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Earth's life support systems detailed notes for OCR A-level geography paper 1 and a whole essay on carbon capture store
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EARTH’S LIFE SUPPORT SYSTEMSImportance of water
To moderate temperature
● Water helps to create thermal conditions on earth. E.g oceans occupy 70% of Earth’s surface & they
moderate temp by absorbing heat, storing it & releasing it slowly
● Clouds made up of tiny water droplets & ice crystals reflect around ⅕ of incoming solar radiation &
lower surface temp
● Water vapour = potent GHG -> absorbs long wave radiation from Earth helping to maintain avg global
temp almost 15℃ higher than they would be otherwise
Its importance for flora, fauna & people
● Water makes up 65-95% of all living organisms = growth, reproduction, metabolic functions, etc
● Plants which manufacture their own food need water for photosynthesis, respiration & transpiration
● Plants also require water to maintain their rigidity [plants wilt when they run out of water] & to transport
mineral nutrients from soil
● In people & animals water is the medium used for all chemical reactions in the body including the
circulation of O2 & nutrients
● Sweating = cooling process in humans whereas in fur covered mammals pant
● Water is also essential resource for economic activity as it’s used to generate electricity, irrigate crops,
provide recreational facilities & satisfy public demand [drinking water, sewage disposal] as well as in a
huge range of industries - food manufacturing, brewing, paper making & steel making
Importance of carbon to life on Earth
➔ Carbon is stored in carbonate rocks e.g limestone, sea floor sediments, ocean water, atmosphere &
biosphere. Life is carbon based = build on large molecules of carbon atoms e.g proteins, carbohydrates
➔ Carbon is used as an economic resource - fossil fuels power the global economy. Oil is also used as a
raw material in the manufacture of products e.g plastics, paints, synthetic fabrics.
➔ Agricultural crops & forests trees also store large amounts of carbon available for human use as food,
timber, paper, etc
THE WATER & CARBON CYCLES
★ At the global scale, water & carbon flow = closed systems
★ At the macro-scale, the global water cycle consists of 3 main stores = atmosphere, ocean & land. The
oceans are by far the biggest store & atmosphere is the smallest
★ Water moves between stores through precipitation, evapotranspiration, run-off & groundwater flow
★ Global carbon cycle = long term storage in sedimentary rocks holds 99.9% of all carbon on Earth
★ Flows- carbon cycle = photosynthesis, respiration, oxidation [decomposition, combustion] & weathering
THE WATER & CARBON CYCLES AS OPEN & CLOSED SYSTEMS
➔ SYSTEMS are groups of objects & the relationships that bind the objects together. On a global scale
the water & carbon cycles are CLOSED SYSTEMS driven by the sun’s energy [which is external to the
earth]. Only energy [& not matter] cross the boundaries of the global water & carbon cycle = closed
➔ St smaller scales e.g drainage basin or forest ecosystem, materials as well as the sun’s energy cross
system boundaries = OPEN SYSTEMS
FIGURES:
● clouds reflect & absorb 20% of insolation
● of the world's water, 97% is saline sea water
● Almost 80% of total freshwater is locked up in ice & glaciers
● 20% of freshwater is in the ground
● surface fresh water e.g lakes & rivers constitute only about 1/150 or 0.007% of 1% of total water
● oceans supply about 90% of the evaporated water that goes into the water cycle
● The atmosphere contains a very small store of water - 0.001% of Earth's total water
● Antarctica holds almost 90% of the global ice mass
, ● the Greenland ice cap contains only 10% of the total global ice mass
● surface fresh water [e.g glaciers, rivers, reservoirs, wetlands] represent about 3% of all water on Earth
● largest STORE of CARBON => Earth's crust = 100,000,000 pg/pictograms. Intermediate & deep ocean
= 37,000 pg. Fossil fuels [underground] = 10,000 pg
● smallest STORE of CARBON = plants = 600 pg [pictograms]
● largest TRANSFER of CARBON:
○ Photosynthesis = 120 pg/year
○ Decomposition = 60 pg/year
○ Plant respiration = 60 pg/year
○ Ocean loses = 90 pg/year
● smallest TRANSFER of CARBON = deforestation & land use change = 1 pg/year
● Forest fires release more carbon into the atmosphere than forests can capture
● [Afforestation] Forests are capable of sequestering up to 200 tonnes of carbon per hectare in a mature
forest in the UK. Forest soils are capable of holding more than twice this amount of carbon
INPUTS & OUTPUTS OF WATER
● Inputs of water to the atmosphere include water vapour evaporated from the oceans, soils, rivers &
vapour transpired through the leaves of plants. Together these processes are called evapotranspiration
● Moisture leaves the atmosphere as precipitation (i.e rain, snow, hail, etc.) & condensation (e.g. fog).
● Ice sheets, glaciers release water by ablation (melting & sublimation).
