Because radiocarbon dating can be compromised by metal emissions in the air, dendrochronology, or tree-ring dating of wooden objects, beats it in accuracy "by miles," said Michael Worthington. British-born Worthington, of Oxford Tree-Ring Laboratory in Baltimore, has worked on Westminster Abbey, Salisbury Cathedral, and the Tower of London in England; and on Mount Vernon, President John Quincy Adams' Massachusetts birthplace and other historical sites in the U.S. In the Carolinas, he has dated more than a half-dozen buildings, mostly for private clients .