  We propose a phenomenological model for the early universe where there is a
smooth transition between an early "quintessence" phase and a radiation
dominated era. The matter content is modelled by an appropriately modified
Chaplygin gas for the early universe. We constrain the model observationally by
mapping the primordial power spectrum of the scalar perturbations to the latest
data of WMAP7. We compute as well the spectrum of the primordial gravitational
waves as would be measured today. We show that the high frequencies region of
the spectrum depends on the free parameter of the model and most importantly
this region of the spectrum can be within the reach of future gravitational
waves detectors.
