  We examine the case for Quark-Novae (QNe) as possible sources for the
reionization and early metal enrichment of the universe. Quark-Novae are
predicted to arise from the explosive collapse (and conversion) of sufficiently
massive neutron stars into quark stars. A Quark-Nova (QN) can occur over a
range of time scales following the supernova event. For QNe that arise days to
weeks after the supernovae, we show that dual-shock that arises as the QN
ejecta encounter the supernova ejecta can produce enough photons to reionize
hydrogen in most of the Inter-Galactic medium (IGM) by z ~ 6. Such events can
explain the large optical depth tau_e ~ 0.1 as measured by WMAP, if the
clumping factor, C, of the material being ionized is smaller than 10. We
suggest a way in which a normal initial mass function (IMF) for the oldest
stars can be reconciled with a large optical depth as well as the mean
metallicity of the early IGM post reionization. We find that QN also make a
contribution to r-process element abundances for atomic numbers A > 130. We
predict that the main cosmological signatures of Quark-Novae are the gamma-ray
bursts that announce their birth. These will be clustered at redshifts in the
range z ~ 7-8 in our model.
