What gets preserved?
The archaeological record is comprised of finds which can be categorised mainly into artefacts (literally handmade objects) and biofacts (organic/natural remains). Finds such as the Oldowan stone tools at Gona, Ethiopia are an example of inorganic artefacts, in the form of stone tool flakes, which pushed the dates for the earliest stone tool manufacturing from 1.8 to 2.6mya (McPherron et al, 2010). The reason we could reliably produce these dates is because stone artefacts survive well and they aren't biodegradable, meaning there is more evidence to find to support this hypothesis.
On the other hand, organic artefacts and biofacts make up a minority of the archaeological record; being materials such as wood and skins, they are biodegradable. However, even though organic finds are limited, they can provide much better evidence of material culture than inorganics, as it is most likely that tools would be made organics like wood, animal parts etc. Supporting this idea, Sillitoe & Hardy (2003: 556) make the observation that the majority of material culture, such as tools, of the current Wola tribe of Papua New Guinea wouldn't survive archaeologically, just like prehistoric artefacts. Therefore, the way we classify the archaeological record is biased (see Fig.1) (Beck & Jones, 1989); certain articles are preserved, and others aren’t, and we should remember that a large portion of artefacts we find are actually refuse. This means our understanding of the archaeological record is pushed towards certain cultures and aspects of life based on the interpretation of the available evidence.
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| Fig.1: The causes of bias in the archaeological record, and some ways to respond. |
How are artefacts preserved?
John Coles (cited in Renfrew & Bahn, 2008: 72) Estimates that around 75% of evidence at a site is organic and thus may not be preserved, this is due to the fact that in order to be preserved effectively, specific conditions must be met. Survival of materials depends largely on the climate and the surrounding matrix, but also must be kept in a stable moisture environment (extremely arid/cold) or an anaerobic/anoxic state (Renfrew & Bahn, 2008: 63-7). Bones, for example, are preserved in alkaline material, which is why discoveries of human remains are often made in limestone caves and caverns; although this creates a geographical bias, restricting our understanding of where people lived to certain areas (see Fig.1).
A cold or frozen environment effectively refrigerates materials, keeping them preserved for long periods of time, a famous example of which is the discovery of 'Ötzi the Iceman' (see Fig.2) in the Ötztal Alps near Hauslabjoch on the border between Austria and Italy. The body of a man was found frozen in a glacier, and radiocarbon dated to around 5100-5300 years ago, preserved because the ice hadn’t thawed until he was found, which kept conditions such as the moisture stable (Barfield, 1994). The body was kept so well that even his stomach contents could be identified, allowing archaeologists to build a picture of how and where he lived based on the types of pollen they found (Groenman-van Waateringe, 2011). And the many items he was found with, for example a copper axe, provided “unprecedented insight” into life and culture of Neolithic-Copper Age central Europe (Müller et al, 2003).
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| Fig.2: The preserved body of Ötzi and tools |
In much the same way, organic materials can also be kept stable and preserved in arid environments; many destructive micro-organisms cannot thrive in an environment with a lack of water. Hogup and Danger Caves, Utah were inhabited by humans up to 10,000 years ago, and were dry enough to preserve 142 human coprolites. This allowed archaeologists to examine the diet and lifestyles of the inhabitants, after which they found the oldest evidence of the human exclusive parasite Enterobius vermicularis (human pinworm), which were radiocarbon dated to 7837years ago. Similarly, excavations were carried out in Lovelock Cave, Nevada, where coprolites preserved in the arid conditions showed that the inhabitants had extremely course diets of seeds, hulls and tough plant fibres (Heizer & Napton, 1969: 563) and North America's oldest sling (made of Apocynum) was found preserved on the mummified body of a child (Heizer & Johnson, 1952: 139).
Materials can be kept in an anaerobic/anoxic state in waterlogged environments; this prevents the destruction of materials by harmful bacteria, allowing them to be preserved. Three complete wooden spears (around 2m in length) were found at Schöningen in an unusually dense deposit that precluded air penetration, stopping bacterial decay (Klein, 2013: 113-4). Dated to around 400kya alongside the bones of several butchered horses, they provided the oldest compelling evidence of human hunting activity (Thieme, 1997). Similarly the Ohalo II site at the Sea of Galilee was established after a period of droughts and pumping from the lake revealed a series of submerged brush hut dwellings (see Fig.3) dated to around 23kya (Hole, 2004). The discovery of organic remains of fruits, seeds and wooden objects in context offered insight into the lifestyle of people during the LGM; but the main point of interest was the discovery of preserved bedding (see Fig.3). It consisted of partially charred Puccinellia confer convoluta leaves and stems, covered by a thin compact layer of clay arranged around a central hearth, and became the oldest evidence of in situ bedding (Nadel et al. 2004: 6821-4).
