The acid soluble chloride/bromide ratios of 66 limestones and 74 dolomites and the water soluble chloride/bromide ratios of 65 limestones and 42 dolomites were determined for samples from Recent to Precambrian age (2 b.y.). A progressive increase occurs in the chloride/bromide ratio from the Precambrian to Recent and is interpreted as representing an increase in the chloride/bromide ratio of sea water over the past 2 × 109 years. It is postulated that removal of bromine from sea water by sedimentation of bromine-enriched organic matter and crustal recycling of sedimentary rocks is responsible for the increase in the chloride/bromide ratio of sea water.

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