  Recent detailed simulations of Galactic Chemical Evolution have shown that
the heavy elements, in particular [Fe/H], are expected to exhibit a weak, or
absent, correlation with stellar ages in the early Galaxy due to the lack of
efficient mixing of interstellar material enriched by individual Type II
supernovae. A promising alternative "chronometer" of stellar ages is suggested,
based on the expectation that the light elements Be and B are formed primarily
as spallation products of Galactic Cosmic Rays.
