A moon rock collected by a U.S. Apollo mission is estimated to be 4.50 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 206Pb per 1.150 g of 238U in the rock? The half-life of 238U is t1/2 = 4.47 × 109 years.

Question

Josh · Accepted Answer

What is t? Everytime I put 4.50*10^12 for t then I take the e of it I get an error and if I do it negative I get 0. Don't understand this problem at all.

DrBob222 · Answer

I would do this.
k = 0.693/t^{1/2

Then ln(No/N) = kt

You know N is 1.150g U and k from above. solve for No which gives you grams U you started with.

g U initially - g U now = g U changed to Pb.

Then convert g U convert to g Pb 206.

g U changed x (206/238) = ? Pb now.}