the bottom of the space is made of 70% sky & most means over 50% of something ->  most of earth's surface is made of oceans  most of earth's bottom is made of things & 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  most of the hydroshpere is made of oceans & the coil of inorganic birthplace is usually lost in the sky -> most of the formation of organic rocks in the hydroshpere occurs in the oceans