The 8th millennium BC spanned the years 8000 BC to 7001 BC (c. 10 ka to c. 9 ka). In chronological terms, it is the second full millennium of the current Holocene epoch and is entirely within the Pre-Pottery Neolithic B (PPNB) phase of the Early Neolithic. 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. Global environment In the geologic time scale, the first stratigraphic stage of the Holocene epoch is the "Greenlandian" from about 9700 BC to the fixed date 6236 BC and so including the whole of the 8th millennium. The Greenlandian followed the Younger Dryas and essentially featured a climate shift from near-glacial to interglacial, causing glaciers to retreat and sea levels to rise. Towards the end of the 8th millennium, the Holocene Climate Optimum (HCO) – also called the Holocene Thermal Maximum (HTM) – began as a warm period lasting roughly 4,000 years until about 3000 BC. Insolation during summers in the northern hemisphere was unusually strong with pronounced warming in the higher latitudes such as Greenland, northern Canada and northern Europe with a resultant reduction in Arctic sea ice. During the 8th millennium, there were four known volcanic eruptions which registered magnitude 5 or 6 on the Volcanic Explosivity Index (VEI). These were at Rotoma Caldera in New Zealand's Taupō Volcanic Zone about 7560 BC; Lvinaya Past in the Kuril Islands about 7480 BC; Pinatubo on the island of Luzon in the Philippines about 7460 BC; and Fisher Caldera, on Unimak Island in the Aleutians about 7420 BC. The biggest eruption was at Fisher Caldera, VEI 6, producing more than of tephra. The date of c. 7640 BC has been theorised for the impact of Tollmann's hypothetical bolide with Earth. The hypothesis holds that there was a resultant global cataclysm such as early Holocene extinctions or possibly the legendary Universal Deluge. Bolides are asteroids or comets. According to radiometric dates, the main occupation phases recognized at Shillourokambos took place between the end of the 9th millennium BC and the end of this millennium, long before the Khirokitia Culture. The fact remains that its disappearance in the Middle Phase at Shillourokambos, in the second half of this millennium, is not an isolated incident but one of a number of expressions of