● Precipitation & meltwater drain from the land surface as run-off into rivers. Most rivers flow to the
oceans. Large part of water falling as precipitation on land reaches rivers only after infiltrating & flowing
through the soil
● After infiltrating the soil, water under gravity may percolate into permeable rocks or aquifers. This
groundwater eventually reaches the surface as springs or seepages & contributes to run-off
THE GLOBAL CARBON CYCLE
➢ global carbon cycle principal stores: atmosphere, oceans, carbonate rocks, fossil fuels, plants & soils
➢ Carbonate rocks e.g limestone & chalk & deep-ocean sediments are the biggest carbon store. Most of
the carbon that isn’t stored in rocks & sediments is found in the oceans as dissolved CO2
➢ Carbon storage in the atmosphere, plants & soils is relatively small.
THE SLOW CARBON CYCLE
● Carbon stored in rocks, sea-floor sediments & fossil fuels is locked away for millions of years
● CO2 diffuses from the atmosphere into the oceans where marine organisms e.g clams & corals make
their shells & skeletons by fixing dissolved carbon together with calcium to form calcium carbonate. On
death, the remains of these organisms sink to the ocean floor. There they accumulate and over millions
of years, heat & pressure convert them to carbon-rich sedimentary rocks
● Typical residence times for carbon held in rocks are around 150 million years
● Some carbon-rich sedimentary rocks, subducted into the upper mantle at tectonic plate boundaries, are
vented to the atmosphere in volcanic eruptions. Others exposed at or near the surface by erosion &
tectonic movements are attacked by chemical weathering
● Chemical weathering processes e.g carbonation are the result of precipitation charged with CO2 from
the atmosphere, which forms a weak acid. The acid attacks carbonate minerals in rocks, releasing CO2
to the atmosphere & in dissolved form to rivers & oceans
● On land, partly decomposed organic material may be buried beneath younger sediments to form
carbonaceous rocks e.g coal, lignite, oil and natural gas. Like deep-ocean sediments, these fossil fuels
act as carbon sinks that endure for millions of years.
THE FAST CARBON CYCLE
, ● Carbon circulates most rapidly between the atmosphere, the oceans, living organisms (biosphere) and
soils. These transfers are between 10-1000x faster than the slow carbon cycle = plants &
phytoplankton in the oceans are the key components of the fast cycle. Through photosynthesis they
absorb CO2 from the atmosphere and combine it with water to make carbohydrates (sugars/glucose).
Photosynthesis is a fundamental process & the foundation of the food chain.
● Respiration by plants & animals results in the release of CO2. Decomposition of dead organic material
by microbial activity also returns CO2 to the atmosphere.
● In the fast cycle, carbon exchange also occurs between the atmosphere & the oceans. Atmospheric
CO2 dissolves in ocean surface waters while the oceans ventilate CO2 back to the atmosphere
THE PROCESSES OF THE WATER CYCLE
WATER BALANCE EQUATION:
Precipitation (P) = Evapotranspiration (E) + Streamflow (Q) ± Storage
The principle flows in the water cycle that link various stores: precipitation, evaporation, transpiration, run-off,
infiltration, percolation & throughflow
Precipitation
● Precipitation forms when vapour in the atmosphere cools to its dew point & 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
● Precipitation also varies in character & this impacts the water cycle at the drainage basin scale.
○ Most rain on reaching the ground flows quickly into streams & rivers. But in high latitudes &
mountainous catchments, precipitation often falls as snow & may remain on the ground for
several months. Thus there may be a considerable time lag between snowfall & run-off
○ Intensity is the amount of precipitation falling in a given time. High-intensity precipitation moves
rapidly overland into rivers
○ Duration = length of time that precipitation event lasts. Prolonged events, linked to depressions
& frontal systems, may deposit exceptional amounts of precipitation & cause river flooding
○ In some parts of the world precipitation is concentrated in a rainy season. During this season
river discharge is high & flooding is common. In the dry season rivers may cease to flow
TRANSPIRATION: Transpiration is influenced by temperature & wind speed. It is also influenced by water
availability to plants. E.g deciduous trees shed their leaves in climates with either dry or cold seasons to
reduce moisture loss through transpiration.
CONDENSATION:
● Condensation is the phase change of vapour to liquid water
● It occurs when air is cooled to its dew point. At this critical temp air becomes saturated with vapour
resulting in condensation. Clouds form through condensation in the atmosphere.
● Cumuliform clouds, with flat bases 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) & cool. As cooling reaches the dew point, condensation begins
& clouds form.
● Stratiform or layer clouds develop where an air mass moves horizontally across a cooler surface (often
ocean). This process is known as advection.
● Cirrus clouds, formed at high altitude, consist of tiny ice crystals. They don’t produce precipitation so
have little influence on the water cycle.
Condensation at or near the ground produces dew & fog. These deposit large amounts of moisture on
vegetation & other surfaces
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