Chapter 4
Earth's life support systems
OCR A-Level Geography
4.1 How important are water and carbon to life on Earth? - correct-answers-Key idea ➡
Water and carbon support life on Earth and move between the land, oceans and
atmosphere.
The importance of water in supporting life on the planet - correct-answers-Scientists
believe that water is the key to understanding the evolution of life on Earth as it
provides a medium that allows organic molecules to mix and form more complex
structures.
The ubiquity of liquid water on Earth is due to the distance of Earth from the Sun
(149.89 million km): it lies in the so-called 'Goldilocks zone', which is 'just right' for water
to exist in its liquid form (H₂O).
Distance of Earth from the Sun - correct-answers-149.89 million km, 93.14 million miles
Water and the creation of benign thermal conditions - correct-answers-Water helps to
create benign thermal conditions on Earth. For example, oceans, which occupy 71 per
cent of Earth's surface, moderate temperatures by absorbing heat, storing it and
releasing it slowly.
Water also moderates the environment in other ways. Clouds made up of tiny water
droplets and ice crystals reflect around a fifth of incoming solar radiation and lower
surface temperatures.
At the same time water vapor, a potent greenhouse gas, absorbs long-wave radiation
from the Earth helping to maintain average global temperatures almost 15°C higher
than they would be otherwise.
The uses of water for flora, fauna and people - correct-answers-Water comprises up to
65-95% of all living organisms and is crucial to their growth, reproduction and other
metabolic functions.
Examples include photosynthesis (in plants/flora) and economic activity.
Flora - correct-answers-Plant life
Fauna - correct-answers-Animal life
Photosynthesis (The uses of water for flora, fauna and people) - correct-answers-
Plants, which manufacture their own food, need water for photosynthesis, respiration
and transpiration. Photosynthesis takes place in the leaves of plants combining CO ₂
sunlight and water to make glucose and starches. Respiration in plants and animals
converts glucose to energy through its reaction with oxygen, releasing water and CO ₂ in
the process.
Plants also require water to maintain their rigidity (plants wilt when they run out of
water) and to transport mineral nutrients from the soil. In people and animals’ water is
the medium used for all chemical reactions in the body including the circulation of and
nutrients. Transpiration of water from leaf surfaces cools plants by evaporation.
Sweating is a similar cooling process in humans. In fur-covered mammals, reptiles and
birds, evaporative cooling is achieved by panting.
Economic activity (The uses of water for flora, fauna and people) - correct-answers-
Water is an essential resource for economic activity. It is used to generate electricity,
irrigate crops, provide recreational facilities and satisfy public demand (drinking water,
,sewage disposal), as well as in a huge range of industries including food
manufacturing, brewing, paper making and steel making.
The importance of carbon to life on Earth - correct-answers-Carbon is a common
chemical element. It is stored in carbonate rocks such as limestone, sea floor
sediments, ocean water (as dissolved CO₂), the atmosphere (as CO₂ gas), and in the
biosphere.
Life as we know it is carbon based: built on large molecules of carbon atoms such as
proteins, carbohydrates and nucleic acids.
Apart from its biological significance, carbon is used as an economic resource. Fossil
fuels such as coal, oil (hydrocarbons) and natural gas power the global economy.
One example is oil's usage as a raw material in the manufacture of products ranging
from plastics to paint and synthetic fabrics. Agricultural crops and forest trees (a.k.a.
carbon sinks) also store large amounts of carbon available for human use as food,
timber, paper, textiles and many other products.
Carbon sinks - correct-answers-A forest, ocean, or other natural environment viewed in
terms of its ability to absorb carbon dioxide from the atmosphere.
Biosphere - correct-answers-Consists of all life on Earth and all parts of the Earth in
which life exists, including land, water, and the atmosphere.
The global water cycle - Reservoirs and stores - correct-answers-Page 99.
The water and carbon cycle - correct-answers-At the global scale, water and carbon
flow in closed systems between the atmosphere, the oceans, land and the biosphere.
The cycling of individual water molecules and carbon atoms occurs on time scales
varying from days to millions of years.
The water cycle inputs/outputs/stores/transfers - correct-answers-Inputs - precipitation
including rain and snow, and solar energy for evaporation.
Outputs - evaporation and transpiration from plants (evapotranspiration), runoff into the
sea, percolation of water into underlying rock strata.
