Early farmers polluted the sea 4000 years ago

Humans have been polluting the environment for at least 4000 years. So says a team that has analyzed sediment from the South China Sea--but not everyone is convinced. Several civilizations hit a crisis point 4000 years ago. The global climate cooled, and this has been linked to the collapse of the Akkadian Empire in Mesopotamia and the end of the Indus valley civilization of South Asia. Cooling was also felt on Hainan island off China's south coast say Fangjian Xu at the China University of Petroleum, Qingdao, and his team. There was also a rise in heavy metal pollution in the South China Sea. The group looked at two sediment cores from south-east of Hainan, and calculated "enrichment factors" for several metals. A value of 1 or below is no enrichment while values between land 3 suggest "minor enrichment".