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Radioactive Dating Geochronology

Radioactive Dating Geochronology. CHM 1020 Sinex. Calculating the age…. First-order radioactive decay kinetics. P  D. P/P o methods – assume P o is known and constant , measure P, ages to 10t 1/2 carbon-14 (t 1/2 = 5730 yr) anthropology or any once living objects

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Radioactive Dating Geochronology

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  1. Radioactive DatingGeochronology CHM 1020 Sinex

  2. Calculating the age… First-order radioactive decay kinetics P  D P/Po methods – assume Po is known and constant, measure P, ages to 10t1/2 carbon-14 (t1/2 = 5730 yr) anthropology or any once living objects new Kr-81 (t1/2 = 230,000 yr) for ice cores tage = -ln(P/Po)/k

  3. Any living thing – modern Po value P -----> D P/Po measure P remaining Five dead things – rank age from oldest (1) to youngest (5)

  4. Calculating the age… First-order radioactive decay kinetics P  D D/P methods – dating rocks on Earth, Moon, and meteorites, measure D/P by mass spectrometry 206Pb/238U (t1/2 = 4.47 billion yr) 207Pb/235U (t1/2 = 704 million yr) 208Pb/232Th (t1/2 = 14.0 billion yr) 87Rb/87Sr (t1/2 = 49.6 billion yr) tage = ln(1+D/P)/k(best for Pb/U in zircons)

  5. Assume Do = 0 P -----> D D/P ratio by mass spec At time of formation when clock is set Five rocks – rank age from oldest (1) to youngest (5)

  6. Now Do > 0 P -----> D D/P ratio by mass spec At time of formation when clock is set What happens if daughter is present when the clock is set? Now you need to develop an isochron plot S = stable reference isotope

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