A comparison of the Ca+ emission luminosity-after correction for spectral-type effects-for the Pleiades, Ursa Major, and Hyades stars and the Sun indicate an emission decay which varies as the inverse square root of the age. Further, the rotational decay curve is found to satisfy the same law. It is further suggested that lithium depletion follows the same law but only as far as the Hyades age, after which the depletion proceeds exponentially. Since Ca+ emission is linearly proportional to magnetic field strength at the surface, one can predict that the surface fields are proportional to angular velocity and decay as the inverse square root. The above results are predicated Qi' the standard Hyades age (0.4 billion years).