Chemistry 1046

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Geologists can estimate the age of rocks by their uranium-238 content. The uranium is incorporated in the rock as it hardens and then decays with first-order kinetics and a half-life of 4.5 billion years. A rock contains 65.7% of the amount of uranium- 238 that it contained when it was formed. (The amount that the rock contained when it was formed can be deduced from the presence of the decay products of U-238.) How old is the rock?

  • Chemistry 1046 -

    k = 0.693/t1/2
    ln(No/N) = kt
    No = 100
    N = 65.7
    k from above.
    solve for t in years.

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