Conditions for Life on Earth

Early conditions on Earth
1. The Earth was formed about 4.6 billion years ago
  1. The physical features of Earth made it suitable for the eventual development of life by controlling the abiotic factors needed by living organisms
Features of Earth that created suitable conditions for life
1. Mass
  1. The mass of the earth was great enough to prevent most gases from escaping into space
    1. This allowed for the creation of an atmosphere
  2. The atmospheric pressure was high enough to prevent all liquid oxygen from boiling
2. Distance from the Sun
  1. The light emitted from the sun and the distance from the sun created suitable temperatures on Earth
  2. The time taken for the Earth to rotate created a day/night cycle
    1. This prevented extreme heating or cooling of the planet
3. Axis or Rotation
  1. Axis of rotation is at an angle to the Earths orbit, this creates seasons
4. Speed of Rotation
  1. The 24 hour rotation prevents temperature extremes
5. Magnetic Field
  1. The Earths magnetic field deflects the 'solar winds', which prevents biologically damaging radiation reaching the Earths surface
Life first developed on Earth about 3.5 billion years ago
1. The atmosphere contained some toxic gases like ammonia
2. There was no oxygen
3. Solar energy reaching the ground contained high levels of ultra-violet radiation
4. The chemical composition of the sea included increasingly complex organic molecules
  1. Single celled life eventually formed, likely around geothermal vents on the seabed
    1. These are archaea, they are similar to bacteria, some are anaerobic and are still around today
Conditions on Earth the allowed life to develop
1. Presence of liquid water
  1. All living things require water for survival
    1. It performs essential physiological functions and controls many environmental conditions
  2. Solvent Water
    1. The 'general physiological solvent'. Most chemical reactions in living organisms involve reactants that are dissolved in water
  3. Transport within organisms
    1. Water is the solvent in blood and sap, where it transports dissolved gases, sugars, amino acids, mineral nutrients, waste products, etc.
  4. Temperature Control
    1. The evaporation of water absorbs heat, reducing temperatures
  5. Anomalous expansion on freezing
    1. Water is most dense at 4°C, so water cooler than that floats. This stops convection currents from cooling the whole body of water
  6. High specific heat capacity
    1. Water warm and cools slowly, this helps moderate the rate and size of temperature change
  7. Aquatic Habitats
    1. Oceans, seas, lakes, marshes and rivers
  8. Absorption of UV radiation
    1. This protected living organisms before the ozone layer developed and absorbed the UV in the stratosphere
2. Temperature Range
  1. Most areas of Earth have temperatures between 0°C and 35°C
    1. Most areas are warm enough to have liquid water, but not hot enough to denature proteins
3. Atmospheric Gases
  1. Carbon dioxide for photosynthesis and the synthesis of carbohydrates , proteins and lipids
  2. Nitrogen for protein synthesis
4. Solar Isolation
  1. Sunlight provides the energy for photosynthesis
  2. The heat produced by the absorption of sunlight provides the energy that drives the water cycle, and warms the Earths surface and oceans
How life on Earth caused environmental change
1. Atmospheric Oxygen
  1. By 2.7 billion years ago, some Archaea had developed the ability to photosynthesise and release oxygen
    1. For millions of years all oxygen produced reacted with iron in the oceans
      1. Once all the iron had reacted with oxygen, the surplus dissolved oxygen built up in the oceans, much was released into the atmosphere where concentrations started to rise about 2.45 billion years ago
  2. Oxygen in the atmosphere absorbed UV light
    1. This created a dynamic equilibrium of reactions involving O3, O2, and O
  3. The time period of oxygen building up in the atmosphere lasted about 540m years
    1. The time period was called Proterozoic
2. Carbon Sequestration
  1. Carbon dioxide is a greenhouse gas and helps retain heat energy
  2. Photosynthetic organisms absorb carbon dioxide, some of which is stored in geological sediements
    1. E.g. Carbonate rocks and fossil fuels
  3. The reduction in atmospheric Co2 helps prevent long-term temperature rise
    1. The suns brightness increases by about 10% every billion years
3. Biogeochemical Cycles
  1. As a greater variety of organisms evolved, inter-connect biological processes developed,which produced biogeochemical cycles
    1. This meant that relatively small amounts of some nutrients could support life for a long time without becoming depleted
4. Transpiration
  1. Once plants had evolved and colonised land, transpiration returned water vapour to the atmosphere
    1. This caused rainfall in other areas,allowing for the growth of more plant life

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Conditions for Life on Earth

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