Radioactivity

1. A granite rock is thought to be about 2 billion years old. why is it not possible to determine the age of the Rock using carbon-14 dating?

2. A hair sample has 80% of its original carbon-14 present. what is the age of the sample?

3. A bone fragment has lost 75% of its original carbon-14. what is the age of the bone fragment?

4. an organic sample is 28,650 years old. what percent of the original carbon-14 still present in the sample?

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  1. The half live of C14 is only about 6,000 years and this is not suitable to a rock sample of that age. There is a section is the link below that talks about which methods are best for various ages.
    http://en.wikipedia.org/wiki/Radiometric_dating

    2. k = 0.693/t1/2
    Look up t1/2 in your text or notes and solve for k.
    Then ln(No/N) = kt.
    Set No = 100
    N = 80
    k from above
    Solve for t.

    #3 is the same process as #2.
    4. ln(No/N) = kt
    No = 100
    N = x
    k from above
    t = 28,650 years.
    Solve for N and convert to the percentage to the starting 100.

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  2. 2 years

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