---
title: "The Carbon Cycle on Two Timescales"
description: "Carbon moves fast between air, ocean and life, and slowly between rock and everything else through weathering and volcanism. Burning fossil carbon moves an amount that belongs to the slow cycle into t"
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: 2026-09-12
---

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# The Carbon Cycle on Two Timescales

Carbon moves fast between air, ocean and life, and slowly between rock and everything else through weathering and volcanism. Burning fossil carbon moves an amount that belongs to the slow cycle into the fast one, which is why the surplus takes so long to clear.

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

- Separate the fast and slow carbon cycles by reservoir and turnover time
- Explain how silicate weathering acts as a thermostat over geological time
- Estimate how long an added pulse of carbon dioxide stays in the atmosphere, and say what removes it

## Lesson: Carbon on two clocks

Carbon never sits still. Plants and algae pull carbon dioxide from the air into sugars, and breathing plus rotting send it straight back. A single atom can travel from air to leaf to animal and back to air in just a few years. That is the fast cycle, and you live inside it.

Some carbon takes the slow road. It gets buried in sediments, locked into rock, or stored in the deep ocean for thousands or even millions of years. Over geological time, slow processes such as silicate weathering act like a thermostat on this buried stock. Fast and slow differ by reservoir and by turnover time.

Burning coal, oil, and gas digs up ancient slow-cycle carbon and dumps it into the fast loop all at once. The ocean soaks up a large share, which shifts its chemistry and turns the water more acidic. Because the slow lock-away works over thousands of years, the surplus lingers far longer than the few years a fast-cycle atom needs for one lap.

**Tip.** Judge every carbon claim by its clock. Fast claims resolve in years, slow ones in millennia. Clearing today's surplus takes far longer than adding it did, and the ocean's buffering help is not free.

**Recap.** Fast carbon laps in years while slow carbon rests for millennia, so fuel carbon lingers.

## 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)
- [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)