Aqueous solution of salts in more or less constant ratio, whose composition depends on several factors among which predominate living organisms, detrital sedimentation and the related chemical reactions. Sea-water accounts for more than 98% of the mass of the hydrosphere and covers just over 70% of the globe. Because of the composition and stability of the oceans, and the way they are controlled, they are of great importance to the climate, and great attention has been given to studying the effects of pollution. Man's activities are believed to be accelerating the change in the composition of sea-water.