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HOME > PAST ISSUE > March-April 2003 > Article Detail

FEATURE ARTICLE

Dating Ancient Mortar

Although radiocarbon dating is usually applied to organic remains, recent work shows that it can also reveal the age of some inorganic building materials

?sa Ringbom, John Hale, Jan Heinemeier, Lynne Lancaster, Alf Lindroos

Even more than digging implements, archaeologists need tools for finding the age of the objects they study. After all, many sites and remains—in caves, in deserts, on the sea floor—require no excavation, but all must be dated. When archaeologists of the future write the history of their discipline, the second half of the 20th century will stand out for the development of many scientific methods for ascertaining the age of artifacts. This article is an account of how our Scandinavian-American team, which includes a nuclear physicist, a geologist, an art historian and two archaeologists, developed the means for dating ancient building materials that contain lime mortar.

Figure 1. Enigmatic stone tower . . .Click to Enlarge Image

In the early days, archaeologists trying to make age determinations often depended on information supplied by others. Principally, they relied on historians, who knew the chronologies of literate societies of the past five millennia, with their written inscriptions on seals, records, tombs, monuments and coins. Archaeologists also relied on geologists, who could sometimes make age determinations based on the association of human remains with geological features of known age.

Unfortunately, this dependence on historical dates and geological associations left large areas of the human past untouched. But beginning in the late 1940s, a new world opened with the development of radiocarbon dating for organic remains, tree-ring dating for wood, thermoluminescence for fired clay and potassium-argon dating for volcanic materials. Of these, radiocarbon dating had the most universal importance for archaeology. So vital was its discovery that the pioneer of the field, Willard F. Libby, was awarded the Nobel Prize for Chemistry in 1960.





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