(I) The average salt concentration in the oceans at the present time is around 35 grams per litre of sea water. (II) Geological evidence shows that this figure has remained constant for the last 1.5 billion years. (III) Actually, this means that the oceans must lose nearly three billion tons of salt each year to balance the amount that enters them. (IV) Suggested mechanisms for this process include loss through sea spray, chemical reactions at the sea floor, biological activity, and the formation of salt deposits on land. (V) It is true that floating ice would not change sea levels if it melted.