This lesson is designed to introduce youth to geomorphology and how it is use by archaeologists to understand a site’s context and temporal affiliation.
Grade Level: 6-8
Objective: The lesson will introduce learners to the field of geomorphology, soil development, and how these relate to an archaeological site.
Learning Outcomes: Learners will be able to discuss why archaeologists need to understand the geomorphology of a landform when conducted a site investigation, including how and why they study site stratigraphy and site soils.
STEM: geology
Materials: soil sampler/corer, Munsell Soil Color Chart, soil triangle, soil profile drawing
Time: 60 minutes
Overview: Geomorphology is the study of landforms. There are a lot of ways that archaeologists use geology and geomorphology. The Landscape Analysis focuses on the different types of landforms people used for settlement and subsistence. In this lesson, we will examine how those landforms were created.
Geomorphology helps archaeologists predict how deep they may find an archaeological site on a particular landform. Soils on a floodplain are accumulated as the river overflows its banks and deposits new soil. This means that sites may be buried over time. People in the past conducted activities on a floodplain given the proximity to certain plants that grew on it and the animals that visited it, its nearness to water for drinking, cooking, and travel, and for the nutrient-rich soils to grow crops.
When archaeologists excavate a site, they maintain the context and association of the material culture and features. One way they do this is by excavating in units to maintain a record of where across a site something was identified. Another way is to excavate only a small amount at a time as they move down through the unit soils. Archaeologists may excavate in 5 or 10 cm levels, maintaining a flat unit floor as they dig. If the soil color/texture changes before the 5 cm or 10 cm has been completed, they will stop that level and take notes. The color and texture of soil tells archaeologists about the natural and cultural environment in which it was formed. At the end of an excavation unit, archaeologists study the profile (or the cut face) of each wall (see example below).
The wall profile helps archaeologists examine the stratigraphy of a site, or the sediments deposited in layers over time. Stratigraphy can tell us about how old occupations are at a site through the Law of Superposition. The soil at the top of a site is the most recent (think of the garbage in your garbage can). As you excavate down through the soil, you are going back through time. Objects in same layer are the same age. Layers that cut into others are younger (Cross-cutting Relations). On a floodplain, the cultural deposits can be many meters deep. Often people reoccupied a landform and, therefore, we see different time periods of use represented in subsequent soil layers. On a hilltop, there is not the same soil deposition and sites from different time periods may be separated by only a thin layer of soil or not at all.
Soil color can tell us about soil formation. Geologists and archaeologists use a Munsell Soil Color Chart to document soil colors at a site (see example below). Darker soil indicates organics (plant and/or animal, possibly including humans) in the soil, while lighter soils indicate that either the organics were leached out (gone) or there were no organics on the land at that time. Soil texture can be silt, clay, or sand, or a combination of these (see soil triangle below).
Example of a stratigraphic profile drawing.
Munsell Coil Color Chart.
Soil texture triangle.
Vocabulary: geomorphology, stratigraphy, stratigraphic profile, cross-cutting relations, Law of Superposition
Procedure: Discuss with learners what geomorphology is and why it is important for archaeologists to study landforms. Refer them to the landscape lesson. Give students an example of a stratigraphic profile (see examples) and have them figure out the order from oldest to youngest stratum. Remind them of superposition and cross-cutting relations. Have learners share their results to see if they all came up with the same order.
Take students outside to a specific landform – floodplain, terrace, or hilltop. Ask them what they would expect the soil to look like – color and texture. Ask them what is the deepest they think they could find archaeological sites on that landform (floodplains – very deep [can be a meter or more]; hilltops – shallow [ca. 50 cm or less]). Using a soil probe/corer, extract a soil core for the students to explore the soil strata. Have them determine the color (using a Munsell) and texture (use the soil triangle) of each stratum.
Assessment Activities: Each learner will order a stratigraphic profile’s strata and examine a soil core and record its soils.
Wrap up: Learners will discuss why archaeologists study the geomorphology of a site – what it tells us about an archaeological site.