Stirring an aqueous suspension of D and U for six days at room temperature resulted in a product primarily composed of D-U cocrystal hydrate (D-U hyd, Figures and). Dry grinding of D and U for 2 h resulted in a product with an amorphous PXRD pattern (Figure ) which, upon aging 60 in H 2 O vapor for seven days at room temperature, transformed to D-U hyd (Figure ). The input of mechanical energy, considered an important energy source for prebiotic chemistry, is not a prerequisite for D-U hyd formation in moisture. Gentle homogenization of D and U with the spatula and aging in H 2 O vapor at room temperature also resulted in the formation of D-U hyd (Figures and). We monitored the grinding of D and U with a stoichiometric amount of H 2 O by in situ synchrotron PXRD (Figure ). It showed that D-U hyd started to form within the first minute of grinding, and the reaction mixture was phase pure by 30 min (Figures and). Additionally, we studied the base-pairing of D and U under low-temperature conditions (Figures ). After 30 min of grinding D and U with a stoichiometric amount of H 2 O at ca. 80 K, PXRD analysis confirmed the formation of D-U hyd (Figure ).