Radiometric dating

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Radiometric dating

  1. 1. Radiometric Dating (pg 8)TRILOBITE - early arthropod - EXTINCT!
  2. 2. • Fossil - preserved remains of ancient life - found in sedimentary rock - studied by paleontologists
  3. 3. • Sedimentary rock - formed as small particles settle on bottom of ocean, lake or river
  4. 4. • Older rock layers usually deeper in earth
  5. 5. • Fossils form as organic material replaced by minerals (petrified)
  6. 6. • Relative dating - places rock layers in a temporal sequence based on depth
  7. 7. • Absolute dating: Gives a rock layers age in years• Radiometric Dating - dates rock based on decay of radioactive isotopes.• Radioactive isotopes (such as Carbon-14 and Potassium-40) break down at a steady rate.
  8. 8. Isotopes• Radioactive isotopes contain extra neutrons, making them unstable• For example, normal carbon (C-12) contains 6 protons and 6 neutrons. Radioactive C-14 contains 6 protons and 8 neutrons• Over time, Carbon-14 decays, becoming Nitrogen-14
  9. 9. • Half life =Amountof time for half of isotope to decay• K-40 = 1.3 billion years• C-14 = 5,730 years
  10. 10. • Scientists measure amount of remaining radioactive isotope and compare it to original amount to age rocks and fossils• Ex) Potassium-40  Argon-40• Argon gas gets trapped in the rock

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