The 9th millennium BC spanned the years 9000 BC to 8001 BC (11 to 10 thousand years ago). In chronological terms, it is the first full millennium of the current Holocene epoch that is generally reckoned to have begun by 9700 BC (11.7 thousand years ago). It is impossible to precisely date events that happened around the time of this millennium and all dates mentioned here are estimates mostly based on geological and anthropological analysis, or by radiometric dating. In the Near East, especially in the Fertile Crescent, the transitory Epipalaeolithic age was gradually superseded by the Neolithic with evidence of agriculture across the Levant to the Zagros Mountains in modern-day Iran. The key characteristic of the Neolithic is agricultural settlement, albeit with wooden and stone tools and weapons still in use. It is believed that agriculture had begun in China by the end of the millennium. Elsewhere, especially in Europe, the Neolithic continued. Global environment In the geologic time scale, the first stratigraphic stage of the Holocene is the "Greenlandian" from about 9700 BC to the fixed date 6236 BC and so including the whole of the 9th millennium. The starting point for the Greenlandian has been correlated with the end of the Younger Dryas and a climate shift from near-glacial to interglacial, causing glaciers to retreat and sea levels to rise. It has been estimated that the Bering Land Bridge was inundated around 8500 BC by the rising sea levels so that North America and Asia were again separated by the waters of the Bering Strait and the Chukchi Sea. It is generally believed that there was a migration across the land bridge from eastern Siberia into North America during the Last Glacial Maximum. Sometime after the American glaciers melted, these peoples expanded southward into the wider continent to become the Native Americans. After the land bridge was inundated by the rising sea water, no further migration was possible from Siberia. During the millennium, there were three known volcanic eruptions which registered magnitude 5 or more on the Volcanic Explosivity Index (VEI). These were at Ulleungdo (aka Ulreung), an island east of the Korean Peninsula about 8750 BC; Grímsvötn, north east Iceland about 8230 BC; and Taupo Caldera, New Zealand about 8130 BC. The biggest eruption was at Grímsvötn, VEI 6, producing some of tephra. Population and communities As the Neolithic began in the Fertile Crescent, most people