The process by which a region is divided into relatively distinct, nearly horizontal, layers. Sedimentary rock often consists of various strata because the rock was laid at different times when different materials were being deposited. Lakes and oceans also consist of strata where plant and animal life may be very different depending on the temperature and amount of light available. The atmosphere is divided into strata that differ in density, temperature, chemical composition, and other factors. In the lower atmosphere, temporary stratification, such as temperature inversions, may occur, often resulting in severe pollution conditions.