Stores - puddles, rivers, lakes (surface storage), soil, groundwater storage and water
stored in vegetation.
Transfers - infiltration, percolation, overland flow, through flow, groundwater flow.
Evapotranspiration - correct-answers-The combined amount of evaporation of water
from soil and transpiration of water from plants. Correlates with species richness.
Evaporation - correct-answers-The change of a substance from a liquid to a gas,
particularly in soil.
Transpiration - correct-answers-Evaporation (the change of a substance from a liquid to
a gas) of water from the leaves of a plant.
The water cycle (Diagram) - correct-answers-
The carbon cycle inputs/outputs/stores/transfers - correct-answers-Inputs - carbon
dioxide added to the atmosphere by human activities.
Outputs - dissolved carbon carried from the land in solution by rivers.
Stores - marine sediments and sedimentary rocks, oceans, fossil fuel deposits, soil
organic matter, atmosphere, terrestrial plants,
Transfers - photosynthesis, respiration, combustion, decomposition, diffusion,
weathering and erosion, burial and compaction, carbon sequestration,
The carbon cycle (Diagram) - correct-answers-
The global carbon cycle - Principal carbon stores - correct-answers--Atmosphere: 600
(billion tons of carbon in store)
-Oceans: 38,700 (billion tons of carbon in store)
, -Sedimentary (carbonate) rocks: 60,000-100,000,000 (billion tons of carbon in store)
-Sea floors sediments 6,000 (billion tons of carbon in store)
-Fossil fuels: 4,130 (billion tons of carbon in store)
-Land plants: 560 (billion tons of carbon in store)
-Soils/peat: 2,300 (billion tons of carbon in store)
Satellite image of global water vapor (mm) - correct-answers-
The slow carbon cycle - correct-answers-Through a series of chemical reactions and
tectonic activity, carbon takes between 100-200 million years to move between rocks,
soil, ocean, and atmosphere.
(Transfers of carbon compounds over extensive timescales (possibly millions of years).)
Page 101.
The fast carbon cycle - correct-answers-Capture of atmospheric carbon dioxide by
plants to create glucose and other sugars, which fuels the ecosystem. As these sugars
are used in cellular respiration, carbon dioxide is produced.
(Relatively rapid transfers of carbon compounds over years, decades and centuries.)
Page 101.
The processes of the water cycle - correct-answers--The water balance
-Flows
-Catchment hydrology
The water balance (The processes of the water cycle) - correct-answers-The water
balance equation summarizes the flows of water in a drainage basin over time. It states
that precipitation is equal to evapotranspiration and streamflow, plus or minus water
entering or leaving storage: P = R + ET + ΔS
Where P is precipitation, R is streamflow, ET is evapotranspiration, ΔS is the change in
storage (in soil or the bedrock / groundwater)
Where Δ - correct-answers-Uppercase delta (Δ) at most times means "change" or "the
change" in math’s. Consider an example, in which a variable x stands for the movement
of an object.
So, "Ax" means "the change in movement." Scientists make use of this mathematical
meaning of delta in various branches of science.
The drainage basin water cycle - correct-answers-
Flows (The processes of the water cycle) - correct-answers--Precipitation
-Transpiration
-Condensation (Cumuliform clouds, Stratiform, Wispy, cirrus clouds, Lapse rates, Cloud
formations and lapse rates)
Flows definition (The processes of the water cycle) - correct-answers-The principal
flows in the water cycle that link the various stores are: precipitation, evaporation,
transpiration, run-off, infiltration, percolation and throughflow.
Precipitation (Flows (The processes of the water cycle)) - correct-answers-Precipitation
is water and ice that falls from clouds towards the ground. It takes several forms: most
commonly rain and snow, but also hail, sleet and drizzle.
Precipitation forms when vapor in the atmosphere cools to its dew point and condenses
into tiny water droplets or ice particles to form clouds. Eventually these droplets or ice
particles aggregate, reach a critical size and leave the cloud as precipitation.
Dew point - correct-answers- (Condensation begins) The temperature at which the
water vapor in the air becomes saturated.
Transpiration (Flows (The processes of the water cycle)) - correct-answers-
Transpiration is the diffusion of water vapor to the atmosphere from the leaf pores
(stomata) of plants. It is responsible for around 10 per cent of moisture in the
atmosphere.
