Samples of internet dating profiles
The stunning improvements in the performance of mass spectrometers during the past four or so decades, starting with the landmark paper by Wasserburg et al.
Yet the earth would still have had an initial (created) Pb isotopic endowment.
U decay in those rocks added daughter Pb isotopes to the common or initial Pb isotopes in them, inherited from the rock’s sources.
So the Pb isotope ratios measured in these rocks today must be interpreted before their U-Pb ages can be calculated.
Nor can the measured Pb isotope ratios be used to somehow decide what proportions of them are the initial Pb without recourse to unprovable assumptions about the mineral or rock’s history or their interpreted U-Th-Pb ages within an assumed deep time history.
Nevertheless, the ultimate foundation of this U-Pb dating methodology is the assumption that the earth formed from the solar nebula.