Evaporation is a geologic process that concentrates the ion solute residues in the ocean basins. At a fundamental level, evaporation is the transition of the molecule of a liquid from the liquid state to the gaseous state by diffusion from the surface of the liquid.

Driven by solar energy, the only significant loss of water from the ocean basin occurs via evaporation. As the ocean surface and atmospheric interface is small compared to the total volume of the ocean, estimates of the time a particular molecule remains in the liquid phase range in the order of thousands to tens of thousands of years before once again entering the atmosphere as part of the hydrologic cycle.

Because solutes (e.g., dissolved salts) from weathering and erosion are not as volatile (i.e., as easy to move into the gas or vapor phase as the water molecules, evaporation plays a significant role in the formation of many geologic features (e.g., Great Salt Lake, Dead Sea, etc.).

Evaporation is usually also responsible for the majority of the loss of water from precipitation and results in a high cycling of water molecules during the hydrologic cycle.

Evaporation may be driven by solar energy or be a directed process used to concentrate an aqueous solution of nonvolatile solutes and a volatile solvent. In evaporation, a portion of the solvent is vaporized or boiled away, leaving a thick liquid or solid precipitate as the final product. The vapor is condensed to recover the solvent or it can simply be discarded. A typical example is the evaporation of sea water to produce salt.

Evaporation may also be used as a method to produce a liquid or gaseous product obtained from the condensed vapor. For instance, in desalinization processes, sea water is vaporized and condensed in a water-cooled heat exchanger and forms the fresh water product.

Although evaporation can be driven by the random motion of molecules near the liquid-gas interface, the addition of heat to a system speeds the evaporative process.

See Also

Caliche; Condensation; Drainage Calculations and Engineering; Leaching; Oceans and Seas; Phase State Changes; Runoff