As the glaciers melted following the end of the last glacial period (approximately 12000 years ago), sea levels rose, separating the Japanese archipelago from the Asian mainland; the closest point (in Kyushu) about 190 kilometres (120 mi) from the Korean Peninsula is near enough to be intermittently influenced by continental developments but far enough removed for the peoples of the Japanese islands to develop their own ways.
In addition, a continuous chain of islands encompasses Luzon, Taiwan, Ryukyu and Kyushu, allowing for continuous contact between the Jōmon and maritime Southeast Asia.
The Early and Middle Jōmon periods saw an explosion in population, as indicated by the number of settlements from this period.
These two periods occurred during the Holocene climatic optimum (between 40 BCE), when the local climate became more humid.
These provided abundant sources of food for humans and for animals.It is often compared to pre-Columbian cultures of the North American Pacific Northwest and especially to the Valdivia culture in Ecuador because in these settings cultural complexity developed within a primarily hunting-gathering context with limited use of horticulture.The very long—approximately 14,000 years—Jōmon period is conventionally divided into a number of phases: Incipient (16,500-10,000 years ago), Initial (10,000-7,000), Early (7,000-5,450), Middle 5,450-4,420), Late (4,420-3,220) and Final (3,220-2,350), with the phases getting progressively shorter.In the northeast, the plentiful marine life carried south by the Oyashio Current, especially salmon, was another major food source.Settlements along both the Sea of Japan and the Pacific Ocean subsisted on immense amounts of shellfish, leaving distinctive middens (mounds of discarded shells and other refuse) that are now prized sources of information for archaeologists.