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Homework Help: Uranium isotope relative abundance at diff times

  1. Feb 28, 2009 #1
    1. The problem statement, all variables and given/known data

    The relative abundance of uranium isotopes in today’s earth crustal material is:
    99.2745% 238U
    0.7196% 235U
    0.0055% 234U
    What were the relative abundances when the earth was formed 4.6x109 years ago?

    2. Relevant equations

    t = age = 1/lambda * ln(N/No)

    N = No*e^lambda*t

    3. The attempt at a solution

    i dont know how to approch this...
  2. jcsd
  3. Feb 28, 2009 #2


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    Homework Helper

    Welcome to PF.

    What are the half-lives of the 3 isotopes?

    Since they all decay to Thorium then maybe if you work them backwards you can turn back the clock to see what was around 4 and a half billion years ago?
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