4.1 How important are water and carbon to life on Earth?

Question 1

4.1 How important are water and carbon to life on Earth?

Answer 1

Key idea ➡ Water and carbon support life on Earth and move between the land, oceans and atmosphere.

Question 2

The importance of water in supporting life on the planet

Answer 2

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 ti 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).

Question 3

Distance of Earth from the Sun

Answer 3

149.89 million km, 93.14 million miles

Question 4

Water and the creation of benign thermal conditions

Answer 4

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 vapour, 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.

Question 5

The uses of water for flora, fauna and people

Answer 5

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.

Question 6

Flora

Answer 6

Plant life

Question 7

Fauna

Answer 7

Animal life

Question 8

Photosynthesis (The uses of water for flora, fauna and people)

Answer 8

Plants, which manufacture their own food, need water for photosynthesis, respiration and transpiration. Photosynthesis takes place in the leaves of plants combining CO₂ 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 CO₂ 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.

Question 9

Economic activity (The uses of water for flora, fauna and people)

Answer 9

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.

Question 10

The importance of carbon to life on Earth

Answer 10

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.

Question 11

Carbon sinks

Answer 11

A forest, ocean, or other natural environment viewed in terms of its ability to absorb carbon dioxide from the atmosphere.

Question 12

Biosphere

Answer 12

Consists of all life on Earth and all parts of the Earth in which life exists, including land, water, and the atmosphere.

Question 13

The water and carbon cycle

Answer 13

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.

Question 14

The water cycle inputs/outputs/stores/transfers

Answer 14

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.

Question 15

Evapotranspiration

Answer 15

The combined amount of evaporation of water from soil and transpiration of water from plants. Correlates with species richness.

Question 16

Evaporation

Answer 16

The change of a substance from a liquid to a gas, particularly in soil.

Question 17

Transpiration

Answer 17

Evaporation (the change of a substance from a liquid to a gas) of water from the leaves of a plant.

Question 18

The carbon cycle inputs/outputs/stores/transfers

Answer 18

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,

Question 19

The global carbon cycle - Principal carbon stores

Answer 19

Atmosphere: 600 (billion tonnes of carbon in store)
-Oceans: 38,700 (billion tonnes of carbon in store)
-Sedimentary (carbonate) rocks: 60,000-100,000,000 (billion tonnes of carbon in store)
-Sea floors sediments 6,000 (billion tonnes of carbon in store)
-Fossil fuels: 4,130 (billion tonnes of carbon in store)
-Land plants: 560 (billion tonnes of carbon in store)
-Soils/peat: 2,300 (billion tonnes of carbon in store)

Question 20

The slow carbon cycle

Answer 20

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.

Question 21

The fast carbon cycle

Answer 21

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.

Question 22

The processes of the water cycle

Answer 22

-The water balance
-Flows
-Catchment hydrology

Question 23

The water balance (The processes of the water cycle)

Answer 23

`The water balance equation summarises 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)

Question 24

Where Δ

Answer 24

Uppercase delta (Δ) at most times means “change” or “the change” in maths. Consider an example, in which a variable x stands for the movement of an object.
So, “Δx” means “the change in movement.” Scientists make use of this mathematical meaning of delta in various branches of science.

Question 25

Flows (The processes of the water cycle)

Answer 25

-Precipitation -Transpiration -Condensation (Cumuliform clouds, Stratiform, Wispy, cirrus clouds, Lapse rates, Cloud formations and lapse rates)

Question 26

Flows definition (The processes of the water cycle)

Answer 26

The principal flows in the water cycle that link the various stores are: precipitation, evaporation, transpiration, run-off, infiltration, percolation and throughflow.

Question 27

Precipitation (Flows (The processes of the water cycle))

Answer 27

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 vapour 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.

Question 28

Dew point

Answer 28

(Condensation begins) The temperature at which the water vapour in the air becomes saturated.

Question 29

Transpiration (Flows (The processes of the water cycle))

Answer 29

Transpiration is the diffusion of water vapour to the atmosphere from the leaf pores (stomata) of plants. It is responsible for around 10 per cent of moisture in the atmosphere. Like evaporation, transpiration is influenced by temperature and wind speed. It is also influenced by water availability to plants.

Question 30

Transpiration example (Flows (The processes of the water cycle))

Answer 30

Deciduous trees shed their leaves in climates with either dry or cold seasons to reduce moisture loss through transpiration.

