Phytoliths are microscopic plant remains that can be recovered from archaeological contexts or lake cores to reconstruct past environments and the diets of ancient peoples. In archaeology, samples can be taken from ancient tools or soils from archaeological contexts. Soil samples recovered from stratigraphy excavated during the Izapa Household Archaeology Project were processed to see how plant use and ambient vegetation at Izapa changed through time. I used the specialized facilities at Smithsonian Tropical Research Institute (STRI) to process them during my 2017-2018 postdoctoral fellowship. I am grateful for the guidance of Irene Holst and Dolores Piperno throughout the process.
Processing phytolith samples involves several steps before they can be analyzed. This includes removing clay from the samples, using mesh screens of different sizes to separate different “fractions” of material (fine, medium, coarse), cooking the samples in Hydrochloric acid to eliminate organic materials, and isolating the phytoliths through flotation. Depending on the samples, it can take several weeks to complete this process. Once they are processed, sample slides are analyzed under the microscope, where the size, shape, and other identifying features are used to identify remains of plants at the family, and sometimes even species, level.
IHAP samples during clay removal
Organic materials are removed by cooking samples in Hydrochloric acid
Different “fractions” were divided in mesh screens and placed into sample vials
Starch grains are microscopic plant remains that can be recovered from archaeological contexts to understand which plant foods ancient peoples were eating and how they were processed. From 2017-2018 I analyzed samples recovered during the Izapa Household Archaeology Project at the Smithsonian Tropical Research Institute (STRI) in Panama, where specialized facilities exist to extract and identify starch grains. In the field, residues were recovered from domestic artifacts like ceramic vessels and grinding stones. At STRI the samples were then processed in the lab with a heavy liquid (in this case, Cesium chloride) to cause these microscopic particles to float. After a series of runs through the centrifuge, a pipette is used to collect any starch grains present in the sample and place them on a slide. The slide is analyzed under a polarizing microscope, where features such as size and shape are used to identify the family or even species of plant present on the tool.
Sample tubes during processing
Yam starch grain (Dioscorea spp.) recovered from an IHAP grinding stone
This season while working in the New World Archaeological Foundation lab in San Cristobal de las Casas, Chiapas, I worked on a side project creating 3D models of complete and nearly complete vessels recovered during the 2014 Izapa Household Archaeology Project excavations. The vessel depicted here is half of a miniature jar dating to the Early Classic period (ca. AD 200-400). The model was created using close-range photogrammetry, a process that uses digital photographs taken from different positions to create a 3D model. For more on photogrammetry, see my page on 3D methods.
This model was created by taking pictures with a small point-and-shoot camera (Nikon CoolpixS9500) and was processed using Agisoft’s Photoscan software. To help the program match points (to help overlap the photos taken from different angles) I included “targets” in all of the photos. Targets used here included 2 clothespins of different shapes and sizes and a 10 cm scale bar. Photos were taken around the vessel from 17 different positions. These are marked in Photoscan by the blue rectangles indicating the photo number. With the help of Photoscan, you can make 3D models quickly and at a low cost with simple materials. In addition to having digital models of the vessels for presentation purposes, I hope to use a 3D printer to create replicas of these digital models that can be returned to members of the Izapa community.
The pXRF setup for obsidian sourcing at the New York State Museum
The Izapa Household Archaeology Project is still underway and currently in its analysis stage. Above is a picture of obsidian sourcing using portable X-Ray Fluorescence (pXRF) at the New York State Museum. Obsidian is a volcanic glass that was used by many early Mesoamerican cultures to make tools. Each volcanic source that produces obsidian has its own chemical signature, allowing archaeologists to determine its volcano of origin. Most obsidian from Izapa comes from sources in Guatemala, but some pieces originate as far away as the Sierra de Pachuca source in central Mexico. The goal of the project is to check how well obsidian procurement at Izapa relates to trends in ceramic patterns from the Terminal Formative or “Protoclassic” period (ca. 150 BC- AD 200) to the Early Classic period (ca. AD 200-550), an important period of cultural development in Mesoamerica. During this era, the institution of divine kingship was developing in the Maya area. Meanwhile, many sites experienced an abandonment or decline in population. This analysis will help us to better understand Izapa’s relationship with sites in Chiapas, Guatemala, and central Mexico during this important period of change.
Note: The Izapa Household Archaeology Project obsidian was exported with permission from the Mexican Consejo de Arqueología to conduct these sourcing analyses. It will be returned to Mexico at the close of the Izapa Household Archaeology Project.
Kelly with one of the figurine heads her team found this week
Week 8 was another big one for the Izapa Household Archaeology Project. We expanded excavations this week and now have six pits open at once, and opened five new units on three new mounds. The new units have already yielded some exciting finds, including stone architecture and more complete vessels. This week we also found our first figurine heads, a rarity at Izapa. Everyone is working very hard to keep up with all the cool new finds, but we’re feeling very lucky!
Reconstructing the wall in preparation for photos
Excavations continued as usual this week. We finished up some of our long-open excavation units in preparation for opening up new pits next week. This week’s highlight was a visit from Lizzie Wade, a writer for Science magazine. Lizzie plans to write an article featuring the Izapa Household Archaeology Project within a article on the archaeology of neighborhoods.
Update: Wade’s article was released on May 16, 2014. The article is now free to access and can be found here: http://www.sciencemag.org/content/344/6185/684.full