A mechanism of proposed for the formation of the thin layers of enhanced sodium concentration observed in the atmospheric sodium layer. The proposed mechanism involves the wind-shear distortion of initially thick sodium clouds of limited horizontal extent, originally produced by the deposition of material of extraterrestrial origin. This mechanism explains almost all the observed characteristics of the enhanced layers, including their height of occurrence, small vertical extent, vertical motion, rapid growth and decay and highly variable duration. ¿ American Geophysical Union 1988