Earth's life support systems
OCR A-Level Geography
4.1 How important are water and carbon to life on Earth? - correct-answers-Key idea ➡
Water and carbon support life on Earth and move between the land, oceans and
atmosphere.
The importance of water in supporting life on the planet - correct-answers-Scientists
believe that water is the key to understanding the evolution of life on Earth as it
provides a medium that allows organic molecules to mix and form more complex
structures.
The ubiquity of liquid water on Earth is due to the distance of Earth from the Sun
(149.89 million km): it lies in the so-called 'Goldilocks zone', which is 'just right' for water
to exist in its liquid form (H₂O).
Distance of Earth from the Sun - correct-answers-149.89 million km, 93.14 million miles
Water and the creation of benign thermal conditions - correct-answers-Water helps to
create benign thermal conditions on Earth. For example, oceans, which occupy 71 per
cent of Earth's surface, moderate temperatures by absorbing heat, storing it and
releasing it slowly.
Water also moderates the environment in other ways. Clouds made up of tiny water
droplets and ice crystals reflect around a fifth of incoming solar radiation and lower
surface temperatures.
At the same time water vapor, a potent greenhouse gas, absorbs long-wave radiation
from the Earth helping to maintain average global temperatures almost 15°C higher
than they would be otherwise.
The uses of water for flora, fauna and people - correct-answers-Water comprises up to
65-95% of all living organisms and is crucial to their growth, reproduction and other
metabolic functions.
Examples include photosynthesis (in plants/flora) and economic activity.
Flora - correct-answers-Plant life
Fauna - correct-answers-Animal life
Photosynthesis (The uses of water for flora, fauna and people) - correct-answers-
Plants, which manufacture their own food, need water for photosynthesis, respiration
and transpiration. Photosynthesis takes place in the leaves of plants combining CO ₂
sunlight and water to make glucose and starches. Respiration in plants and animals
converts glucose to energy through its reaction with oxygen, releasing water and CO ₂ in
the process.
Plants also require water to maintain their rigidity (plants wilt when they run out of
water) and to transport mineral nutrients from the soil. In people and animals’ water is
the medium used for all chemical reactions in the body including the circulation of and
nutrients. Transpiration of water from leaf surfaces cools plants by evaporation.
Sweating is a similar cooling process in humans. In fur-covered mammals, reptiles and
birds, evaporative cooling is achieved by panting.
Economic activity (The uses of water for flora, fauna and people) - correct-answers-
Water is an essential resource for economic activity. It is used to generate electricity,
irrigate crops, provide recreational facilities and satisfy public demand (drinking water,
,sewage disposal), as well as in a huge range of industries including food
manufacturing, brewing, paper making and steel making.
The importance of carbon to life on Earth - correct-answers-Carbon is a common
chemical element. It is stored in carbonate rocks such as limestone, sea floor
sediments, ocean water (as dissolved CO₂), the atmosphere (as CO₂ gas), and in the
biosphere.
Life as we know it is carbon based: built on large molecules of carbon atoms such as
proteins, carbohydrates and nucleic acids.
Apart from its biological significance, carbon is used as an economic resource. Fossil
fuels such as coal, oil (hydrocarbons) and natural gas power the global economy.
One example is oil's usage as a raw material in the manufacture of products ranging
from plastics to paint and synthetic fabrics. Agricultural crops and forest trees (a.k.a.
carbon sinks) also store large amounts of carbon available for human use as food,
timber, paper, textiles and many other products.
Carbon sinks - correct-answers-A forest, ocean, or other natural environment viewed in
terms of its ability to absorb carbon dioxide from the atmosphere.
Biosphere - correct-answers-Consists of all life on Earth and all parts of the Earth in
which life exists, including land, water, and the atmosphere.
The global water cycle - Reservoirs and stores - correct-answers-Page 99.
The water and carbon cycle - correct-answers-At the global scale, water and carbon
flow in closed systems between the atmosphere, the oceans, land and the biosphere.
The cycling of individual water molecules and carbon atoms occurs on time scales
varying from days to millions of years.
The water cycle inputs/outputs/stores/transfers - correct-answers-Inputs - precipitation
including rain and snow, and solar energy for evaporation.
Outputs - evaporation and transpiration from plants (evapotranspiration), runoff into the
sea, percolation of water into underlying rock strata.
