Recent detection of a large optical depth to Thomson scattering by Wilkinson Microwave Anisotropy Probe (WMAP) implicates in new considerations about reionization epoch. Nowadays it is possible to simulate hydrogen reionization for redshift 15 < z < 20, although the greater difficult problem consists to know what are the first ionizing sources in the universe. Observations on Gunn-Peterson effect reconciled with WMAP findings suggests z ∼6 as the redshift for complete reionization. Study on the formation history of supermassive black holes (SMBHs) in galaxies suggests an interplay among QSOs activity and star rate formation. On this aspect, QSOs work as clocks of star formation in spheroids. Observations of magnesium abundance in QSOs for various redshifts show that star formation in these systems began very early.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html