What Is Archaeology? How Do Archaeologists Work?
What is Archaeology? Why Do Archaeologists Dig?
Archaeology is a way of learning about the past by studying the things people made and used (artifacts) and the places where they once lived (sites). Archaeological sites form when people live in a place over time, build and repair houses, do routine things like prepare food and throw things away on rubbish heaps. Over time these and other activities cause things to become buried in the ground.
How does this happen? As one example, the walls of a house might collapse, covering its floor and the things inside. If people rebuild the house, they might break apart the collapsed wall and spread its remains to create a level surface on which to build again. In this way, layers (or strata) build up as people continue to live in the same place. This building up of site layers creates a site’s stratigraphy. When layers are concentrated in one place they create features that archaeologists call mounds. Finding evidence of old walls and floors helps the archaeologist to learn whether a mound was formed primarily through the collapse of buildings like houses.
Things also get buried in the ground through everyday housekeeping activities, for example when food scraps like animal bones or parts of plant foods are swept up and thrown away in a pit or on a rubbish heap. Broken objects are also tossed on rubbish piles. Over time these rubbish piles build up to create what archaeologists call middens. When people discard things in the same place over a long period of time, the layers of midden can form a tall mound. All of these discarded and buried things provide clues about people’s lives—what they ate, the tools they used, the houses they lived in and more.
How do Archaeologists Do Their Work?
Archaeologists work in teams as they excavate. They carefully remove soil layers at old sites to recover artifacts (things made and used by people). As they dig, they make notes about the contexts in which artifacts are found. Context refers to the spatial relationships of things found in the ground to one another and to features like floors, hearths or pits. An artifact's context includes information on its horizontal relationships within an excavation unit or site and also its vertical relationships to a unit's or site's stratigraphic layers.
Stratigraphic relationships can tell us which things are older and which are more recent in time based on what archaeologists call the principle of superposition. This principle tells us that, unless the soil layers have been disturbed by animals burrowing in the ground or some other action, things buried in deeper levels or strata are older than things found in the levels above them. As an example, a pot sitting on a house floor buried by a collapsed wall must come from an earlier time than a pot found on the floor of a house built over top of that collapsed wall.
Archaeologists use the word associations to talk about these spatial relationships. Associations can give important clues about how things were used in the past. For example, a large grinding stone might have been used to prepare food or it might have been used to shape and sharpen metal tools. Looking at the stone alone might not tell us about its use. But if we know that the grinding stone was found in association with kitchen equipment and a cooking hearth, we have a clue that it was used to prepare food. If the grinding stone was found sitting close by a forge where metals were made, it was more likely used to shape and sharpen tools. In this way, archaeologists are like detectives using clues from associations to learn about past life-ways.
The importance of associations to archaeology’s detective work is why archaeologists use careful digging and recording techniques. Before excavating, archaeologists set up a grid across a site. The grid is made up of parallel lines which intersect at right (90 degree) angles: lines oriented north/south intersect with lines oriented east/west. A grid makes it possible to locate points using coordinates, for example by measuring a point’s location as a distance (measured in meters or centimeters) and direction (north, south, east or west) from the grid’s anchor or zero point (known as the site datum). Any point’s horizontal location can be described in this way, for example as 5 meters to the north and 4 meters to the west of datum, or 10 meters to the south and 6 meters to the east of datum.
The site grid sets up the square units in which archaeologists dig. In Banda, archaeologists name their excavation units by the coordinates of the unit’s northeast corner peg. In this way you can know that an excavation unit named 2W 2S is located two meters in the direction west and two meters in the direction south of the site datum. A unit named 14N 22E is located 14 meters in the direction north and 22 meters in the direction east of the site datum.
Archaeologists write notes and draw maps as they dig. These record describe the spatial relationships of finds within excavation units. Finds include artifacts and features like walls, house floors or hearths. Archaeologists measure how far an artifact or feature is from the unit’s northeast corner (in centimeters, south and west of this corner), and in this way record the horizontal location of the artifact or feature. Because all measurements relate to the site grid, this allows archaeologists to create maps that show the horizontal relationships among finds from across the site.
Archaeologists also record vertical spatial positions of finds. They measure these using a piece of string pulled tight and made level using a bubble or line level. The horizontal position of the string relates to a “datum” standard. The datum standard is a level horizontal surface (a plane) from which points are measured as above or, more often in archaeology, below datum. A measuring tool like a ruler is held at a right angle (90 degrees) to the string. This creates the vertical or plumb line that is needed to make sure that depth measurements are accurate. These careful measurements of depth above or below datum help archaeologists to understand how finds from across the site relate to one another in terms of their vertical spatial relationships.
