Around 2,200 B.C, agricultural societies around the world experienced an abrupt cooling and a critical mega-drought. Humans had been progressing nicely since the end of the last Ice Age, and suddenly this cooling, and accompanying droughts, forced the collapse of civilizations in Egypt, Greece, Syria, Palestine, Mesopotamia, the Indus Valley, and the Yangtze River Valley, which led to migrations and regenerations in other areas. Evidence of this period, now called the 4.2 kiloyear climatic event, has been found on all seven continents and it has become the reason for the most recent unit of the Geologic Time Scale, now called the Late Holocene Meghalayan Age.