The methods used by archaeologists to gather data can be applied to any time period, including the very recent past. One archaeologist in the U.S. has become known for his study of the garbage discarded by the people of Tuscon, Arizona in the 1970s! This “garbology” project proved that even recent artifacts can reveal a lot about the people who used and discarded them.
Over the past 150 years archaeologists have developed many effective methods and techniques for studying the past. Archaeologists also rely upon methods from other fields such as history, botany, geology, and soil science.
In this section of Methods of Gathering Data you will learn how archaeologists gather and analyze information by utilizing historical research techniques, field methods for data recovery, and laboratory analyses.
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Historical Research Techniques
Every archaeology project begins with a research design –a plan that describes why the archaeology is being done, what research questions it hopes to answer, and the methods and techniques that will be used to gather and analyze the artifacts and other archaeological materials. It will also outline where artifacts recovered from the project will be stored, and how the research will be reported and shared with the public.
Archival research is often the first step in archaeology. This research uncovers the written records associated with the study area. If the area was inhabited during historical times (in the past several hundred years in North America) the archaeologist will look for primary historical documents associated with the study area. This archival research may take the archaeologist to public or university libraries, the local historical society or courthouse—or even into people’s homes! Primary historical documents that archaeologists may consult before beginning their field research include: maps and/or photographs of the area, newspapers, land and tax records, and diaries and letters. Open this History Toolkit to learn more about investigating the past with primary sources.
In addition to primary historical documents, archaeologists will look for site reports that have been prepared by other archaeologists who have studied this area. These reports will describe what was found in this area during any previous archaeological investigations and will help guide the new research. Documentation files for all of the recorded prehistoric and historic sites in each state are maintained in the State Historic Preservation Office, along with archaeological research reports pertaining to sites in the state.
Oral history is another research method that archaeologists and historians may use to gather information. It includes any kind of information passed down by word of mouth, like stories you have been told about your family history, as well as traditions that your family observes. Archaeologists today collaborate with descendants of Native American peoples, and with African American communities who are only a few generations removed from the lives of their enslaved or free ancestors, to better understand the cultural traditions of their pasts. Archaeologists working on the 19th century Levi Jordan Plantation in Texas have interviewed descendants of both the plantation owners and the enslaved plantation workers as part of their research. These archaeologists hope to include the “voices’ and perspectives of all of the past peoples who lived and worked on this plantation into their research. They have created the Levi Jordan web site
to share this information with the public and to allow the public to communicate with the archaeologists.
At Castle Rock Pueblo in southwestern Colorado archaeologists have learned about the past culture of the Anasazi peoples through both the objects left behind, and the oral traditions of modern Puebloan people. Now get ready to take an electronic field trip back in time to Castle Rock Pueblo in AD 1200 and solve a mystery while you are there.
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In the Field
While historians and archaeologists both use written documents to learn about the past, only archaeologists are trained to find and interpret archaeological sites. Here you will learn about some of the field methods archaeologists use to find sites and, when necessary, to excavate them.
Tools of the Trade
You may think of shovels when you think of digging, but the most important piece of equipment in the archaeologist’s toolkit is actually the trowel. A trowel is used to carefully remove thin layers of soil from test units. Of course, many other tools are used by archaeologists in the field and lab to dig, sift, measure, and analyze artifacts. View some of these computer animations of tools and equipment that archaeologists use. Some, like the Scanning Electron Microscope (SEM) are very specialized and high tech. Others, like tape measurers, toothbrushes, brooms and dustpans, are household objects! You can also view photographs of archaeologists using some of these tools on sites.
How Do You Find Sites?
Archaeologists use a number of different methods to find sites—and sometimes they are found just by accident! The prehistoric burials at Low Hauxley on the coast of England were discovered by an observant beach walker who noticed a stone box sticking out of a sand dune after a storm. A burial ground with remains of more than 400 17th and 18th century Africans was discovered during building construction in New York City. The African Burial Ground was made a National Monument because of its importance and significance.
