  The solar interior has been scrutinized by two different and independent
probes during the last twenty years with important revisions of the solar
model, including a recent heavy element abundance revision. Today, we get a
quantitatively coherent picture (even incomplete) of the solar (stellar)
radiative zones. In this review, we recall the clues for solar gravitational
settling definitively established by the seismic determination of the
photospheric helium content. We comment also on the need for mixing in the
transition region between radiation and convection in the case of the Sun and
of population II stars. We finally list the open questions and the importance
to continue more precise investigations of the solar (stellar) radiative zone
in detecting gravity modes with the project DynaMICS.
