  Using the guidelines on SN element production provided by XMM-Newton, we
summarize the results of ASCA observations on the element abundance in groups
and clusters of galaxies. We show that while the metal production in groups
could be described by a stellar population with a standard local IMF, clusters
of galaxies require a more top-heavy IMF. We attribute an excess heavy element
production to an IMF evolution with redshift. Dating the galaxy formation in
clusters by observations of the star-formation rate, we conclude that the IMF
variations have occurred preferentially at z>~4. We further combine our
metallicity measurements with the mass function of clusters to estimate the
role of clusters in the evolution of the metal content of the Universe. We
argue that at no epoch stars are a major container of metals, unless groups of
galaxies are not representative for the star-formation. This lends further
support for the reduced (0.6 solar) mass-averaged oxygen abundance in the
stellar population.