Question 31

Condensation (Flows (The processes of the water cycle))

Answer 31

-Cumuliform clouds -Stratiform -Wispy, cirrus clouds -Lapse rates -Cloud formations and lapse rates

Question 32

Condensation definition (Flows (The processes of the water cycle))

Answer 32

Condensation is the phase change of vapour to liquid water. It occurs when air is cooled to its dew point. At this critical temperature air becomes saturated with vapour resulting in condensation. Clouds form through condensation in the atmosphere.

Question 33

Condensation at or near the ground (Flows (The processes of the water cycle))

Answer 33

Condensation at or near the ground produces dew and fog. Both types of condensation deposit large amounts of moisture on vegetation and other surfaces.

Question 34

Dew

Answer 34

Tiny drops of water that form on cool surfaces at night, when atmospheric vapor condenses.

Question 35

Cumuliform clouds (Condensation (Flows (The processes of the water cycle)))

Answer 35

Cumuliform clouds, with flat bases and considerable vertical development most often form when air is heated locally through contact with the Earth's surface. This causes heated air parcels to rise freely through the atmosphere (convection), expand (due to the fall in pressure with altitude) and cool. As cooling reaches the dew point, condensation begins and clouds form.

Question 36

Wispy, cirrus clouds (Condensation (Flows (The processes of the water cycle)))

Answer 36

Wispy, cirrus clouds, which form at high altitude, consist of tiny ice crystals. Unlike cumuliform and stratiform clouds they do not produce precipitation and therefore have little influence on the water cycle.

Question 37

Stratiform (Condensation (Flows (The processes of the water cycle)))

Answer 37

Stratiform or layer clouds develop where an air mass moves horizontally across a cooler surface (often the ocean). This process, together with some mixing and turbulence, is known as advection.

Question 38

Lapse rates (Condensation (Flows (The processes of the water cycle)))

Answer 38

-Environmental lapse rate (ELR): The ELR is the vertical temperature profile of the lower atmosphere at any given time. On average the temperature falls by 6.5°C for every kilometre of height gained. -Dry adiabatic lapse rate (DALR): The DALR is the rate at which a parcel of dry air (I.e. less than 100 per cent humidity so that condensation is not taking place) cools. Cooling, caused by adiabatic expansion, is approximately 10°C/km. -Saturated adiabatic lapse rate (SALR): The SALR is the rate at which a saturated parcel of air (i.e. one in which condensation is occurring) cools as it rises through the atmosphere. Because condensation releases latent heat, the SALR, at around 7°C/km, is lower than the DALR.

Question 39

Cloud formations and lapse rates (Condensation (Flows (The processes of the water cycle)))

Answer 39

Clouds are visible aggregates of water or ice or both that float in the free air. We have seen that they form when water vapour is cooled to its dew point. Cooling occurs when: -Air warmed by contact with the ground or sea surface, rises freely through the atmosphere. As the air rises and pressure falls it cools by expansion (adiabatic expansion). This vertical movement of air is known as convection. -Air masses move horizontally across a relatively cooler surface a process known as advection. -Air masses rise as they cross a mountain barrier or as turbulence forces their ascent. a relatively warm air mass mixes with a cooler one.

Question 40

Adiabatic expansion

Answer 40

The expansion of a parcel of air due to a decrease in pressure. Expansion causes cooling.

Question 41

Atmospheric instability

Answer 41

-Lighter, warm or moist air is overlain by denser cold or dry air. -Some air sinks, some air rises. -Condition that promotes vertical motions.

Question 42

Catchment hydrology (The processes of the water cycle)

Answer 42

-Evaporation -Interception -Infiltration, throughflow, groundwater flow and run-off -Cryospheric processes

Question 43

Evaporation (Catchment hydrology (The processes of the water cycle))

Answer 43

Evaporation is the phase change of liquid water to vapour and is the main pathway by which water enters the atmosphere. Heat is needed to bring about evaporation and break the molecular bonds of water. But this energy input does not produce a rise of temperature in the water. Instead the energy is absorbed as latent heat and released later in condensation. This process allows huge quantities of heat to be transferred around the planet: from the oceans to the continents; and from the tropics to the poles.

