Elizabeth Allen, age 8, of Utica, N.Y., for her question:

How did all the salt get into the ocean?

Andy's faithful old readers grow up and younger ones come along. Many of the same old questions pop into the heads of the younger readers. They must be answered, but Andy hates to repeat himself. So he always finds a new way to answer or a new bit of information to add to an old favorite.

Almost everyone has wondered why the tangy water of the sea is so salty. The oceans are fed by rains and rivers; rain pours down drops of fresh water and rivers pour in streams of more fresh water. None of this fresh water, you would think, can add salt to the salty sea. True, the salt does not fall down with the fresh rainwater, but every day more and more salt is added to the sea by the running rivers.

A great river gathers its water from countless smaller streams that come running down from far and wide. All this running water licks the ground, the rocks and stones as it gurgles along its way. Its  little tongues dissolve scraps and fragments from the soil and even softer scraps from the solid rocks.

These dissolved particles disappear, just as a pinch of salt disappears when you dissolve it in a glass of water. The running streams dissolve gold and silver and other minerals from the land. But most of their dissolved minerals are chemical salts of various kinds. All these and other invisible particles are swept along by the running rivers and dumped with their waters into the ocean.

The sea never gives these salty chemicals back to the land. As the smiling sun beams down, it evaporates or dries up water from the surface of the sea. But only the fine particles of water change into gas and go off to mingle with the air. Almost all of the dissolved chemicals are left behind. The ocean holds onto the salty chemicals stolen from the land, and every day the running rivers dump still more chemicals into the seas. This has been going on for millions and millions of years, so the salty sea gets saltier every year.

The water in the rivers seems fresh to us, and it does indeed have much less salt than ocean water. But all river water gathers up traces of salty chemicals as it runs over the ground. There are a lot of rivers in the world, and the experts tell us that every year they add several billion tons of salty chemicals to the ocean.

The experts think that millions of years ago, when the world was young, its oceans were filled with fresh water. Year by year the running rivers stole all kinds of chemicals from the land. Year by year they emptied these dissolved salts and other chemicals into the sea. We are told that there are now about 50 quadrillion tons of dissolved salt in the world's salty seas.