Extended Data Fig. 7: Proposed multistep formation process of the organic phase.

A, As the parent body warmed, NH₃ and CO₂ from ices reacted to form carbamate via gas–grain or solid-state reactions before H₂O ice melted. B, Carbamate underwent partial polymerization to produce a water-insoluble organic phase at low temperatures that formed or was deposited on grain surfaces (gray). C, Further warming melted H₂O ice and decomposed any unpolymerized carbamate into NH₄⁺ and CO₃²⁻ dissolved in water (blue). D, Aqueous alteration led to the precipitation of some calcites (white circles) and initiated conversion of anhydrous silicates to phyllosilicates (textured fills of the circle and square). Calcites precipitated as either isolated grains or grains that stuck to or nucleated on the organic surfaces. E, Organic coatings from adjacent grains adhered, producing a layered structure with embedded carbonates and voids. Any mantles around ice grains would collapse or fold. F, Further aqueous alteration may have then folded the polymer sheets to produce more complicated structures, triggered additional chemistry, and set the final morphology (dark gray). Panels A and B occur at cryogenic temperatures below the melting of the H₂O–NH₃ eutectic, whereas panels C–F occur after the melting of H₂O ice.