Why is the Ocean Salty?

Well, we have been having a disagreement with our son, over his grades.  We think he should be getting only ones, of course, and he keeps coming home with threes and fours.  He’s smart enough, but less than a diligent student is putting it mildly.

Physics is one of his bad subjects.  We didn’t have physics at all when I was a kid.  I suppose it may have just been covered under ‘science.’  In fact, there’s a lot of stuff they learn today that we didn’t learn.  That’s the point of this story.

Anyway, the question he had to write about tonight was “Why is the ocean salty?”  He thought he was going to get away with “Because it has a lot of salt in it.”  He did point out that it’s 3.5%, which was a new factoid for me, you learn something new every day.

So, why is the ocean salty.  I started to explain to Sam that it must be something in the ocean because the water running into it is fresh, but I soon realized I didn’t know what I was talking about, I do tend to natter on a bit before I really research a matter, I write comments when I’ve only read the headline, stuff like that.  But, when I went to ASK.com, some of the answers were not much better.  Some went on a bit about the actual mineral content of seawater, but essentially that was it: the ocean is salty  because it has salt in it.

But, quite a few of the entries were more informative.  Apparently, it is from the rivers.  Obviously, rainwater is fresh, but as it seeps through the soil and washes over the rocks, it picks up salts and other minerals.  It’s still fresh water (or sweet water, as they say in most languages) because the amount of minerals is so small, but they reach the sea and they stay.  H2O evaporates, salt doesn’t, and the oceans are getting it from all the rivers in the world, all the time.  It builds up.

There were a couple of different theories, and some dispute  about by how much less the ocean was saline millions of years ago, and whether it’s remaining constant or becoming saltier, and something about ions, but I didn’t get that.

It was an interesting, educational experience.

Anyway, Sam read through a few of the answers, and then I asked him why the oceans were salty and he said “Nobody knows.”  I made him change that answer on the paper.