U pb dating of zircon
Once radioactive decay of U and Th started after creation, daughter Pb isotopes were added inside the earth.Then catastrophic plate tectonics during the Flood stirred the mantle and via partial melting added new rocks to the crust.Zircon (Zr Si O) in particular has been the focus of thousands of geochronological studies, because of its ubiquity in felsic igneous rocks and its claimed extreme resistance to isotopic resetting (Begemann et al. However, accurate radioisotopic age determinations require that the decay constants or half-lives of the respective parent radionuclides be accurately known and constant in time.
Ironically it is the slow decay rates of isotopes such as Sm used for deep time dating that makes precise measurements of their decay rates so difficult.
These new rocks rapidly accumulated more Pb isotopes due to the concurrent accelerated radioactive decay of U and Th in them during the Flood.
Thus, without being able to unequivocally distinguish the daughter Pb atoms produced by in situ U and Th decay from the initial Pb atoms in a mineral or rock, it is impossible to determine their absolute U-Pb ages.
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.
From a creationist perspective, the 1997–2005 RATE (Radioisotopes and the Age of The Earth) project successfully made progress in documenting some of the pitfalls in the radioisotope dating methods, and especially in demonstrating that radioisotope decay rates may not have always been constant at today’s measured rates (Vardiman, Snelling, and Chaffin 2000, 2005).