Fourier Transform Infrared Spectroscopy (FTIR)
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FIELD GEOCHEMISTRY Richard E. Terry Plant and Wildlife Sciences Department, Brigham Young University, Provo, UT, USA
Definition Geochemical analysis: The chemical analysis of elements associated with soils, rocks, and minerals. Ethnoarchaeology: The application of archaeological techniques to elucidate contemporary human activities. Chelate: Complex organic molecules that surround metallic ions to hold them in solution and prevent their chemical precipitation. Introduction Examinations of the physical and chemical properties of soils produce data that augment archaeological information on the structures and artifacts left behind by ancient peoples. In fact, the soil is a palimpsest of the physical changes and chemical residues associated with both ancient and contemporary human activities on the land surface. The origin of the term palimpsest dates to classical times, but it commonly refers to medieval manuscripts on parchment that were reused, because the medium was valuable and more durable than papyrus or paper. The old ink was partially effaced to clear the sheet for new writing, and in most cases, vestiges of the previous text, though faded and indistinct, could still be discerned. This aptly describes the soil medium as a cumulative recorder of human activities from ancient to contemporary times (Bailey, 2007; Dore and López Varela, 2010). Soils can store pollen, phytoliths, bones, architectural components, and nonperishable artifacts over sequential occupations;
however, perishable organic implements and food that are readily decomposed and seldom survive to become part of the artifactual record may have initially accounted for as much as 90 % of an ancient household’s artifact inventory (Cavanagh et al., 1988; Dahlin et al., 2007). Such organic materials associated with food preparation and consumption can lose their carbon and nitrogen components, which decompose to gaseous and soluble substances, yet phosphorus (P) and certain trace nutrients – including iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn) – are adsorbed onto soil particles or are precipitated as insoluble compounds and remain for centuries at the location of ancient use. These and other geochemical residues of human activities serve as invisible artifacts. Nonperishable artifacts associated with abandoned habitations and public structures were often picked up and moved and then reused at distant locations. In most cases, the soils and earthen floors of former landscapes are not transported, and thus the geochemical residues within soils provide excellent in situ evidence of ancient use (Barba et al., 1996; Wells et al., 2000; Parnell et al., 2001; Parnell et al., 2002; Barba, 2007). Geochemical analyses of soils and floors have become established archaeological methods for locating ancient sites. The results further define the types and extent of human activities within those sites and help in the interpretation of those activities (see reviews by Wilson et al., 2005; Wilson et al., 2006; Holliday and Gartner, 2007; Walkington, 2010).
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