Throughout the three million known years of the Stone Age humans relied on gravity to hold their vertical stone walls together until (as often happened) they were shaken apart by earthquakes against which they had almost no tensionally cohering resistance. Gravity pushed humanity’s stone structures inward toward the Earth’s center. Humans had to build their structures on bedrock “shoes” to prevent them from sinking vertically into Earth’s center. Stone buildings could not float on water. But nature had invented low-weight wood of high self-cohering tensile strength (averaging approximately 10,000 p.s.i.) and of relatively low compression-resistive capability (also approximately 10,000 p.s.i.). Wood floated on water and could move useful loads horizontally; wood made good rafts for transporting humans but not for floating heavy cargoes. Thus the high tensile strength of wood, combined with the human discovery of the intertrussing principles of structuring and the low overall displacement weights involved, made possible for humans to design and fabricate air-enclosing wooden vessels whose structure and space enclosure combined to produce highly successful wooden vessels of the sea that could carry great cargoes.