A-LEVEL GEOGRAPHY
EDEXCEL
CARBON
PRACTICE QUESTIONS + ANSWERS
6.1
Explain the geological processes that influence the levels of carbon in the atmosphere. (6) 2021
One geological process that influences the level of carbon in the atmosphere is the rate of photosynthesis
occurring within plant matter on Earth’s surface. Photosynthesis involves leaves of plants absorbing carbon
dioxide from the atmosphere and storing it as converted glucose within the plant. Therefore, if there are higher
rates of photosynthesis taking place, there will be more carbon absorbed into plants, leaving a lower carbon
concentration in the atmosphere.
Soils will also contain large amounts of carbon from dead plants and animals, and the extent to which soil is
being interfered with will determine how much of the stored carbon is released into the atmosphere. Peat and
boreal forests are very large carbon sinks, as they store huge amounts of carbon that would otherwise be in
the atmosphere.
Explain the significance of the lithosphere in the carbon cycle (6)
The lithosphere stores roughly 83 million petagrams of carbon, which is over 99% of all carbon on earth. The
flows into the lithosphere are from dead animals and biomass that have decomposed and been compressed to
release the carbon stored in their skeletons and bodies, through a process called diagenesis. Limestone holds
the majority of this carbon, and has a high concentration of calcium carbonate. Eventually the compressed
biomass will form crude oil, which can move easily through the permeable rocks in its liquid state.
The large size of the store means it is very significant as a part of the carbon cycle; fluctuations in and out of it
will have large impacts on the rest of the cycle.
Explain the role of tectonics in the carbon cycle (6)
Tectonics will cause the process of outgassing, where volcanoes eject molten rock which contains carbon that
was previously trapped underground. Lots of gaseous carbon will also be released before and after an
eruption, which all contributes to higher flows and stores of carbon in the atmosphere. Tectonics will also form
fold mountains, which are oceanic plates being pushed together to form mountains like the Himalayas. These
oceanic plates store huge amounts of carbon, as they are part of the lithosphere, and when they become
mountains they are vulnerable to weathering like rain, which will chemically remove carbon from the rocks and
transfer it to the oceans.
Explain how carbon can become locked in terrestrial stores in a long term geological timescale. (8)
HINT: You should discuss formation of sedimentary rocks (including some information from 6.2 about ocean
processes) and also explain how fossil fuels can form rocks.
Sedimentary rock stores carbon through the continued building up of dead biomatter like plants and marine
life. The animals will hold carbon in their skeletons and shells, while the plants store carbon from
,photosynthesis, and as they collect on the seabed the pressure builds up on the lower layers, causing them to
go through a process called diagenesis. This is where they become compressed and form sedimentary rocks
like limestone. The ocean contributes to this process through the carbonate pump, where dead zooplankton
die and fall to the ocean floor to build up and contribute to lithification.
1. Ocean process of the carbonate pump, whereby carbon has taken a long route to reach the end goal of
sequestering in rocks.
2. The process of dead matter forming limestone and other sedimentary rock, diagenesis.
3. Fossil fuels like oil result from compressed biomatter, these fossil fuels can turn into coal when
compressed for a long enough time period
Explain how carbon can be released back into the atmosphere by the long term carbon cycle (6)
HINT: You should discuss outgassing and the release from weathered rocks.
Carbon is stored in the lithosphere in sedimentary rocks, and can be released back into the atmosphere
through the process of outgassing. This is where rocks in the lithosphere that contain a large amount of carbon
are ejected in volcanic eruptions and released back into the atmosphere, thereby releasing the carbon that
was previously stored.
Additionally, carbon becomes stored in sedimentary rocks at the bottom of the ocean through many layers of
sediment building up and compressing. Through tectonic processes, this ocean floor will be pushed together to
form fold mountains like the Himalayas. These fold mountains contain large amounts of carbon which are now
vulnerable to weathering when rainwater chemically erodes the carbon stored within and washes it away, to
the ocean and then to the atmosphere.
