Erosion over millions of years inevitably destroys all volcanic islands. Great pieces of the island will submerge, leaving only a ridge of cliff in the ocean. Despite this destruction, animals have evolved to live on these dying islands.
Geographically the world can be divided into five oceans, the Pacific, Atlantic, Indian, Southern and Arctic. These oceans cover around 70 percent of the earth and although we can't measure it exactly, it is estimated to have a volume of 1370 million cubic kilometres.