III.  Absolute Dating

A. Radiometric Dating

  1. Radioactive decay - the spontaneous transformation of an unstable parent isotope into a stable daughter at a constant rate.
  2. Half-Life - time it takes for 1/2 the unstable parent to transform into stable daughter (fig. 17.20)

B. Processes (fig. 17.8)

  1. alpha particle emission
  2. beta particle emission
  3. electron capture

C. Useful Isotopes (Table 17.1)

Parent

Daughter

half-life

U235 (uranium)

Pb207 (lead)

4.5 billion

K40 (potassium)

Ar40 (argon)

1.3 billion

Rb (rubidium)

Sr (strontium)

49 billion

D. Potential Problems

  1. actually dating mineral, not rock
  2. must have a closed system

E. Carbon 14 dating (fig. 17.24)

F. Tree-ring dating (fig. 17.26)

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