Marianna Russo, age 11, of Tucson, Ariz.,for her question:

WHICH IS THE DEEPEST OCEAN?

The oceans are huge hollow basins in the earth's rocky crust, filled and brimming over with salty sea water. Actually, they are linked together in one huge global ocean that covers almost three quarters of our watery world. Their edges slop over shallow slopes around the shores. But most of the water is held in midocean where steep sided walls plunge down to the bottom of the basins.

On the floor of the ocean there are massive mountains, level plains and deep valleys. If all its ups and downs were leveled, its average depth would be more than two miles. The vast Pacific, which covers more than a third of the globe, is the deepest ocean. Its average depth is about 14,000 feet, or almost three miles. Its deepest known ditch is called Challenger Deep  which plunges 36,198 feet below the surface.