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Microarchaeology: Seeing More Than What Meets The Eye

March 11, 2014 10:03 am

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By: Michael B. Toffolo, Tel Aviv University

Figure 1: Example of heavily sampled section from the Iron Age levels of Ashkelon, Israel (scale bar: 20 cm). Photo credit: Michael B. Toffolo.

Figure 1: Example of heavily sampled section from the Iron Age levels of Ashkelon, Israel (scale bar: 20 cm). Photo credit: Michael B. Toffolo.

If you worked on an archaeological excavation in Israel as a volunteer, at some point you probably saw people collecting dirt into little plastic vials from a blue-tagged section that were then brought to a folding table with scientific instruments and a laptop. These days this is the first encounter with microarchaeology, which happens on a regular basis at sites such as Tell es-Safi/Gath, Megiddo, Ashkelon, Manot and Boker Tachtit.

But what is microarchaeology? Archaeologists have been looking for tinier and tinier remains for many years but thanks to new methods and mindsets, microarchaeology is coming into its own. The term defines the study of the microscopic archaeological record – everything that requires instruments in order to be seen. But there is much more than that involved. I had the opportunity to fully understand the implications of microarchaeological research by spending the last four years as a visiting Ph.D. student at the Kimmel Center for Archaeological Science at the Weizmann Institute in Rehovot (Israel) under the supervision of Dr. Elisabetta Boaretto, nuclear physicist and director of the Dangoor Research Accelerator Mass Spectrometry (D-REAMS) Radiocarbon Laboratory. Here is a brief account of my impressions of a world that has been almost completely unseen.

Figure 2: Setup of the on-site lab at Tell es-Safi/Gath, Israel. The instrument next to the blue box is an FTIR spectrometer. Photo credit: Bridget A. Alex.

Figure 2: Setup of the on-site lab at Tell es-Safi/Gath, Israel. The instrument next to the blue box is an FTIR spectrometer. Photo credit: Bridget A. Alex.

As with all archaeology, everything starts in the field. The first thing is to identify a good problem, because not all archaeological questions can be answered with the help of instrumentation. Most microarchaeological questions are related to formation processes of the stratigraphic sequence. Just how did all that dirt get there, by what natural and human processes were layers deposited and modified over time? Then comes the sampling phase, as sediments are carefully collected without slowing down the dig too much.

Samples are analyzed within minutes at an on-site lab using a Fourier-Transform Infrared spectrometer (FTIR), which gives the mineralogical composition of the sediment or artifact, and are later subjected to further analyses. Such analyses include the study of microscopic mineral plant remains called phytoliths that reveal the presence of particular taxa. Other analyses include the description of thin sections of sediments (materials mounted on slides and sliced to approximately 0.03mm thickness for examination under special microscopes) that reveal the microstratigraphy or minute accumulation of layers at the site. The presence of metallic compounds in sediments with X-ray fluorescence (XRF) can also be measured. In these ways it is possible to get real-time information on what is being excavated and to decide how to proceed with fieldwork. Microarchaeological sampling strategy is modified accordingly and more targeted samples are collected in order to solve the initial problem.

Figure 3: Indoor lab of the Leon Levy Expedition to Ashkelon, Israel, where phytolith analysis takes place in the afternoons, after fieldwork. Photo credit: Michael B. Toffolo.

Figure 3: Indoor lab of the Leon Levy Expedition to Ashkelon, Israel, where phytolith analysis takes place in the afternoons, after fieldwork. Photo credit: Michael B. Toffolo.

All the results obtained with instruments, i.e. the microscopic record, are integrated with the information retrieved by the visual study of artifacts and architecture, i.e. the macroscopic record. The interaction between “macro” and “micro” is constant during the process. Science specialists get their hands dirty in the field and archaeologists are involved in laboratory work.  A generation ago things were quite different. Archaeologists and scientists used to work in parallel lines, with too little communication. Samples were usually sent to specialists who often had no idea of the original context of the collected materials, whereas the results of scientific analyses were too difficult to evaluate for archaeologists trained only in humanities, that is, in the study of the macroscopic record. Sometimes, the outcome of this “interaction” was minimal benefit through maximal effort.

Fig. 4: FTIR spectrum of a sediment sample from Tell es-Safi/Gath. Different peaks or groups of peaks determine the presence of specific mineral phases. Photo credit: Michael B. Toffolo.

Fig. 4: FTIR spectrum of a sediment sample from Tell es-Safi/Gath. Different peaks or groups of peaks determine the presence of specific mineral phases. Photo credit: Michael B. Toffolo.

Today we know that context is crucial in the interpretation of scientific datasets. In the social sciences, including archaeology, an object viewed in isolation from the whole is not the real thing, be it a Philistine Bichrome krater, a lime plaster floor, or an accumulation of fossil goat dung. Every item becomes meaningful only when analyzed in the light of the processes that led to its deposition within the stratigraphic sequence. This is why physical scientists decided to join field operations. The Kimmel Center pioneered this approach to the archaeological record, and did it in a systematic way. We are not talking about a single specialist visiting the site for a few days, but rather an entire team spending weeks at the site trying to solve archaeological problems. To the best of my knowledge, outside of Paleolithic archaeology, this approach is still unparalleled.

Fig. 5: Phytoliths are microscopic plant remains made of opal, and are usually preserved in archaeological deposits. Left: phytolith floors appear as white patches on surfaces, often mistaken with lime plaster floors – which are instead made of calcite (scale bar: 20 cm). Right: phytoliths seen in plane polarized light through a petrographic microscope, after extraction from sediments (magnification: 200x). Photo credit: Michael B. Toffolo.

