Observed trends of lithium. Crosses indicate individual stellar abundances, while filled circles show group averages. Solid lines represent the atomic diffusion model predictions (see Fig. 6), which have an original abundance as given by the dashed line [﹩\mathrm{log}\,\varepsilon ( \mathrm{Li}\,) =2.54\pm 0.1﹩]. The dark shaded area shows the predicted primordial lithium abundance ["CMB+BBN:" ﹩\mathrm{log}\,\varepsilon ( \mathrm{Li}\,) =2.64\pm 0.03﹩; Spergel et al. 2007].