Day of (Zoo)Archaeology

Hello from Perth, Western Australia! My name is Carly and I’m a zooarchaeologist, which means that I work with animal remains (usually bones) to explore how people and animals interacted in the past. Right now, I’m in the late stages of my PhD research. I’ve been working on my PhD for almost 3 years, and I’m planning to submit my thesis in February. Last year when I wrote my Day of Archaeology post I was in Sydney, preparing charcoal samples for radiocarbon dating. This year, I’m writing the part of my thesis that puts those dates into context, allowing me to analyse and interpret my data.

Sorting through excavated material in the lab

Sorting through excavated material in the lab

A chuditch (sometimes called a "native cat") might end up in a site as food, but they're also predators! Working out how they ended up in the assemblage - and what other bones they might have contributed - is something I need to think about. Image source: Wikimedia Commons, licensed under Creative Commons Attribution-Share Alike 3.0 Unported.

A chuditch (sometimes called a “native cat”) might end up in a site as food, but they’re also predators! Working out how they ended up in the assemblage – and what other bones they might have contributed – is something I need to think about. Image source: Wikimedia Commons, licensed under Creative Commons Attribution-Share Alike 3.0 Unported.

Because I’m working from home today, I won’t have a chance to get into the lab, but on a normal day I usually try to get in a few hours of lab work. Most of the data collection required for my thesis is now complete, but I still have to finish identifying animal remains from a small portion of my assemblage. The main site I’m working on is a large limestone cave located a few hours drive north of Perth. This cave was periodically used for shelter by Aboriginal people over tens of thousands of years, but it was also used by carnivores like the thylacine, dingo, chuditch (an Australian “native cat”), and owls. This history of site use means that the bones I look at include animals from the size of a grey kangaroo to small native mice! With this information I can look at how Aboriginal people selected and used certain animals for food, what the environment was like, and how that changed through time.

The skull of a thylacine

The skull of a thylacine from the museum’s reference collection

Identifying animals requires a lot of time spent learning about the animals and their anatomy, and comparing specimens to reference collections held by my university and the Western Australian Museum. I’ve been very fortunate to have generous supervisors and mentors who have spent many long hours with me in the field, the lab, and at the museum, sharing their knowledge. Faunal identification skills are not something that can be learned just by reading books: the best way to learn is to hold the bones in your hands, and to learn from an expert.

Some animals are easier to identify than others (like these fragments of bettong jaws)... which is why access to good reference collections is important!

Some animals are easier to identify than others (like these fragments of bettong jaws)… which is why access to good reference collections is important!

Having worked through most of the assemblages now, I have a pretty good feel for the animals that were present in my sites, and how they are connected to people’s use of the sites, environmental changes, and each other. Now, I’m starting to analyse the data and look for patterns or things that stand out. I’m also writing up results, and in a month I’ll be in Europe presenting some of these results at two conferences. That’s where today’s tasks come in!

Thesis writing (in fact, any writing) can be a long, drawn out process filled with draft after draft and plenty of revisions, so I try to mix my day up a little. Today I’ll be writing, creating some tables and graphs showing the distribution of different animal species through time, and drafting a conference paper. I might even do some mapping if I get time… conference presentations need high quality maps! While I love the challenge of the field and lab-work side of archaeology, the writing and analytical side of the job requires almost as many diverse skills. But I have to admit, after a few days of office work, I do love to get back into those bones!

Just some of the reference materials used to identify kangaroo and wallaby teeth!

Just some of the reference materials used to identify kangaroo and wallaby teeth!

 

Radiocarbon dating: the science that helps archaeologists ‘time travel’

One of the things I love most about archaeology is the variety of work. I’m currently working on my PhD, which means that a “typical” week could see me in the lab, on fieldwork, writing, teaching, at a conference or workshop, or meeting with people to chat about research. This week, I’m at the Australian Nuclear Science and Technology Organisation (ANSTO) in Sydney, learning to prepare charcoal samples for radiocarbon analysis. The ‘Day of Archaeology’ actually falls on my last day/travel home to Western Australia, so rather than focus on one day I thought I’d share what I’ve been doing for the past week.

Sadly for Superman, radiocarbon dating is only useful for samples that are less than ~50,000 years old. Photo credit: radio-carbon testing via photopin (license)

Sadly for Superman, radiocarbon dating is only useful for samples that are less than ~50,000 years old. Photo credit: radio-carbon testing via photopin (license)

Accurate dates are very important for archaeological research. Scientific dating of excavated material, using techniques like radiocarbon analysis and optically stimulated luminescence (OSL), provides a time frame with which to assess the archaeological record. But most archaeologists are not chemists or physicists, so we often collect and send our samples to specialist laboratories, and then wait weeks or months before we receive an email with results of the analysis with limited understanding of what goes on in the meantime. Sometimes these samples are sent off accompanied by a whispered prayer to the universe: ‘please let them arrive safely, be large enough, and be uncontaminated!’

I’ve collected and sent many samples for analysis before, but this week I was fortunate enough to travel to ANSTO to meet their researchers and learn how charcoal samples are prepared and pre-treated for analysis. This opportunity is courtesy of an AINSE research grant, and means that I’ve been able to work on samples I collected during my fieldwork last year.

ANSTO uses an isotope analysis technique called “Accelerator Mass Spectrometry”, or AMS, for radiocarbon analysis, which involves firing a sample of carbon through a particle accelerator to measure carbon isotope ratios. This method can be used to get accurate ages from very small samples (as small as 10 mg); very useful for archaeologists as we really don’t like destroying our samples!

Charcoal samples packaged and ready for submission to the radiocarbon laboratory.

Charcoal samples that were collected in the field, and then packaged ready for submission to the radiocarbon laboratory.

Before a sample can be analysed, it needs to go through a series of pre-treatments to remove contaminants, and combustion to prepare it for analysis in the mass spectrometer. The charcoal is converted into carbon dioxide, before going through a series of processes to extract contaminants (like nitrogen). The carbon dioxide gas is then heated (with hydrogen gas and an iron catalyst to remove the oxygen) to produce graphite – solid carbon – before it is finally ready to be sent through one of ANSTO’s particle accelerators (check out this video to see more about the particle accelerator, or this one for a more detailed explanation of what goes on inside it).

Sample being cleaned of excess sediment and cut into small pieces for chemical pre-treatment.

Sample being cleaned of excess sediment and cut into small pieces for chemical pre-treatment.

So this week, I’ve been dealing with the first half of this process: sample pre-treatment and combustion. It’s a fairly straightforward process – even for a non-chemistry-minded person such as myself – similar to following a recipe (albeit one that involves sterile facilities and acids!). Pre-treatment involves scraping the outside off the charcoal sample, then treating it with acid, then an alkali solution, and then acid again. The sample is then dried and repackaged into small glass vials before being combusted at around 900°C.

Samples sat in first acid wash

Samples sat in first alkali solution to remove humic acids.

So that’s been my work for this week: travel to a facility on the other side of the country, and a week in a small, sterile lab learning a new skill. Who says archaeology isn’t glamorous? As I post this, I’m packing up and getting ready to head back to the airport to fly home. It’s been a fun, challenging week as I’ve tried to wrap my head around the chemistry and physics involved in the process.

As for my samples? I won’t know how old they are for another few weeks. But having now seen them through the stages of collection, preparation and pre-treatment, I’ll be keeping a close eye on my email inbox for the results!


Many thanks to the staff at ANSTO’s Institute for Environmental Research for their efforts in teaching me about these processes. Any errors are mine.