Time evolution of the logO/H variation obtained from solar metallicity chemical evolution models, using three different SFHs (an IB and two extended SFH, both with a difference of a factor of six between the actual SF value and the value 30 Myr ago, but with different shapes), and two SNe cases: one where all massive stars produce a SNe explosion and another where stars more massive than 25 M_⊙ suffer a direct collapse to black holes (where only the IB case is shown). In all cases a star formation efficiency of 10% is assumed. The arrow in the top right shows the maximum enrichment reached by the three SFHs.