CoachThe G-dwarf problem is the shortage of metal-poor long-lived stars in the solar neighbourhood compared with the prediction of the closed-box model: far fewer of the long-lived dwarf stars of spectral type G have low metallicities than a closed box would have made.
![A two-phase model of [ / Fe] in a closed box: the plateau at +0.4 is the ratio made by core-collapse supernovae; Type Ia supernovae, which begin when the gas has reached [ Fe/H] = -1, then add iron at a steady rate, until the ratio is solar at [ Fe/H] = 0. The plateau and the knee are those seen in the stars of the Galaxy; the shape between is the model’s. At the Sun’s metallicity, 60\,\% of the iron in this model has come from Type Ia supernovae.](/images/onecourse/chapters/earth-5/b3-origin-of-elements/fig-0f241a64d0d0.svg)