Earth is covered by one hydrosphere or one layer of connecting water.
Even though the ocean is broken up into seven ocean parts, all the oceans are connected, one flowing into the other. The Pacific Ocean, covering 64,186,000 square miles, is nearly as large as the Atlantic and Indian Oceans combined. It contains a little more than half of all the water in the world's oceans. If all that water were piled on top of the United States the land would be submerged under 88.2 miles of water. If the same amount of sea water was to be piled up onto all of the available land above sea level on this planet, the land would be 5.7 miles below the water's surface.