Quote:
Over the last 78 years numerous determinations have been made of the total 40K decay half-life, obtained by direct counting experiments and by comparing radioisotope ages derived from more than one dating method applied to the same rocks or minerals. The determinations since 1997 have converged with close agreement toward the total 40K decay half-life value of 1.2524±0.0064Byr. But that determination in 2011 ignored the two liquid scintillation direct counting determinations in 2002 and 2004 which had agreed on a slightly lower total 40K decay half-life value of 1.248±0.003Byr. So neither of these values has yet been adopted for standard use by the uniformitarian geochronology community. There are important sources of systematic error in all 40Ar-39Ar (and K-Ar) ages that arise from uncertainties in the two 40K decay constants and the K-Ar isotopic data for neutron fluence monitors (the Ar-Ar dating standards). Even though it is crucial to determination of the total 40K decay half-life, the branching ratio between 40K β-decay to 40Ca and electron capture decay to 40Ar with γ-rays emitted is still not definitively agreed upon. The value of 0.1162 was used in 2011 in spite of the value of 0.1194±0.007 carefully determined in 2000, which confirmed the value of 0.1195±0.0014 determined in 1973. The uncertainties in the crucial 40K/K abundance ratio also need to be considered, because there is no agreement on it. The value of 0.011672±0.000041% determined in 1975 is still adopted, but the value of 0.011668±0.000008% determined in 2013 has yet to be recognized. Therefore, when all these factors are considered the total 40K decay half-life is thus known to no better than ±2% at the 2σ level, and the 40Ar*/40K ratios for individual standards are only known to better than ±2% in some cases, while interlaboratory discrepancies of more than 2% in the 40Ar/39Ar ages of secondary standards like the Fish Canyon Tuff sanidine suggest larger uncertainties. Thus independent determinations of the branching and 40K/K abundance ratios are still needed, as well as new laboratory investigations to determine the total 40K decay half-life. Yet, in spite of the many experiments directly measuring the total 40K decay half-life, the adopted value ultimately depends on deriving it by adjusting (that is, massaging) K-Ar and Ar-Ar ages to conform to U-Pb and Pb-Pb ages obtained from different minerals respectively in the same rocks. But many unprovable assumptions are also involved, not the least being that the radioisotope systems closed at the same time and subsequently remained closed. Furthermore, even this U-Pb “gold standard” has unresolved uncertainties due to the U decay constants being imprecisely known, and to measured variations of the 238U/235U ratio in terrestrial rocks, ores, and minerals, and in meteorites. Both of these factors are so critical to the U-Pb method, as well as the additional factor of knowing the initial concentrations of the daughter and index isotopes, so it should not be used as a standard to determine other decay constants. There is also evidence decay rates of the radioisotopes used for rock dating have not been constant in the past, as well as the possibility of a slight decline in the measured values of the total 40K decay half-life during the 78 years of determinations. This only serves to emphasize that if the K-Ar and Ar-Ar dating methods have been calibrated against the U-Pb “gold standard” with all its attendant uncertainties, then they cannot be absolute, and therefore they cannot be used to reject the young-earth creationist timescale. Indeed, current radioisotope dating methodologies are at best hypotheses based on extrapolating current measurements and observations back into an assumed deep time history for the cosmos.
Full Article