Explain why some fluxes in the carbon cycle are on a longer time scale than others (6)
1. There are very short fluxes that happen through respiration of living organisms; carbon is respired
when it is taken in through photosynthesis, when plants are eaten, when carbon is absorbed by
zooplankton etc. — these stores do not need all the carbon they absorb, therefore the flux of carbon
will be very quick
2. Longer fluxes such as release when a plant or animal dies, when carbon is upwelled in the physical
pump — in these stores, the carbon is needed for a long time by organisms, or is physically held by a
powerful force (the ocean)
6.2
Explain the importance of soils in the carbon cycle (6)
Soils hold around 2,000 Pgc, with much of it stored as dead biomatter like plants and animals. Soils absorb the
carbon from falling trees that have stored carbon within it from photosynthesis, and from dead animals that use
carbon for skeletons and shells. The higher the concentration of organic matter within the soil, the more carbon
it can store. Peat and bogs are large stores of carbon, and they trap biomass away from oxygen so it doesn’t
start decomposing, called sequestration. If these stores are disrupted they release all the carbon to the
atmosphere.
1. Storing all carbon that is dropped by dead organisms
2. As a store of carbon keeping carbon out the atmosphere
, Explain why some soils store more carbon than others, (6)
The concentration of organic material in the soil will affect how much carbon soil can store. This is because it
is the organic material that will sequester the carbon through chemical processes, and therefore the more
organic material there is, the more carbon can be sequestered. Organic material includes leaves, dead
organisms etc. Colder soils like permafrost are also able to hold more carbon than warm soils.
Additionally, soil that remains untouched for long periods of time can build up the amount of carbon it stores,
but soil that is continually disrupted will not be able to build up its storage. For example soil that is being
planted will be ploughed regularly and the carbon it has stored in the last year will be released.
Assess the role of biological processes in sequestering carbon (12)
Biological processes include photosynthesis, decomposing, biological pumps etc.
Photosynthesis is responsible for drawing in carbon from the atmosphere in the largest flow in the carbon store
at 123 Pgc. Carbon is used by plant matter to make glucose and grow larger, in a positive feedback
mechanism that takes in more and more carbon. The carbon is stored in the living plant matter until it is eaten
by animals or dies, which can be on a fairly long timescale.
When the plant dies, it is absorbed by soil or peat and sequestered there for a very long timespan, as peat can
sequester carbon within its many layers of biomatter until humans disrupt the store and either overturn it, burn
it, or drain it of water. This is a very large store of carbon at 1,950 PgC, and helps to regulate the amount of
carbon in the atmosphere.
However, the lithosphere is a much more important store in the sequestration of carbon. The lithosphere holds
83 million PgC
EDEXCEL
CARBON
PRACTICE QUESTIONS + ANSWERS
6.1
Explain the geological processes that influence the levels of carbon in the atmosphere. (6) 2021
One geological process that influences the level of carbon in the atmosphere is the rate of photosynthesis
occurring within plant matter on Earth’s surface. Photosynthesis involves leaves of plants absorbing carbon
dioxide from the atmosphere and storing it as converted glucose within the plant. Therefore, if there are higher
rates of photosynthesis taking place, there will be more carbon absorbed into plants, leaving a lower carbon
concentration in the atmosphere.
Soils will also contain large amounts of carbon from dead plants and animals, and the extent to which soil is
being interfered with will determine how much of the stored carbon is released into the atmosphere. Peat and
boreal forests are very large carbon sinks, as they store huge amounts of carbon that would otherwise be in
the atmosphere.
Explain the significance of the lithosphere in the carbon cycle (6)
The lithosphere stores roughly 83 million petagrams of carbon, which is over 99% of all carbon on earth. The
flows into the lithosphere are from dead animals and biomass that have decomposed and been compressed to
release the carbon stored in their skeletons and bodies, through a process called diagenesis. Limestone holds
the majority of this carbon, and has a high concentration of calcium carbonate. Eventually the compressed
biomass will form crude oil, which can move easily through the permeable rocks in its liquid state.
The large size of the store means it is very significant as a part of the carbon cycle; fluctuations in and out of it
will have large impacts on the rest of the cycle.
Explain the role of tectonics in the carbon cycle (6)
Tectonics will cause the process of outgassing, where volcanoes eject molten rock which contains carbon that
was previously trapped underground. Lots of gaseous carbon will also be released before and after an
eruption, which all contributes to higher flows and stores of carbon in the atmosphere. Tectonics will also form
fold mountains, which are oceanic plates being pushed together to form mountains like the Himalayas. These
oceanic plates store huge amounts of carbon, as they are part of the lithosphere, and when they become
mountains they are vulnerable to weathering like rain, which will chemically remove carbon from the rocks and
transfer it to the oceans.
