Surface reactions on warm (at least 60 K) graphite grains between lattice C atoms and impinging H and O atoms within or in the vicinity of H II regions can provide a prolific source of H2CO and other interstellar molecules. It is proposed that similar reactions in the primitive solar nebula led to the formation of the organic molecules found in carbonaceous chondrites. From this and related evidence, it is argued that most of the solid material in the solar system may have originated as interstellar grains
