EARTH’S LIFE
SUPPORT SYSTEMS
, TOPIC ONE - HOW IMPORTANT ARE WATER AND CARBON TO LIFE ON EARTH
TOPIC ONE A - THE CARBON CYCLE
IMPORTANCE OF CARBON
● Carbon dioxide in the atmosphere traps heat close to the earth, thus regulating global temperatures
● Plants require carbon for photosynthesis
- These plants can then be used for food and biofuel production for humans
● Carbon stored in ocean water is taken up by marine organisms such as coral and shellfish to form shells and
skeletons
● Carbon in the form of hydrocarbons can sometimes be used as fuel
- For example crude oil (petroleum), which is distilled in refineries to produce gasoline, kerosene, and
other products. This is then burned as fuel
- Coal is also made from carbon
● Materials such as wool, cashmere, and silk are made from carbon polymers. Plastic is made from synthetic carbon
polymers
● Carbon is a key component in wood, which is used in construction and paper making, as well as being burned for
heat and energy
● Carbon forms complex molecules in animals (including humans) such as DNA and proteins, making life on earth
possible
STORES IN THE CARBON CYCLE
● Atmosphere (3150 gigatonnes)
● Ocean water (38,700 gigatonnes)
● Biosphere (560 gigatonnes)
● Peat and soils (2300 gigatonnes)
● Sedimentary rock and deep ocean sediments (60,000 - 100,000,000 gigatonnes)
● Fossil fuels (4130 gigatonnes)
PROCESSES IN THE FAST CARBON CYCLE
Photosynthesis
- Light energy is used to react carbon dioxide and water into glucose and oxygen
- Carbon is stored in plants for a long time
- Around 610PgC of carbon is stored in plants
- Photosynthesis removes 120PgC/year of carbon from the atmosphere
Decomposition
- Living organisms begin to decompose shortly after death because of the bacteria and fungi feeding on them
- When these bacteria and fungi respire, carbon dioxide is released into the atmosphere
Respiration
- Removes oxygen from the atmosphere
- Plant respiration represents half of carbon return to the atmosphere (60PgC/year)
Combustion
- Gaseous fuel is oxidised, creating carbon dioxide, water, other chemicals, and heat
- Can be a natural process or caused by humans
PROCESSES IN THE SLOW CARBON CYCLE
Weathering
Chemical weathering (carbonation)
- Rainwater is a weak carbonic acid which slowly dissolves limestone and chalk to produce calcium carbonate
- CaCO3 + H2CO6 = Ca(HCO3)2
- Carbon is released into streams, rivers, oceans and the atmosphere
- The process is most effective beneath a soil cover because the higher concentration of carbon dioxide in the soil
makes rainwater highly acidic
- Transfers 0.3 billion tonnes of carbon to the atmosphere each year
Biological weathering
, - Rainwater mixed with dead or decaying organic material in the soil forms humic acids which attack rock material
- This process is important in humid tropical environments where decomposition is rapid and forest trees provide
abundant leaf litter
Carbon sequestration
The process of capturing and storing atmospheric carbon dioxide in other stores
Biological (organic) pump
Sequesters 50 gigatonnes of carbon dioxide every year
1) Diffusion - carbon dioxide in the atmosphere is absorbed by the ocean and dissolves in the surface ocean
2) Microscopic organisms in the surface of the ocean (phytoplankton) use this dissolved carbon dioxide for food and
to build their structures
- Phytoplankton turn the dissolved carbon dioxide into organic carbon compounds
3) Phytoplankton are part of a food chain. The carbon that is stored in their shells and structures is absorbed by
other parts of the food chain - Carbon in these compounds are passed down the food chain
- These living creatures in the ocean will also respire and release some carbon dioxide back into the
ocean
4) These living creatures in the food chain will eventually die. When this happens, the carbon that is locked away in
them will sink to the bottom of the ocean and over thousands of millions of years will accumulate as carbon rich
remains which turn into sediments at the bottom of the ocean
- As they sink, bacteria will decompose the organisms. This releases carbon dioxide into the deep ocean
as it sinks
Physical (inorganic) pump
1) Carbon dioxide is absorbed by the surface waters
2) Currents transfer the water towards the poles, where it cools
3) The water with dissolved carbon dioxide becomes denser and sinks because it cools down
4) Downwelling occurs in only a few locations
- North Atlantic between Greenland and Iceland
5) The carbon will remain at great depths for hundreds of years
6) Eventually the bottom water is carried up (upwelling)
7) The carbon dioxide diffuses back into the atmosphere
How vegetation sequesters carbon
Trees use photosynthesis to absorb carbon from the atmosphere
This carbon will be stored in the leaves, stems, trunk, and roots of the trees
- Carbon is converted from a gas to an organic compound
Some of this carbon is released through respiration
When the trees die, they decompose as carbon is released into the soil
Burial and compaction
Corals and shelled organisms take up carbon dioxide from sea water and convert it into calcium carbonate to form shells
and skeletons
When these marine organisms die, their shells accumulate on the seafloor
Some carbonate dissolves, producing carbon dioxide
The rest becomes compacted to form limestone
, TOPIC ONE B - THE WATER CYCLE
IMPORTANCE OF WATER
● Water is the medium for many chemical reactions to take place in the body
● Essential for the survival of plants and animals
- Water is essential for photosynthesis, respiration, and transpiration in plants
- Water is used for drinking in humans. It also brings nutrients to cells, flushes out waste from the body,
and regulates body temperature
● Water helps control global temperatures. In the atmosphere clouds (water vapour) reflect around 20% of
incoming short-wave radiation from the Sun back out to space. Water vapour is also a greenhouse gas. It absorbs
reflected long wave radiation
- Without this, the average global temperature would be almost 15 degrees colder than it is today
● Oceans moderate temperatures by absorbing heat and releasing it slowly
- For example, without warm currents originating from the Gulf of Mexico, the UK would be significantly
colder than it is
● Water is vital in a large number of economic activities such as power generation, manufacturing, and agriculture
- Water can be used to produce power (hydroelectric power)
- Water is used in the irrigation of agriculture
STORES IN THE WATER CYCLE
Ocean - 97.25%
Atmosphere - 0.001%
Lakes - 0.01%
Groundwater (aquifers) - 0.68%
Soil moisture - 0.005%
Ice caps and glaciers - 2.05%
TRANSFERS IN THE WATER CYCLE
Evapotranspiration
- Water evaporates (goes from liquid to gas). Water vapour enters the atmosphere
- Transpiration is the movement of water from the plant to the atmosphere
- Influenced by temperature, windspeed, water availability and vegetation type
Condensation
- Water vapour condenses to form water droplets
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, the droplets aggregate, reach a critical size, and leave the clouds
- Rain, snow, sleet, hail
Through flow
- Water travelling through the ground
- Movement of water laterally through soil store
Percolation
- The vertical movement of water down through bedrock
Surface runoff
Infiltration
- Movement of water vertically downwards through soil
Interception
- Intercepted rainfall is stored temporarily on branches, leaves and stems
- Throughfall - rainfall is briefly intercepted before dripping to the ground
- Stem flow - during periods of intense or prolonged rainfall, intercepted rainfall may flow to the ground along
branches and stems
