[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.] In the lab the ice core was cut into rods just over three feet long that were stood on a heating pad and melted from the bottom. When the ice core was set to melt at the rate of two inches per minute, Dr. McConnell’s team found they could take 12 measurements per year throughout the Roman era. Silver occurs in lead ores, and the process of separating the silver from lead at high temperatures was a major source of airborne lead.

Source: New York Times May 14, 2018 19:01 UTC