NOREEN A. BUSTER is a geologist at the U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center, located in St. Petersburg, Florida. CHARLES W. HOLMES is retired from the U. S. Geological Survey. Specializing in geochemistry and sedimentology and focusing on geochronological issues, he is currently executive director of Environchron, LLC, and adjunct professor at Eckerd College in St. Petersburg, Florida.