@dajunguo36

If life evolved in the sea, why is physiological saline less salty than sea water? This question leads to an interesting clue about the origin of life. The usual explanation is that the oceans were much less salty when life originated than they are now, so organisms developed biochemical systems that work best at the salt levels that existed back then. But that’s purely wrong. Insofar as anyone can tell, the salinity of the early ocean was probably 1.5 to 2 times the modern value [1][2] or possibly just as salty as now.[3] So, the first organisms came into being when the oceans were pretty salty. And what’s more, oceans, back then and now, have more sodium than potassium but cells have the reverse, more potassium than sodium. Our blood has moderate levels of sodium but the cells in our bodies keep sodium out and retain potassium instead. They maintain that by using a pump (the sodium-potassium pump) that keeps sodium out and retains potassium.[4]

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