  The primordial abundances of Deuterium, he4, and li7 are crucial to
determination of the baryon density of the Universe in the framework of
standard Big Bang nucleosynthesis (BBN). li6 which is only produced in tiny
quantities and it is generally not considered to be a cosmological probe.
However, recent major observational advances have produced an estimate of the
li6/li7 ratio in a few very old stars in the galactic halo which impacts the
question whether or not the lithium isotopes are depleted in the outer layers
of halo stars, through proton induced reactions at the base of (or below) the
convective zone. li6 is a pure product of spallation through the major
production reactions, fast oxygen and alphas interacting on interstellar H, He
(especially in the early Galaxy). The rapid nuclei are both synthesized and
accelerated by SN II. In this context, the \li6 evolution should go in step
with that of beryllium and boron, recently observed by the Keck and HST
telescopes. Li6 adds a new constraint on the early spallation in the Galaxy. In
particular, if confirmed, the Li6/Be9 ratio observed in two halo stars (HD
84937, BD +263578) gives strong boundary conditions on the composition and the
spectrum of the rapid particles involved. We show that Li6 is essentially
intact in halo stars, and a fortiori \li7. We can define a range of the Li6
abundance in the very early Galaxy consistent with Big Bang nucleosynthesis
(5.6 10(-14) to 3. 10(-13) . Following the evolution at increasing metallicity,
we explain the abundance in the solar system within a factor of about 2.
