the surface of the earth is made of 70% ocean & most means over 50% of something ->  most of earth's surface is made of oceans  most of earth's surface is made of oceans & the hydrosphere is a thin layer of water covering the earth 's surface ->  most of the hydroshpere is made of oceans  most of the hydroshpere is made of oceans & the formation of organic rocks is usually found in the ocean -> most of the formation of organic rocks in the hydroshpere occurs in the oceans