We asked how probable is the emergence of a composome within a large collection of randomly drawn assembly compositions. For assemblies with size N=20 generated from a repertoire of NG=20 different environmental compound types, we computed a composome probability of 7X10 -4 (Figure ). We then analyzed the dependence of this probability on N and NG, and discovered a semi-log linear relationship (Figure ). By extrapolation, we were able to infer a reproduction probability of 3X10 -13 for N=NG=100, a size used in most analyses reported in this study. This exceedingly small incidence of reproducing assemblies within compositional space casts doubts on a capacity of an assembly to reach reproduction by randomly disposed compound exchanges or syntheses.