Carbon stores at Higher Level: The same ideas as SL, with different examples: the Groningen gas field and the Dolomites. At HL, carbon in rocks and how fossil fuels formed get their own pages (2.3.12 to 2.3.14).
Practise this as you read
- Sort each store into organic or inorganic, with a reason.
- Compare residence times of fast and slow stores.
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Made by life, or not: Carbon is stored in two kinds of compound. Organic carbon is in the stuff of life; inorganic carbon is in simple compounds such as carbon dioxide.
The points to remember
- Organic carbon is in compounds made by living things: sugars, proteins, fats, wood.
- Organic stores: organisms (plants, animals, microbes) and their dead remains in soil and peat.
- Crude oil, natural gas and coal are organic too: they formed from ancient living things.
- Plants make organic carbon by photosynthesis; it passes to animals by feeding.
Remember it as: Organic: once alive. Inorganic: never alive.
Real example: the Groningen gas field in the Netherlands, once Europe's largest, holds gas that formed from coal: the remains of swamp plants that grew about 300 million years ago.
A common slip: Crude oil, natural gas and coal are organic stores, even though they are found in rocks.
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Most of the Earth's carbon is not in living things at all. It sits in the air, the water and the rocks, as simple compounds.
The points to remember
- Inorganic carbon is in simple compounds not made by living tissue: carbon dioxide, carbonates.
- The atmosphere: carbon dioxide gas.
- The oceans: dissolved carbon dioxide and carbonate, over 40 times the carbon in the air.
- Soils: carbonates and carbon dioxide in the air spaces (soils also hold dead organic matter).
- Rocks such as limestone and chalk hold the most carbon of all.
Real example: the Dolomites in northern Italy are mountains of limestone built by ancient coral reefs over 200 million years ago: a huge inorganic carbon store (more on 2.3.12 and 2.3.13).
What does not count: Plants, animals, cars and factories are not inorganic stores, and a flow such as burning or photosynthesis is not a store at all.
Stores differ in how long carbon stays in them. Some turn over in a few years, others hold carbon for millions of years.
The points to remember
- A store is in equilibrium when carbon absorbed is balanced by carbon released.
- Residence time is the average time a carbon atom stays in a store.
- Short in the air (about 4 years) and in plants (about 10 years).
- Long in the deep ocean (up to 1000 years) and in rocks (millions of years).
- Fossil fuels: hundreds of millions of years, unless people mine and burn them.
- Burning moves this slow carbon into the air in days, faster than sinks can take it back.
Remember it as: Fast stores turn over in years; slow stores in millions of years.
Fast stores
- Atmosphere: about 4 years
- Plants: about 10 years
- Soils: decades
Slow stores
- Deep ocean: up to 1000 years
- Fossil fuels: hundreds of millions of years
- Rocks: millions of years
Real example: gas from Groningen had stayed underground for about 300 million years. Since drilling began in 1963, much of it has been burned for heating, moving that carbon into the air in days.
Why it matters: Fossil carbon had left the active cycle. Burning puts it back far faster than it was stored, so the air's store fills up (see 2.3.7 and 6.2).
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How this comes up: Paper 2, Section A: distinguish the two kinds of store, with an example of each [2].
The Dolomites in Italy and the Groningen gas field in the Netherlands are both large stores of carbon found in rock.
Distinguish between an organic and an inorganic carbon store, using these two examples.
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