Earth's Life Support Systems

• Water


  Key to the evolution of life on Earth as it provides a medium that allows organic molecules to mix and form more complex structures
• The Earth Lies in the "Goldilocks zone" such a distance from the sun that is just right for water to exist in liquid form
• Although water ice exists on Mars, there is evidence that very small amounts of liquid water flow on the surface
• Scientists believe finding water in liquid form greatly increases the chances of finding life
• Oceans occupy 71% of the Earth's surface
• Oceans

  • Moderate temperatures by absorbing heat, storing it and releasing it slowly
• Clouds

  • Made up of tiny water droplets and ice crystals, reflect 1/5th of incoming solar radiation, so lowering surface temperatures
• Water vapour

  • A greenhouse gas, absorbs long wave radiation from the Earth, helping keep temperatures 15 degrees higher
• Water accounts for 65-95% of all living organisms and is crucial for their growth, reproduction, and other metabolic functions
• Plants

  • Need water for photosynthesis, respiration and transpiration
  • Require water to maintain their rigidity and stop them wilting and to transport mineral nutrients from the soil
• Water is essential for economic activity


  • Generate electricity
  • Irrigate crops
  • Recreational facilities
  • Satisfy public demand
  • Industries
• Main inputs and outputs of the water cycle -

  • Precipitation: Water and ice that falls from the clouds to the ground. When water vapour in the atmosphere cools to dew point and condenses... it changes state to liquid water droplets.. these droplets/ice aggregate together until they reach a critical size... then they fall from the cloud as precipitation - Collision Theory/Bergeron Findeison Theories. Precipitation varies in type depending on the latitude in terms of in tensity and duration. In some places there is a concentrated wet season.
• Main inputs and outputs of the water cycle -

  • Snowmelt/Ablation: Loss of ice due to melting, evaporation and sublimation. Globally, runoff from snowmelt is a major component of the global movement of water, particularly in colder climates where there is a spring snowmelt. Up to 75% of water in Western USA comes from snowmelt.
• Water cycle


  1. Evapotranspiration

  2. Evaporation

  3. Transpiration
• Evapotranspiration


  Evaporation, liquid water turning into water vapour. The main pathway by which water enters the atmosphere.
• Evapotranspiration


  • Heat is needed to break the molecular bonds
  • Heat is released as latent heat during condensation
  • Allows huge quantities of heat to transfer around the planet
• Transpiration


  Diffusion of water vapour into the atmosphere from leaf stomata - responsible for 10% of moisture in the atmosphere
• Transpiration


  • Influenced by temperature, wind speed and the amount of water available to the plants
  • Deciduous trees shed their leaves in the winter to reduce water loss
• CO2 in the atmosphere gets absrob by plants via photosynthesis, animals - methane. Plants and animals decompose and turn into fossil fuels, then combustion happens in which pollution causes CO2 to return to the atmposhere, in which CO2 diffuses into the oceans, then via sedimantation CO2 gets stored in limestone + shells.
• Major stores in the carbon system


  • Carbonate rocks such as limestone and chalk, as well as deep ocean sediment
  • Oceans
  • Atmosphere
  • Living and dead organic matter above and below the ground
• Biggest store


  Carbonate rocks such as limestone and chalk, as well as deep ocean sediment
• Carbon absorption in oceans


  1. Cold polar winds absorb most CO2 from the air (diffusion)

  2. Warm equatorial waters have a slow diffusion rate

  3. Ocean currents carry the CO2 - upwelling at the equator and downwelling at the poles
• Atmosphere


  A relatively small store of carbon BUT it is crucial and represents most of the carbon in circulation at any one time
• In the northern hemisphere the highest concentrations are focussed around the major emission sources - North America, Europe - but are dispersed by the winds
• Spring and summer vegetation/leaf growth


  Absorbs large quantities of carbon from the atmosphere in the northern hemisphere via photosynthesis
• In the winter when the leaves have fallen

  The quantity of carbon in the atmosphere increases
• In the southern hemisphere large fluxes enter the atmosphere where there are forest fires
• Land carbon stores


  • Living and dead organic matter above and below the ground
  • Tropical and boreal forests - 86% of the world's above ground carbon
  • Deserts and the tundra are poor stores of carbon
• Carbon cycle


  1. Precipitation

  2. Decomposition

  3. Respiration

  4. Combustion

  5. Weathering
• Precipitation


  Atmospheric CO2 dissolves in rain, forming weak carbonic acid (naturally). Increases in anthropogenic emissions are making rainfall more acidic, which in turn makes the oceans more acidic and is harmful to marine life.
• Decomposition


  Decomposer organisms break down dead organic matter, extracting energy and releasing CO2 into the atmosphere and minerals into the soil. Rates of decomposition depend on the climate - faster when it is warm and humid and slower when it is cold and dry.
• Respiration


  The reverse of photosynthesis. Carbon flows rapidly in and out of the atmosphere via photosynthesis and respiration.
• Combustion


  When organic matter burns in the presence of oxygen, it releases CO2. Occurs naturally via wildfires. Fossil fuels are burnt for energy - carbon is released from the geological store into the atmosphere, then making its way into the oceans.
• Weathering


  The in-situ breakdown of rocks at the earth's surface. Rain contains dissolved CO2 - weak carbonic acid. Carbonation slowly dissolves limestone and chalk and releases carbon into streams, rivers and the ocean, then the atmosphere. Weathering is most effective beneath soil cover as the CO2 in soil adds to the acidity. Chemical weathering transfers 0.3 billion tonnes of carbon into the atmosphere and oceans per year.
• Water cycle specific to TRF

  • Rates of low and distinct stores
  • High temperatures 25-30 degrees allow large amounts of moisture to be stored
  • Absolute and relative humidity are high
  • Strong evapotranspiration - precipitation feedback loop with half of incoming rainfall returned to the atmosphere
  • High average annual precipitation throughout the year
  • High intensity, convectional rainfall
  • High interception and evaporation
  • Rapid runoff related to intense rainfall and well drained soils
  • Significant storage of water in deep soils and aquifers
  • Water losses out of the drainage basin = river flow and clouds blown out of the region
  • Inward flux of moisture blown in from the Atlantic
• Water cycle in TRF


  1. Heavy daily, convectional rainfall

  2. Trees intercept some of the rain

  3. Some rain reaches the ground

  4. Trees take up water from the soil

  5. Water evaporates

  6. Back to the start
• Carbon cycle in Tropical Rainforests (TRF)

  • Rates of carbon stores are low and distinct
• Carbon stored in large forest trees

  • 180 tonnes per hectare above ground
  • 40 tonnes in roots
• Carbon stored in rainforest soils

  90-200 tonnes per hectare
• Compared to other forests

  Exchanges between atmosphere, biosphere and soil are rapid