Thomas H. Bryson, age 12, of Fayetteville, Tenn.,for his question:
What is the Mariana Trench?
More than seven tenths of our world is under water and the floor of the seas is even more uneven than the crinkled continents, The average depth of the oceans is about two and a half miles, far deeper than any diver can go. What’s more, the ocean depths are blacker than midnight, for sunlight pierces nn more than a mile, even in the clearest seas. For many years, experts here and there have been charting the floors of the seas with echo making equipment. The map of the sea floor grew as hills and mounds, a vast mountain range, cliffs and sloping plains, ditches and still deeper pits were sketched in place.
In 1957, scientists of 66 nations worked together in the International Geophysical Year, a project to gather all possible information about our wonderful planet. The total world picture from all their information is still being sorted and assembled, One big job was to make a planet¬wide map of the ocean beds. It turns out that this hidden geography is rougher than the early chart makers suspected. However, the Mariana Trench, discovered in 1939, still rates as the deepest ditch in the ocean floor.
The floor of the sea begins at the shores and beaches of the islands and land masses. The continents are surrounded by shallow, sloping areas called the continental shelves. The shelves may be ten, 20 or more than 100 miles wide. They end where a steep cliff plunges down to the floors of the ocean basins. The I.G.Y. scientists charted enough to give us a picture of the world wide ocean floor.
Mountains and hills, rises and ridges were found in unexpected places on the floors of the ocean basins. The Atlantic Ridge, a mighty range down the Atlantic Ocean was already known.
An I,G,Y, discovery linked this ridge with others in the Pacific, making an undersea range 40,000 miles long. In the Worth Pacific they charted four east to west fracturesy great cracks in the earths crust thousands of miles longs maybe 30 feet wide and more than two miles deep, Ringed around the entire pa6ific is A. series of trenches, deeper but not so long as the fractures. Due north of New Zealand, the Tonga Trench joins the Kermadec Trench to cut a ditch 1,600 miles long and almost seven miles below the surface.
The Mariana, Trench at one time called Mindanao Trench is a shorter ditch in the ocean floor some 200 miles southwest of Guam. Its deepest pit is Challenger Deep, 35,630 feet below the surface, 100 feet deeper than the Tonga, If we could set Mt, Everest, the worlds highest mountains into this ditch, its peak would be under a mile of sea water.