Bobby Johnson, age 10, of Palouse, Wash., for his question:
WHY IS THE OCEAN SALTY?
The amount of salt in the ocean is amazing. Of course, we cannot measure all the salt in the ocean, but by measuring a small sample scientists can give us an estimate. For example, one cubic mile of average sea water contains about 166 million tons of dissolved salts. From this we can estimate the total amount in the worldwide ocean to be around 50 quadrillion tons. What's more, the seas get a little saltier with every passing day.
Countless thousands of rivers and streams flow overthe land and empty into the sea. Whether they are turbulent or gently rippling, these waters pick up all kinds of minerals from the rocks and soil as they move along. The mineral that comes out most readily is salt (sodium chloride), but compounds of magnesium, calcium and potassium are also part of the bounty that reaches the oceans.
The earth's atmosphere also plays a part in the salty ocean story. When the warm, dry air evaporates water from the sea's surface, it leaves most of the dissolved chemicals behind. However, countless tiny fragments of minerals are carried aloft by wind currents, absorbed into clouds, and eventually fall back to the earth in raindrops. And millions of tons of sea salt are returned to the land by dry ocean winds.
Scientists tell us that some oceans are saltier than others, but that all are becoming a fraction more salty all the time. It is estimated that there are enough minerals in the ocean to make a solid layer about 185 feet thick over the entire ocean floor and about three quarters of the solid material is salt.
The salty oceans and seas contain about 97 percent of all the water on the earth, and more and more scientists are looking for ways to utilize this vast natural resource to supplement man's increasing need for water. The problem is getting rid of the salt. Unfortunately all methods of desalination take huge amounts of energy, which is expensive whether it comes from hydroelectric, fuel burning or nuclear power plants. Even so, more than 200 desalting plants have been built throughout the world from Australia to California, and from Greenland to South America. Most of these small plants serve such places as remote military posts, oil drilling desert regions, island resorts or industrial plants.
Billions of years ago, the infant earth was so hot that showers turned to steam when they landed on the surface. Later the storm laden skies poured down rain in deluges, helping to cool the bare land. Floods dashed down the slopes, filling the ocean basins and forming the first seas. These waters were relatively fresh because the streams did not have much time to dissolve salty chemicals as they flowed down rocky inclines.