Archaeologists use special techniques to recover artifacts and record (describe) features. Some artifacts are found in place (in situ) as the archaeologist carefully digs by using a hoe or trowel to scrape away dirt within a unit. After making measurements and writing notes on an artifact’s spatial location (its provenience), the artifact is removed and placed in a bag together with its provenience information for further study. But not all artifacts are found in place. Many are recovered from excavated soil as it is sifted or sieved through wire mesh screens. Screening or sieving the dirt separates artifacts from the soil and helps archaeologists to find small things that were not seen as the soil was being excavated. The size of a screen’s mesh determines the size of artifacts found. Very small objects—for example, small seed-sized beads—can pass through a screen unnoticed.
For this reason, archaeologists often use a technique called flotation to process some of the excavated soil. The soil is placed in a metal basket lined with very fine wire mesh (like window screen). The basket is lowered into a container filled with water and gently shaken. As it is shaken, the soil dissolves, passing through the mesh and leaving behind small objects like beads in the bottom of the basket. At the same time, light objects like seeds or pieces of wood charcoal float to the top as the water dissolves the soil. These are skimmed off with a fine mesh ladle and carefully set aside to dry. Flotation is laborious and is therefore used to process only small samples of excavated dirt. But archaeologists learn important things from studying the small artifacts and fragile remains of plants recovered using this technique.
Archaeologists study artifacts and their associations. While many people associate archaeology with digging, most of the work that archaeologists do comes after “the dig.” Artifacts like pottery, metal tools or beads are carefully identified, described and compared. Specialized scientific analyses may be done to study the materials used to make artifacts and their sources (e.g., see Making Things from Clay). Archaeologists study animal bones, seeds, wood charcoal and other biological materials to identify their species (the kind of animal or plant) and ecological associations (their habitat and the other plants and animals with which they live). And archaeologists do careful analyses of spatial relationships between finds which helps to build an understanding of the associations of artifacts with one another and with features like floors or hearths.
Like detectives solving a mystery, archaeologists piece together information from all these and other kinds of analyses to build a picture of how people lived at different times in the past.
How Old Is It?
If you found a five pesewa coin on the ground, you could easily say how old it is. The date when the coin was made or “minted” is stamped on the coin. However, most artifacts do not have a date stamped on them, so how do archaeologists know how old things are?
Archaeologists talk about the age of artifacts and their contexts in two ways: in terms of their relative age or their absolute age.
Relative ages or dates tells us about the order or sequence of things in time, but not the interval of time (how many years) between them. In other words, we can say that one thing is older than another, but without knowing how many years or centuries older. As an example, using the principle of superpositioning, an artifact’s stratigraphic location can help us to know which things are earlier and which are later in time.
Archaeologists use stratigraphy to study how artifact styles change over time. Today we are familiar with how clothing styles or the look of cars changes over the years. In a similar way, the styles of things that people made and used in the past changed too. Pottery is an example. Because clay is a plastic medium and can be used to make pots of different shapes and sizes decorated in many ways, archaeologists study how pottery styles changed over time. They do this by comparing pottery from different stratigraphic layers.
These changes in pottery styles are used to establish what archaeologists call phases. Within a phase, pottery styles are similar; between phases the styles are relatively different. Archaeologists use stratigraphy to order the phases in time (a kind of relative dating), but understanding how long a phase lasted requires what archaeologists call absolute dates.
Absolute ages or dates are calendar dates, like knowing that a five pesewa coin was minted in the year 1965. Historical texts often have calendar dates written on them and these can tell us the exact date of an event, like the day when a chief was enstooled or the year of a war. Calendar dates in archaeology more often refer to long time spans like the 19th or 20th century, or a range of centuries like the 13th--16th centuries. These are “absolute” dates because we know both their order (which is older?) and interval (how much older?).
Most absolute dates in archaeology come from scientific dating techniques like radiocarbon dating. This is a way to determine the age of organic things—in other words, things that once lived. All living things have the chemical element carbon (C) in their bodies. Carbon enters living things through plant photosynthesis (the process by which plants grow). Carbon is then transferred to animal bodies when they eat plants. Carbon has several forms (or isotopes), and radiocarbon dating is based on the fact that one of them—carbon-14 (14C)—is radioactive. This means that it decays over time into other chemical elements. As long as a plant or an animal is alive, the amount of 14C in its system stays the same because it is taking in carbon through food. But when an organism dies, it stops taking in new carbon and the amount of 14C is reduced through a process called radioactive decay. This decay happens at a constant rate—called a half-life--which is the amount of time it takes for the 14C to decrease to one half of its original amount. The half life of 14C is around 5,730 years. This means that it takes many thousands of years for 14C to decrease to the point where it can no longer be measured by scientists.