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| Fig.3: Layout of dwelling (left), preserved grass bedding (right) |
Alongside preservation in cold, arid or waterlogged conditions, there are incidents where materials are preserved due to ‘freak conditions’ such burial in volcanic ash. The footprints of Australopithecus afarensis discovered in Laetoli, Ethiopia (by Mary Leakey in 1978) were believed to have been preserved by rapid cementation by natrocarbonatite and melilitite ashes erupted from the nearby Sadiman volcano (Zaitsev, 2011). They were formed when hominin walked through a wet ash-fall, and their preservation has allowed archaeologists to determine the way that early hominin walked by examining the shape and angles of the prints (Raichlen et al, 2010).
Problems with preservation
Since there are many problems in regards to how well materials are preserved, archaeologists must find ways to deal with these problems. The use of scientific methods in archaeology has improved the understanding we can draw from the archaeological record. For example, Young and Bamforth (1990) explore the problems faced when trying to differentiate between natural wear and signs of use in stone tools. They argue that macroscopic approaches often lead to misinterpretation, and cannot compare to careful microscopic analysis. Improved methods of analysis have led to new techniques of interpreting evidence too, as Hurcombe (2008) explains; by examining the organic residue on lithics, a new understanding of Neolithic craft culture (such as basket weaving) was established (see Fig.4). This is often supported by 'experimental archaeology', a process designed to 'replicate past phenomena' (Mathieu, 2002, cited in Outram, 2008), this could be anything from hafting stone tools to test effectiveness, to building ancient dwellings and destroying them to monitor the decay (Carrell, 1992: 4).
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| Fig.4: An Archaeologist uses a stone tool to cut reeds, then identifies the wear |
Experimental archaeology is useful when it comes to trying to understand how things we find were used in the past, but there are some things that simply aren't preserved at all, such as behaviour. One of the closest ways we can get to understanding behavioural patterns is through an ethnoarchaeological process; London (2000: 2) explains that by living in contemporary traditional societies and observing the people, archaeologists can record data to improve their understanding of ancient artefacts. Hunter-gatherer societies in many parts of the world have been the focus of much ethnoarchaeological attention; Atherton (1983) describes the way in which the study of African hunters and foragers has shed new light on the debate over the transition between foraging and agriculture. He explains that in contrast to John Pfeiffer's 'Eureka' theory (1976: 23), in which the transition was a sudden irreversible one; based on the passive reaction to agriculture shown by today's hunter-gatherers, prehistoric communities may have acted in the same way, choosing not to use them or only when necessary. When studying the indigenous San Bushmen of central Botswana, an observation was made that there was a distinct difference between foragers, who move their camps to follow food, and collectors, who gather resources and return to a semi-static camp. This identification allowed archaeologists to determine the lifestyles of prehistoric communities based on the types of camps discovered (Binford, 1980: 5-10). Though we must remember when taking an ethnoarchaeological approach that contemporary hunter-gatherers are not living fossils.
Conclusions
I believe that preservation of materials is extremely important when building an understanding of the archaeological record; if evidence fails to be preserved then our interpretation of the past would be extraordinarily limited. The preservation of inorganic materials can be useful, but based on fairly certain knowledge that most prehistoric material culture would have been organic; it is not the best evidence. Organics may be the best, but unfortunately they are perishable and are only preserved under specific conditions. However archaeological science, experimental and ethnoarchaeology provide ways to deal with this lack of evidence, and form an ever improving understanding of the archaeological record.
References:
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Image references:
Fig.2: Holden, C. (2003). Isotopic Data Pinpoint Iceman's Origins. Science 302(5646), pp.759+761.
Fig.3: Nadel, D. et al. (2004). Stone Age Hut in Israel Yields World's Oldest Evidence of Bedding. Proceedings of the National Academy of Sciences of the United States of America 101(17), pp.6821-6826.
Fig.4: Hurcombe, L. (2008). Organics from inorganics: using experimental archaeology as a research tool for studying perishable material culture. World Archaeology 40(1), pp.83-115.