A new dating method finally is allowing archaeologists to incorporate rock paintings into the tapestry of evidence used to study life in prehistoric times. In the study, Marvin W. Rowe points out that rock paintings, or pictographs, are among the most difficult archaeological artifacts to date. They lack the high levels of organic material needed to assess a pictograph's age using radiocarbon dating, the standard archaeological technique for more than a half-century. Rowe describes a new, highly sensitive dating method, called accelerator mass spectrometry, that requires only 0.05 milligrams of carbon (the weight of 50 specks of dust). That's much less than the several grams of carbon needed with radiocarbon dating.