Summary notes OCR A Level Geography Earth's life support systems
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Course
Earth Life and Support Systems
Institution
OCR
Book
OCR A Level Geography Second Edition
Highly detailed summary notes of OCR A Level geography's specification on earth's life support systems. Includes notes on all 4 subtopics: 4.1 How important are water and carbon to life on earth, 4.2 How do the water and carbon cycles operate at contrasting locations, 4.3 How much change occurs ove...
Summary notes OCR A Level Geography Coastal Landscapes
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Earth Life and Support Systems
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KQ1: How important are water & carbon to life on Earth
Importance of water
1. Humans: agriculture, health (drinking water), sanitation, industry
2. Flora & Fauna: for biomass & structure, photosynthesis
3. Climate: oceans as a store of carbon, stores of water also regulate temperatures
on earth
Importance of carbon
1. Humans: basis of almost all human activity e.g., provides 80% of global energy
2. Flora & Fauna: photosynthesis, release of carbon as part of respiration
3. Climate: regulates climate through natural greenhouse gas effect
Cycles as systems:
Closed
- Global scale = closed, driven by the sun’s energy not matter
Open
- Local scale = open, e.g., drainage basin or forest ecosystem so energy & matter
moves across system boundaries
Distribution & sizes of stores
Carbon stores
- Atmosphere = ~600 Gt (residence time 6 years)
- Terrestrial biomass = ~560 Gt (residence time 18 years)
- Oceans = surface ~700 Gt (25), deep ~38,00 (1250)
- Sedimentary rocks = 60-100 million Gt (residence time 150 million years)
Water stores
- Atmosphere = 13,000km3/ 0.0001%
- Ice & glaciers = 29,000/ 2%
- Land = 39,000km3
- Oceans = 1,370,00km3/ 97%
Inputs to the water cycle
- Precipitation
- Ablation (melting & sublimation)
- Evapotranspiration
Inputs to the carbon cycle
- Respiration
- Combustion
- Precipitation
- Photosynthesis
- Decomposition
- Weathering (chemical & physical processes breakdown rock releasing CO2)
Slow carbon cycle = processes & carbon storage over long geological timescales
E.g. chemical weathering- carbonation result of precipitation = weak acid attacking carbonate
minerals in rocks, releasing CO2 in the atmosphere
Long term store = intermediate & deep ocean, sedimentary rock, fossil fuels
Fast carbon cycle = processes & carbon storage over short geological timescales
E.g. carbon exchange between the atmosphere & vegetation
Short term store = permafrost, surface ocean, terrestrial ecosystem, atmosphere
, Processes (link various stores)
Water cycle
- Precipitation (movement of surface & soil water into underlying impermeable rock)
- Evapotranspiration
- Run-off
- Infiltration
- Percolation
- Throughflow (water flowing horizontally through the soil to the stream & river channel)
KQ2: How do the water & carbon cycles operate in contrasting locations
Case study of a tropical rainforest (Amazon)
Water cycle (flows & stores)
Temperature
- 25-30 degrees (due to intense insolation throughout the year)
Precipitation
- High average rainfall >2000mm with no dry season
- 50-60% of precipitation is recycled back into the atmosphere by evapotranspiration
(convectional rainfall- ground heated up in the morning by intense solar radiation)
- 10% of precipitation is intercepted by forest trees
(due to abundance of vegetation- forest trees)
Evapotranspiration
- High due to hot temperatures, moisture & vegetation
- Feedback loops-> sustain high precipitation
- Hence ~50%-60% of rainfall is returned to the atmosphere via evapotranspiration
Run-off
- River discharge may peak depending on seasonal variation of rainfall
Atmosphere
- Store large amounts of moisture due to high temps-> high absolute & relative
humidity
Physical factors affecting stores & flows of water
1. Geology: large parts of Amazon basin are an ancient shield area comprising of
impermeable, crystalline rocks (igneous & metamorphic) with minimal storage
capacity-> high rapid run-off
2. Relief: mainly lowlands, gentle relief = water moves across surface (throughflow)
to streams & rivers
3. Temperature: high temperatures = high rates of evapotranspiration
Human factors affecting stores & flows of water
1. Deforestation: est 1970 ⅕ of primary forest destroyed-> reducing water storage in
forest trees, soils (eroded) & permeable rocks (due to more rapid run off). In terms
of flows less evapotranspiration & thus precipitation
Significance- huge on water cycle & may change climate at local & regional
scales converting rainforest to grassland-> increases run-off by a factor of 27
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