The USGS National Geochronological Database is a central repository for published radioisotope ages from across the United States. It contains 18,575 records with 29,043 age determinations using eight different radioisotope methods: potassium-argon (40K-40Ar), rubidium-strontium (87Rb-87Sr), samarium-neodymium (147Sm-143Nd), thorium-lead (232Th-208Pb), lead-lead (Pb-Pb), uranium-lead (235U-207Pb, 238U-206Pb), and fission tracks (FT). We created a “Concordance Metric” which measures a calculated “Concordance Score” for each record by looking at each pair of unique ages within the record, arriving at a score from 0.00 to 1.00, where 1.00 means total concordance within the record (all the age ranges overlap) and 0.00 means total discordance (none of the age ranges overlap). We adopted several approaches to identifying and quantifying the frequency of radioisotope age concordance in the database: (1) we calculated the frequency of “internal concordance” within each method; (2) we calculated the frequency of concordance where ages from two radioisotope methods were available for the same record; (3) we calculated the frequency of concordance where ages from three or more radioisotope methods, at least two of which were not in the U-ThPb decay chain, were available for the same record; and (4) we calculated the frequency of concordance where ages calculated using at least three of the four U-Th-Pb methods were available for the same record. Overall, the average concordance score for the whole database is 0.64. Only 4,875 of the 18,575 records (26.2%) included more than one calculated age. Of these, 1,135 (23.3%) had a concordance score of 0.00 and 2,593 (53.2%) had a concordance score of 1.00. There were 998 records with age determinations using three or more U-Th-Pb methods. Concordance scores for these records ranged from 0.18 to 0.79, averaging 0.57. Only 34 records included ages using three or more different radioisotope methods where at least two were not U-Th-Pb, and only one of these (2.9%) had a concordance score of 1.00. We also found a systematic pattern in radioisotope discordances, somewhat similar to the pattern identified previously by the RATE (Radioisotopes and the Age of The Earth) group. RATE found that β-decaying isotopes tended to yield younger ages than α-decaying isotopes; 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. ABSTRACT I. INTRODUCTION Radioisotope dating is in many ways the cornerstone of the modern geological synthesis, connecting rock units to absolute numerical ages. Young-earth creationists have highlighted several problems with radioisotope dating methods, one of which is the phenomenon of discordance. Kurt Wise summed it up well in his 2002 book Faith, Form, and Time: “If accurate, each radiometric method should produce the same radiometric age. In actuality, however, multiple methods usually yield multiple, non-overlapping ages” (p. 63). Other creationists have published detailed studies of specific rock units, revealing evidence of discordance and identifying systematic trends within those data. However, so far there has not been a large-scale study to confirm the prevalence of discordance. Wise (2002) supported his claim with a footnote that read: “The National Geochronological Database (USGS Digital Data Series DDS-14, 1995) contains thousands of rocks dated with multiple methods. A careful examination of these records shows that the methods rarely yield the same ages” (p. 256). We decided to interrogate the National Geochronological Database to examine Wise’s claim and to extend the work of other creationists. II. PREVIOUS WORK Several creationists have published on the phenomenon of radioisotope age discordance. Woodmorappe (1979) compiled about 350 radioisotope age determinations that were at least 20% too young or too old given their expected geologic age, along with some examples of discordant radioisotope age determinations. Numerous other instances of discordant radioisotope ages are described in Woodmorappe (1999) and Nethercott (2021). However, the most systematic creationist investigation of radioisotope discordance was carried out by the RATE (Radioisotopes and the Age of The Earth) research group, convened by the Institute for Creation Research and the Creation Research Society in 1997 (Vardiman et al. 2000, 2005). RATE published new radioisotope ages using the K-Ar, Rb-Sr, Sm-Nd, and PbPb systems for ten rock units, including lava flows at Mt. Ngauruhoe, New Zealand; the Somerset Dam layered mafic intrusion, Queensland, Australia; the Beartooth andesitic amphibolite, Wyoming; and basalts and diabase sills of the Apache Group, central Arizona; in Micah D. Beachy, and Benjamin R. Kinard, Cedarville University, 251 North Main Street #6486, Cedarville, OH 45314. mdbeachy@cedarville.edu, benjaminkinard@cedarville.edu Paul A. Garner, Biblical Creation Trust, P.O. Box 325, Ely, CB7 5YH, United Kingdom. paul@biblicalcreationtrust.org © Cedarville University International Conference on Creationism. The views expressed in this publication are those of the author(s) and do not necessarily represent those of Cedarville University. 9th 2023 Beachy, M.D., B.R. Kinard, and P.A. Garner. 2023. How often do radioisotope ages agree? A preliminary study of 29,000 radioisotope ages in the USGS National Geochronological Database. In J.H. Whitmore (editor), Proceedings of the Ninth International Conference on Creationism, pp. 387-411. Cedarville, Ohio: Cedarville University International Conference on Creationism. HOW OFTEN DO RADIOISOTOPE AGES AGREE? A PRELIMINARY STUDY OF 29,000 RADIOISOTOPE AGES IN THE USGS NATIONAL GEOCHRONOLOGICAL DATABASE KEYWORDS radioisotope dating, geochronology, concordance, discordance, concordance metric, accelerated decay, USGS National Geochronological Database
RkJQdWJsaXNoZXIy MTM4ODY=