The first step in an archaeological excavation is surveying the area. This can be done either with remote sensing or direct visual observation.
Archaeologists conducting a survey
Archaeologists also use non-invasive techniques to survey sites known as remote sensing. There are many methods including aerial photography which is simply taking pictures from an airplane, hot air balloon or even a remote controlled drone; ground penetrating radar which is used to locate artifacts hidden below ground, and LIDAR, which uses lasers to scan the surface from the air through vegetation.
LIDAR image of a site
An Archaeologist using Ground Penetrating Radar
After archaeologists have thoroughly surveyed the site they begin excavation. They start by setting up a grid and connecting the grid to a datum. A datum is a fixed reference point, often one placed by the U.S.G.S.
A USGS datum
The next step is to dig several test pits. Test pits are a small hole dug to determine the location, density and spread of artifacts.
Archaeologists dig a shovel test pit as part of a site survey
Then archaeologists excavate the site using trowels, shovels, and various other tools. They carefully remove dirt and note the precise location of any artifacts found. The context of the artifact is just as important as the artifact itself, so the artifacts are always carefully mapped and documented.
Archaeologist using a trowel
The dirt removed from the site is screened to search for any small artifacts that may have been missed during the initial excavation.
Archaeologists with the National Park Service Screening
Archaeologists also look for features while excavating a site. A feature is evidence of a human activity that is not movable, and usually has a vertical component. An aspect of a site that is only horizontal, such as a road, is not a feature. An example is a frequently used fire ring will leave evidence behind in the soil, but it cannot be moved with the occupants.
Evidence of fires uncovered at an archaeological site-a feature
After archaeologists have excavated the site completely, or to the extent the project planned, they fill the site back in and take the artifacts to be analyzed. The artifacts are taken to a lab, either locally or at the archaeologist’s home institution. They are analyzed and classified based on the research questions of the archaeologist.
An artifact, pottery, that has been photographed for documentation-A scale is often included to show the size of the artifact.
The artifacts are grouped with other artifacts of the same type. A type can be based on a variety of characteristics such as function or style.
A group of artifacts that are all projectile point type
Archaeologists also try to determine how old artifacts are. This can be done relative to other artifacts using stratigraphy-the idea that older artifacts are below newer ones.
An excavation showing the layers used to date the artifacts relative to each other
Artifacts can also be dated absolutely, or with an age or year they are from. This can be done using artifacts found in the site with known dates. These artifacts are known as diagnostic artifacts. They also can be used to determine the culture the artifacts are from. Artifacts can also be dated using dendrochronology, which uses the annual growth rings in trees to establish an age for artifacts.
A tree with annual growth rings
Artifacts can also be dated using radiocarbon dating. This uses the decay of carbon and the ratio of C-12 to C-14 to determine the age of the artifact. It is only effective up to 68,000 years. It is also not very accurate for more recent artifacts. Using all of the information about the artifacts, including context, typology, dating and more, archaeologists can piece together the events and culture of past society.