Figure 1. The distribution of concordance scores for all 4,875 records in the National Geochronological Database with two or more radioisotope age determinations. Method Pb-Pb Rb-Sr 235U- 207Pb 238U- 206Pb 232Th-208Pb K-Ar FT Pb-Pb X 0.40 0.54 0.43 0.18 0.14 0.00 Rb-Sr 0.40 X 0.40 0.32 0.26 0.51 0.21 235U- 207Pb 0.54 0.40 X 0.79 0.55 0.27 0.14 238U- 206Pb 0.43 0.32 0.79 X 0.55 0.24 0.07 232Th-208Pb 0.18 0.26 0.55 0.55 X 0.34 0.12 K-Ar 0.14 0.51 0.27 0.24 0.34 X 0.50 FT 0.00 0.21 0.14 0.07 0.12 0.50 X Method (greater on left) Pb-Pb Rb-Sr 235U- 207Pb 238U- 206Pb 232Th-208Pb K-Ar FT Pb- Pb X 54.4% 84.7% 83.2% 84.2% 67.1% 54.9% Rb-Sr 45.6% X 55.1% 60.3% 55.4% 64.0% 70.8% 235U- 207Pb 14.6% 43.6% X 85.0% 64.4% 77.5% 85.7% 238U- 206Pb 16.1% 38.1% 9.2% X 56.0% 71.9% 87.1% 232Th-208Pb 15.4% 44.1% 33.9% 42.6% X 69.6% 82.4% K-Ar 32.9% 35.9% 21.7% 28.1% 30.4% X 72.1% FT 45.1% 29.2% 14.3% 12.9% 17.7% 26.5% X Table 2. The proportion of concordant pairwise age comparisons from our “Two Methods” dataset. Table 3. The percentage of pairs for which the age calculated using one method was greater than the age calculated using another. The method giving the older age is in the left-hand column; the method giving the younger age is along the top. Some pairs gave the same age, and so are not counted as being greater for either method. BEACHY, KINARD AND GARNER How often do radioisotope ages agree? 2023 ICC 390
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