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7.2: Excavating

  • Page ID
    110710
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    GET OUT THE SHOVELS!

    When the excavation method has been selected, actual digging can begin. Archaeologists are systematic when they excavate since, as mentioned earlier, archaeological data cannot be renewed. At this point, archaeologists know where they are digging and what methods they will use to dig. The next decisions to be made are related to how they will dig.

    Preparing to Dig

    Finally, the last step before the archaeologists begins to move dirt, there must be some preparation. Decisions have to be made on the tools needed, excavation units to be mapped out, and the unit levels need to be determined.

    Tools

    The tools used in excavation will depend on the research design and the goals of the investigation as well as the site conditions. Obviously, shovels and trowels will always be required when digging. However, the tools of excavation can be as large as a backhoe or front-end loader to as small as a dental pick or chopstick to work on recovering a small or delicate artifact. Basically, archaeologists will use any tool that can get the job done without damaging the artifacts that are hidden in the ground. Large equipment, such as a back-hoe, would be used to uncover a larger area by removing overlying topsoil that may be covering a site. However, the operators must be very experienced and the process is monitored by the watchful eye of an archaeologist in order to avoid disturbing any important archaeological finds.

    The list of tools of an archaeologist is endless. However, it is not just tools for digging and recovering artifacts. Remember archaeology is much more than digging up the past, it is also recording and preserving the details about the findings. This means their toolkit also includes surveying and GPS equipment, mapping tools, cameras, notebooks, and laptops.

    176339326_2bb6895185_w.jpg
    Figure \(\PageIndex{1}\): A back-hoe clearing topsoil from a site.
    118761548_a4d9af032b_w.jpg
    Figure \(\PageIndex{2}\): An archaeologist meticulously recovers skeletal remains.
    5272571744_da36199a37_w.jpg
    Figure \(\PageIndex{3}\): The archaeologist toolkit includes notebooks and sketchpads, not just tools for digging.

    Excavation Units

    After the site has been cleared, the next step is to map out your excavation units. You have probably seen photographs of excavations, in this text and in other texts and publications, in which the “holes” are square rather than round. Why does the shape of the hole matter? By digging a square hole, archaeologists can easily calculate how many artifacts and other items are present per unit—in this case, a measure of volume. Since a square is made up of two equally sized right triangles, archaeologists ensure that the holes they dig are perfectly square using the Pythagorean Theorem: a2 + b2 =c2. Using this calculation when the initial grid lines of the map are drawn and when individual units are established will ensure that each archaeological unit is a perfect square.

    Levels

    The next decision, likely made before excavation begins, is how deep each level will be since the excavation is in three dimensions—length, width, and depth. Some archaeologists elect to tie the depth of each level to the natural strata of the site with each layer representing a level. Sometimes based on the site conditions, archaeologists select an arbitrary strata depth such as 10 or 20 centimeters regardless of the stratigraphic layers. Arbitrary strata are most often used when the natural strata is not known or more than 10 cm thick.

    natural strata

    A layer of rock or soil that is formed by natural processes.

    arbitrary strata

    A standard measured vertical subdivision of an excavation unit that does not follow the natural strata.

    Let The Digging Begin!

    When excavators reach the bottom of a natural or arbitrary strata level, several things occur. First, the archaeologist typically takes measurements of the depth of excavation across the entire square to ensure it was excavated to precisely the same depth throughout. This is important as the surface, where excavation begins, is typically naturally uneven, but the bottom of the strata level should be flat. Since the ground is rarely level, a plumb bob or line level is often used when taking the measurements. The archaeologist and workers then draw sketches of the excavated layer and its stratigraphic profile and photograph the entire unit, the stratigraphic profile, and important characteristics of the soil to document the stratigraphy. One photograph documents the unit’s location on the grid system and the depth of the layer excavated using a sign and a tool such as a trowel pointing north to make it easy to orient the unit and identify its location later.

    4230345986_b2bc13076e_w.jpg
    Figure \(\PageIndex{4}\): Recording depth from a datum plumb line.

    This process continues until the archaeologists have gathered all the information they can from the unit, encounter something unexpected (such as the water table or bedrock), or come to the end of the project. Before the unit is backfilled, they take high-quality photographs and draw sketches of it. Sometimes, before backfilling a site, the archaeologists put something modern, such as a contemporary soda can, at the final depth excavated. This indicates their stopping point to archaeologists who resume excavation there in the future. The depth and, of course, the marker are indicated in the archaeological report.

    Screening

    As excavation proceeds, the material removed from the excavation units is sorted using a screen. The screening method used varies with the circumstances, including the type of matrix or soil and the artifacts or other archaeological remains they expect to uncover. Typically, screens consist of a wooden frame with window screening material affixed to the bottom. The soil is put into the screening box, and workers sift the soil through the screen, which leaves larger chunks and objects behind. The screens’ dimensions vary based on the artifacts of interest to the archaeologist. The mesh’s hole size can be anywhere from one-half to one-sixteenth inch. During the screening process, workers sift the materials and pull out artifacts and ecofacts.

