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Evolution – Radiometric Dating Evidence

Learn how radiometric dating supports the theory of evolution, understand half-lives, isotopes, and decay rates. Practice problems included to master the concept.

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Evolution – Radiometric Dating Evidence

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  1. Evolution – Radiometric Dating Evidence The present is the key to the past James Hutton Geologist that proposed the idea of deep time

  2. What is Evolution ? • Theory supported by evidence • Biological evolution - changes in living organisms • Sharing of common ancestors (branched tree of life) • Darwin term: descent with modification • Think: With your table buddy discuss and list at least four concepts learned that support the theory of evolution.

  3. Radiometric Dating

  4. Relative Dating • Compares fossils & rock layers to show “age” • Older fossils and rocks are generally deeper

  5. Radiometric Dating • Absolute /actual • More precise • Decay of UNSTABLE radioisotopes from unstable parent to stable daughter (Example Uranium to lead in Zircon) • Isotopes release energy particles at a rate specific for each isotope. • Half-life- amount of time it takes for half the original (parent) isotope to decay (to daughter)

  6. Bullet what this graph shows!

  7. Radiometric Dating Supports Evolution • decay, at known, predictable rates. • Pairing: Parent isotope to daughter atom • varying half-lives of different isotopes allow cross referencing. • Confirming different techniques • Repeatable

  8. Don’t make this too difficult! Steps1) Determine the percent parent isotope remaining 2) Use the graph to find the number of half-lives 3) Multiply half-life from graph x number of half-life for isotope to find how old the sample is. After one half-life how much of a parent isotope would be remaining?

  9. After 2 half-lives how much of the parent isotope is remaining?

  10. Question After Three half-lives, what percent of the parent isotopes remain?

  11. Do Practice Problems: Steps 1) Determine the percent of parent isotopes remaining. 2) Use the graph determine half-lives that the isotope has gone through 3) Multiply the half-lives by the known half-life for that isotope

  12. Answer Question # 1 An original rock with 60 atoms of Uranium 238. Half-life is 4.5 billion years • After one half-life, how old is the sample • How many atoms are remaining? • After two half-lives, how many parent atoms are remaining?

  13. Question #2: A sample has 5 atoms of radioactive (parent) uranium 235 remaining and 65 (daughter) atoms of lead (Pb) present. a) What percentage of radioactive isotopes remaining? b) Graph reads: c) half-life of uranium 235 is 704,000,000 million years so the age of the sample is

  14. Question 3: If an element has a half-life of twenty million years and there is 6.25% parent isotope remaining, how old is the rock? Graph Read from Y axis 6.25% remaining: Multiply 4 half lives X 20,000,000 years =

  15. Question 4: The radioactive isotope carbon 14 is used to date a once living organism. Carbon 14 has a half-life of 5730. • If there are 20 atoms of parent isotope and 5 of daughter isotope remaining, what is the age of the fossil. Steps: Determine % of parent isotopes remaining: Step: Number of half lives: Multiply the number of half-lives X half life

  16. Question #5: Potassium 40 can also be used to date biological fossils since potassium is found in living organisms. Potassium 40 has a half life of 1.28 billion years and decays to argon. If 5% of original isotope is remaining use the graph to find the number of half-lives the sample has completed. Multipy the half lives 4.1 X 1.28 billion years to find

  17. Question #6: Uranium 238 has a half life of 4.5 billion years. If you have 20 atoms of uranium 238, how many are remaining after one half life? • 10 Uranium 238 isotopes remain and 10 will now have been converted into daughter atoms. • After one more half-life how many will remain?

  18. Question 7: Rubidium-87 has a half-life of 48.8 billion years. 100 atoms of rubidium decays into daughter atoms and now 25% remain. • How many atoms are remaining? • How many half-lives has rubidium gone through: • What is the age of the fossil

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