The Carbon Cycle on Two Timescales · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Carbon on two clocks

Science · Earth's Systems · ages 17-18
Name ______________________   Date ____________

  1. Where does slow-cycle carbon hide?

    • Leaves, lungs, and fresh fruit
    • Sediments, rock, and the deep ocean
    • Clouds, rain, and rivers

  2. In the fast cycle, how does carbon dioxide return to the air?

    • Rocks melt it back each night
    • The ocean boils it out daily
    • Breathing and rotting release it

  3. Burning fossil fuels moves slow, ancient carbon into the fast cycle.

    Circle one:   True   False

  4. Why does the carbon dioxide we add linger so long?

    • Plants refuse to photosynthesize at all
    • The slow lock-away works over thousands of years
    • Breathing has stopped worldwide

  5. A carbon atom laps from air to leaf to animal and back. About how long is one lap?

    • Thousands of years
    • A few seconds
    • A few years

  6. The ocean soaks up much of our extra carbon dioxide. What is the catch?

    • Its chemistry shifts and the water grows more acidic
    • The ocean sends it all straight back at once
    • Marine life eats the extra carbon overnight

  7. A country burns coal while animals breathe nearby. Why will the coal surplus outlast the breath?

    • Coal carbon belongs to the slow cycle, breath does not
    • Breath contains no carbon at all
    • Coal smoke never reaches the air

  8. A friend says slow natural processes will clear this year's emissions by next spring. What is wrong?

    • Rocks cannot hold any carbon at all
    • Slow processes work over millennia, not seasons
    • Weathering adds carbon instead of removing it
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Carbon on two clocks W1-mt_OXBubQOPk7-s1

  1. Sediments, rock, and the deep ocean · Slow reservoirs hold carbon for thousands or millions of years.
  2. Breathing and rotting release it · Living things breathe it out and dead things rot it back.
  3. True · Fuels are slow stock burned all at once into the quick loop.
  4. The slow lock-away works over thousands of years · Only slow processes can re-bury the surplus, and they crawl.
  5. A few years · The fast loop turns over on a scale of years.
  6. Its chemistry shifts and the water grows more acidic · Dissolved CO2 acidifies seawater and disturbs shell builders.
  7. Coal carbon belongs to the slow cycle, breath does not · Breath already laps the fast loop, while coal adds new slow stock to it.
  8. Slow processes work over millennia, not seasons · The geological thermostat steadies carbon over thousands of years.
Worksheet · LightMySky