Abstract We consider the evolution of the light elements, especially beryllium and boron but also lithium, in the Galaxy as derived from observations within 1kpc of the Sun. The interest in Li has much to do with the evaluation of the universal baryon abundance via primordial nucleosynthesis, but the difficulties of interpretation have led to the need to understand Li synthesis within the Galaxy, and this entails understanding many processes, both stellar and interstellar. In the case of Be, and B although measurable abundances produced in the primaeval fireball were predicted in certain models, these are largely (but not totally) discounted observationally. However understanding the evolution of Be and B as tracers of Galactic chemical evolution is important. While most experts in nucleosynthesis have concentrated on the linear relation between B/Be and Fe, (or O) in the Galactic halo, and taken disc evolution rather for granted, we show that it is vital to use a valid chemical evolution model for the disc to explain the observations. We present such a model, and emphasize its implications for the infall of low metallicity gas to the disc as the driving element in star formation during the whole disc lifetime.

Keywords Galaxy: Disc, Gas accretion, Evolution, Nuclear Reactions, Nucleosynthesis, Abundances

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