  Light element ($^6$Li, $^7$Li and $^9$Be) depletion isochrones for halo stars
have been calculated with standard stellar evolution models. These models
include the latest available opacities and are computed through the sub-giant
branch. If $^6$Li is not produced in appreciable amounts by stellar flares,
then the detection of $^6$Li in HD 84937 by Smith, Lambert \& Nissen (1993) is
compatible with standard stellar evolution and standard big bang
nucleosynthesis only if HD 84937 is a sub-giant. The present parallax is
inconsistent with HD 84937 being a sub-giant star at the $2.5\, \sigma$ level.
The most metal poor star with a measured $^9$Be abundance is HD 140283, which
is a relatively cool sub-giant. Standard stellar evolution predict that $^9$Be
will have been depleted in this star by $\sim 0.3$ dex (for ${\rm T_{eff}} =
5640$ K). Revising the abundance upward changes the oxygen-beryllium relation,
suggesting incompatible with standard comic ray production models, and hence,
standard big bang nucleosynthesis. However, an increase in the derived
temperature of HD 140283 to 5740 K would result in no depletion of $^9$Be and
agreement with standard big bang nucleosynthesis.
