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Habitable Earth

  • Earth is unique (at least within our solar system) in its ability to sustain complex life
  • What is needed for complex life?
    • Temperatures that permit liquid water
    • An oxygenated atmosphere

Water

  • Forms the basis of all life forms on earch
  • Can dissolve many substances more than most other liquids, enables key chemical reactions in cells
  • Allows cells to use nutrients, minerals, and chemicals in biological processes

Oxygen

  • Key factor in the habitability of planets
  • Essential for the existence of life on earth
  • Energy source: living organisms store energy in molecules (fat, sugars, etc), release energy when combined with oxygen
  • 21% of earths dry atmosphere
  • Almost completely absent in early earth
  • 3.5 billion years ago mostly nitrogen and carbon dioxide.
    • Only found in small concentrations
    • Reacted with other chemicals rapidly moving form the atmosphere
    • Cyanobacteria (first algae)
      • conducted photosynthesis
    • $C0_2$ levels in atmosphere gradually decreased and $O_2$ increased, allowing for life

System

  • A network of relationships, parts elements and or components that interact and influence one another through the exchange of energy, matter, and/or information
  • Functions together to act as a whole
    • Responds to inputs and outputs
  • Earth's system examples
    • Processes that change landscape (erosion, substrate movement)
    • Species interactions
    • Cycle Chemical interactions
  • Two General Types of Systems
    • Open System: some energy or material moves into or out of system
    • Closed System: no such movements occur, doesn't change any matter with its surroundings
  • Static System
    • Fixed condition
    • System stays in that condition
  • Dynamic Condition
    • Changes (over time), often continually

Stability or Steady State

  • Stable System
    • Condition that remains, unless disturbed
    • If disturbed it returns to the same condition and the cause of disturbance stops
  • Steady state is not attained or maintained for a very long time

Basic System Concepts

  • Dynamic Equilibrium
    • The steady state that all natural systems move towards without the influence of people
    • Seldom attained or maintained for long
  • Linear Flow
    • if you add the same amount of anything to a compartment in a system, the change will always be the same
    • if you add salt to a glass of water the salinity will increase linearly
  • Non Linear Flow
    • The effect of adding a specific amount of something changes depending on how much has been added before
    • If you add 10 wolves to a forest, the amount of deer that they will eat will depend on the number of wolves already present in the forest
  • Lag Time
    • The delay between a cause and the appearance of its effect
  • Average Residence Time
    • How long on average a quantity will remain in a reservoir of a system
    • Equal to reservoir size divided by the rate of output

Exponential Growth

  • Related to
    • Rate of growth measured in %
    • Doubling time in years
  • EG is positive feedback and incompatible with sustainability

Feedback loops

  • Occur when outputs of a system are routed back as inputs as part of a chain of cause and effect that causes a loop or circuit
  • Feedback
    • When on part of system changes
    • These affect another part of the system
    • Which then affects first change
  • Negative Feedback
    • Increase in output leads to later decrease
    • Move the system in opposite direction
    • Neutralizes and stabilizes the system
  • Positive Feedback
    • Drives system towards an extreme
    • an increase in output leads to a further increase in output
      • Destabilizing
    • More growth, people have more children, more output, destabilizes

Earths Temperature Regulation

  • Negative Feedback
    • Warmer temperatures cause ice to melt over the tundra
    • More plants can grow
    • Plants use up $CO_2$, causing earth to cool
  • Positive Feedback's
    • Colder temperatures will lead to growth of the polar ice caps
      • Ice reflects more light back into space than land and sea
      • More light is reflected to space, earth cools further
    • Warmer temperatures lead to increased water vapor in atmosphere (humidity higher)

Elements

  • What are the most abundant elements on earth?
    • Oxygen (air)
    • Hydrogen (water)
    • Silicon (crust)
    • Carbon (living)