Big Bang Nucleosynthesis and a New Approach to Galactic Chemical Evolution

Big bang production of deuterium is the best indicator of the baryon density; however, only the present abundance of D is known (and only locally) and its chemical evolution is intertwined with that of 3 He. Because Galactic abundances are spatially heterogeneous, mean chemical-evolution models are not well suited for extrapolating the pre-solar D and 3 He abundances to their primeval values. We introduce a new approach which explicitly addresses heterogeneity by statistically tracing the history of the pre-solar material back to its primeval beginning. We show that the decade-old concordance interval η ≈ (2-8) × 10 -10 based on D and 3 He is well founded.