Frances Dobies, age 12, of 1Jhitesboro, New York, for her question:

What happens as light penetrates the ocean?

If we could harness all the solar radiation that falls upon our planet every second, it could supply mankind's total energy needs for about a couple of years. Some of this solar energy is visible daylight and since we live on a watery world, most of it falls on the global ocean. Our stupendous quota takes about eight minutes to dash to meet us across 93 million miles of space. Surely, one would suppose, it has enough strength to penetrate two or three miles through the water to the ocean floor.

But about one third of the solar radiation that reaches the earth is reflected back into space by dust and vaporous clouds and some is absorbed by the gaseous atmosphere. Only about 47 per cent of our total quota reaches the surface. Around us, solid surfaces absorb and reflect the sunbeams to reveal the scenery in daylight colors. The solid ground changes the invisible range of infrared light into heat.

So it goes on the land, where barriers of dense rock prevent sunlight from penetrating below the solid surface. But the seas are filled with liquid water  ¬which is less dense than solid rock and sometimes as transparent as glass. One might expect the daylight to penetrate all the way down to the bottom of the ocean abyss. Actually, the deepest it can go is about 2,000 feet and only the strongest wave lengths can go this deep.

Solar radiation is a blend of assorted wave lengths. The longer wave lengths of visible light are filtered out as the sunbeams penetrate downward through the water. At a depth of 200 to 300 feet the long rays of red, orange and yellow have gone, plus most of the heat energy. If the sunlit upper level is clean and clear, its shiny surface mirrors the blues and pearly greys of the shy above.

Below this level, the water is tinted with the shorter green and the shortest blue wave lengths. As the depleted sunbeams penetrate on doom to about 1,000 feet, the last of the green rays are stolen. Below this level the dim water is an unforgettable blend of deep vibrant blue and vivid purple. Under favorable conditions, such rays reach down to 2,000 feet. Below this level, the chilly sea water is blacker than blackest midnight.

Each level is its own ecology system and its populations tend to blend their color schemes with the locally tinted water. For example, herring and mackerel throng through the sunlit surface level. Their backs are glistening blues or silvers and their undersides are pasty pale. The surface water mirrors the blue grey skies  ¬and conceals the fish from hungry gulls overhead. When hungry sharks look up from below, they confuse the pale fishy tummies with the pale daylight above the water.