Fig. 1: X-ray amorphous contributions to terrestrial soil and Gale crater XRD patterns.

A XRD pattern (Co Kα) showing crystalline phases and the presence of an amorphous hump in the Rietveld fitted background from the clay-size fraction of selected soils; an amorphous hump is observed in the Rietveld fitted background of the clay-size fraction from all soils (Figs. S6, S9, S12, S15, S18, S21, S24). Some peaks attributed to serpentine extend beyond the y-axis scaling in the Eunice Bluff and Devil’s Punchbowl soils. B Amorphous humps from the clay-size fraction of ultramafic soils compared to Grater crater samples showing the similarity in the amorphous hump position. The selected Gale crater samples possess the most Fe-rich amorphous material observed to date^1,2,3. Gale crater amorphous material “humps” are generally centered between 22° and 26°2θ^1,2,3 with amorphous material richer in Fe and poorer in Si having humps centered at ≥26°2θ¹. Important caveats should be noted for this panel. The heights and locations of the Rietveld background fits are not Fhkl weighted and should not be taken as directly indicating a particular amorphous material, nor are they directly comparable to the plotted Gale crater amorphous material fits as those plots show directly modeled amorphous material contributions from FULLPAT fitting of Gale crater XRD samples^1,2. C The relative contribution of X-ray amorphous material to all clay-size fraction samples examined by XRD was determined as the integrated area under the amorphous hump showing the highest amount of X-ray amorphous material in the Tablelands soils, consistent with the preferential formation and persistence of this material under cold and wet conditions.