Why Is the Ocean Salty?
“Water, water everywhere,/ Nor anyِ drop toِ drink.” This famous line, spoken byِ the lost sailor inِ Samuel Taylor Coleridge’s poem The Rime ofِ the Ancient Mariner, sums upِ oneِ ofِ the basic difficulties ofِ life atِ sea: humans needِ water toِ survive, butِ seawater isِ too salty toِ drink.
The average salt content ofِ ocean water isِ 35 parts perِ thousand, which—while itِ may notِ sound likeِ much—works outِ to 120 million tons ofِ salt perِ cubic mile ofِ seawater.
And thereِ areِ aboutِ 332,519,000 cubic miles (1,386,000,000 cubic km) ofِ water inِ the ocean.
It comesِ from theِ land, mostly.
It thenِ flows overِ the land, eroding rocks andِ picking upِ small amounts ofِ salt andِ other dissolved minerals.
At thisِ point, theِ water isِ still basically fresh; thereِ isِ some salt inِ it butِ usually notِ enoughِ to makeِ itِ undrinkable.
The idea thatِ salt wasِ gradually deposited inِ the sea byِ rivers wasِ firstِ suggested byِ the British astronomer Edmond Halley inِ 1715.
Halley tookِ hisِ observation a step fartherِ andِ proposed thatِ salinity ofِ seawater couldِ serve asِ a kind ofِ clock thatِ couldِ beِ used toِ determine theِ age ofِ the ocean (and thus, heِ assumed, Earth).
He reasoned thatِ dividing theِ total volume ofِ ocean water byِ the rate atِ which salt wasِ deposited inِ the ocean wouldِ show howِ long itِ hadِ taken forِ the ocean toِ reach itsِ current level ofِ salinity.