Question

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.

Answer 1

I would do this.
k = 0.693/t<sup>1/2</sub>

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.

Answer 2

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.