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Radiometric Dating “clocks in rocks”

Radiometric Dating “clocks in rocks”. Absolute Dating. Gives a numerical age Works best with igneous rocks & fossils Uses isotopes. Isotopes- different number of neutrons. Carbon 14 ( 14 C) 2 “extra” neutrons radioactive. Common dating isotopes. radioactivity. Nuclei break apart

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Radiometric Dating “clocks in rocks”

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  1. Radiometric Dating“clocks in rocks”

  2. Absolute Dating • Gives a numerical age • Works best with igneous rocks & fossils • Uses isotopes

  3. Isotopes- different number of neutrons • Carbon 14 (14C) • 2 “extra” neutrons • radioactive

  4. Common dating isotopes

  5. radioactivity • Nuclei break apart • Emit particles or waves (radiation)

  6. Radiation Ionizing Radiation Radioactive Atom Alpha Particle Neutron Particle Beta Particle Gamma Ray (X Ray)

  7. Cosmic 28 mrem Terrestrial 28 mrem Radon 200 mrem Internal 40 mrem Medical X-Rays 40 mrem Nuclear Medicine 14 mrem Consumer Products 10 mrem Natural Sources Man-Made Sources Other 3 mrem Average Annual Dose

  8. Comparison of Radiation Dose Doses shown in bar graph are in units of mrem

  9. The time required for the amount of radioactive material to decrease by one-half 1200 1000 800 Activity 600 400 200 0 New 1 Half- 2 Half- 3 Half- 4 Half- Life Lives Lives Lives Half-Life

  10. Half-lives

  11. Half life problem • If you begin with 80 grams of 14C after a time, 20 grams are left. How old is the sample?

  12. 14 Carbon • Only accurate for ages less than 100,000 years • Parent gets too small to accurately measure

  13. Mass spectrometermeasures D/P ratio

  14. Preparing a rock for mass spectrometer

  15. Using daughter/parent ratio • 1) D/P ratio • 2) figure out number of half-lives • Use graph • 3) multiply number of half-lives by the time of one half-live • Example: 240 g 14N ; 8 g 14C

  16. Another half-life problem • 1,000 grams of radioactive element is in a rock when it is formed. The element’s half-life is 2 million years. After a time, 125 grams of the original element remain. How old is the rock?

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