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Archaeochemistry Techniques
Techniques and methods used by archaeochemists working on the Liang Bua project
I’m Linda Prinsloo. I’m a research fellow at the University of Wollongong. And I specialize in vibrational spectroscopy. Vibrational spectroscopy is the study of the vibrations of molecules. At room temperature, all molecules are moving around. And if you heat them, they will move at a higher energy. So I can use this to have a fingerprint of different kinds of molecules as they all move at different frequencies, or vibrate at different frequencies, to use a more scientific term. So there are two ways in which I can do it. The one Raman spectroscopy. And the other one is FTIR spectroscopy. Now in both techniques, I add energy to the molecules and then I measure at what energy they vibrate.
Now, you might ask me what will that help me to know what a molecule is? So if you think about the little mouse jumping on a trampoline, it will be doof, doof, doof, doof, doof. So that little mouse will send out vibrations of a certain frequency. And if you were to put the elephant on the same trampoline, it would more something like dooof, dooof dooof. So even if I don’t know or can see it’s the elephant or the mouse, the vibrations will tell me which one it is. So if I have a database of vibrations of a large number of molecules, I can select those that are of interest to me and I can compare it to known samples.
So I’m an analytical chemist. And I’m interested in looking at organic residues on stone tools, as well as in the sediment, just to try to piece together the chemical processes that occurred at the site and also work out how the Hobbit lived basically. I use mass spectrometry. It’s a technique used to analyze individual molecules found in the specimen. Everything is made out of molecules. And so we can get a profile of the molecular identity of the things that we will find in the stone tools. It might help us understand what the Hobbit ate, how they lived. Together with Matt Thomas, Mike, and Richard, we wrote a sampling protocol, which was applied in the field.
So we do have input on how the samples are collected. We don’t just do it ourselves, obviously, because the archaeologists do that. And then from the site, the samples get sent to the lab, where Richard has a look at them, for use with analysis and also microscopy. And he identifies or screens the stone tools for any interesting residues that we may find. And then if there is anything interesting, then it will come to Linda and Luke, which work on spectroscopy. And that’s another good analytical technique to use to screen the stone tools and get some sort of molecular information of the composition of the sample. And then my step is the final step. It’s a destructive method.
We basically isolate the residue, process it so that it makes it amenable to mass spectrometry, and then identify the molecules and separate them in the sample. Regarding the artifacts of Liang Bua, we’re basically looking at stone tools. And these stone tools have been used many, many years ago by the people who lived in the cave. And we hope that by using Raman and infrared spectroscopy, we can identify some of the molecules that became attached to the tools through the working of the people using the tool. So, for instance, if someone were cutting meat with a tool, we would hope to find some remnants of bone, fatty acids, something like cholesterol on the artifact.
While if they were working with plants, we would expect to find some cellulose, or ligand, or the ingredients of plant materials on the tools. It is quite difficult because the samples are very old and some of the material has become degraded. Obviously, an archaeological site is not a sterile site. And our technique requires quite sterile conditions. And so we have issues like contamination, people not wearing gloves. But that’s expected at an archaeological site. So we just work within the confines of our environment. And also degradation– at Liang Bua, it’s quite hot. It’s quite humid. And these conditions aren’t very good for preservation of residues.
So in the laboratory, we have to follow a process whereby we can eliminate some of the contamination that could have been left on the samples by the people who excavated the samples, people who put it in storage afterwards, and sometimes even by ourselves just handling the samples. It’s the last part of the analysis. And from the information gathered from everybody else, then we’re ready to interpret properly. So there’s a standing hypothesis. We go through the process of analysis. It’s a multi-step approach. And then we either support or refute the hypothesis that was set. I’m not originally from archeology. I’m an analytical chemist. But we’re hoping to find some amazing things.
If interesting residues are found by scientists when artefacts are screened in the laboratory, they will be sent for analysis by archaeochemists using spectroscopy and mass spectrometry techniques.
Vibrational spectroscopy (the study of the vibrations of molecules) involves the process of adding energy to molecules and measuring at what energy they vibrate. Two types include Raman spectroscopy and FTIR spectroscopy:
“So if I have a database of vibrations of a large number of molecules, I can select those that are of interest to me and I can compare it to known samples” (Dr Linda Prinsloo)
Chromatography and mass spectrometry (techniques used to separate and characterise individual molecules found in a specimen) helps to uncover the chemistry of organic residues preserved on artefacts and the chemical processes that occurred at a particular site. This is often the final analytical step, as they are destructive methods that require the residue to be isolated and the identified molecules separated from the artefact or sediment sample:
“Everything is made out of molecules, and so we can get a profile of the molecular identity of the things that we will find on the stone tools. It might help us understand what the hobbits ate, how they lived.” (Dr Susan Luong)
Multidisciplinary Input
Although working in a laboratory setting, the team of archaeochemists involved in the Liang Bua project contributed also to improving our understanding of the archaeological processes operating in the field. For example, they have developed a sampling protocol that governs how the samples should be collected in the field to minimise the chances of contamination.
Significant Findings
The work of archaeochemists has helped to identify molecules attached to stone tools as a result of people using these tools in the past.
“So, for instance, if someone were cutting meat with a tool, we would hope to find some remnants of bone, fatty acids, something like cholesterol on the artefact. While if they were working with plants, we would expect to find some cellulose, or ligand, or the ingredients of plant materials on the tools”. (Dr Linda Prinsloo)
Conversation starter
The work of archaeochemists requires a sterile environment, but an archaeological site is far from sterile (see 3.11 Contamination: Refining Methods). In light of this, consider the following questions:
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How do processes of degradation and contamination affect the work of archaeochemists?
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What can be done to minimise these effects?
This article is from the online course:
Homo Floresiensis Uncovered: The Science of ‘the Hobbit’
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Homo Floresiensis Uncovered: The Science of ‘the Hobbit’
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