Extinction of major components of marine communities during Permian time was the most devastating event in the history of life. The pattern of extinction suggests that, among other possibilities, salinity changes in the oceans could have been a primary contributing factor. New data on Permian halite deposits show that the volume is far greater than previously suspected, amounting to at least 10 percent of the volume of salt presently in solution in the oceans. This amount is well over one-half the volume that, if removed from modern oceans, would produce brackish conditions resulting in mass extinctions in modern marine communities. Inasmuch as there may be considerably more Permian halite than has yet been discovered or dated as Permian, and as vast amounts of halite may have been lost from Permian deposits through solution in the past 225 m.y., it is considered probable that development of brackish oceans was an important factor in Permian extinctions.