An archaeological predictive model is a tool that indicates the probability that an archaeological site will occur in a certain area. It helps determine where you look for sites based on factors like distance from water, ground steepness, soil type, and other factors that influence where people settle or perform certain tasks. The methods used to find sites will depend upon the kind of research questions that the archaeologist is trying to answer. If highway or housing construction is planned, archaeologists may need to know of any archaeological sites on the property. First they will check if any previous surveys have been done in the area and, if so, what was found. If no previous sites have been recorded, the archaeologist will conduct an archaeological survey to determine if the area contains any sites.
If sites are found, the archaeologist will want to know how many, their location, and how the sites relate to each other. Usually, to save time and money, only a sample of the area is tested.
A surface survey is a systematic examination of the land. A team of archaeologists will walk in straight lines back and forth across the study area looking for evidence of past human activity, including stone walls or foundations; artifacts made of stone, ceramics, or metal; color changes in the soil that may indicate features such as hearths, middens (garbage pits), or storage pits They will use a compass and long tape measure to make sure they walk in a straight line and will record the exact location of all evidence they find. Artifacts are collected and put in bags with a label of their exact location. Features, which cannot be removed, are photographed and drawn. This technique is useful in plowed fields.
Shovel Test Pits
Shovel test pits (or “STP’s”) are a series of shallow pits dug in an area that archaeologists believe to be a potential site, revealing artifacts or features. Usually test pits are done where the ground has not been farmed or plowed and it contains a lot of surface vegetation. The soil may be screened (sifted) to recover small artifacts and often profiles (pictures) of the test pits are drawn to record what the soil looks like in each unit.
There are a number of non-invasive techniques archaeologists can use to find sites without having to dig. Examples of geophysical surveys that do not involve disturbing the soil include are magnetometry, resistivity and ground penetrating radar or GPR.
Evaluating Site Significance
After conducting a survey an archaeologist will have enough information to determine if any significant archaeological resources are located in the study area. If no sites are found, or if the sites are not determined to be “significant” as defined by the law in the National Historic Preservation Act then construction may proceed. The archaeologist will write and file a site report in the State Historic Preservation Office, which describes their research. If significant sites were found, an excavation may be planned. In the next section we will discuss how important data is recovered from archaeological sites through excavation.
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Believe it or not archaeologists do not often excavate (dig) entire sites! Archaeology is a destructive science—meaning that once a site is excavated it is gone forever. The artifacts and information gathered remain, but the site itself can never be recreated. Excavating sites is also costly and time consuming. Once the dig is done, archaeologists have a professional responsibility to analyze all of the artifacts and information obtained, to report on their research in scholarly journals and to the public, and to curate the collections. For all of these reasons, archaeologists generally excavate sites only when they are threatened by destruction from construction or development or when they may reveal important information about past cultures. And they usually excavate only a small portion of any site.
Although archaeologists work on all kinds of sites and in all parts of the world, the same basic process is followed everywhere when an excavation is planned.
Before an excavation begins, archaeologists write a research design. This outlines “who, what, where, when, how, and why ” the fieldwork is being carried out. This important document is reviewed before archaeologists are granted permission to excavate a site. In the U.S. this plan must be reviewed by the State Historic Preservation Office (SHPO) where the work will be carried out. If an American archaeologist wants to work in a foreign country, permission must be granted by the appropriate agency in that government. Tribal (Indian) lands in the U.S. have their own review processes and some tribes have their own archaeology programs that control access to sites on tribal lands. Once a research design is approved and permits area granted, a team is put together and the necessary tools and materials are gathered.
Gridding the Site
Once a site has been excavated, it is gone forever. Because of this, archaeologists must record exactly where all of the artifacts and features on a site are located. Before any soil or artifacts are removed from a site, a site grid is created. A datum point, or fixed reference point from which all measurements are taken, is established and a rectangular grid is superimposed over the whole site. Each square in the grid is precisely measured and assigned a number. These squares are often referred to as units. This system allows the archaeologist to create a precise map of the site and to record the exact location of all the features and artifacts on the site.