Question 44

Interception (Catchment hydrology (The processes of the water cycle))

Answer 44

Vegetation intercepts a proportion of precipitation, storing it temporarily on branches, leaves and stems. Eventually this moisture either evaporates (interception loss) or falls to the ground. Rainwater that is briefly intercepted before dripping to the ground is known as throughfall. During periods of prolonged or intense rainfall, intercepted rainwater may flow to the ground along branches and stems stemflow.

Question 45

Infiltration, throughflow, groundwater flow and run-off (Catchment hydrology (The processes of the water cycle))

Answer 45

Rain falling to the ground and not entering storage follows one of two flowpaths to streams and rivers. -Infiltration by gravity into the soil and lateral movement or throughflow to stream and river channels. -Overland flow across the ground surface either as a sheet or as trickles and rivulets to stream and river.

Question 46

Conflicting ideas about Infiltration, throughflow, groundwater flow and run-off (Catchment hydrology (The processes of the water cycle))

Answer 46

Two conflicting ideas explain the flowpaths followed by rainwater. One relates overland flow to the soil's infiltration capacity or the maximum rate it can absorb rain. Thus, it is argued that when rainfall intensity exceeds infiltration capacity overland flow occurs. The second idea states that rainfall, regardless of its intensity, always infiltrates the soil. Overland flow only occurs when soil becomes saturated and the water table rises to the surface. This process is known as saturated overland flow.

Question 47

Where soils are underlain by permeable rocks - Infiltration, throughflow, groundwater flow and run-off (Catchment hydrology (The processes of the water cycle))

Answer 47

Where soils are underlain by permeable rocks, water seeps or percolates deep underground. This water then migrates slowly through the rock pores and joints as groundwater flow, eventually emerging at the surface as springs or seepages. Groundwater levels on the chalk in southern England follow a distinct seasonal pattern. By late October the water table is beginning to rise as temperatures and evapotranspiration fall. This recharge continues until late January. Groundwater levels then decline throughout the late winter, spring and summer, reaching their lowest point in early autumn.

Question 48

Cryospheric processes (Catchment hydrology (The processes of the water cycle))

Answer 48

Ablation is loss of ice from snow, ice sheets and glaciers due to a combination of melting, evaporation and sublimation. Meltwater is an important component of river flow in high latitudes and mountain catchments in spring and summer. Rapid thawing of snow in upland Britain in winter is a common cause of flooding in adjacent lowlands (e.g. Welsh uplands and the Lower Severn Valley, Pennines and the Vale of York).

Question 49

Sublimation

Answer 49

A change directly from the solid to the gaseous state without becoming liquid.

Question 50

The processes of the carbon cycle

Answer 50

-Carbon exchanges -Carbon sequestration in the ocean

Question 51

Carbon exchanges (The processes of the carbon cycle)

Answer 51

-Precipitation -Photosynthesis -Weathering -Respiration -Decomposition -Combustion

Question 52

Precipitation (Carbon exchanges (The processes of the carbon cycle))

Answer 52

Atmospheric CO₂, dissolves in rainwater to form weak carbonic acid. This is a natural process. However, rising concentrations of CO₂, in the atmosphere, due to anthropogenic emissions, have increased the acidity of rainfall. This has contributed to increased acidity of ocean surface waters with potentially harmful effects on marine life.

Question 53

Photosynthesis (Carbon exchanges (The processes of the carbon cycle))

Answer 53

The flux of carbon from the atmosphere to land plants and phytoplankton via photosynthesis averages around 120 gigatonnes (GT) a year. Using the Sun's energy, CO₂, from the atmosphere and water, green plants and marine phytoplankton convert light energy to chemical energy (glucose) through the process of photosynthesis. 6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂ (Carbon dioxide + water + energy from light produces glucose and oxygen) Plants use energy in the form of glucose to maintain growth, reproduction and other life processes. In doing so they release CO₂ to the atmosphere in respiration.

