Cosmic Deuterium Or A Hydrogen Interloper ?
  Two groups have independently reported the possible detection of extragalactic deuterium in the absorption spectrum of the same high redshift, low metalicity QSO. Although the high value for the inferred deuterium abundance poses no problems for cosmology (i.e., big bang nucleosynthesis), it is in apparent conflict with solar system observations of deuterium and helium-3. This latter inconsistency is explained and made quantitative and it is shown that, unless the inferred D/H ratio is too high by a factor of three, these data challange our understanding of the stellar and galactic evolution of helium-3. This conflict is resolved if the observed absorption feature is, in fact, due to a hydrogen interloper rather than to high z, low Z deuterium. 
Gary Steigman