Over recent decades, developments in radiocarbon dating techniques have revolutionised our ability to establish the age of archaeological material and to interpret the past (see CA 359). In this month’s Science Notes we will be exploring how, thanks to further advances in this field, ‘the most significant group of Early Neolithic pottery ever uncovered in London’ has shed intriguing light on the capital’s prehistoric past.
Neolithic finds from central London are extremely rare, previously limited to a few individual fragments of pottery and stone axes – and so the discovery of almost 6.5kg of ceramics of this period, comprising 436 fragments from at least 24 separate vessels, was always going to be an important find.
Discovered by MOLA (Museum of London Archaeology) during excavation on behalf of Brookfield Properties at Principal Place in Shoreditch – the location of the new Amazon UK HQ – the pot sherds have now been analysed using a brand-new radiocarbon dating technique on traces of milk fats extracted from their surfaces.
This method, developed by a team from the University of Bristol, was recently described in the journal Nature (https://doi.org/10.1038/s41586-020-2178-z), and represents an important advance for the archaeological community. While typological dating has been practised for over a century, it is more difficult with pre-Roman pottery, where different types are often less distinctive and there are no coins or historical records to help contextualise them.
Previously, radiocarbon analysis could help to date pottery finds only indirectly, by establishing the age of bones or other organic materials buried with them, but the new method allows for dating of the pots themselves using fatty acids from food residues – perhaps from milk or cheese – which have been absorbed by their porous clay during cooking. Other sources of carbon associated with pottery, such as the organic temper which occasionally survives firing, or superficial food crusts, were also considered for radiocarbon dating, but these are rare and prone to contamination. The absorbed food residues proved to be by far the best option, as they occur very commonly and often in high concentrations.
How does the new process work? It begins with the selection of potsherds that have land-based animal fats present (as the presence of residue from fish could affect the results), after which a concentration of fatty acid esters is obtained from each sample, and preparative capillary gas chromatography (pcGC) is used to isolate individual compounds. An accelerator mass spectrometer (AMS) is then used to produce radiocarbon measurements for the isolated compounds.
This method was tested on pottery from several sites in Britain, continental Europe, and Africa, which had already been precisely dated by other means and which were up to 8,000 years old. When the radiocarbon dates from the absorbed fatty residues had been obtained, statistical analysis was carried out to test the compatibility of these results with existing chronologies from the sites. This demonstrated that the new approach was as accurate as the radiocarbon dating of other more commonly used materials such as bones, seeds, and wood.
As for the pottery fragments found at Principal Place, the new method has revealed that they were used c.5,500 years ago: within a window of 138 years c.3600 BC. This places them around 400 years after the first farmers are thought to have arrived in Britain from continental Europe (see CA 290), making the assemblage a significant resource for understanding the Early Neolithic in this area.
Further clues to the pots’ use comes from organic residue analysis, which indicates that they were used for processing dairy products, and for cooking beef and mutton. There was little sign of pork, perhaps because this meat was roasted on a spit rather than stewed. Meanwhile, analysis of the vessels’ outer surfaces revealed that they were not purely functional objects: some had been decorated by pressing fingertips or roe deer hooves into the clay.
Above all, this discovery presents the strongest evidence to-date that, by the early Neolithic, the occupants of the land that became the City of London were living a less mobile, more farming-based lifestyle. Only a few houses of this period have been identified in south-east England so far, but the discovery of this large group of pottery fragments suggests the possible presence of a significant settlement nearby.
The new technique represents a potentially revolutionary advancement in radiocarbon dating techniques, which will have a huge impact on future archaeological studies. Pottery typology is one of the most widely used dating techniques in the discipline, and the ability to date pottery directly and to anchor the different vessel types securely to a calendrical timescale will make a great difference to our understanding of prehistory.