Question 54

Weathering (Carbon exchanges (The processes of the carbon cycle))

Answer 54

Weathering is the in situ breakdown of rocks at or near the Earth's surface by chemical, physical and biological processes. Most weathering involves rainwater which contains dissolved CO₂, derived from the soil as well as the atmosphere. As we have seen, rainwater is a weak carbonic acid, which slowly dissolves limestone and chalk in a process known as carbonation. carbonation = CaCO₃ + H₂CO₃ → Ca(HCO₃)₂ (Calcium carbonate + carbonic acid produces calcium bicarbonate)

Question 55

Respiration (Carbon exchanges (The processes of the carbon cycle))

Answer 55

Respiration is the process in which carbohydrates (e.g. glucose) fixed in photosynthesis are converted to CO₂ and water. Respiration = C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Question 56

Respiration in Plants and Animals (Carbon exchanges (The processes of the carbon cycle))

Answer 56

Plants and animals absorb oxygen which 'burns' these carbohydrates and provides the energy needed for metabolism and growth. Respiration is the reverse of photosynthesis. Whereas photosynthesis absorbs CO₂ and emits oxygen, respiration absorbs oxygen and releases CO₂. Respiration and photosynthesis are the two most important processes in the fast carbon cycle. The volume of carbon exchanged by respiration and photosynthesis each year is one thousand times greater than that moving through the slow carbon cycle.

Question 57

Decomposition (Carbon exchanges (The processes of the carbon cycle))

Answer 57

Decomposer organisms such as bacteria and fungi breakdown dead organic matter, extracting energy and releasing CO₂, to the atmosphere and mineral nutrients to the soil. Rates of decomposition depend on climatic conditions. The fastest rates occur in warm, humid environments such as the tropical rainforest. In contrast, decomposition is slow in cold environments like the tundra or drylands such as tropical deserts.

Question 58

Combustion (Carbon exchanges (The processes of the carbon cycle))

Answer 58

Combustion occurs when organic material reacts or burns in the presence of oxygen. The combustion process releases CO₂ as well as other gases such as sulphur dioxide and nitrogen oxides. Combustion is a natural fuel use in many ecosystems. Wildfires caused by lightning strikes are essential to the health of some ecosystems such as the coniferous forests of the Rocky Mountains. Long, cold winters slow the decomposition of forest litter which builds up on the forest floor. Fire shifts this log jam, freeing carbon and nutrients previously inaccessible to forest trees. It also opens up the forest canopy, creating new habitats and increasing biodiversity.

Question 59

Combustion sources (Carbon exchanges (The processes of the carbon cycle))

Answer 59

Combustion also results from human activities such as the deliberate firing of forest and grassland in order to clear land for cultivation or improve the quality of grazing. More important is the combustion of fossil fuels. Despite international efforts to curb CO₂ emissions, oil, coal and natural gas power the global economy and their consumption continues to grow. Currently the burning of fossil fuels transfers nearly 10 GT of CO₂ a year from geological store to the atmosphere, oceans and biosphere.

Question 60

Carbon sequestration in the ocean (The processes of the carbon cycle)

Answer 60

-Physical (inorganic) pump -Biological (inorganic) pump -Vegetation

Question 61

Physical (inorganic) pump (Carbon sequestration in the ocean (The processes of the carbon cycle))

Answer 61

The physical carbon pump involves the mixing of surface and deep ocean waters by vertical currents, creating a more even distribution of carbon - both geographically and vertically - in the oceans. Initially CO₂ enters the oceans from the atmosphere by diffusion. Surface ocean currents then transport the water and its dissolved CO₂ polewards where it cools, becomes more dense and sinks.

Question 62

Downwelling - Physical (inorganic) pump (Carbon sequestration in the ocean (The processes of the carbon cycle))

Answer 62

Downwelling occurs in only a handful of places in the oceans. One of these places is in the North Atlantic between Greenland and Iceland. Downwelling carries dissolved carbon to the ocean depths where individual carbon molecules may remain for centuries. Eventually deep ocean currents transport the carbon to areas of upwelling. There cold, carbon-rich water rises to the surface and CO₂ diffuses back into the atmosphere.

Question 63

Downwelling

Answer 63

The downward movement of fluid, especially in the sea, the atmosphere, or deep in the earth.

Question 64

Biological (organic) pump (Carbon sequestration in the ocean (The processes of the carbon cycle))

Answer 64

Carbon is also exchanged between the oceans and atmosphere through the actions of marine organisms. Globally nearly half of all carbon fixation by photosynthesis takes place in the oceans. Around 50 GT of carbon is drawn from the atmosphere by the biological pump every year.

Question 65

Vegetation (Carbon sequestration in the ocean (The processes of the carbon cycle))

Answer 65

Land plants, especially trees in the rainforests and boreal forests, contain huge stores of carbon. Most of this carbon, extracted from atmospheric CO₂ through photosynthesis, is locked away for decades.