Calculations by the Australian-French collaboration based on their ice-core analysis showed that during the period 366 B . C . to at least 36 A . D ., a period when the Roman Empire was at its peak, 70 percent of the global atmospheric lead pollution came from the Roman-operated Rio Tinto mines in what is now southwestern Spain.
12.
The analysis of Greenland Summit ice cores as a part of the Greenland Ice Sheet Project-2 ( GISP-2 ) and Greenland Icecore Project ( GRIP ) estimated that the Younger Dryas started about 12, 800 ice ( calendar ) years BP . Depending on the specific ice core analysis consulted, the Younger Dryas is estimated to have lasted 1, 150 1, 300 years.