Scientists can estimate the age of an archaeological sample like a charred piece of wood, a seed or an animal bone by measuring how much 14C it contains. In a simple example, if the scientist finds half of the amount of 14C in an archaeological sample compared to a living organism, the scientist knows that the organism (the plant or the animal) died approximately 5,730 years ago (the half-life of 14C). If the amount measured is one quarter of the original amount found in a living organism, the scientist knows that the organism died approximately 11,460 years ago (two half-lives of 14C, so 2 x 5,730).
While the accuracy of radiocarbon dating techniques have improved since the technique was first used in archaeology in the 1960s, radiocarbon dates are always “approximate”—they have a statistical range of accuracy shown by a “plus” or “minus” number of years around a mean or average date. At its most accurate, a radiocarbon date can estimate the age of a sample to within a time span of perhaps plus or minus 40 years (an 80-year time span). More often, however, the dates are less precise, which is why archaeologists most often give absolute dates in terms of spans of centuries, for example, 13th--15th century. For these and other reasons, archaeologists try to date as many samples as possible as a way to increase the accuracy of their age estimates.
How do archaeologists use radiocarbon dates on organic materials to date other artifacts and contexts? Here is where carefully recorded “associations” are important. Pieces of radiocarbon-dated wood charcoal found in stratigraphic layers are used to estimate the age of those layers. For example, a date on charcoal from a cooking hearth can be used to estimate the age of the hearth and the pots around it. In this way, non-organic artifacts and features are most often dated by association with a dated organic material. In other words, they are not directly dated themselves. The accuracy of these dates by association depends on the quality of those associations.
Archaeologists use radiocarbon dates to study the duration of pottery phases. Organic materials from the stratigraphic layers associated with the pottery are dated using the radiocarbon method and the pottery is dated by association. This enables archaeologists to develop working chronologies of artifact styles grouped into phases. These are “working” chronologies in the sense that they can be revised based on further study. A new group of radiocarbon dates or excavations at a new site may lead to changes in the working chronology of an area.
The working chronology for Banda area archaeology is based on large-scale excavations at three sites known as “kataas” (old places) in the Nafaanra language. These are Makala Kataa, Kuulo Kataa and Ngre Kataa. Banda Research Project archaeologists have also done smaller excavations at many other sites across the region which have helped to build a working chronology. In our current understanding, the phases in this working chronology for the Banda area cover a period of roughly 1000 years. From most recent in time to earlier in time, the phases and their approximate dates are:
- Makala phase from about 1725 to about 1900 (CE)
- Early Atlantic phase from about 1600 to 1700 (CE)
- Kuulo phase from about 1400 to 1600 (CE)
- Late Ngre-Early Kuulo phase from about 1325 to 1525 (CE)
- Ngre phase from about 1230 to 1400 (CE)
- Volta phase from about 1100 to 1300 (CE)
Who Lived Here?
People today are often identified by the cultural or ethnic and linguistic groups or the places from which they come. Each of these ways of identifying people simplifies the interactions and relationships that cut across boundaries of such groups. We know today that people often speak more than one language. Peoples' parents or ancestors may have come from different places than the family lives today. And 21st-century ethnic groups are social units that bear traces of colonial-era ways of classifying and governing people. Because of these simplifications, we need to be careful not to jump to conclusions about the identity of people who lived in an area and contributed to its heritage.
People who live in the Banda area today come from many places and--as oral histories tell us--Banda has long been a place to which people have come to settle from other areas. Oral histories describe how Nafana people came to Banda from their earlier home in Kakala. Other family histories describe how their ancestors came to settle in the Banda area from other places. These families coming from different places and speaking different languages enriched the area’s heritage through their knowledge and practices. People who came from different places and spoke different languages married one another and in this way came to share knowledge and ways of doing things. People living in the Banda area interacted with people from other areas by traveling and trading, learning from them and sometimes borrowing ways of doing things from people living elsewhere in Ghana and beyond.
For these reasons and more, archaeologists cannot answer the question “Who lived here?” in terms of an ethnic, a linguistic or a family group. Artifacts do not speak languages and they do not come with ethnic or family labels attached. But as explored elsewhere in this exhibit, archaeology can help us to learn about communities of practice and the learning networks that connected people to one another geographically and through time. The grandfathers and grandmothers of many people from different areas enriched the history and cultural heritage of the Banda area, and knowing about their ways of living and doing things in the past can help us to better understand possibilities for living well together today.