Traces of Paleolithic culture, mainly stone tools, occur in Japan from around 30,000 BCE onwards.The earliest "Incipient Jōmon" phase began while Japan was still linked to continental Asia as a narrow peninsula.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.These types continued to develop, with increasingly elaborate patterns of decoration, undulating rims, and flat bottoms so that they could stand on a surface.The manufacture of pottery typically implies some form of sedentary life because pottery is heavy, bulky, and fragile and thus generally unusable for hunter-gatherers.The earliest pottery in Japan was made at or before the start of the Incipient Jōmon period.
This was already similar to modern cultivated forms.
Within the archipelago, the vegetation was transformed by the end of the Ice Age.
In southwestern Honshu, Shikoku, and Kyushu, broadleaf evergreen trees dominated the forests, whereas broadleaf deciduous trees and conifers were common in northeastern Honshu and southern Hokkaido.
The fact that this entire period is given the same name by archaeologists should not be taken to mean that there was not considerable regional and temporal diversity; the chronological distance between the earliest Jōmon pottery and that of the more well-known Middle Jōmon period is about twice as long as the span separating the building of the Great Pyramid of Giza from the 21st century.
Dating of the Jōmon sub-phases is based primarily upon ceramic typology, and to a lesser extent radiocarbon dating.