CHONGQING, Sept. 3 (Xinhuanet) -- Chinese and American archaeologists have found out that the earliest salt production activity took place in China at least 3,000 years ago.

    Their findings were reported in the latest issue of the Proceedings of the National Academy of Sciences in the United States.

    Experts from the two countries detected credible evidence of a large-scale salt production base at an archeological site dating back to more than 3,000 years ago in southwest China's Chongqing municipality.

    Field research proved that the pottery vessels unearthed from the Zhongba archeological site in Zhongxian County share characteristics with those found in other salt-production areas inthe world.

    Chemical analysis of soil at the site and excavated potteries found residue substances, including calcium, magnesium, and calcium carbonate created in salt-making.

    Sodium and chlorine, the two chemical elements in salt, were also found inside the pottery.

    The research team included distinguished archaeologists Rowan Flad from Harvard University and Wang Changsui from the University of Science and Technology of China.     Enditem