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Chapter 8.2 Lecture Chronological Time

Chapter 8.2 Lecture Chronological Time. Counting lifetimes in the Bible. Comparing cooling rates of iron pellets. Determine sedimentation rates & compare. Estimate age based on salinity of the ocean. Age Estimates of Earth. all age estimates were off by billions of years.

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Chapter 8.2 Lecture Chronological Time

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  1. Chapter 8.2 Lecture Chronological Time

  2. Counting lifetimes in the Bible Comparing cooling rates of iron pellets. Determine sedimentation rates & compare Estimate age based on salinity of the ocean. Age Estimates of Earth all age estimates were off by billions of years some were more off than others!

  3. Absolute Dating Methods Radioactive Decay sequences acts as an atomic clock we see the clock at the end of its cycle analogous to starting a stopwatch allows assignment of numerical dates to rocks. Radioactive isotopes change ( decay ) into daughter isotopes at known rates. rates vary with the isotope 235 40 14 e.g., U , K , C, etc. > > + +

  4. Decay unstable nuclei in parent isotope emits subatomic particles and transform into another isotopic element (daughter). does so at a known rate, measured in the lab Half-life The amount of time needed for one-half of a radioactive parent to decay into daughter isotope. • Assumptions?-you bet Cross-checks ensure validity of method.

  5. All atoms are parent isotope or some t 0 known ratio of parent to daughter 1 half-life period has elapsed, half of the t material has changed to a daughter 1 isotope (6 parent: 6 daughter) 2 half-lives elapsed, half of the parent t remaining is transformed into a daughter 2 isotope (3 parent: 9 daughter) 3 half-lives elapsed, half of the parent remaining is transformed into a daughter t 3 isotope (1.5 parent: 10.5 daughter) We would see the rock at this point. Rate of Decay

  6. Think pair share: Practice Problem: You find a rock with 7/8 the daughter & 1/8 the parent. If the parent material has a half-life of 50,000 years, how old is the rock? Method: 1. Use the ratio of Parent to Daughter to find out how many half lives have gone by 2. Multiply the number of half lives gone by times the value of the half life

  7. Answer: 3- ½ lives have gone by so rock is 3 x 50,000yr or 150,000 yrs old

  8. Radioactive Isotopes Radioactive Isotopes • analogous to sand in an hour glass • analogous to sand in an hour glass - - we measure how much sand there is we measure how much sand there is > represents the mass of elements > represents the mass of elements - - we measure the ratio of sand in the bottom to sand in the top we measure the ratio of sand in the bottom to sand in the top - - at the end (present) at the end (present) > daughter (b) and parent (t) > daughter (b) and parent (t) - - we know at what rate the sand falls into the bottom we know at what rate the sand falls into the bottom > the half life of the radioactive element > the half life of the radioactive element - - how long would it take to get the amount sand in the observed how long would it take to get the amount sand in the observed ratio starting with all of it in the top? ratio starting with all of it in the top? 100 Parent Parent % parent remaining Daughter Daughter 50 25 13 time----------->

  9. Five Radioactive Isotope Pairs Five Radioactive Isotope Pairs Effective Dating Range Minerals and Isotopes Half-Life of Parent Rocks That Can (Years) Parent Daughter (Years) Be Dated Uranium 238 Lead 206 4.5 billion 10 million to Zircon 4.6 billion Uraninite Uranium 235 Lead 207 704 million Muscovite Thorium 232 Lead 208 14 billion 48.8 billion Biotite Potassium feldspar Rubidium 87 Strontium 87 4.6 billion 10 million to Whole metamorphic 4.6 billion or igneous rock Potassium 40 Argon 40 1.3 billion 100,000 to Glauconite 4.6 billion Muscovite Biotite Hornblende Whole volcanic rock

  10. Radiocarbon and Tree- Ring Dating Methods Carbon-14 dating is based on the Carbon-14 dating is based on the • • in an organic ratio of C-14 to C-12 ratio of C-14 to C-12 sample. sample. > Valid only for samples less than 70,000 > Valid only for samples less than 70,000 years old. years old. > Living things take in both isotopes of > Living things take in both isotopes of carbon. carbon. > When the organism dies, the "clock" starts. > When the organism dies, the "clock" starts. Method can be validated by cross-checking with tree rings

  11. Carbon 14 Cycle

  12. If you are still having trouble check out these videos: • Radioactive decay • Carbon Dating

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