ୱେବ୍Chronology. The approximately 14,000 year Jōmon period is conventionally divided into several phases, progressively shorter: Incipient (13,750–8,500 BC), Initial (8,500–5,000), Early (5,000–3,520), Middle (3,520–2,470), Late (2,470–1,250), and Final (1,250–500). [14]