Stores - puddles, rivers, lakes (surface storage), soil, groundwater storage and water
stored in vegetation.
Transfers - infiltration, percolation, overland flow, through flow, groundwater flow.
Evapotranspiration - correct-answers-The combined amount of evaporation of water
from soil and transpiration of water from plants. Correlates with species richness.
Evaporation - correct-answers-The change of a substance from a liquid to a gas,
particularly in soil.
Transpiration - correct-answers-Evaporation (the change of a substance from a liquid to
a gas) of water from the leaves of a plant.
The water cycle (Diagram) - correct-answers-
The carbon cycle inputs/outputs/stores/transfers - correct-answers-Inputs - carbon
dioxide added to the atmosphere by human activities.
Outputs - dissolved carbon carried from the land in solution by rivers.
Stores - marine sediments and sedimentary rocks, oceans, fossil fuel deposits, soil
organic matter, atmosphere, terrestrial plants,
Transfers - photosynthesis, respiration, combustion, decomposition, diffusion,
weathering and erosion, burial and compaction, carbon sequestration,
The carbon cycle (Diagram) - correct-answers-
The global carbon cycle - Principal carbon stores - correct-answers--Atmosphere: 600
(billion tons of carbon in store)
-Oceans: 38,700 (billion tons of carbon in store)
, -Sedimentary (carbonate) rocks: 60,000-100,000,000 (billion tons of carbon in store)
-Sea floors sediments 6,000 (billion tons of carbon in store)
-Fossil fuels: 4,130 (billion tons of carbon in store)
-Land plants: 560 (billion tons of carbon in store)
-Soils/peat: 2,300 (billion tons of carbon in store)
Satellite image of global water vapor (mm) - correct-answers-
The slow carbon cycle - correct-answers-Through a series of chemical reactions and
tectonic activity, carbon takes between 100-200 million years to move between rocks,
soil, ocean, and atmosphere.
(Transfers of carbon compounds over extensive timescales (possibly millions of years).)
Page 101.
The fast carbon cycle - correct-answers-Capture of atmospheric carbon dioxide by
plants to create glucose and other sugars, which fuels the ecosystem. As these sugars
are used in cellular respiration, carbon dioxide is produced.
(Relatively rapid transfers of carbon compounds over years, decades and centuries.)
Page 101.
The processes of the water cycle - correct-answers--The water balance
-Flows
-Catchment hydrology
The water balance (The processes of the water cycle) - correct-answers-The water
balance equation summarizes the flows of water in a drainage basin over time. It states
that precipitation is equal to evapotranspiration and streamflow, plus or minus water
entering or leaving storage: P = R + ET + ΔS
Where P is precipitation, R is streamflow, ET is evapotranspiration, ΔS is the change in
storage (in soil or the bedrock / groundwater)
Where Δ - correct-answers-Uppercase delta (Δ) at most times means "change" or "the
change" in math’s. Consider an example, in which a variable x stands for the movement
of an object.
So, "Ax" means "the change in movement." Scientists make use of this mathematical
meaning of delta in various branches of science.
The drainage basin water cycle - correct-answers-
Flows (The processes of the water cycle) - correct-answers--Precipitation
-Transpiration
-Condensation (Cumuliform clouds, Stratiform, Wispy, cirrus clouds, Lapse rates, Cloud
formations and lapse rates)
Flows definition (The processes of the water cycle) - correct-answers-The principal
flows in the water cycle that link the various stores are: precipitation, evaporation,
transpiration, run-off, infiltration, percolation and throughflow.
Precipitation (Flows (The processes of the water cycle)) - correct-answers-Precipitation
is water and ice that falls from clouds towards the ground. It takes several forms: most
commonly rain and snow, but also hail, sleet and drizzle.
Precipitation forms when vapor in the atmosphere cools to its dew point and condenses
into tiny water droplets or ice particles to form clouds. Eventually these droplets or ice
particles aggregate, reach a critical size and leave the cloud as precipitation.
Dew point - correct-answers- (Condensation begins) The temperature at which the
water vapor in the air becomes saturated.
Transpiration (Flows (The processes of the water cycle)) - correct-answers-
Transpiration is the diffusion of water vapor to the atmosphere from the leaf pores
(stomata) of plants. It is responsible for around 10 per cent of moisture in the
atmosphere.
