  The thermodynamics of the diffuse, X-ray emitting gas in clusters and groups
of galaxies are affected by a certain amount of non-gravitational energy input,
as indicated by the scaling properties of X-ray halos. Such a view has been
recently confirmed by the detection of an excess entropy in the center of
groups. It is not easy, however, to identify unambiguously the source and the
epoch of such excess entropy. Here we show that the observations of high z
clusters will help in reconstructing both the dynamic and the thermodynamic
history of the diffuse cosmic baryons.
