissolved in the oceans, in living things and soil, and in fossil fuels and rocks. Carbon is never made or destroyed; it moves between these stores, and the carbon cycle is the map of those moves.
The carbon atoms in your body have been in dinosaurs, in ocean water and in the air, many times over. They are billions of years old and still in use.
Last lesson: Earth has four spheres. This lesson follows one substance through all of them: carbon.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: the biggest store
ExploreTry it on the board and compare what happens with your prediction.
Explore: the stores and the flows
Each box is a store (how much carbon is there); each arrow is a flow (how much moves each year). Press Run 10 years and watch the stores.
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Run 10 years with every process on. Does the carbon in the air change much?
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: stores in every sphere
In your book: draw the four spheres as four boxes. In each, write at least one carbon store. Draw arrows for two flows you know, and label each.
Which sphere is each carbon store in?
Carbon dioxide in the air
Carbon dioxide dissolved in sea water
Carbon in trees and animals
Dead leaves and roots in soilSoil is where biosphere and geosphere meet; the dead plant matter counts as biosphere here.
Coal, oil and natural gas
Limestone (calcium carbonate) rock
Fast or slow? How long does carbon usually stay in each store?
Carbon dioxide in the air
Carbon in a gum tree
Dead leaves in the soil
A coal seam
Limestone rockIts carbon returns to the air only when the rock is worn away or heated, usually over millions of years.
Elaborate TypicalUse the same idea in a new context.
Elaborate: carbon in the landscape
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Place everything in the landscape into its sphere.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: shells to stone
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Run 50 years with every process on.
Use the board. This ticks when you get there.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Carbon is stored in every sphere: atmosphere (carbon dioxide), hydrosphere (dissolved in the oceans), biosphere (living things, dead matter, soil) and geosphere (fossil fuels, limestone and other rocks).
The oceans hold far more than the air; rocks hold the most of all.
Carbon is never made or destroyed. It flows between stores: the carbon cycle is the map of those flows.
A store stays steady when the flows into it balance the flows out.
For teachers
Students identify carbon stores in each of Earth's spheres, distinguish stores from flows, and explain that carbon moves between stores without being made or destroyed (AC9S9U03, node 2). About 23 minutes.
I can name a carbon store in each of Earth's four spheres.
I can explain the difference between a carbon store and a carbon flow.
I can explain that carbon moves between stores but is never made or destroyed.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It sits between What are Earth's spheres? (node 1) and Where does the carbon in a tree go? (node 3), which uses the same cycle board to switch flows on and off.
Not a hinge node, but it sets up the cycle: students who confuse stores (amounts) with flows (amounts a year), or think burning destroys carbon, struggle with every later carbon lesson.
Board notes: the cycle board shows four stores; rocks (the largest store) are left out because their carbon moves over millions of years. Store sizes are rounded: air about 600 GtC before industry (about 875 today), living things and soil about 2150, oceans about 38 000, fossil fuels about 1000. Boxes are not to scale.
Running the lesson
Engage: tally the predictions. Most will say the air; the oceans are the surprise.
Explore: ask why the air's store barely moved when the arrows show large flows.
Explain: the sphere sort and the store-or-flow question are the success criteria.
In your own words: the four boxes with stores and two labelled flows are the evidence.
The hard part (on purpose)
Telling a store from a flow. If a student calls photosynthesis a store, point to the units (tonnes, or tonnes a year) and ask which one is moving.
When students get stuck
A student says burning destroys carbon. Ask: What gas comes out of a chimney? Fix: Carbon dioxide: the same carbon atoms, now in the air. Carbon moves; it isn't destroyed.
A student thinks the air holds most of Earth's carbon. Ask: Look at the oceans' store on the board. How many times bigger is it? Fix: About 50 times. Rocks hold more still.
A student thinks a steady store means nothing is moving. Ask: If a bath's tap is on and the plug is out, can the water level stay the same? Fix: Yes, when in equals out. The same goes for carbon stores.
Stretch and support
Stretch: If carbon is never destroyed, where does the carbon in coal come from? (Plants that took carbon dioxide from the air millions of years ago, buried before they could decay.)
Support: Give a four-row table: Sphere | A carbon store | What form the carbon is in.
Where it leads
Next: Where does the carbon in a tree go? (photosynthesis and respiration, node 3), then fossil fuels (node 4).
In class: a "carbon atom's journey" dice game around stores; dissolving carbon dioxide from breath in limewater.
What each step is for
Engage: the biggest store: Students picture carbon mostly in the air (because of climate news) or in living things; the oceans and rocks are the surprise.
Explore: the stores and the flows: Running the cycle and seeing stores barely change while large flows move carbon each year separates 'store' from 'flow' and shows carbon is conserved.
Explain: stores in every sphere: Placing each store in a sphere and naming its form (gas, dissolved, living, fossil, rock), then stating conservation, is the node.
Elaborate: carbon in the landscape: Placing real things into spheres checks that students can find carbon stores in a familiar scene.
Elaborate: shells to stone: Limestone made from shells links the biosphere, hydrosphere and geosphere and shows a store that changes over millions of years.
Now you can
Name a carbon store in each of Earth's four spheres.
Explain the difference between a carbon store and a carbon flow.
Explain that carbon moves between stores but is never made or destroyed.