  From X-ray observations of galaxy clusters one derives the mass of the
intracluster medium along with its chemical composition. Optical/infrared
observations are used to estimate the mass of the stellar components of
galaxies, along with their chemical composition and age. This review shows that
when combining all this information, several interesting inferences can be
drawn, including: (1) galaxies lose more metals than they retain; (2) clusters
and the general field have converted the same fraction of baryons into stars,
hence the metallicity of the $z = 0$ Universe as a whole has to be nearly the
same we see in clusters, $\sim$1/3 solar; (3) for the same reason, the thermal
content of the intergalactic medium is expected to be nearly the same as the
preheating energy of clusters; (4) a strong increase of the Type Ia supernova
(SN) rate with lookback time is predicted if SNe Ia produce a major fraction of
cosmic iron; (5) the global metallicity of the $z\approx 3$ Universe was
already $\sim$1/10 solar; and (6) the Milky Way disk formed out of material
that was pre-enriched to $\sim$1/10 solar by the bulge stellar population.