Excavating a Unit
Archaeologists use a statistical sampling method to select which squares or units they will excavate. To begin they will collect surface artifacts, then remove any ground cover using a shovel and trowel. All soil removed from a unit is screened (sifted) to recover small artifacts and ecofacts whose exact location, both horizontally and vertically, is recorded. Artifacts from each unit are stored in plastic bags that are labeled with the site and excavation unit numbers and level. The unit may be dug in arbitrary levels (such as every 10 cm) or by following the natural stratigraphy (layers) of the unit. These short video clips show how to prepare a test unit for excavation. Phil Harding--of the popular British archaeology series “The Time Team”-- demonstrates the proper way to use a trowel to remove soil from a unit.
Over time both natural processes like the decay of organic matter, and cultural (caused by humans) processes, create soil layers. In cross section these soil layers resemble a layer cake, with the oldest layers on the bottom and the most recent layers on the top. This is called the Law of Superposition and is one of the most important principles in archaeology. Stratigraphy is the study of geological or soil layers that is used to determine the relative age of each layer. There are many factors that can disturb the stratigraphy on a site and make it hard to determine the relative ages of the layers. Look at how 4,000 years of natural and cultural processes can combine to create and disturb the stratigraphy on an archaeological site. Stratigraphy is one clue used by archaeologists to determine the relative age of an artifact or site. In the next section we will look t other ways of determining how old something is.
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In the Lab
Archaeologists spend much more of their time in the laboratory analyzing artifacts and data than they do in the field. In this section, you will learn how archaeologists analyze artifacts, features, and other information recovered in the field to help answer their research questions. During the investigative process, they also seek to learn when site was occupied, the purpose of the objects recovered, what the people ate, the kinds of structures they lived and worked in, with whom they traded, and much more. They may also look at how the site they are analyzing relates to other sites that are nearby or quite distant. The analysis will depend upon what research question the archaeologist began the project with.
“How old is it?”
There are a variety of techniques that can be used to find out how old an artifact or an archaeological site is. Stratigraphy can determine the relative age of soil layers and artifacts and can help us understand the order in which events occurred. However if an artifact of known age such as a coin with a mint date is found in a soil layer it can tell us when something occurred. Tree-ring dating, or dendrochronology is one of the oldest dating methods used by archaeologists. It is based on the principle that trees produce growth rings each year and the size of the rings will vary depending upon rainfall received each year. Archaeologists have built up long sequences of rings from tree trunks that extend back centuries. In the American Southwest tree ring dating goes back to 59 BC. Radiocarbon (C14) dating is the most widely used method to date objects made of organic matter. Potassium-argon dating can be used to date extremely old – up to 100,000 years old. Obsidian hydration dating is used on artifacts made from volcanic glass. This is just a sample of the many physical and chemical dating methods that archaeologists have used to date archaeological sites.
Artifacts are important sources of information for archaeologists. Artifacts can tell us about the diet, tools, weapons, dress, and living structures of people who made and used them. Recovered artifacts are washed, sorted and catalogued, and stored after they are brought back from the field. Archaeologists analyze individual artifacts but also may sort them into groups to see patterns. For example, they might weigh all of the oyster shells together or count all of the nails and consider them as one unit. Where artifacts are found on the site provides a clue to the kinds of activities that occurred such as stone tool or weapon production or food preparation. The type of material the artifact is made of is another important piece of information that can inform whether the materials were obtained locally or by trading with another group. Artifacts provide a window into the lives of peoples who lived before.
A feature shows human activity but unlike most artifacts it cannot be removed from the archaeological site. A feature might be a stain in the soil that is evidence of a former fence post. Photographs, drawings, and soil samples of the fence post collected by the archaeologist are part of the scientific record of that feature and are just as important as the nails and other artifacts that might be found nearby. Features like soil stains can reveal the outlines of prehistoric or historic structures such as houses and barns, or longhouses and earthen lodges. Other types of features include hearths (fire pits), storage pits, and middens –what archaeologists call garbage dumps! Privies (outhouses) are important features in historical archaeology sites because people used to dump their garbage as well as broken pottery and other housewares into them.
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Historical Research Techniques
In the Field
- Gridding An Archaeological Site
In this activity students establish a grid over an archaeologialsite and determine the location of artifacts within each grid.
- What’s in the Soil?
Students cut out and identify illustrations of artifacts, and paste them into layers of soil to illustrate the stratigraphy found on an archaeological site.
How Old Is It?