The Galactic thick and thin disks: differences in evolution
  Recent observations demonstrate that the thin and thick disks of the Galaxy have different chemical abundance trends and evolution timescales. The relative abundances of $\alpha$-elements in the thick Galactic disk are increased relative to the thin disk. Our goal is to investigate the cause of such differences in thick and thin disk abundances. We investigate the chemical evolution of the Galactic disk in the framework of the open two-zone model with gas inflow. The Galactic abundance trends for $\alpha$-elements (Mg, Si, O) and Fe are predicted for the thin and thick Galactic disks. The star formation histories of the thin and thick disks must have been different and the gas infall must have been more intense during the thick disk evolution that the thin disk evolution. 
T.V. Nykytyuk, T.V. Mishenina