The mineralogical composition of the all cited samples and their relative spectrum of U-Pb zircon ages are reported in Table 1. Another reason for believing it is that if we calculate Pb-Pb dates on this basis, the dates we get are in agreement with dates produced by other methods where they can be applied: this would hardly be possible if we were using the wrong figures for the initial lead isotope ratios. Over the course of 14 machine runs and spot analyses the 2 sigma concordia age uncertainty is 0.
The thick red line represents the 30 point running average of these values with 1 sigma standard error shown by the thin red lines. So, conversely, if we count the fission tracks and we measure the amount of uranium, then we can figure out how much time it must have taken to produce the fission tracks. The isotopes[ edit ] There are a number of isotopes of interest in U-Pb dating.