Friday, 26 July 2013

Day of Archaeology 2013

Paisley Caves – a view from the microscope

Today's post is for the Day of Archaeology 2013, go check out their website for lots of great posts about the diverse things archaeologists get up to on a day to day basis.

Wednesday, 24 July 2013

A dung debate?

I never imagined I would end up being a specialist on the subject of archaeological poop, but there you go. Coprolites, animal dung, palaeofaeces you name it. So I was very intrigued by an article published in the Proceedings of the National Academy of Sciences last week, claiming evidence for the earliest use of manure by European farmers 8000 years ago.

Firstly let's consider the different methods that we can use to identify dung in the archaeological record. These can be divided into direct and indirect methods. The former include definitive evidence for the presence of dung, that is actual dung pellets, or lipid biomarkers which are found exclusively in dung (i.e. faecal sterols and bile acids from the gut). The latter include evidence which is suggestive of dung, for example weed seed assemblages. Although indirect indicators are often the only thing available in archaeology, in my opinion one cannot make definitive statements based on indirect evidence. The best we can do is suggest likely possibilities, or hypotheses that can be further tested. The PNAS article uses a new indirect indicator - nitrogen isotope values of crops - to suggest the addition of dung to the plants (specifically an increase in N 15 in manured crops - Bogaard et al. 2007, Fraser et al. 2011). I am not an isotope expert, so cannot comment too much on the reliability of this new method, though the comparison of 'inferred' values of forrage to show enriched levels in cereals seems problematic. Herbivore forrage values were only estimated for 6 of the 13 sites studied, using a very indirect method of taking herbivore bone collagen values and subtracting an estimated 4‰ average to compensate for trophic shift. I would much prefer to see real values measured on actual forrage plants.

Let's also consider archaeological evidence for the presence of agriculture - crop remains (preferably domestic forms), farming tools, crop processing tools. To say that agriculture is present at a site, we would like to see a number of these indicators. Multiple lines of evidence are better than one. Likewise, in order to say manuring was taking place, we would like to see definitive evidence for the presence of dung, and also evidence that it was being deliberately applied to crops. There is no mention in the PNAS article of any other evidence that would support the hypothesis of manuring at the sites investigated. Although it is a reasonable interpretation to make, I would prefer to see more direct evidence of manuring practise rather than relying on something as indirect as nitrogen isotopes in crops. Even in the case of sterol biomarkers, which provide direct evidence of the presence of dung, or even when actual dung pellets are observed, it seems to me a bit of a leap to say that this indicates deliberate manuring of crops. Another possibility is that animals simply wandered around in the same area as crops were being grown, adding their dung deposits without intention.

How can we say for sure that people were deliberately and consistently manuring these crops? This would require 'manuring markers' to be present in the majority of crops over time. Unfortunately it is impossible to determine this, as the istope analysis was conducted on bulk samples i.e. multiple individual grains (this number varied from 2 to 'at least 10' according to the paper) were combined together for analysis, giving an average signal for all the crops from a single stratigraphic unit. How do we know what the variation in manure presence was across these individual plants and across different periods? And are 2-10 individual grains really representative of agricultural practises? These are very low numbers of samples which always makes me a little uneasy, even if it is sometimes the case in archaeology that we just have to work with what we have rather than having statistically significant numbers of samples.

The article mentions significant diversity in N values within some of the sites, interpreted as local variation in manuring rates, comparable to modern 'traditional' farming regimes. Couldn't this just be local variation in the presence of manure? Just some random thoughts - I actually really like the article, and the hypothesis is a good one. I'm just not keen on making definitive statements when there are other possible explanations. Hopefully further testing of the hypotheses will provide other lines of evidence in support!

Comments welcome as always.

Changing perspectives

July appears to be whizzing by nicely. Unusually for me, I am still in the UK. For the past 10 years (has it really been that long?!) I have spent every summer abroad doing fieldwork, and for most of those summers at least a few weeks have been spent collecting samples at Catalhoyuk in Turkey. This year will be the second year that I have been unable to go - last year I was coming to the end of my contract on the Feeding Stonehenge project and had to stay in the lab, and this year I have too many teaching commitments and writing to complete. Depsite this I will still be doing some UK based fieldwork in the next couple of weeks, more on that as it happens. Lucky for me in the age of social media and blogging, I can keep up to date with the latest news from Catalhoyuk as it happens via Scott Haddow's blog, A Bone to Pick. Scott is a member of the osteoarchaeology team at Catalhoyuk and has been posting regular updates, including an amazing find of intact woven textile in a baby burial. It is funny how much more emotive such finds are now that I am a parent. Up until this point I have always had quite a sense of detachment when working with human remains. I guess in some ways it can only be useful to have a sense of empathy during interpretation, though of course it is important to maintain a sense of objectivity.

Honeycomb weathering at Tynemouth Priory
And in entirely unrelated news, here is a lovely example of honeycomb weathering for your geoarchaeological viewing pleasure, from a recent visit to Tynemouth Priory on the Northeast coast of England. You can see examples of this distinctive weathering pattern concentrated in specific parts of the priory and surrounding walls, presumably due to the direction of prevailing winds.

Monday, 15 July 2013

Micrograph of the Month: Fabulous Floors

Floors at Kamiltepe, Azerbaijan. 1. shows the constructed floors, 2. is a layer of ashy debris with 3. is a fragment of bone and 4. shows more debris, this time with single crystals of gypsum.
This month's micrograph shows more deposits from the site of Kamiltepe in Azerbaijan. I have mentioned the site in a few previous blog posts, where you can find a link to an article which has a bit more detail on the preliminary micromorphology results from other parts of the site. Analysis of the deposits is still in progress, but already there are some great examples of prehistoric floors. Floors like these have been extensively studied from sites like Catalhoyuk, largely by Dr Wendy Matthews of the University of Reading. The floors at Kamiltepe are a lot dirtier than those at Catalhoyuk - the latter which are notable for their cleanliness and lack of activity residues. In the micrographs here we can see fragments of bone, microcharcoal and organic debris. In the micrograph on the left we can see a second floor constructed directly on top of the activity debris. No meticulous sweeping of the floors here!

Monday, 8 July 2013

July - Post Holes and Space Daggers

Space Dagger!
Apart from my latest project, which I made a seperate blog about here, there are a few things that are new this month. I am pleased to share a short article I wrote for The Post Hole, a very impressive and professional looking journal that is run by students at the University of York. I wrote a short piece related to the Teaching and Learning project I was involved in before I moved to Edinburgh, Archaeology Under the Microscope, that introduces microarchaeology and the importance of 'hands on' practical experience of laboratory work and microscopy in archaeology. You can access the article here, and do check out the rest of the website and previous issues. I also recieved a fab package in the post this month from fellow archaeology blogger Danny Welch, who writes an excellent blog, Archaeology Test Kitchen, about his experimental archaeology experiences making and using lithic artefacts. I present to you the Space Dagger, a nifty little tool hand crafted from obsidian with real sinew, pine pitch glue and antler. I keep thinking how lovely the crafting debris would look in thin section...and maybe I should conduct some organic residue analysis on the blade and glue...