Meteoric ablation creates layers of metal atoms in the atmosphere around 90 km. Although Ca and Na have similar elemental abundances in most minerals found in the solar system, surprisingly the Ca abundance in the atmosphere is less than 1 % that of Na. This study uses a detailed chemistry model of Ca, largely based on laboratory kinetics measurements, in a whole-atmosphere model to show that the depletion is caused by inefficient ablation of Ca and the formation of stable molecular reservoirs.