Connecting the primordial and Galactic deuterium abundances

The deuterium abundances inferred from observations of the interstellar medium (ISM) within 1-2 kpc of the Sun range over a factor of 3 and the corresponding oxygen abundances show an even larger dispersion. While the lower D (and O) abundances likely result from depletion on to dust, the higher D abundances are consistent with the big bang nucleosynthesis-predicted primordial D abundance and chemical evolution models of the Galaxy with infall of primordial or nearly primordial material. The large ranges in deuterium and oxygen abundances suggest that the effects of depletion and/or infall have not been homogenized in the local ISM.