Present-day outcomes are shown in 128Xe–132 Xe–136Xe isotopic space for different model parameter combinations. Four parameters are explored: parameters affecting the mantle processing-rate history (Mres and Nres), the initial mantle 130Xe concentration (LV = 0.1%–1%), and CC (Extended Data Fig. 3). In each panel, three of these parameters are held constant and the other is varied to illustrate model sensitivity to the varied parameter. Each cloud of points represents the range of present-day 128Xe/132Xe and 136Xe/132Xe generated by different regassing histories given the specified Nres, Mres, LV and CC. The red rectangle indicates the estimated present-day mantle 128Xe/132Xe and 136Xe/132Xe range. Dots that fall within the red rectangle represent the family of regassing histories that successfully reproduce present-day mantle composition for each parameter combination. The reference case shown in the main-text figures (Mres = 90%, Nres = 8, LV = 1%, CC = 1) is shown as a cloud of black points in all panels. The orange square is U-Xe, the brown diamond is average carbonaceous chondrites (AVCC) and the blue circle is the modern atmosphere. a, Higher mantle processing rates push present-day compositions towards fissiogenic Xe components. b, Lower late-veneer fractions correspond to present-day compositions closer to fissiogenic Xe components. c, A relatively low mass of the convecting mantle means that the mantle must be more depleted in U to satisfy mass balance with the continental crust (Methods). Thus, for low Mres, the impact of fission is muted compared to high Mres. d, The continental crust model has a limited effect on present-day Xe isotopic compositions.