A Short History of Nearly Everything

by Bill Bryson

It also answered one of the great puzzles of oceanography—something that many of us didn’t realize was a puzzle—namely, why the oceans don’t grow saltier with time. At the risk of stating the obvious, there is a lot of salt in the sea—enough to bury every bit of land on the planet to a depth of about 150 metres. It had been known for centuries that rivers carry minerals to the sea and that these minerals combine with ions in the ocean water to form salts. So far no problem. But what was puzzling was that the salinity levels of the sea were stable. Millions of gallons of fresh water evaporate from the ocean daily, leaving all their salts behind, so logically the seas ought to grow more salty with the passing years, but they don’t. Something takes an amount of salt out of the water equivalent to the amount being put in. For a very long time, no-one could figure out what could be responsible for this. Alvin’s discovery of the deep-sea vents provided the answer.