Absolute Time

Radioactive Decay

Parent Isotope -->Daughter Isotope + Decay Particle + Energy

Daughter Isotope

Parent Isotope

Half LifeTime it takes for half of the parent isotope to decay into daughter isotope

Radioactive Isotopes Used for Absolute Dating

parentparent daughterdaughter half life (years)half life (years)235U 207Pb 4.50 x 109

238U 206Pb 0.71 x 109

40K 40Ar 1.25 x 109

87Rb 87Sr 47.0 x 109

14C 14N 5730

Radioactive Decay & Telling Time

Information Required for Radiometric Dating

• Initial Parent Isotope Content

• Half Life of Isotope• Current Parent Isotope

Concentration• Closed System

Remember:

Age = Amount of Change Rate of Change

Mass Spectrometer

What can be dated?

When does a system become “Closed”?

(i.e., What are you dating?)

Cooling of Igneous Rock

Metamorphism

Death of Organic Material

Sedimentary Rocks:What are we dating?

Lab 3

Geologic Provenances of Washington

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