234U–206Pb and 238U–206Pb appear on the left, and 235U–207Pb on the right, showing consistent common Pb values for each cave. The y intercept represents the common lead ratio; yellow bars show the assigned range for common Pb in age calculations. Groups refer to the regression groups in Supplementary Table 1 with solid black lines showing regression fits. Grey contours show the percentage change in calculated age resulting from changing the common Pb composition by its assigned uncertainty. Dashed black lines show reference isochrons and ungrouped data are shown by grey circles. Uncertainties (2σ) are sometimes smaller than the symbol size. Particular details for each plot are as follows. A, Estimate of the common 208Pb/206Pb for Ledyanaya Lenskaya Cave in 234U/206Pb–208Pb/206Pb isotope space. 234U is used in the plot instead of 238U to suppress scatter in the U/206Pb ratio due to variations in the 234U/238U initial ratio. All but two of the ungrouped data have age uncertainties due to common Pb of <1% and are thus insensitive to the common Pb correction. Most data that are more sensitive to the common Pb composition (that is, those between the 1% and 3% contours) are included in the regressions to estimate the common Pb composition. B, Equivalent plot in 235U/207Pb–208Pb/207Pb isotope space for the estimation of the common 208Pb/207Pb ratio for Ledyanaya Lenskaya cave. Groups 3 and 4 correspond to the clump of ungrouped data close to the horizontal axis at about 0.225 on A. Note that 235U/207Pb ages are substantially more sensitive to the common Pb correction; these ages are used as a check on U–Pb concordance rather than to derive the dates used in the paper. C, Estimate of the common 208Pb/206Pb for Botovskaya Cave in 238U/206Pb–208Pb/206Pb isotope space. Groups 1, 3, 4 and 6 (plotted as squares) are unpublished data from about 2 Ma samples included here only to provide additional constraint on the common Pb composition (Supplementary Table 1). Ages used here are from the data plotted as circles. As for Ledyanaya Lenskaya Cave, the common Pb estimate includes the data for which the correction matters most as far as is possible. D, Equivalent plot in 235U/207Pb–208Pb/207Pb isotope space for the estimation of the common 208Pb/207Pb ratio for Botovskaya Cave. 235U/207Pb data are more sensitive to the common Pb correction.