1. The problem statement, all variables and given/known data The half life of U-238 is approximately 4.4 billion years, while U-235 is approximately 700,000,000. A Uranium ore has 0.75% U-235. Assuming there was an even amount of both types of Uranium when the Earth was formed, estimate the age of the Earth. 2. Relevant equations N = N0 - kt where N = amount after time t N0 = amount at time=0 k = decay constant t = time 3. The attempt at a solution I don't do a lot of derivation at my school, but I want to get a lot better at it. N = N0 - kt dN / dt = -kt dN = -kt dt ∫ - kt dt (definite integral from t to t0 = -k(t - t0) I'm not really sure to go from here.