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A moon rock collected by a U.S. Apollo mission is estimated to be 3.60 billion years old by uranium/lead dating. Assuming that the rock did not contain any lead when it was formed, what is the current mass of Pb206 in the rock, if it currently contains 1.565 g of U238 ? The half-life of U238 is 4.47×109 years .

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jadabug21000

Answer:

I think it is 3.7E9 years according to the problem.

Explanation:

Here is what I would do.

k = 0.693/t1/2 and solve for k.

Then ln(No/N) = kt

You know k and t, solve for N/No.

If I understand the problem, the current mass U238 is 1.185g.  

So you know No/N and N, solve for No which is the amount of U the sample started with. mass U238 initially - mass U today = mass U decayed and convert that to g Pb today.

mass Pb206 today = mass U decayed x (206/238) = ?