How Archaeologists Excavate a Site
Finding the Site:
Archaeologists first perform a survey where the goal is to identify any archaeological sites in a given area. This can be done in several ways. Archaeologists may simply walk across a site and carefully observe the ground, consult historic texts or maps, analyze aerial photographs or even employ satellite imagery.
Archaeologists excavate sites in a scientific way with excavation units organized on a grid system, as seen in the images at left. They carefully uncover artifacts, features and ecofacts, recovering and recording information in a systematic way. Because digging removes artifacts from their association with each other and from their association with features, keeping records at all stages in the excavation is essential. Architectural elements that have to remain in place or be reburied must be sketched and photographed, and their location indicated on a site map.
Excavating the Site:
Archaeologists excavate stratigraphically, that is, they dig in layers. The excavation ends when the archaeologists reach subsoil, the sterile layer of sand laid down during the last ice age.
The image at left shows a photograph of the soil layers visible in the ‘wall’ of an excavated grid square.
Soil layers are usually created by natural processes like the decay of leaves and organic matter, but cultural activities (like dumping unwanted soil) creates layers too. In cross section, soil layers resemble a layer cake, with the oldest layers on the bottom and the most recent layers on the top. Each new layer of soil, or stratum, signals a different event or time period.
Artifacts and other Finds
An artifact is any object that is made or modified by humans. During a dig, artifacts are recovered using screens, as seen at left. Man-made artifacts can be small as a pin to large timbers from a shipwreck or building. Examples of modified artifacts include bones and stone, shaped or carved for use. A bone removed from a carcass and then used to scrape an animal skin is an artifact.
A feature provides evidence of human activity but unlike most artifacts it cannot be removed from the archaeological site. A fence post pulled from the ground long ago would leave a stain in the soil where the post once stood. This stain is a feature. Photographs, drawings, and soil samples of the fence post feature are just as important as the nails and other artifacts that might be found nearby. Features like soil stains can reveal the outlines of structures long-gone such as houses and barns. Other types of features include fireplaces, cellars, graves and building foundations.
Once a site is excavated, the artifacts and other finds are analyzed for any patterns. The finds are also dated when possible. Chemistry, physics, biology and history all come together to help date artifacts. The excavation is considered complete once the final report and interpretation of the findings has been completed.
The process of excavation essentially destroys an archaeological site. Artifacts are excavated and removed from where they had been deposited on a site. This is why mapping and photographs are vital. Future archaeologists can refer to maps and photographs looking for locations for further research or perhaps a re-interpretation of the site.