A Review of Lichenometric Dating and Its Applications to Archaeology

Lichenometry—a method developed by geologists for dating Holocene moraines and other landforms—has many potential applications in archaeology. Maximum-diameter lichenometry can suggest ages for features that were initially lichen-free, such as the moai of Easter Island, and rock surfaces exposed by toolstone quarrying. Size-frequency analysis can provide dates for structures built of lichen-covered rocks, such as game-drive walls and blinds, meat caches, and tent rings. Both methods require local calibration curves, best constructed by measuring lichens on substrata of known exposure age. Most lichenometric studies have involved yellow members of the crustose genus Rhizocarpon, which grow slowly and can live for as long as 10,000 years. Lichenometry has been particularly successful on siliceous rock types in arctic, subarctic, and alpine-tundra environments. The effects of wildfire and of competition from foliose lichens make the technique less well suited for forested terrain. Few data are available for tropical or desert environments or for calcareous substrata. The reliability of a lichenometric date will depend on the quality of the calibration curve, the size of the sample, the nature and postoccupational history of the substratum, and the ability of the archaeologist to recognize potential disturbance factors. An ecological perspective is essential. Known archaeological applications and problems are discussed.