Thursday, May 25, 2017

Why we wash mud: environmental sampling.

Archaeologists spend a huge amount of time unearthing and recording artefacts recovered during the excavation process. However some of the most important clues to past lives is not found in the stone and metal work of structures and material culture, but in the microscopic remains of organic material.

Samples are laid out in trays, ready for processing.
To understand the bigger picture of the past we use environmental analysis to uncover past landscapes of an archaeological site. Environmental sampling is an important aspect of archaeology as humans interact within their environments, which in turn have shaped human activity and behaviours (Dincauze 2008). Human life is heavily influenced by the presence of plants, animals and climates creating a relationship interdependent between all aspects of life.

Detail of a sample.
As climates and activities continuously change they produce a record left behind in the micro organic remains of plants and animals. Usually these remains get missed during the process of excavation, which focuses on picking up macro biological remains, material artefacts, and uncovering structures. We collect many buckets of mud and soil on-site to wash and sieve. We then separate micro organic artefacts into different categories for further microscopic analysis.

Microscopes in the laboratory.
The micro biological remains that get recovered from site contexts are rich in archaeological information about human relationships within their landscapes (Jones 2011). This process of environmental sampling enables reconstruction and the interpretation of past settlements, resource economies, and local ecology.

Part-processed finds (wet-sieving)
Further analysis of the plant and animal remains can answer some important questions about daily lives of individuals who occupied the site in the past, such as;

  • What flora and fauna were present within an environment at a certain time and how would this have changed over time influenced by climate, human presence and natural processes?
  • The temporality of occupation; was a site used seasonally, temporarily or permanently?
  • Did the site have single usage or multiple occupations, including the span of usage?
  • What were human daily activities, including food production and past diets, material manufacturing processes and ritual actions?
  • Can any economic and social status be identified through traded artefacts (as this can give an indication as to whom they might have had social networks with)?

Water pours through sieves to process finds.
Natural and cultural processes alter environments. These alterations can be interpreted by analysing preserved organic material using environmental sampling methods (Jones 2011). This analysis records small remains that are sometimes invisible to the human eye without a microscope. The remains are sorted into categories by type, such as charcoal, pollen, spores, molluscs, phyloliths, insects and wood (Campbell et al. 2015).

When the material is initially collected from the archaeological site, it is sorted by hand where appropriate. Other key techniques employed are wet-sieving and floatation. Both are low-tech methods that require simple set ups and plentiful water supplies.

Students hand wash artefacts and pass samples through sieves.
Samples are usually collected from all deposits and contexts to provide a representative sample. These samples can either be selected at random or systematically but usually a mixture of both is collected (Campbell et al. 2015). Steps are taken to avoid cross contamination. It is also essential that samples are recorded and labelled to create an organised database for further research.

Campbell, G, Moffett, L and Straker, V (2015) A Guide to the Theory and Practice of Methods, from Sampling and Recovery to Post-excavation (Historic England)
Dincauze, D F (2008) Environmental Archaeology: Principles and Practice (Cambridge University Press)
Jones, D M (2011) Environmental Archaeology: A Guide to the Theory and Practice of Methods, from Sampling and Recovery to Post-excavation (English Heritage)

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