  The early Universe was characterized by the presence of heavy particles that
decoupled at different temperatures leading to different phases of the
Universe. This had a consequences on the time evolution of the thermodynamic
and the cosmological parameters characterizing each phase of the early
Universe. In this study, we derive the analytic expressions of the equations
governing the time evolution of these parameters in the early eras of the
Universe namely, the radiation era, the quark-gluon plasma era, the hadron era
and the mixed era. The parameters under concern include the energy density, the
entropy density, the temperature, the pressure in addition to Hubble parameter
and the scale factor. Having these expressions allows us to give estimations of
the times corresponding to the beginning and ending of each era of the Universe
as will be presented in this work.
