ance” scores ranged from 0.56 (for fission tracks) to 0.84 (for Pb-Pb). In other words, fission track ages were the least “internally consistent” and Pb-Pb ages were the most “internally consistent.” When age determinations from two methods were compared, average concordance scores ranged from zero (fission tracks vs. Pb-Pb) to 0.79 (238U-206Pb vs. 235U-207Pb). The remainder had average concordance scores between 0.06 and 0.55. Thus, there is significantly less concordance between methods than within a single method. It is noteworthy that the discordances in the database appear not to be random, but systematic. Systematic discordances were also described by the RATE group in their case studies. However, RATE found that β-decaying isotopes tended to yield younger ages than α-decaying isotopes while in our study 40K followed this pattern but 87Rb did not. RATE also reported that within α- or β-decaying methods, the heavier isotope tended to yield older ages. In our study, we found the same pattern with the exception that 85.0% of 235U-207Pb ages were older than the corresponding 238U-206Pb ages. However, 235U and 238U are probably too similar in atomic weights, valence as ions and geochemical behavior for this observation to have much significance. It should also be noted that 238U-206Pb and 235U-207Pb ages are the ones that overlapped the most, and only 22.5% of the 1,715 records in which the 235U-207Pb ages are older are discordant. Perhaps the differences between our results and those of the RATE group can be explained as stochastic effects or the result of confounding factors such as magma mixing, inheritance and isotopic fractionation in minerals but they warrant further investigation and might necessitate modification of some aspects of the RATE hypothesis of accelerated nuclear decay. Nevertheless, the fact that discordances appear to be systematic and not random is intriguing and seems to require some kind of explanation. However, our analysis is a preliminary one and more detailed scrutiny of the database is required to confirm our results. The age data used in our analysis was taken from the “age” and “error” columns of the database but in some cases ages or error ranges were incorrectly reported in other parts of the database (e.g. the “comments” column) and were thus not included in our analysis. In other cases, the age information was incomplete, for example instances where the model ages used to construct an isochron were reported but not the actual isochron age. There was also a lack of consistency in how isochron ages were reported in the database, with some generated from multiple ages reported in a single record and others generated from ages reported in multiple records. In addition, there were some apparent errors in the database, for example the exact same “age” and “error range” reported multiple times for supposedly different age determinations. The task of identifying and fixing all of these problems was beyond the scope of this preliminary study and further work will be needed to explore whether these data quality issues, each of which is small, cumulatively affect our initial results and conclusions. We propose several avenues of future research: (1) Given the availability of a newer, updated version of the database (Hillenbrand et al. 2023), as well as the data quality issues described above, our analysis should be re-run using the latest edition of the database, after a thorough audit has been carried out to identify and, where possible, correct any remaining errors. (2) For this study, we devised and applied a simple concordance/ discordance metric. However, a further analysis could measure degrees of discordance, for example noting by how many standard errors and/or by what percentage of the total age a discordant age is actually discordant. Such quantification may provide further insights into the systematic discordances that are observed and what might explain them. (3) In this study, we did not compare ages generated by different types of radioisotope age determination (e.g. model ages vs. whole rock isochron ages vs. mineral isochron ages vs. concordia ages). A future study could compare ages from these different types of determinations to look for other patterns of concordance and discordance. (4) In this study, we did not compare radioisotope age determinations on different minerals, but it would be instructive to see whether certain minerals systematically yield different ages than other minerals. The standard geological explanation for many discordant mineral ages involves the different blocking temperatures of minerals. For example, age determinations based on minerals with high closure temperatures might be expected to be older because they are more likely to reflect the original crystallization age and less likely to be affected by subsequent metamorphic reheating events. Future research could test this hypothesis by seeing whether there is a consistent correlation between the oldest ages and the highest blocking temperatures. (5) Geoscience Australia (2021) has compiled an online database of radioisotope age determinations from Australia, called “Geochronology and Isotopes.” This database is analogous in many ways to the USGS National Geochronological Database, and it may be useful as the subject of similar research in the future. It contains significantly fewer entries than the USGS database (6,036 records as of May 2023) but is more up-to-date and better maintained. It includes K-Ar, Rb-Sr, U-Pb, and FT ages. There are also some Ar-Ar ages and four rhenium-osmium (Re-Os) ages. As with the USGS database, however, the Australian database contains almost no Sm-Nd ages. VI. ACKNOWLEDGEMENTS We would like to thank Drs. John Whitmore and Adam Hammett for their advice and assistance. Three anonymous reviewers gave us much helpful feedback and many constructive suggestions. This work was made possible by a grant from the Genesis Fund and by donations to Biblical Creation Trust. REFERENCES Austin, S.A. 2000. Mineral isochron method applied as a test of the assumptions of radioisotope dating. In L. Vardiman, A.A. Snelling, and E.F. Chaffin (editors), Radioisotopes and the Age of the Earth: A Young-earth Creationist Research Initiative, pp. 95-121. El Cajon, California: Institute for Creation Research, and St Joseph, Missouri: Creation Research Society. Austin, S.A. 2005. Do radioisotope clocks need repair? Testing the assumptions of isochron dating using K-Ar, Rb-Sr, Sm-Nd, and Pb-Pb isotopes. In L. Vardiman, A.A. Snelling, and E.F. Chaffin (editors), Radioisotopes and the Age of the Earth: Results of a Young-earth Creationist Research Initiative, pp. 325-392. El Cajon, California: Institute for Creation Research, and Chino Valley, Arizona: Creation Research Society. Austin, S.A., and A.A. Snelling. 1998. Discordant potassium-argon model and isochron “ages” for Cardenas Basalt (Middle Proterozoic) and associated diabase of eastern Grand Canyon, Arizona. In R.E. Walsh (editor), Proceedings of the Fourth International Conference on Creationism, pp. 35-52. Pittsburgh, Pennsylvania: Creation Science Fellowship. Geoscience Australia. 2021. Geochronology and Isotopes Data Portal. Retrieved May 16, 2023, from https://portal.ga.gov.au/persona/geochronology. [For download options, select “Geochronology and Isotopes” > “Geochronology” > “Geochronology – All” > “About”.] Hillenbrand, I.W., K.D. Thomson, L.E. Morgan, A.K. Gilmer, A.D. Dombrowski, K.F. Warrell, J.R. Malone, A.K. Souders, A.M. Hudson, M.A. Cosca, J.B. Paces, R.A. Thompson, and A.J. Park. 2023. USGS Geochron: A Database of Geochronological and Thermochronological Dates and Data. United States Geological Survey data release. DOI: 10.5066/P9RZNPIF. Isaac, R. 2007. Assessing the RATE project. Perspectives on Science and Christian Faith 59, no. 2 (June):143-146. BEACHY, KINARD AND GARNER How often do radioisotope ages agree? 2023 ICC 396
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