From Academic Kids
The continental shelf is the extended perimeter of each continent, which is covered during interglacial periods such as the one we live in by relatively shallow seas and gulfs. The shelf typically ends at a very steep slope (called the shelf break). The sea bottom below the break is the continental slope which has a much steeper gradient than the shelf. It merges into the flat ocean floor, the abyssal plain.
The width of the continental shelf varies significantly. It is quite common for an area to have virtually no shelf at all, especially where the foreedge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone such as off the coasts of Chile or the west coast of Sumatra. The largest shelf—the Siberian shelf in the Arctic Ocean—stretches to 1500 kilometers in width. The South China Sea lies over another extensive area of continental shelf, the Sunda shelf, which joins Borneo, Sumatra, and Java to the Asian mainland. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf. The average width of continental shelves is about 80 kilometers. The depth of the shelf also varies. It may be as shallow as 30 m or as deep as 600 m.
Along the continental shelves sediment is carried from erosion of the land. Combined with the sunlight available in shallow waters, the continental shelves teem with life compared to the biotic desert of the oceans' abyssal plain. Cod from the Grand Banks off Newfoundland fed Europe's poor for half a millennium before they were fished out. If anoxic conditions in the sedimentary deposits prevail, the shelves may in geologic time become sources of fossil fuels.
The relatively accessible continental shelf is by far the best understood part of the ocean floor. Virtually all commercial exploitation, such as oil and gas extraction, from the sea takes place on the continental shelf. Sovereign rights over their continental shelves were claimed by the marine nations that signed the Convention on the Continental Shelf drawn up by the UN's International Law Commission in 1958, (http://www.un.org/law/ilc/texts/contsh.htm) partly superseded by the 1982 United Nations Convention on the Law of the Sea.