On average, seas and oceans contain 3.5% salt. The salt level in the Dead Sea is 27.5%. Salt, present in the seas and oceans of the globe, comes from the erosion of the earth's crust. It comes from lakes and rivers. The Jordan supplies the Dead Sea. The Dead Sea is located in an arid valley where the water evaporates more quickly than on the high seas. Thus, under the effect of accelerated evaporation, the salt is more concentrated. Photo credit: Nicole Baster