Comparison of the measured (symbols with error bars) and simulated (histograms) ⁶⁰Fe/Fe ratio as a function of the terrestrial archive’s layer age for model A (upper panel) and B (lower panel). Simulation data is set upon the instrumental background derived specifically for 237KD, which is indicated by the dashed line. The grey levels of the histograms refer to the ⁶⁰Fe survival fractions employed.