Interstellar cloud material in meteorites

In addition to material of apparently circumstellar origin, many primitive meteorites contain material for which an origin in interstellar clouds is indicated. Such material, apparently organic in nature, is revealed by enrichments of deuterium relative to terrestrial material. Astronomical observations have shown that simple organic molecules in dense interstellar clouds have large D/H ratios. The H-isotopic compositions of those molecules are believed to be the result of ion-molecule reactions taking place at low temperatures.