Archeologists are concerned with the activities of people and nature that create evidence of a cultural past. Such evidence, which may include any remnant of human habitation, is referred to as the archeological record. The processes that produce this evidence are called formation processes.
There are two types of formation processes: cultural and environmental. Cultural formation processes are those that follow the actual use of an artifact, e.g., reuse, discard, disturbance, and archeological recovery. Environmental formation processes are those agents that impact cultural materials at any stage of their existence.
The four cultural formation processes are reuse, cultural deposition, reclamation, and disturbance. Reuse might include recycling , secondary use, or use by another party. Cultural deposition processes take cultural materials from the context in which they are used in a culture and place them in an environmental context; examples include discarded dishes, burials, and abandonments. Reclamation processes are those in which archeological materials are retrieved for reuse by a culture; examples include scavenging, looting of previously deposited artifacts, and archeological recovery. Disturbance processes alter the earth's surface and alter archeological materials, deposits and sites; examples include plowing and land leveling.
Environmental formation processes include the chemical, physical, and biological processes by which nature alters cultural materials. The scale at which these processes affect cultural material may be at the artifact level (e.g., the rotting of wood or the corrosion of metals), the site level (e.g., the burrowing of animals), or the regional level (the burial or erosion of sites).
Archeologists must sort out the contributions of the various formation processes to achieve new understandings of past human behavior . An artifact such as a hand axe would be expected to acquire signs of wear in the course of normal use, but could also acquire similar patterns of wear from cultural and environmental processes. By identifying ways that formation processes have altered an artifact, the archeologist can better assess the way the artifact was used in the culture that produced it.
Finding an archeological site
Besides drawing on information from large archeological sites such as Stonehenge and Angkor Wat, archeologists must also rely on data from a myriad of much smaller sites if they are to construct an accurate interpretation of the economic, environmental, and ideological factors that governed occupation of the larger sites. In many cases, the only evidence of human occupation must come from the remnants of seasonal campsites, and artifacts such as stone tools or bones.
In order to efficiently sample sites within a region and locate very small sites, archeologists have developed a variety of ground-survey and remote-sensing techniques.
Remote sensing and geophysical analysis
Although some archeological sites can be recognized above ground, the majority lie beneath the ground's surface. Remote sensing techniques allow archeologists to identify buried sites. In addition, by examining the ways human intervention have altered the surface near a site (e.g., through the construction of refuse pits or hearths), the archeologist may be able to identify patterns of previous usage.
Archeologists may employ techniques borrowed from the fields of geophysics and geochemistry to detect and map archeological sites and features. Many geophysical techniques, including electrical resistance measurements of the soil above a site and magnetic measurements of a pottery kiln, were first employed by archeologists in the 1940s and 1950s.
Satellite detectors have also been used to monitor the reflected solar radiation above a site. The characteristics of the reflected light allow the archeologist to identify differences in soil or vegetation covering a site, and at sufficiently high resolutions, to recognize archeological features. In this way, archeologists have been able to map out drainage canals once used by Mayan farmers, but now lying beneath the umbrella of the Yucatan rainforest .
Airborne thermal detectors, capable of monitoring the surface temperature of the soil and covering vegetation, take advantage of differences in the way materials retain heat to isolate archeological features from surrounding soil. With this technique, buried Egyptian villages appear to glow at night beneath thin layers of sand .
Electrical resistivity measurements of the soil are sensitive to the presence of water and dissolved salts in the water. Because constriction materials such as granite or limestone have a higher electrical resistance than the surrounding soil, electrical resistivity measurements may be of use in determining the locations of buried structures such as stone walls.
The magnetic properties of soil depend on the presence of iron particles, which when heated to sufficiently high temperatures tend to align themselves with the
earth's magnetic field . However, the earth's magnetic field and intensity change over time . Wherever human activity alters the iron compounds in the soil by subjecting them to high temperatures, for example by building fires in a hearth or firing pottery in a kiln, the heated soil upon cooling takes on magnetic properties that reflect the direction and intensity of the earth's magnetic field at the time of cooling. Since archeologically related changes in local magnetic fields may only amount to one part in 10,000, and because of daily fluctuations in the magnetic field due to electrical currents in the ionosphere, this technique usually requires monitoring of the earth's field at a reference point during the archeological investigation.
Other electromagnetic measurements used to probe a site may examine the soil for phosphates and heavy minerals often associated with past human habitation.
Three dimensional representations of a buried feature may be constructed using ground-sensing radar or resistivity profiling to obtain vertical geophysical cross-sections across a site. When placed beside each other, these sections create a three-dimensional image of buried objects.
The techniques of ground surveying date to the 1930s and 1940s. Ground surveys require no special equipment, just an observant archeologist with some knowledge of what might be found at a site. Ground survey records may include notes about any visible cultural features and artifacts on the site, site measurements, preparing maps or sketches of the site, and sometimes gathering small collections of artifacts. Surface artifacts may be gathered either as random grabs or complete samplings in a given area.
Initially, the archeologist must determine the size, depth, and stratification of a site. Second, the age or ages of the site must be determined. Third, the types of artifacts and features present at the site must be identified. And finally, information about the environment and the way that it influenced human habitation at the site must be known.
Site assessment techniques fall into two categories: destructive and nondestructive. Surface collecting, testing with shovels, digging pits, and mechanical trenching all disturb the site, and are considered destructive. Nondestructive techniques include mapping and remote sensing.
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Krivanek, R. "Specifics and Limitations of Geophysical Work on Archaeological Sites." Archaeological Prospection 8, no. 2 (2001): 113-134.
Maloney, Norah. The Young Oxford Book of Archeology. New York: Oxford University Press, 1997.
Sullivan, George. Discover Archeology: An Introduction to the Tools and Techniques of Archeological Fieldwork. Garden City, NY: Doubleday & Company, 1980.
Waters, Michael R. Principles of Geoarchaeology: A North American Perspective Tucson, AZ: University of Arizona Press, 1997.
Smith, Monica L. "The Archaeology of a 'Destroyed' Site." Historical Archaeology 35, no. 2 (2001): 31-40.
KEY TERMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
—A man-made object that has been shaped and fashioned for human use.
- Electrical resistivity
—A measure of the resistance (opposition) an object poses to electrical current flowing through it.
- Magnetic field
—The electromagnetic phenomenon producing a magnetic force around a magnet.
—A method of detecting distant objects based on the reflection of radio waves from their surfaces.
- Solar radiation
—Energy from the sun.
—A method of describing the ages of different strata of rocks or soil, based on the assumption that the oldest material will usually be found at the bottom layer.
- Thermal detector
—A device that detects heat.