Conditions for life on earth

• Atmosphere

  • Mass of Earth and the force of gravity retain an atmosphere
  • Gases are resources
• Insolation

  Temperature range controlled by insolation and atmospheric processes
• Roles of

  • Albedo
  • Absorption of infrared energy
  • Atmospheric gases
• Gases were present in the atmosphere and dissolved in the oceans (where life began)
• Gases

  • Carbon dioxide
  • Methane
  • Nitrogen
• Carbon dioxide

  A source of carbon to make organic molecules: carbohydrates, proteins, lipids
• Methane


  A source of carbon and energy for metabolism
• Nitrogen

  For protein synthesis
• Water

  • Solvent for biological reactions
  • High heat capacity reduces temperature fluctuations
  • Anomalous expansion when freezing stops convection currents
  • Absorbed UV light protecting life in deeper water
• Sunlight was a major source of the energy that warmed the Earth
• Sunlight absorbed by the Earth's surface

  Re-emitted by the Earth as infrared and absorbed by atmospheric gases
• Position in the solar system

  • Temperature controlled by distance from the Sun
  • Orbital behaviour controls daily and seasonal variations in insolation and temperatures
• Distances where life would be possible 100m-250m km from the Sun (the Goldilocks zone)
• Rotation is fast enough that there is not excessive heating during the day or cooling at night
• The tilt on its axis produces seasonal variations in temperature and insolation
• Magnetosphere

  • Protects from harmful solar radiation
• How the presence of life has caused environmental change

  1. Oxygen production by photosynthetic bacteria, algae and plants

  2. Formation of the ozone layer

  3. Carbon sequestration by photoautotrophs

  4. Development of biogeochemical cycles
• Oxygen released by photosynthesis was consumed by reactions with dissolved iron in the oceans, forming Proterozoic iron sediments (approx. 2.45 years ago)
• Oxygen that built up in the atmosphere absorbed UV light from the Sun, producing monatomic O, which reacted to produce O3
• Some of the carbon captured by photosynthesis entered long-term lithosphere stores such as fossil fuels and carbonate rocks, reducing atmospheric CO2 levels and preventing excessive temperature rise as the energy output of the Sun increased
• Living organisms are involved in all biogeochemical cycles, maintaining linked dynamic equilibria
• How historical conditions for life were monitored in the past and how these methods have been developed over time

  1. Limitations of early methods

  2. Improved methods
• Proxy data can be inaccurate as many variables, that can't be measured, may have influenced the data
• Lack of rapid communications made data sharing more difficult
• Many monitoring technologies have only been developed recently
• Early equipment was often simple, inaccurate and not standardised
• Researchers were not evenly distributed around the world
• Improved methods

  • Collection of long-term data sets
  • Use of electronic monitoring equipment
• Improved methods

  • Gas analysis of ice cores
  • Isotope analysis
• CO2 concentrations are used in long-term analysis of climate change
• The ratio of oxygen16 to oxygen 18 allows estimation of past temperatures
• Levels of beryllium10 indicate past solar activity. Peaks of beryllium 10 can be used to date-match data from different ice cores
• These allow the collection of: continual/frequent data sets, data over larger areas, data higher in the atmosphere/in locations where it is impractical to have human researchers