Saturday, 5 November 2011

Radiometric dating

Radiometric dating is the way we find the age of a rock that has unstable isotopes. we find the half-life to find the ratio of parent atoms to daughter atoms.

e.g's of radiometric dating

K^40 -> Ar^40   This is used in sedimentry and metamorphic rocks  halflife= 1260ma

Uranium-238 -> lead-206   This is used to find the age of igneous rocks halflife= 4500ma

Rb^87 -> Sr^87   This is used in very old igneous rocks - very long halflife = 50,000ma 

Problems of radiometric dating 

  • Sedimentry- hard to date-> they erode easily, contain different minerals, layed down different times (Diachronus) and they need the mineral glauconite. 
  • Argon is a gas so its almost impossible to find out the age in K^40 dating
  • There is a margin of error in the dating-  +- 15ma
  • Matamorphic - not a closed system. when it melts the time clock resets back to zero

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