COVER—Kelly Cheng; 1—Courtesy Marla Toyne; 3—(clockwise from top left) Courtesy Valeri Stoichkov, Courtesy Soprintendenza Archeologica di Pompei, Courtesy Randy Haas, REUTERS/Alamy Stock Photo, E. Grixoni; 4—Azoor Photo Collection/Alamy Stock Photo; 6—Photo by Andrew Ward; © Institute of Fine Arts–New York University; 9—Courtesy Durham University; 10—Courtesy Durham University, REUTERS/Alamy Stock Photo; 11—Courtesy Valeri Stoichkov (2); 12—Mick Sharp/Alamy Stock Photo, Courtesy Bill Lipe, Royal Museums Greenwich; 14—Institute of Cultural Relics and Archaeology, Inner Mongolia Autonomous Region, Courtesy Randy Haas (2); 15—Courtesy Soprintendenza Archeologica di Pompei; 18—Randy Prentice/Alamy Stock Photo, Courtesy Julia Russ, Karl Reinhard, and the Morrison Microscopy Core Research Facility at the Nebraska Center for Biotechnology, the University of Nebraska-Lincoln, E. Grixon, Paola Mancini; 20—Courtesy Chris Lintz, Courtesy Paul Katz; 22—(clockwise from top left) Payette National Forest Heritage Program, Universidad de…