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Carbon on two clocks

Science · Earth's Systems · ages 17-18

Name ______________________ Date ____________

Which set of timescales matches, in order, some biological transfers, deep-ocean circulation and storage in sedimentary rock?
- Days to years; millions of years; centuries to millennia
- Days to years; centuries to millennia; millions of years
- Centuries to millennia; days to years; millions of years
Which process returns carbon from organic matter to the air as CO2?
- Photosynthesis stores carbon as new sugar
- Burial stores organic carbon in sediments
- Respiration and decomposition release CO2
Burning fossil fuels transfers carbon from geological storage into the active air-land-ocean system.
Circle one: True False
Where water and fresh silicate rock are available, how can warming produce a feedback that opposes an atmospheric CO2 rise over geological time?
- Warming can reduce degassing and lower CO2 emissions
- Warming can slow weathering and lower CO2 removal
- Warming can speed weathering and raise CO2 removal
An invented model starts with 100 units of added carbon in air. It leaves 60 after 100 years and 20 after 1,000 years. What percentage of the starting amount remains in air at year 1,000?
- 20% of the starting amount
- 60% of the starting amount
- 80% of the starting amount
As extra CO2 dissolves in seawater, which chemical changes can make calcium carbonate shell formation harder?
- A pH rise and less carbonate for shell building
- A pH fall and less carbonate for shell building
- A pH fall and more carbonate for shell building
Compare burning coal with an animal respiring carbon from recently grown food. What difference matters for total carbon in the active air-land-ocean system?
- Both add geological carbon when they release CO2
- Respiration adds geological carbon; coal only shifts active carbon
- Coal adds geological carbon; respiration shifts active carbon
Leah says silicate weathering and burial will erase this year's entire added CO2 pulse by next spring. Which reply identifies the timescale problem?
- Weathering and burial act too slowly to meet that deadline
- Rapid molecular exchange sets the time to clear the added CO2
- Early ocean uptake sets the time to bury the added CO2

Answer key

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

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Days to years; centuries to millennia; millions of years · Some biological transfers take days to years, deep-ocean circulation takes centuries to millennia, and sedimentary rock can store carbon for millions of years. The alternatives swap these timescales.
Respiration and decomposition release CO2 · Respiration and decomposition can release CO2 from organic matter. Photosynthesis transfers carbon into organic matter, while burial stores carbon.
True · Fossil fuels contain carbon stored underground over geological time. Burning them transfers that carbon into the active system, releasing CO2.
Warming can speed weathering and raise CO2 removal · Warming can increase silicate weathering where conditions allow. Together with carbonate formation and burial, this increases long-term CO2 removal and opposes the initial rise.
20% of the starting amount · At year 1,000, 20 of the starting 100 units remain: 20 / 100 x 100 = 20%. The other 80% is outside the air at that time, not necessarily permanently buried.
A pH fall and less carbonate for shell building · Extra dissolved CO2 lowers pH and reduces carbonate availability. Corals and many shell-building organisms use carbonate to form calcium carbonate.
Coal adds geological carbon; respiration shifts active carbon · Coal transfers geological carbon into the active system. Respiration shifts carbon from recently grown food within that system. Once mixed, CO2 behaves alike regardless of its source.
Weathering and burial act too slowly to meet that deadline · Some uptake occurs earlier, but weathering and burial remove the long atmospheric tail over much longer timescales. Fast molecular exchange does not erase the net addition.