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**Relative/Absolute Dating**

Quiz Review Relative/Absolute Dating

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1. Relative Dating Which layer is older – 1, 3, 6 ?

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2. Relative Dating Which layer is older – 2, 3, 4 ?

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3. Relative Dating Which layer is older – 2, 4, Event B ?

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4. Absolute Dating The radioactive isotope C14 decays into the stable decay element N15 with a half-life of 5730 years. What fraction of the original C14 will be remaining in the sample after 11,460 years? (1, ½, ¼, 1/8)

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5. Absolute Dating How many half-lives have elapsed to yield a sample with 125 atoms of C-14 and 375 atoms of N-15? (Hint: Think in terms of percentage of C14 remaining…)

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6. Absolute Dating If the C14 isotope has gone through 3 Half-lives, and the Half-Life of C14 is 5730 years, “How Old is the Substance at hand?”

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**Answers to Review Q’s Slide 1 – Rock Layer 6 Slikde 2 – Rock Layer 4**

(3 is cross-cutting 1+6, so it’s the youngest, 1 and 6 are sedimentary rocks with 1 on top of 6. Therefore, Rock layer 6 is oldest.) Slikde 2 – Rock Layer 4 (Rock layer 3 is cross-cutting everything, so it’s the youngest. Rock layer 2 is cross-cutting 4, so it’s younger than 4. Therefore, Rock layer 4 is the oldest.)

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**Answers to Review Q’s Slide 3: Rock Layer 4 Slide 4: ¼**

(Rock Layer 2 and Event B are both cross-cutting Rock Layer 4. Therefore, Rock layer 4 had to be there before the cross-cutting occurred.) Slide 4: ¼ (11,460 is 2 half-lifes of C14 (5730 x 2 = 11,460). Each ½ Life reduces the amount present by ½. Therefore ½ of ½ = ¼)

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**Answers to Review Q’s Slide 5: 2 Half-Lives Slide 6: 17,190 years**

C14 = 125 atoms N15= 375 atoms, to figure the %C14 remaining = 125/500 (total atoms) which = 0.25 or ¼ or 2 Half-lives. Slide 6: 17,190 years If 1 half-life = 5730 years, then 3 half-lifes must = 3 x 5730 years = 17,190 years.

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That’s All for Today!!

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