  It appears that the Lyman alpha forest is becoming thick at a redshift of
about 5.5, cutting off the higher redshift intergalactic medium from view in
neutral hydrogen. However, the effects of star formation at higher redshift are
still readable in the intergalactic metal lines. In this paper I use
observations of 32 quasars with emission redshifts in the range 2.31 to 5.86 to
study the evolution of the intergalactic metal density from z = 1.5 to z = 5.5.
The C IV column density distribution function is consistent with being
invariant throughout this redshift range. From direct integration, I determine
Omega_CIV to be in the range (2.5 - 7) \times 10^{-8} and Omega_SiIV in the
range (0.9 - 3) \times 10^{-8} between z = 1.5 and z = 5. The metallicity at z
= 5 exceeds 3.5 \times 10^{-4}, which in turn implies that this fraction of the
universal massive star formation took place beyond this redshift. This is
sufficient to have ionized the intergalactic medium.
