and activity presented in @Claire12 is likely incorrect given that the early activity of the Sun is not known and would have depended sensitively on the Sun’s initial rotation rate (@Johnstone15; @Tu15). In Fig. \[fig:XUVtracks\], three possible evolutionary tracks for the Sun’s rotation are shown, with the grey shaded area showing the range of solar X-ray fluxes at 1 AU that I consider.

In Table. \[table:grid\], I give a summary for each considered case of the input XUV spectrum fluxes and the expected age ranges that the early Sun, or any solar-mass star, would have these fluxes. For the age ranges, I use the slow and rapid rotator tracks for X-ray emission shown in Fig. \[fig:XUVtracks\]. These tracks give the expected evolutions of solar mass stars born at the 10th and 90th percentiles of the distribution of rotation rates. Therefore, for each input spectrum, the lower limit on the age is the age at which the slow rotator reaches the corresponding activity level of the spectrum and the upper limit is the age at which the fast rotator reaches this activity level. This is meant as an approximate measure of the expected age for a given X-ray flux and does 