Excavation Methods

Archeological excavation involves the removal of soil, sediment, or rock that covers artifacts or other evidence of human activity. Early excavation techniques involved destructive random digging and removal of objects with little or no location data recorded. Modern excavations often involve slow, careful extraction of sediments in very thin layers, detailed sifting of sediment samples, and exacting measurement and recording of artifact location.

About the time of the American Revolution, the then-future U.S. president Thomas Jefferson began excavating Indian burial mounds that had been constructed on his property in Virginia. His technique, which was to dig trenches and observe the successive strata, or layers of soil, anticipated the techniques of modern archaeology.

Between 1880 and 1890, General Pitt-Rivers initiated the practice of total site excavation, with emphasis on stratigraphy and the recording of the position of each object found. In 1904, William Mathew Flinders Petrie established principles of surveying and excavation that emphasized the necessity of not damaging the monuments being excavated, of exercising meticulous care when excavating and collecting artifacts, of conducting detailed and accurate surveys, and of publishing the findings as soon as possible following the excavation. In the same year, the archeologists R. Pumpelly and Hubert Schmidt, working in Turkestan, had already begun using sifting techniques to save small objects, and were recording the vertical and horizontal locations of even the smallest objects in each cultural layer.

Today, archeology is still equated with excavation in the popular mind. Most sites are no longer fully excavated unless in danger of destruction from building or erosion. Archaeologists leave a portion of some sites unexcavated to preserve artifacts and context for future research. Furthermore, there are now many alternatives to excavation for studying an archeological site, including surface archeology in which surface-exposed artifacts are detected and recorded; remote sensing; and the examination of soil and plant distributions. These techniques are nondestructive, and permit the archeologist to easily examine large areas. But even today, in almost all archeological projects, there comes a time when it is necessary to probe beneath the surface to obtain additional information about a site.

Before any excavation is begun, the site must be located. Techniques used to find a site may include remote sensing (for example, by aerial photography), soil surveys, and walk-through or surface surveys. The digging of shovel tests, augured core samples and, less commonly, trenches may also be used to locate archaeological sites. Soil samples may be collected from various sites and depths to determine whether any buried features are present.

When planning an archeological excavation, archeologists often use nondestructive techniques such as electrical resistivity meters and magnetometers to locate structures and artifacts on the site without digging. Soil testing may shed light on settlement patterns connected with the site. Aerial photography can also provide useful information Dinosaur dig site, where it is thought that approximately 10,000 animals were buried by cretaceous volcanic ash flows. Photograph by James L. Amos. Corbis. Reproduced by permission. for planning the excavation. In unobstructed fields, past human occupation of an area is evident through visible soil stains left by plowing, digging, and construction.

Before beginning the actual excavation, an archeologist prepares a topographical map of the site that includes such details as roads, buildings, bodies of water, and various survey points. This allows researchers to compare site location with natural landforms or regional terrain to establish settlement patterns, a theory about where people used to live and why they chose to live there.

Prior to excavating the site, a series of physical gridlines are placed over it to serve as points of reference. In staking out the grid, the archeologist essentially turns the site into a large piece of graph paper that can be used to chart any finds. The site grid is then mapped onto a sheet of paper. As objects are discovered in the course of the excavation, their locations are recorded on the site map, photographed in place, and catalogued.