Georgia Spencer discusses the role geochemistry can play in uncovering historical geographies.
With streamlined education systems and ever-growing separation of the Sciences and Arts, one might be forgiven for believing in the segregation of disciplines; after all, how could chemistry contribute to history, and politics to archaeology.
However, cooperation of disciplines may be the key to unlocking new ideas. Academics provides a perfect platform for interdisciplinary and international collaboration. As Goethe once said, “Science and art belong to the whole world, and before them vanish the barriers of nationality” (Goethe, 1813 quoted in Calrns, 1976: 266). Humanity has come leaps and bounds in learning about the world around us yet much remains a mystery, including our own origins. Historians and archaeologists provide a wealth of information available to anyone who happens to stroll into a museum, yet much more lies within the artefacts than meets the eye.
Advances in chemical analytical techniques have proven endlessly valuable in understanding the past. During the Eighteenth Egyptian Dynasty, two monolithic stone blocks were mined and erected in Thebes, presently Luxor, then carved to form the Colossi of Memnon as a memorial for the pharaoh Amenhotep III. As Egyptian power and fortune waned, the monoliths were attacked by various armies, yet none were successful in destroying them. The Colossi, made of quartzite, one of the hardest natural rocks, survived intact until an earthquake struck in 27 B.C where one monolith lost its upper half. They remained broken until almost two centuries later when the Roman emperor Septimius Severus conducted repairs.
In the seventies, Robert Heizer took an interest in the Colossi conundrum that had puzzled historians for years – what was the original source of these blocks? Heizer, along with his team, came up with a solution, conducting a type of analysis called ‘elemental fingerprinting’. Quartzite consists mostly of silicon and oxygen with small amounts of other elements. The exact composition of the quartzite is unique to its source and characterisation of the material can provide strong evidence for its origin. The team found that the original rock that formed the Colossi was transported upstream from a quarry near Cairo over 400 miles away. The reconstructed Colossus, however, contained quartzite from only 130 miles away where it would have been transported downstream. It is possible the Egyptians had no knowledge of the closer quarry at the time, or perhaps they deemed the original quartzite to be of superior quality and therefore worthier of being used as a memorial for their ruler. Politics or economics may also play a role in this, as perhaps the Egyptians had a trade agreement that went ignored by the Romans.
Analysis such as this can be furthered in complexity; Valerie and Harmon Craig took it upon themselves to do so using marble artefacts. Instead of simply using the elemental composition of a material, the duo focused instead on isotopic composition. Isotopes occur when some atoms of a specific element contain different numbers of neutrons, such as in carbon and phosphorus. Isotopes of an element vary in weight and can thus be separated over time by biological and geological processes. The isotopic composition of a material at a source depends on local atmospheric and biological conditions. Variations can, therefore, provide another fingerprint and further evidence for the source of a given material. The Craigs focused on classical marble statues and found distinct patterns in the percentage of certain carbon and oxygen isotopes, 13C and 18O, within the marble. Using their data, they compiled a plot that showed the isotopic compositions of many common quarries used in Greece (Figure 1).
This provides a neat reference but, as with many things in science, it doesn’t stay simple for long. Work from other researchers complicated the plot where additional data points start overlapping, giving up to six possible sources for a specific isotopic composition (Figure 2). Despite the newfound mess of data, the method pioneered by the Craigs is by no means useless. Additional isotopes can be brought into consideration to clear up any ambiguity; elements such as strontium and chromium provide useful tiebreakers in such situations.
Of course, it doesn’t stop there. Once a method has been created and improved, the next logical step is to apply it to other situations. In this case, flint and obsidian can be analysed and traced to their sources. These materials were most commonly used during the Stone Age and provide a helpful reference for the movements of our ancestors. How did a flint tool that originated in East Anglia end up in northern France? Perhaps the Englishmen went to war and lost it or the tool was stolen from its homeland. Perhaps the migration was a result of trade rather than violence. The role of analytical science in these situations is not to provide answers, but to provide evidence on which following theories from other disciplines can be based.
As with many methods, there are limitations to the analysis of these materials. Not every source can be found as many were used centuries ago and may no longer be accessible, and the sources that have been discovered may not be suitably distinguishable from one another. The main focus of the artefacts in question is often the human element to them – who created them, how they were used – yet this very human interaction may alter the chemical makeup of the artefact and hinder identifying its source.
Nonetheless, the contribution of chemical analysis cannot be forgotten or brushed aside. It’s only with the cooperation of multiple disciplines that theories and ideas can be constructed and broadened as efficiently as possible. Uniting experts to provide alternate perspectives furthers our understanding of the world. Our ancestors were not confined to a single field, so neither should we. It’s only with a deepened understanding of our history and our world that we can begin to shape our future.
CALRNS, T. 1976. Archaeological dating by thermoluminescence. Analytical Chemistry, 48 (3): 266.
CRAIG, H. AND CRAIG, V. 1972. Greek marbles: determination of provenance by isotopic analysis. Science, 176 (4033): 401-403.
GERMANN, K., HOLZMANN, G. AND WINKLER, F. J. 1980. Determination of marble provenance: limits of isotopic analysis. Archaeometry, 22 (1): 99-106.
Georgia Spencer is a third-year MSci Chemistry student. Follow her on Instagram at @g__mari (two underscores) and add her on Animal Crossing: Pocket Camp (her pin is 93365016990).