Evolution of the composition for a one-zone burn at constant T = 9.6 × 10⁹ K and ρ = 6.0 × 10⁹ g cm⁻³ for 10⁶ s starting with a pure ²⁸Si composition. The calculation uses the mesa_204.net isotope listing (see Table 2), the most abundant isotopes are drawn with thick lines, and several isotopes are labeled. The initial composition is quickly erased as NSE for ﹩{Y}_{{\rm{e}}}\;\approx ﹩ 0.5 is established by ﹩\approx ﹩ 10⁻⁸ s. Several orders of magnitude in time pass before weak reactions drive a second period of rearrangement. By ﹩\approx 10﹩ s a second NSE quiescent period with ﹩{Y}_{{\rm{e}}}\;\approx ﹩ 0.403 is established.