Kathryn Joy, age 10, of St. John's Newfoundland, Canada, for her question:

How wide is Newfoundland's continental shelf?

The continental shelves begin where the shores dip their toes into the shallow, coastal tides. Their solid floors dip down and out to sea toward the steep sided basins of the deep oceans. Some of the shelves are wide and some are narrow     but most of them teem with fishes and marine life. One of the world's widest continental shelves is off Newfoundland. This expansive region of shallow seas also is one of the world's richest fisheries.

Seaweeds and specks of floating algae need sunshine, and sunlight pierces down through the shallow waters of most continental shelves. In the hungry sea, the thriving plant life starts a food chain for small animals and for larger and still larger creatures that feed upon each other. The world's widest continental shelf belongs to the Barents Sea. Its waters throng with Marine life, but up there inside the Arctic Circle the fishes are safe through the winter because the surface is icebound,

Around North America, the continental shelves range from a few feet to 100 dies wide    but from the eastern shores of Newfoundland, the shelf dips gently out to sea for 500 miles. One fathom measures water that is six feet deep. This shelf dips gently down 80 to 100 fathoms. Then the seabed swoops down the steeper continental slope to the Atlantic basin. The shelf of Barents Sea reaches a width of 750 miles and depths of 100 to 200 fathoms before it slopes down to the Arctic basin.

Newfoundland's shelf happens to be one of the earth's most fascinating features. Here the warm Gulf Stream from the tropics collides with the cold Labrador Current from the Arctic. Also on this shelf sits the immense, shallow plateau of the famous Grand Banks. Into the region is swept both warm and cold water marine life. It is the world's richest fishery and boats can harvest its open waters through most of the year.

Here and there, icy green Arctic streams and warm dark blue streams from the tropics flow side by side. But the major currents oppose each other in watery warfare and mingle in swirling eddies. What's more they create weathery warfare above the surface. The Gulf Stream's warm air over rides the cold Labrador Current, creating thick blankets of white fog. And into the blinding fogs float hundreds of icebergs that broke from Arctic glaciers. In a few days, many of them melt in the warm Gulf Stream, adding chilly fresh water and more banks of fog.

This fascinating region has a fascinating past. In the Devonian Period of 300 million years ago, the present land and sea areas formed. a dry subcontinent called Greater Acadia. Later it became a swampy region of coal making forests and parts of it sank below sea level. In the Tertiary Period of 60 million years ago, Newfoundland rose high and dry above the water. During the last ice ages, the seas were much lower. Both Newfoundland and its famous continental shelf still bear the scars of the massive glaciers that covered them during the past million years.