The salty sea

A sailor who has spent much of his life at sea is often called an \”old
salt.” This is a sort of joke, meaning that the sailor has probably been
doused with so much sea water that he has become salty! For sea water is
salty—so salty you can’t drink it.

Why is the sea salty? Why isn’t sea water fresh, like the water of
rivers and lakes?

Many of the world’s rivers start high in the mountains and flow down
into the sea. As river water moves along, it dissolves billions of tiny
bits of material out of the ground. Much of this material is salt. A
river carries this dissolved salt with it until it reaches the sea.
Thus, rivers dump tons of salt into the sea every day.

Scientists think the sea also gets some salt from inside the earth. They
think that sea water flows through cracks in the sea bottom and comes
back up through other cracks. As it flows beneath the bottom of the sea,
it picks up salt from the rocks in the earth.

The sea has been collecting salt for thousands of millions of years. All
this salt is spread through the sea by waves, winds, and currents. In
fact, there is so much salt in the sea that if you spread it on the land
it would cover all the land in the world with a layer of salt 150 feet
(45 meters) high! This is why sea water tastes salty.

But if rivers have salt in them, why aren’t they salty? And some
rivers pour into lakes, so why aren’t the lakes salty?

Well, rivers aren’t salty because there’s never very much salt in any
one part of a river. Lakes that have rivers running into them aren’t old
enough to have collected much salt. Lakes are only thousands of years
old, but the salty sea is thousands of millions of years old.

Many other chemicals are also in seawater. These chemicals got there the
same way the salt did, but there is still more salt in the oceans than
any other chemical. Scientists think the other chemicals get used up by
sea creatures that take certain chemicals out of the water to make their
shells and skeletons. Millions of trillions of creatures have done this
for hundreds of millions of years.

Scientists think the sea is in balance now and that it has had about the
same amount of salt for at least five hundred million years.

Salt from the sea has the shape of cubes. The salt you put on food is
also tiny, tiny cubes.