We review the main sources of LiBeB production and show that a primary
mechanism is at work in the early Galaxy involving both ejection and
acceleration of He, C and O at moderate energy, which by nuclear interaction
with
H and He produce light isotopes. The precise measurement of the Be abundance
at [Fe/H] = -3.3 and of 6Li in halo stars find an explanation in this
framework. Thus, the preservation of 6Li in the atmosphere of metal poor
stars implied, points toward the fact the Spite plateau reflects the primordial
value of Li. Consequently, it can be used as a baryodensitometer.Comment: 6 pages, no figure, invited talk, to be published in World
Scientific, Proceedings of the conference "Cosmic Evolution" in the honor of
Jean Audouze and James W. Truran, held at the Institut d'Astrophysique de
Paris, Franc