    When archaeologists are especially interested in locating pollen or other small plant remains, they can use a water screening process called flotation, in which the excavated material is flushed through a water sieve that allows the lighter materials to float to the surface, making them easy to recover. Water screening is also sometimes used for larger objects encased in a matrix that is primarily clay or some other dense or wet soil. In that case, hoses or buckets of water are used to wash the dirt off the objects.

    flotation

    Using water to separate plant remains and seeds from the surrounding matrix.

    Decisions about whether to use wet or dry screening methods and the size of the screen to use have a dramatic impact on the kinds of artifacts that can be recovered and the condition in which they are retrieved. Small artifacts will be lost to time if the screen is too large, and pressure from a water hose can damage or even destroy fragile artifacts. So these seemingly small decisions are a critical part of planning an excavation.

    5926644394_f24cd9dff4_w.jpg
    Figure \(\PageIndex{5}\): A porcelain cup handle found during the process of screening.

    Recording

    During the entire excavation and screening process, workers recover the artifacts, ecofacts, and information about features of the site. Artifacts and ecofacts are preliminarily put in a bag clearly marked with its provenience (three-dimensional coordinate information, including its layer and its specific position relative to the surface—the depth at which it was found). Eventually, a field catalog will be created that records everything that was uncovered in the field. Both identification of the finds and creation of the catalog will be refined once the team returns to the lab.

    field catalog

    A record of all archaeological finds that includes provenience data.

    After The Digging Is Done

    It is important to realize that there is a lot of work to complete after excavating a site—many archaeologists would argue that most of the work is done after they return from the field! A common estimate of the breakdown in time spent in the field versus the lab is 1 to 5. For every 1 week spent in the field excavating, archaeologists expect to spend at least 5 weeks in the lab processing what they found. Some archaeologists wash the artifacts when they return to the lab; others prefer not to wash them because they are interested in obtaining DNA or other types of trace materials for analysis. Each artifact and piece of archaeological material is given a catalog number that corresponds to a listing of it in the permanent catalog, which is built from the field catalog. The permanent catalog, which commonly is a computer database, records the provenience data for the item and a brief description of it and often includes a photo. The catalog number is written on the artifact in permanent, archival ink. These numbers need to be written legibly in an inconspicuous but noticeable place. So, obviously, not across the face of a Pakal’s mask! With such a mask, the catalog number would likely be written on the inside surface of the mask. The items are then placed in bags with the provenience information written on the outside of the bag and, usually, on a small tag placed inside the bag. This seeming duplication of information is critical in case the information on the bag rubs off or something happens to the number on the artifact.

    permanent catalog

    A database of archaeological finds that includes a catalog number, provenience data, description of the artifact or feature, and photographs.

    UNDERWATER ARCHAEOLOGY

    2879054020_faa0f65554_w.jpg
    Figure \(\PageIndex{6}\): Underwater archaeology still requires the same meticulous methods of recording.

    The process used for underwater excavations is somewhat different for obvious reasons. Underwater excavations usually are not designed to recover the artifacts; rather, the task is to record all of the artifacts visible on the lake or sea floor. It is difficult and costly to bring artifacts to the surface, and, once exposed to air, many artifacts, such as metal encrusted with metallic salts, must be stabilized in a laboratory to prevent them from deteriorating. When underwater archaeologists do collect artifacts and bring them to the surface, additional technologies such as suction hoses and baskets with balloons attached are needed.

    The tools used depend on the depth of the water and the types of artifacts being removed. Miniature submarines, submersible watercraft, scuba gear, and other technologies allow archaeologists to see below the surface. Side-scan sonar can also be used to locate shipwrecks and other archaeological sites beneath the surface. Side-scan sonar is similar to LiDAR; sound waves are sent to the ocean floor, and the scanner measures how long it takes for the sound waves to return, creating a topographical map of the floor’s surface. Side-scan sonar mapping is expensive, however, and a somewhat less sophisticated sonar technology used on fishing boats to locate fish has been used successfully in archaeological expeditions.

    side-scan sonar

    A sonar system used to create surface maps of the sea floor, similar to LiDAR.

    IMAGES

    Figure 7.2.1 Clearing the topsoil. (2005). By Wessex Archaeology under CC BY-NC-SA via flickr.

    Figure 7.2.2 Cliffs End Farm - excavating a burial. (2005). By Wessex Archaeology under CC BY-NC-SA via flickr.

    Figure 7.2.3 Çatalhöyük South Area Excavations. (2010). By Çatalhöyük under CC BY-NC-SA via flickr.

    Figure 7.2.4 Recording Depth. (2009). By Brian Hoffman under CC BY-NC-SA via flickr.

    Figure 7.2.5 Porcelain cup handle, Civil War Archaeology in Lafayette Square. (2011). By Baltimore Heritage under CC BY via flickr.

    Figure 7.2.6 Drawing underwater. (2008). By Maritime Archaeology SDU under CC BY-NC-SA via flickr.


    This page titled 7.2: Excavating is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Amanda Wolcott Paskey and AnnMarie Beasley Cisneros (ASCCC Open Educational Resources Initiative (OERI)) .