  Several emerging links between high-redshift observational cosmology and the
Galactic fossil evidence found in the kinematics, metallicities and ages of
Milky Way stars are discussed. In a flat Cold Dark Matter model with
$\Omega\simeq 0.3$ that agrees with present large-scale structure observations,
the oldest stars in the Milky Way should have formed in the first halos where
gas was able to cool, at $z\simeq 20$. These earliest, weakly bound dwarf
galaxies probably turned only a small fraction of their gas to stars, which
should be metal-poor. However, the merging rate in the early universe was much
faster than the present one, so massive halos with more efficient star
formation and metallicities up to the highest values present today in the bulge
could have formed less than $10^9$ years after the oldest stars. The mean
metallicity produced in the universe by a given redshift is related to the mean
surface brightness of star-forming galaxies above this redshift, and also to
the reionization epoch if galaxies were the dominant sources of ionizing
radiation. The biased distribution of the early dwarf galaxies where the first
stars formed should result in an age gradient with radius of the
low-metallicity stars in the Milky Way, with the oldest ones concentrated in
the bulge and the youngest in the outer halo.
