CompuServe Messages

Hi, Kamron– If lead and uranium are both present when a rock is formed, the lead will contain very little of the isotope lead 206, and by checking the amounts of the other isotopes of lead, one can tell how much lead 206 must have been in the original lead. Any excess lead 206 over that amount must be from uranium. Also, they will often be in different minerals – if I find any lead 206 free of other lead isotopes, I know that all of it came from uranium decay. Once in a while, any dating method may give wild results. Something very unusual, like a hydrothermal solution removing lead or adding uranium, perhaps? But when many many samples all give dates that place certain strata at certain dates, and that date fits the pattern from many more samples from other strata, one can be confident it is valid. Oddball readings from a few weird pieces may indicate unknown factors or invalid techniques, but too much of a small-scale local surprise to help validate your theories when confronted with the large-scale consistency of huge numbers of tests. –Doug