--- title: "The Carbon Cycle on Two Timescales" description: "Carbon exchanges among air, living things and oceans on different timescales. Weathering, burial and geological degassing connect these stores with rocks. Fossil-fuel burning adds geological carbon fa" canonical: https://lightmysky.com/learn/science/the-carbon-cycle-on-two-timescales-mt_OXBubQOPk7 source: https://lightmysky.com/learn/science/the-carbon-cycle-on-two-timescales-mt_OXBubQOPk7.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # The Carbon Cycle on Two Timescales Carbon exchanges among air, living things and oceans on different timescales. Weathering, burial and geological degassing connect these stores with rocks. Fossil-fuel burning adds geological carbon faster than long-term sinks remove the surplus. Subject: Science · Area: Earth's Systems · Ages 17 to 18 Page: https://lightmysky.com/learn/science/the-carbon-cycle-on-two-timescales-mt_OXBubQOPk7 ## Ready when they can - Compare biological exchange, deep-ocean circulation and geological storage using reservoir-specific timescales - Explain how silicate weathering and carbonate burial can oppose a CO2 rise over geological time - Interpret a supplied CO2-pulse model and distinguish early uptake from slow removal of the atmospheric tail ## Lesson: Carbon on two clocks You have traced carbon through living things and examined ancient CO2 and climate records. Photosynthesis moves CO2 into organic matter: land plants take it from air, while algae use dissolved CO2 in water. Feeding transfers organic carbon. Respiration and decomposition can release CO2. These exchanges connect air, surface water and life, but different journeys take different amounts of time. *(drawing: Read one biological pathway from left to right. Other transfers, including direct air-ocean exchange, also occur.)* A reservoir is a carbon store. Turnover time is its carbon amount divided by its outward transfer rate under steady conditions. It is not a deadline for every atom. Some biological transfers take days to years. Deep-ocean circulation moves carbon over centuries to millennia. Sedimentary rocks and fossil fuels can store carbon for millions of years. Volcanic and metamorphic degassing return geological carbon as CO2. CO2 dissolved in rainwater reacts with silicate minerals. Rivers carry dissolved products to the ocean. Together with carbonate formation and burial, this pathway removes CO2 over geological time. Rising CO2 warms Earth. Where water and fresh rock are available, warming can speed weathering and long-term CO2 removal. Removal opposes the initial rise: a negative feedback. This slow response is called the silicate-weathering thermostat. Land and ocean uptake reduce part of an added atmospheric CO2 pulse over decades to centuries. Deep-ocean mixing continues over centuries to millennia. Some absorbed carbon can return to air. A remaining atmospheric tail can persist for many thousands of years; weathering and sediment burial remove it more slowly. Rapid exchange of individual molecules does not mean rapid removal of the added amount. CO2 has no single atmospheric lifetime. **Example.** An invented model starts with 80 units of added carbon in air. It leaves 40 after 200 years and 8 after 2,000 years. Find the percentage remaining by dividing the amount left by the starting amount, then multiplying by 100: 8 / 80 x 100 = 10%. Early uptake reduces the amount, yet a tail remains. These values teach model reading; they are not estimates for actual emissions. Coal, oil and gas contain carbon stored underground over geological time. Burning them transfers carbon into the active air-land-ocean system. Respiration from recently grown food moves carbon already in that system. Once mixed, CO2 from either source behaves alike. The long atmospheric tail concerns the extra amount added, not a special kind of fossil CO2 molecule. The ocean exchanges CO2 with air. Extra dissolved CO2 lowers seawater pH, making it more acidic even while it remains alkaline overall. The chemical change also reduces carbonate ions. Corals and many shell-building organisms use carbonate to make calcium carbonate shells and skeletons, so construction can become harder. Ocean uptake stores some added carbon but changes marine conditions. It does not permanently bury all emissions. **Recap.** Carbon stores exchange at different rates. Land and ocean uptake remove some added CO2 early; weathering and burial act more slowly. A remaining atmospheric tail can last many thousands of years. *Lesson, questions and flashcards written for this learning dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Carbon Cycle](https://lightmysky.com/learn/science/the-carbon-cycle-mt_Be1A88GUpu) - [Palaeoclimate: Ice Cores, Isotopes and the Record of Past Change](https://lightmysky.com/learn/science/palaeoclimate-ice-cores-isotopes-and-the-record-of-past-change-mt_JabMZ5ZeaL) - [Weathering, Erosion and How Soil Forms](https://lightmysky.com/learn/science/weathering-erosion-and-how-soil-forms-mt_nQOPOt1VTH) ## Optional connections - [Volcanoes & Mass Extinctions](https://lightmysky.com/learn/science/volcanoes-and-mass-extinctions-mt_QwWo6an9N1) ## Opens up - [Productivity, Nutrient Limitation and Ecosystem Stoichiometry](https://lightmysky.com/learn/science/productivity-nutrient-limitation-and-ecosystem-stoichiometry-mt_QWdZj1G9iT) - [Net Zero & Energy Transition](https://lightmysky.com/learn/science/net-zero-and-energy-transition-mt_Wzj1RETm9A)