  It has been proposed that very massive stars (VMSs) dominated heavy element
production until a metallicity threshold corresponding to [Fe/H]=-3 was
reached. This results in a prompt (P) inventory of elements, the abundances of
which were determined from observations of Galactic halo stars with [Fe/H]=-3.
We calculate Omega_P(E) from the P inventory for a large number of elements in
the IGM. Using the available data on Omega(E_ion) for C IV, O VI, and Si IV in
Ly alpha systems, we find that the ionization fractions calculated from
Omega(E_ion)/Omega_P(E) are, within reasonable uncertainties, compatible with
the values estimated from ionization models for Ly alpha systems. This
agreement appears to hold from z=0.09 to 4.6, indicating that the bulk of the
baryonic matter remains dispersed with a fixed chemical composition. We
conclude that the P inventory was established in the epoch prior to z=4.6. The
dispersal of processed baryonic matter to the general IGM is considered to be
the result of energetic VMS explosions that disrupted baryonic aggregates until
the metallicity threshold was reached to permit normal astration. The formation
of most galaxies is considered to have occurred subsequent to the achievement
of this metallicity threshold in the IGM.
