The majority of the elements and their isotopes from carbon (Z = 6) through
strontium (Z = 38) are made in solar proportions in supernovae with an average
production factor of around 15 (IMF averaged yield expressed as a mass fraction
and divided by the corresponding solar mass fraction). The iron group, Ti through
Ni, is underproduced in massive stars by a factor of several, which is consistent
with the premise that most of the solar abundances of these species were made
recently in thermonuclear (Type Ia) supernovae. In the distant past, the oxygen
to iron ratio was larger, and massive stars probably produced the iron group in
very low metallicity stars