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Radiometric Dating - Coggle Diagram

- - - - Determined the heat flow
    - - Didnt know the earth was being heated continually
        
        Radioactive decay
  - - - All the salt had been added by rivers - result of chemical weathering
    - - Divided it and worked out the earth was 90Ma
- - - - Based on stratigraphy
      - Based on fossil assemblages
      - Gradually fixed as radiometric ages were added
  - - - Breakdown at a statistically constant rate
    - - Time taken for half of the unstable parent atoms to break down to stable daughter atoms
    - - know how many half-lifes have passed
      - Can be measured using a mass spectrometer
- - - - Rarest
      - decays in 2 ways
      - 89% of it decays by emitting beta to form 40Ca
        
        No use for dating - indistinguishable from calcium
      - 11% of it decays by a different mechanism to form 40Ar
        
        A gas
        
        Not formed in any other way
        
        Can easily escape from the mineral lattice
        
        Especially when heated
  - - - uncertainty about its age
      - quoted as 48,800 by the USGS
    - - Solid = harder to lose
- - - - Different parts reach closure temp at different times
        
        Closure temp: The temp at which a system has cooled, no diffusion of isotopes in or out
    - - Cool rapidly such as lava flows
  - - - can provide a date for the formation of the rock
    - - More prone to weathering
      - Alter the ratio of parent to daughter
    - - Leads to a younger age
  - - - closed systems: when a mineral neither gains or loses atoms. Higher the temp more likely the exchange of atoms or ions will be
    - - Closure temp between 150 and 550 degrees
    - - Conflicting possible