The 5th millennium BC spanned the years 5000 BC to 4001 BC (c. 7 ka to c. 6 ka). 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. The exceptions are several neolithic pile dwellings around the Alps whose construction time can be dated to within a year. Communities The rapid world population growth of the previous millennium, caused by the Neolithic Revolution, is believed to have slowed and become fairly stable. It has been estimated that there were around forty million people worldwide by 5000 BC, growing to 100 million by the Middle Bronze Age c. 1600 BC. Europe The Cucuteni–Trypillia culture (aka Tripolye culture) began around 4800 BC. It was centred on modern Moldova and lasted in three defined phases until c. 3000 BC. From about 4500 BC until c. 2500 BC, a single tongue called Proto-Indo-European (PIE) existed as the forerunner of all modern Indo-European languages, but it left no written texts and its structure is unknown. China Chinese civilisation advanced in this millennium with the beginnings of three noted cultures from around 5000 BC. The Yangshao culture was based in the Huang He (Yellow River) basin and endured for some 2,000 years. It is believed that pigs were first domesticated there. Pottery was fired in kilns dug into the ground and then painted. Millet was cultivated. A type-site settlement for the Yangshao was established c. 4700 BC at Banpo near modern Xi'an, Shaanxi. Also about 5000 BC, the Hemudu culture began in eastern China with cultivation of rice, and the Majiabang culture was established on the Yangtze estuary near modern Shanghai, lasting until c. 3300 BC. Australia It is estimated that the distinctive Aboriginal rock carvings near Sydney were created sometime between 5000 BC and 3000 BC. Africa It is estimated that the beginning of the Pastoral Neolithic was in the later phase of the Green Sahara, in the 6th or 5th millennium BC. It was prior to the end of the African humid period (c. 3900 BC) and the desiccation of the Green Sahara. During this time, sub-Saharan Africa remained in the Palaeolithic. As the grasslands of the Sahara began drying after c. 3900 BC, herders moved into the Nile Valley and by the middle of the 3rd millennium BC into eastern Africa. Calendars and