Question

Given the radioactive half-lives of 7.0*108 yrs and 4.5*109 yrs for 235U and 238U, respectively, if the ratio of 235U/238U in a particular rock sample was 2.0% (i.e. 2 235U for every 100 238U atoms) when Earth formed 4.5 billion years ago, approximately what do you expect this ratio to be as measured today? The precise formula for the number of atoms, N, remaining after any particular time, t, starting with an initial amount, N0, is N = N0 exp(-0.693 t/thalf).

Answer 1