Radiometric Dating

1
Radiometric Dating
2
Radiometric Dating Methods

• Radio-Carbon (or carbon-14)
• Potassium-Argon
• Uranium-thorium-lead
• Rubidium-Strontium

3
Carbon 14 Production

• 7N14 0n1 7N15
• 7N15 6C14 1H1
• 6C14 7N14 -1ß0

4
Carbon World Inventory

• Grams of carbon in exchange equilibrium with the
  atmospheric carbon dioxide for each square
  centimeter of the earth's surface.
• Ocean carbonate 7.25 g/cm'
• Ocean dissolved organic 0.59
• Biosphere 0.33
• Atmosphere 0.12
• Total
  8.29 g/cm2
• Since there are 2. 6 C " atoms estimated to be
  formed in the atmosphere by cosmic radiation per
  square centimeter of earth's surface per second,
  the specific radioactivity of carbon should be
• 2. 6 atoms (60 s) cm 2
• --------------- x ------- x -------- 18.8
  disintegrations
• cm 2 s min 8.3 g
  per gram of carbon
• 
  in the reservoir

5
Typical Radioactive Decay Curve
6
Carbon Equilibrium Curve
7
Radiometric Decay Equations
8
Carbon Dating Calculations
9
Age of Earth
10
Radiometric Dating Error
Sources

• Accuracy and dependability of the laboratory
  analyses
• Accurate knowledge of the decay rates
• Constancy of the decay rates over millennia
• Contamination of the samples
• Assumed composition of the ancient (or
  original) material