What is the purpose of the continental shelf?
Perhaps a better way to phrase you question is “How did the continental shelf form?” It’s an excellent question you’ve asked, and here’s one possible answer. First imagine the situation when a new continent is formed, but without an ocean present. The rock that makes up the continent is thicker and less dense than that which makes up the ocean floor, so the continent floats relatively higher on the Earths molten mantle. Big volcanoes on the continent spew out more low-density rock and the continent gets some nice steep sides. Now fill up the low areas (ocean floor) with a bunch of sea water and energize the surface of the resultant seas with lots of wind. Big waves form on the ocean’s surface and travel across the basins to the continental shores. There they crash into the fresh continental rock and begin to break away pieces. Eventually the waves tear away the edge of the continent as fast as the continental volcanoes can create it. So the continent now has even steeper sides and a bi
