  We examine the effects of cosmic strings on structure formation and on the
ionization history of the universe. While Gaussian perturbations from inflation
are known to provide the dominant contribution to the large scale structure of
the universe, density perturbations due to strings are highly non-Gaussian and
can produce nonlinear structures at very early times. This could lead to early
star formation and reionization of the universe. We improve on earlier studies
of these effects by accounting for high loop velocities and for the filamentary
shape of the resulting halos. We find that for string energy scales G\mu >
10^{-7} the effect of strings on the CMB temperature and polarization power
spectra can be significant and is likely to be detectable by the Planck
satellite. We mention shortcomings of the standard cosmological model of galaxy
formation which may be remedied with the addition of cosmic strings, and
comment on other possible observational implications of early structure
formation by strings.
