Dennis Sandgathe: Innovating how Archaeological Sites are Excavated

I have been directing archaeological digs at Palaeolithic cave sites in SW France for over 20 years: sites that were occupied by our extinct Neandertal cousins between 250,000 and 40,000 years ago. And although archaeologists are always trying to improve their research methods, in many ways how we excavate prehistoric sites like these has not changed much over the last century. If we want to learn about our prehistoric ancestors this still generally requires digging in the sites they had lived in: carefully removing the sediments that had accumulated over thousands of years in order to uncover and record the artifacts, like stone tools, that had become buried there.

In recent years many new analytical techniques have become available to archaeologists: for example, we can now recover large lipid and protein molecules (including human DNA!) directly from the sediments themselves – something I would never have dreamed possible when I was an undergrad. These molecules are the chemical residues left behind by the people that lived there, the things they ate, and the plants and animals that also occupied these places with them. Recovering and analyzing these ‘geochemicals’ has the potential to tell us far more about ancient people, their lifeways, and the environments they lived in than studying their stone tools could ever do.

But, in order to get the most out of these new analytical techniques, we have to start collecting our data in different ways. Towards this end, over the past several years my colleagues and I have been developing a novel way to excavate Prehistoric sites. We cut out large, intact blocks of sediment from the site and transports them back to our laboratory where we excavate them very slowly under clean, controlled conditions. We do this mainly by vacuuming up the sediments (with a special vacuum system) in tiny amounts that are deposited directly into sterile glass vials. We collect hundreds - potentially even thousands - of vials. Each vial represents a tiny sample (50 ml!) of sediment and we know exactly where each sample came from in the archaeological site.

We then send these samples out to all our different analytical specialists who will process them to isolate those things they are looking for: DNA analysts who can tell us who had occupied the site, other geochemical analysts who look for large molecules that can identify specific plants and animals that had either used the site or had been brought there as food by the people living there; other analysts who can tell us if sediments have been heated by fire or not and to what temperature; analysts who can tell us what was being burned in ancient fires; analysts who can identify tree species from tiny fragments of charcoal; analysts who examine plant pollen and identify plant species from it; and many others who can help us reconstruct a far more detailed picture of the past than we’ve ever had access to before.