  We present a three-component mixing model for the evolution of O abundance
relative to Fe, taking into account the contributions of the first very massive
(> 100 solar masses) stars formed from Big Bang debris. We show that the
observations of O and Fe abundances in metal-poor stars in the Galaxy by
Israelian et al. and Boesgaard et al. can be well represented both
qualitatively and quantitatively by this model. Under the assumption of an
initial Fe ([Fe/H] = -3) and O inventory due to the prompt production by the
first very massive stars, the data at -3 < [Fe/H] < -1 are interpreted to
result from the addition of O and Fe only from type II supernovae (SNII) to the
prompt inventory. At [Fe/H] = -1, SNII still contribute O while both SNII and
type Ia supernovae contribute Fe. During this later stage, (O/Fe) sharply drops
off to an asymptotic value of 0.8(O/Fe)_sun. The value of (O/Fe) for the prompt
inventory at [Fe/H] = -3 is found to be (O/Fe) = 20(O/Fe)_sun. This result
suggests that protogalaxies with low ``metallicities'' should exhibit high
values of (O/Fe). The C/O ratio produced by the first very massive stars is
expected to be much less than 1 so that all the C should be tied up as CO and
that C dust and hydrocarbon compounds should be quite rare at epochs
corresponding to [Fe/H] < -3.
