The WMAP determination of the baryon−to−photon ratio implies, through Big Bang nucleosynthesis, a cosmological Li abundance larger, by a factor of 2 to 3, than the Li abundance plateau observed in the oldest Pop II stars. It is however inescapable that there be a reduction by a factor of at least 1.6 to 2.0 of the surface Li abundance during the evolution of Pop II field stars with [Fe/H] ≤ −1.5. That the observed Li be lower than cosmologically produced Li is expected from stellar evolution models. Since at turnoff most of the Li abundance reduction is caused by gravitational settling, the presence of 6 Li in some turnoff stars is also understood. Given that the WMAP implications for Li cosmological abundance and the Li Spite plateau can be naturally explained by gravitational settling in the presence of weak turbulence, there appears little need for exotic physics as suggested by some authors. Instead, there is a need for a better understanding of turbulent transport in the radiative zones of stars. This requires simulations from first principles. Rather strict upper limits to turbulent transport are determined for the Sun and Pop II stars.

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The solar evolution has been calculated including all the e †ects of the di †usion of helium and heavy elements. Monochromatic opacities are used to calculate radiative accelerations and Rosseland opacities at each evolution time step, taking into account the local abundance changes of all important (21) chemical elements. The OPAL monochromatic data are used for the opacities and the radiative accelerations. The Opacity Project data are needed to calculate how chemical species and electrons share the momentum absorbed from the radiation Ñux.A detailed evaluation of the impact of atomic di †usion on solar models is presented. On some elements thermal di †usion adds approximately 50% to the gravitational settling velocity. While gravitational settling had been included in previous solar models, this is the Ðrst time that the impact of radiative accelerations is considered. Radiative accelerations can be up to 40% of gravity below the solar convection zone and thus a †ect chemical element di †usion signiÐcantly, contrary to current belief.Up to the solar age, the abundances of most metals change by 7.5% if complete ionization is assumed, but by 8.5%È10% if detailed ionization of each species is taken into account. If radiative accelerations are included, intermediate values are obtained. Di †usion leads to a change of up to 8% in the Rosseland opacities, compared to those of the original mixture. Most of this e †ect can be taken into account by using tables with several values of Z.If one isolates the e †ects of radiative accelerations, the abundance changes they cause alter the Rosseland opacity by up to 0.5% ; the density is a †ected by up to 0.2% ; the sound speed is a †ected by at most 0.06%. The inclusion of radiative accelerations leads to a reduction of 3% of neutrino Ñuxes measured with 37Cl detectors and 1% measured with 71Ga detectors.The partial transformation of C and O into N by nuclear reactions in the core causes a D1% change in the opacities that cannot be modeled by a change in Z alone.The evolution is allowed to proceed to 1010 yr in order to determine the impact at the end of the main-sequence life of solar-type stars. It is found that immediately below the convection zone, the radiative acceleration on some iron peak elements is within a few percent of gravity. The abundance anomalies reach 18% for He in the convection zone but are kept within 12% and 15% for most because of They would have reached 18% in the absence of g rad . g rad .

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