Figure S1. T-W Concordia plots showing secondary standards WC-1 and ‘Prague’ normalised to WC-1’s correct age. Both WC-1 and ‘Prague’ regressions are anchored to the approximate Stacey and Kramers two stage Pb evolution model initial Pb composition (for Phanerozoic samples). Note ‘Prague’ secondary standard has a high failure rate due to significant zonation in U-Pb and Pb-Pb ratios in certain calcite chips.