Fig. 5: Phytoliths are microscopic plant remains made of opal, and are usually preserved in archaeological deposits. Left: phytolith floors appear as white patches on surfaces, often mistaken with lime plaster floors – which are instead made of calcite (scale bar: 20 cm). Right: phytoliths seen in plane polarized light through a petrographic microscope, after extraction from sediments (magnification: 200x). Photo credit: Michael B. Toffolo.

Fig. 6: Block of sediment collected from a section and processed for micromorphology (i.e. the study of the microstratigraphy). Top left: the block is carved and then wrapped with plaster bandages in order to keep it intact. Top right: when the plaster is dry the block is extracted and subsequently carried to the lab. Bottom left: the block is impregnated with polyester resin in order to harden the sediment. Bottom right: finally, the solid block is cut and polished to obtain a 30 µm thin section that will be analyzed with a petrographic microscope. Photo credit: Bridget A. Alex and Michael B. Toffolo.

Fig. 6: Block of sediment collected from a section and processed for micromorphology (i.e. the study of the microstratigraphy). Top left: the block is carved and then wrapped with plaster bandages in order to keep it intact. Top right: when the plaster is dry the block is extracted and subsequently carried to the lab. Bottom left: the block is impregnated with polyester resin in order to harden the sediment. Bottom right: finally, the solid block is cut and polished to obtain a 30 µm thin section that will be analyzed with a petrographic microscope. Photo credit: Bridget A. Alex and Michael B. Toffolo.

This unique integrative approach is also the leitmotiv in the training of students at the Kimmel Center, a sort of marriage between social and natural sciences. Unfortunately, in most universities worldwide Near Eastern archaeology is usually taught as a humanistic discipline. But archaeological sites are made of artifacts and architectures, which in turn are made of chemical compounds and surrounded by a sediment matrix. From my point of view, it is inconceivable to address an archaeological problem without taking into account the fact that layers, like artifacts, are the product of specific human activities that can be traced. An archaeologist has to be able to evaluate an object within its context, even more so today when we are aware of the information hidden in sediments.

Educating a new generation of archaeologists trained both in archaeology and natural sciences, capable of using instrumentation when needed and to critically evaluate datasets and field contexts, is an important goal. At some point in the future this will become a routine. Going from the analysis of organic molecules within a potsherd to the reconstruction of Mediterranean trade routes of ceramics in the Bronze Age, from the detail to the big picture and vice versa will be the norm for an archaeologist. I believe this is the way towards which university teaching should head, even though it is a slow and sometimes frustrating process.

Figure 7: Careful visual examination of sections is the first step in sampling strategy. Photo credit: Michael B. Toffolo.

Figure 7: Careful visual examination of sections is the first step in sampling strategy. Photo credit: Michael B. Toffolo.

Until that time, we need to refocus the interaction between scientists and archaeologists. It is always useful to have science-based specialists on the excavation, as they may come up with different questions compared to archaeologists. Scientific background provides a different mindset that allows scientists to ask interesting questions. But scientists need to spend more time in the field in order to understand completely all the subtleties regarding archaeological contexts. This is done by communicating with archaeologists, who in turn realize the potential applications and limits of microscopes, spectrometers and other instruments. The benefits are mutual.

Figure 8: Dr. Elisabetta Boaretto collecting samples for radiocarbon dating in Tell es-Safi/Gath, Israel. Photo credit: Kimmel Center for Archaeological Science.

Figure 8: Dr. Elisabetta Boaretto collecting samples for radiocarbon dating in Tell es-Safi/Gath, Israel. Photo credit: Kimmel Center for Archaeological Science.

I think this model of close collaboration should become the rule in archaeology, considering that it already proved to be successful. The session titled “Twenty Years of Digging at Megiddo: Macro and Micro Archaeology Discoveries”, which was recently presented at the 2013 ASOR Annual Meeting in Baltimore and chaired by Prof. Israel Finkelstein (Tel Aviv University) and Prof. Eric H. Cline (George Washington University), is a good example of such an endeavor. The talks featured the most recent advances in Iron Age geoarchaeology, metallurgy and radiocarbon dating among others, all based on an integrative approach of the sort described here. Hopefully, this and other similar presentations – with their legacy of published scientific articles – will stimulate not only scholars involved in archaeological research at all levels who wish to explore new possibilities, but also students who are eager to expand their background. The path is marked and can lead to major achievements. Recent high-impact discoveries regarding the earliest evidence for the use of fire by hominins (primates within the genus Homo), the mapping of human lineage by DNA, the refinement of Early Bronze Age radiocarbon chronology in the Levant, or the earliest appearance of pottery in Asia are all based on microarchaeological research. These and other breakthroughs captured the attention of the public worldwide and gained enormous credit in academia, leading to the allocation of substantial funds granted by government-based and international research agencies. Many irons are in the fire, and many more have yet to come.

Figure 9: The Kimmel Center team at work in Megiddo, Israel. Photo credit: Israel Finkelstein.

Figure 9: The Kimmel Center team at work in Megiddo, Israel. Photo credit: Israel Finkelstein.

Michael B. Toffolo is a PhD candidate at Tel Aviv University and visiting PhD student at the Kimmel Center for Archaeological Science (Weizmann Institute). He has begun a postdoctoral fellowship at the Florisbad Quaternary Research Department of the National Museum, Bloemfontein (South Africa).

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Microarchaeology: Seeing More Than What Meets The Eye Reviewed by on . By: Michael B. Toffolo, Tel Aviv University [caption id="attachment_6980" align="alignleft" width="140"] Figure 1: Example of heavily sampled section from the I By: Michael B. Toffolo, Tel Aviv University [caption id="attachment_6980" align="alignleft" width="140"] Figure 1: Example of heavily sampled section from the I Rating: 0

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