Explain how carbon can become locked in terrestrial stores in a long term geological timescale. (8)
HINT: You should discuss formation of sedimentary rocks (including some information from 6.2 about ocean
processes) and also explain how fossil fuels can form rocks.
Sedimentary rock stores carbon through the continued building up of dead biomatter like plants and marine
life. The animals will hold carbon in their skeletons and shells, while the plants store carbon from
,photosynthesis, and as they collect on the seabed the pressure builds up on the lower layers, causing them to
go through a process called diagenesis. This is where they become compressed and form sedimentary rocks
like limestone. The ocean contributes to this process through the carbonate pump, where dead zooplankton
die and fall to the ocean floor to build up and contribute to lithification.
1. Ocean process of the carbonate pump, whereby carbon has taken a long route to reach the end goal of
sequestering in rocks.
2. The process of dead matter forming limestone and other sedimentary rock, diagenesis.
3. Fossil fuels like oil result from compressed biomatter, these fossil fuels can turn into coal when
compressed for a long enough time period
Explain how carbon can be released back into the atmosphere by the long term carbon cycle (6)
HINT: You should discuss outgassing and the release from weathered rocks.
Carbon is stored in the lithosphere in sedimentary rocks, and can be released back into the atmosphere
through the process of outgassing. This is where rocks in the lithosphere that contain a large amount of carbon
are ejected in volcanic eruptions and released back into the atmosphere, thereby releasing the carbon that
was previously stored.
Additionally, carbon becomes stored in sedimentary rocks at the bottom of the ocean through many layers of
sediment building up and compressing. Through tectonic processes, this ocean floor will be pushed together to
form fold mountains like the Himalayas. These fold mountains contain large amounts of carbon which are now
vulnerable to weathering when rainwater chemically erodes the carbon stored within and washes it away, to
the ocean and then to the atmosphere.
Explain why some fluxes in the carbon cycle are on a longer time scale than others (6)
1. There are very short fluxes that happen through respiration of living organisms; carbon is respired
when it is taken in through photosynthesis, when plants are eaten, when carbon is absorbed by
zooplankton etc. — these stores do not need all the carbon they absorb, therefore the flux of carbon
will be very quick
2. Longer fluxes such as release when a plant or animal dies, when carbon is upwelled in the physical
pump — in these stores, the carbon is needed for a long time by organisms, or is physically held by a
powerful force (the ocean)
6.2
Explain the importance of soils in the carbon cycle (6)
Soils hold around 2,000 Pgc, with much of it stored as dead biomatter like plants and animals. Soils absorb the
carbon from falling trees that have stored carbon within it from photosynthesis, and from dead animals that use
carbon for skeletons and shells. The higher the concentration of organic matter within the soil, the more carbon
it can store. Peat and bogs are large stores of carbon, and they trap biomass away from oxygen so it doesn’t
start decomposing, called sequestration. If these stores are disrupted they release all the carbon to the
atmosphere.
1. Storing all carbon that is dropped by dead organisms
2. As a store of carbon keeping carbon out the atmosphere
, Explain why some soils store more carbon than others, (6)
The concentration of organic material in the soil will affect how much carbon soil can store. This is because it
is the organic material that will sequester the carbon through chemical processes, and therefore the more
organic material there is, the more carbon can be sequestered. Organic material includes leaves, dead
organisms etc. Colder soils like permafrost are also able to hold more carbon than warm soils.
Additionally, soil that remains untouched for long periods of time can build up the amount of carbon it stores,
but soil that is continually disrupted will not be able to build up its storage. For example soil that is being
planted will be ploughed regularly and the carbon it has stored in the last year will be released.
Assess the role of biological processes in sequestering carbon (12)
Biological processes include photosynthesis, decomposing, biological pumps etc.
Photosynthesis is responsible for drawing in carbon from the atmosphere in the largest flow in the carbon store
at 123 Pgc. Carbon is used by plant matter to make glucose and grow larger, in a positive feedback
mechanism that takes in more and more carbon. The carbon is stored in the living plant matter until it is eaten
by animals or dies, which can be on a fairly long timescale.
When the plant dies, it is absorbed by soil or peat and sequestered there for a very long timespan, as peat can
sequester carbon within its many layers of biomatter until humans disrupt the store and either overturn it, burn
it, or drain it of water. This is a very large store of carbon at 1,950 PgC, and helps to regulate the amount of
carbon in the atmosphere.
However, the lithosphere is a much more important store in the sequestration of carbon. The lithosphere holds
83 million PgC
