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🌍 How does the carbon cycle work?

Carbon moves among air, life, oceans, and rock — fast biological loops, slow geologic vaults, human imbalance.

lessons

~20 min

to learn

🔬 Science

subject

Adults

level

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What you’ll learn

Carbon on a living planetDefine reservoirs, fluxes, and why atmospheric carbon matters for climate.Carbon moves among air, life, oceans, soils, and rocks. The atmosphere is a smaller pool with outsized climate leverage.
Life’s fast loopTrace photosynthesis, respiration, decomposition, and fire as fast fluxes.Life fixes and releases carbon at huge rates. Net exchange can be small even when gross flows are large.
Oceans and the slow rock cycleExplain ocean uptake, the biological pump, rock pathways, and fossil carbon.Oceans store and transform carbon chemically and biologically. Rocks dominate on geologic time; fossil fuels reopen buried stocks.
Humans rewriting the fluxesDescribe anthropogenic emissions, airborne fraction, ocean acidification, and land sinks.Fossil combustion and land use unbalance the modern budget. Oceans and land absorb some carbon; atmospheric CO₂ still rises.
Budgets, feedbacks, and clear thinkingConnect scientific carbon budgets, feedbacks, and timescale literacy.Budgets are measured ledgers. Feedbacks loop. Solutions and problems must match their clocks.

Questions this course answers

What is the carbon cycle primarily describing?

The cycle is the system of reservoirs and fluxes that relocate carbon across Earth’s major spheres.

Match each term to its meaning

Budgets separate where carbon sits from how fast it moves; atmospheric CO₂ is climate-critical despite not being the largest pool.

Put these biological carbon steps in a sensible loop order starting with CO₂ uptake

Carbon is fixed into life, transferred in food webs, returned by respiration, and finished by decomposers — a repeating loop.

Complete the sentence

Land plants in the Northern Hemisphere draw down CO₂ during the growing season, creating a visible annual cycle.

Why can’t geologic rock weathering alone solve this century’s fossil CO₂ rise?

Silicate weathering and related rock processes are powerful on geologic time but not matched to annual fossil fluxes.

Match each ocean/rock idea to its role

Oceans use chemistry and biology; rocks use deep time; fossil fuels are buried organic carbon returned quickly when burned.

Grounded in trusted sources

IPCC assessment reports — carbon cycle and biogeochemical chapters (public summaries and figures)
NOAA Global Monitoring Laboratory — Mauna Loa CO₂ record and explanations
Global Carbon Project — annual global carbon budget updates
NASA Earth Observatory / NASA science pages on the carbon cycle and ocean carbon
USGS educational materials on the geologic carbon cycle and weathering

Every Wunder lesson is built from real, reputable sources — never invented.

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