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# 14.5: Activity 14D - Applying Numeric Dating

1. If a rock begins with 4000 atoms of a radioactive isotope, how many would remain

a. after one half-life?

b. after two half-lives?

c. after three half-lives?

d. after four half-lives?

2. If an isotope has a half-life of twenty million years, and there is 25% of the isotope remaining in a rock, how old is the rock?

a. 10 million years

b. 20 million years

c. 40 million years

d. 60 million years

3. A scientist radiometrically dates 3 different rocks using 3 separate decay series. If each rock contains 50% of their measured radioactive element and 50% of its corresponding daughter element, which rock is oldest?

Rock A is dated using isotope A (half-life = 50 years)

Rock B is dated using isotope B (half-life = 100 years),

Rock C is dated using isotope C (half-life = 1000 years).

a. Rock A

b. Rock B

c. Rock C

d. Impossible to tell

4. An Archeologist finds some cotton cloth at a burial site and wants to determine the age of the remains. Which isotopic system should they use?

a. Carbon-14

b. Uranium

c. Potassium-Argon

5. The Archeologist determines that there is 16.7% of the parent isotope remaining in the cloth sample. How old is the burial site? Hint: you can find the length of the half-life in the reading above.

a. 13,559 years

b. 14,798 years

c. 16,743 years

d. 1.66 billion years

e. 1.81 billion years

f. 2.05 billion

6. A geologist is trying to date a sequence of sedimentary rocks with abundant fossils and sandstones. Within the sequence is a distinctive clay layer that, under closer inspection, turns out to be fine-grained volcanic ash. Which of the following is the best way to obtain a numeric date for the sequence of rocks?

a. Carbon date the fossils

b. Potassium-Argon date the sands

c. Uranium date the Zircons in the ash

d. Identify the index fossils

7. The geologist determines there is 78.3% of the parent remaining in the sample that they examine. How old is the sequence of rocks? Hint: you can find the length of the half-life in the reading above.

a. 187.5 million years

b. 247.8 million years

c. 390.7 million years

d. 2.504 billion years

e. 1.588 billion years

f. 1.202 billion years

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