I was looking at a program referring to dating the life of the earth and I`m puzzled on a bit that I`m sure must be obvious to geologists. The dating was based on the ratio of lead that was present in combination with uranium. Lead being the final element after the uranium decay. It was this varying ratio from locality that enabled the dating of the area. But doesn`t all the uranium on the earth decay at the same rate and would not all have the same Ur/Pb ratio? Why would the decay, as was stated, of rocks at the bottom of the Grand Canyon be a billion or so years different from those on the surface as determined by the Ur/Pb ratio?