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Summary OCR A-Level Geography Earth Life Support Systems Revision Notes

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OCR A-Level Geography Earth Life Support Systems Revision Notes that helped me achieve an A at Alevel

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ELSS

How important are water and carbon to life on Earth?

Importance of water to life on the planet
- Oceans moderate temperatures by absorbing, storing and slowly releasing heat
- Clouds reflect around 20% of incoming solar radiation and lower surface temperatures
- Water vapour absorbs long-wave radiation from the Earth, maintaining global temperatures almost 15°C higher than they otherwise
would be
- Water is crucial to organisms’ growth/reproduction and metabolic functioning
- Water required for processes such as photosynthesis, respiration, transpiration
- Water is used for chemical reactions in the body for humans and animals
- Resource for agriculture/manufacture/domestic purposes

Carbon is the building block of life on Earth
- Carbon is chemical element with stores including rocks, atmosphere, oceans, sea floor sediments and biosphere
- Life is carbon-based – built on large molecules of carbon atoms such as proteins, carbohydrates and nucleic acids (95% of All Known
Compounds are carbon based).
- Due to store in fossils, it is used as an economic, electrical resource
- Agricultural crops and forest trees, which are used by humans in a variety of ways, also store Carbon

The water cycle:
 The water cycle is stored in solid, liquid and gas forms.
 97% of water is saline and stored in the oceans.
 Only 3% of water is freshwater and is mainly stored in the atmosphere and on land in aquifers and ice caps.
 Water is constantly cycling between stores. This is known as the global hydrological cycle. The hydrological cycle is a closed
system.

The carbon cycle:
 The carbon cycle is a closed system. There are inputs, outputs and transfers, but the amount of carbon remains the same across
the Earth.

The carbon and water cycles are systems with internal inputs, outputs and stores:

 Carbon stores are located in the atmosphere, biosphere, cryosphere, pedosphere, lithosphere, and hydrosphere.

The carbon cycle on land:
 Carbon cycle on land is dominated by photosynthesis.
 Carbon is stored in biomass, such as tropical and temperate forests.
 Carbon is transferred to the soil via decomposition.
 Bacteria action sends carbon (co2) Back into the atmosphere.
 Carbon is cycled rapidly by living organisms. This is known as the fast carbon cycle.
 Human impact on the carbon cycle is considerable due to vegetation clearing and agriculture. Also, the burning of fossil fuels.

The carbon cycle in the ocean:
 Carbon stored in the oceans as dissolved CO2 within the water is also absorbed by marine life through shells and skeletons.
 The input of carbon from the atmosphere is a result of the direct contact between the ocean and the air.
 Phytoplankton in surface waters absorb CO2 in photosynthesis.
 A carbon pump within the ocean occurs due to temperature changes and gravity. (Upwelling and downwelling).
 Human impacts on the ocean are only now being understood, But the warming of the earth has a considerable impact on the
oceans carbon cycle, With warmer oceans less able to take in carbon.

The atmospheric carbon cycle:
 Usually in the form of CO2 or CH4 (Methane). Methane has a 20 times increase in absorbing solar radiation, but only last for
12 years, whereas carbon lasts for 50 plus years.
 Acid rain (Carbonic acid) Erodes sedimentary rocks, further releasing carbon.
 Humans are impacting the carbon in the atmosphere due to increased combustion of fossil fuels.

, The fast carbon cycle:
The key processes in the carbon cycle include photosynthesis, respiration, digestion, decomposition and combustion.
Additionally, The absorption/ Transfer of carbon between the atmosphere in the ocean are the fast cycle.

The slow carbon cycle:
The slow carbon cycle is long term and can take 10s of thousands of years.
1. The transfer of carbon into the oceans from the atmosphere.
2. The deposition of carbon on the ocean floor via downwelling.
3. As sediment and carbon deposit, rock formation occurs, storing and trapping the carbon.
4. As tectonic activity occurs, eventually the plate will come to a collision margin. Either the plate will form new mountains or
be ejected in volcanic eruptions, causing carbon to be released into the atmosphere.

The characteristics of the water cycle
- Inputs and outputs of water make the water cycle budget. Evaporation from the oceans, soils,
lakes and rivers and transpiration from plants make up inputs of water to the atmosphere.
These processes are known as evapotranspiration.
- Moisture leaves the atmosphere as precipitation (rain, snow) and condensation. Water is
released from ice cover by ablation and sublimation.
- Run-off transfers water from the land surface into rivers which flow into the sea. Some
precipitation infiltrates the soil and becomes groundwater flow
- Some water may percolate deeper into rock stores (aquifers)


The processes of the water cycle and definitions of all key terms found on other sheets.
The Arctic Tundra Additional Info:

As temps well below freezing for most of year - water stored as ground ice in permafrost layers. During summer
top layer thaws - meltwater forms many pools and shallow lakes. Drainage is poor and water cannot infiltrate
frozen soil. Sub-zero temperatures prevent evapotranspiration. Humidity low all year round. Precipitation
sparse.

Permeability low due to permafrost and crystalline rocks that dominate arctic tundra geology. Due to
permeability of permafrost porosity and mineral composition of rocks has little influence on both cycles.

Ancient rock underlying tundra has been reduced to gently undulating plain due to millions of years of erosion
and weathering - minimal relief and glacial deposits impede drainage - contribute to water logging in summer
months.

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