Fraction of atmospheric ⁴⁰Ar contributed by radiogenic production as a function of the rock-to-envelope mass ratio for different primordial ⁴⁰Ar enrichments inherited from the PSN. Model assumptions, primordial enrichment cases, potassium abundances, colors, and planetary reference values are the same as in Figure 4; see its caption for details. The horizontal blue dashed line marks equal radiogenic and primordial contributions (f_rad = 0.5), while the red dotted line indicates a radiogenic contribution of 10% (f_rad = 0.1).