How radiocarbon dating helps place the Pharaohs in time

From just a few handfuls of seeds, and fragments of papyrus and textiles, researchers led by a team from Oxford have mapped out an accurate chronology of the kings of ancient Egypt. The international team was led by Christopher Ramsey, Professor of Archaeological Science at Oxford and Director of the Oxford Radiocarbon Accelerator Unit, and involved UK researchers from Oxford and Cranfield along with colleagues from France, Austria and Israel.

In a project supported by the Leverhulme Trust, the research team used radiocarbon techniques to provide new dating evidence for Egypt’s Old, Middle and New Kingdoms. These are three of the most definitive periods of ancient Egypt and the new findings have a wide historical significance. Egyptian chronology anchors the timing of historical events in neighbouring areas, by tying them to the reigns of particular Egyptians rulers. The sequence of Pharaohs is well known, as is the length of their reign, but what has been less certain is exactly where they sit in terms of years. Until now, the chronologies of the ancient Egyptian kingdoms have been based on observation from lists on papyri and stone, enhanced by archaeological evidence. This project allowed those historical chronologies to be checked against dates obtained by the radiocarbon method. This determines the age of an object by measuring its radioactive carbon concentration. It is the most widely used scientific method for dating archaeological artefacts and contexts.

The Oxford-led team dated 211 plants, seeds and papyrus samples – some of them more than 4,500 years old. This included items from Tutankhamun’s tomb and the rooms under the Saqqara step pyramid. They were provided by museum collections from all over North America and Europe, including Oxford’s Ashmolean and Pitt Rivers Museums.

Samples from more recent periods of Egyptian history – whose ages are precisely known – were also radiocarbon dated to test the reliability of the methodology. This included material from the Oxford University Herbaria – a vast collection of plant specimens, archived and housed in the Department of Plant Sciences, which have been brought back to Oxford from all over the world since 1608. They include environmental samples which were collected in Egypt in the eighteenth and nineteenth centuries and therefore had known collection dates. ‘This’, says Professor Ramsey, ‘was critical to the success of the study because we were able to use seeds and plant material from sites that have been precisely dated. This allowed us to check for a “reservoir effect”; that is a way in which the technology we were using might itself produce inaccurate findings. And there was a minor difference, of a couple of decades, in some cases. This is something we can probably explain as being a growing-season effect, but it does need to be taken into account.’

One of the benefits of having an international team was that the tests could be run in different laboratories – in the UK, France and Austria – to allow cross checking and to diminish the possibility of results being produced that are affected by local factors. OxCal, a computer program devised by Professor Ramsey, was used to combine the dates for the seeds, baskets, textiles, plants stems and fruit with historical information about the order and length of each of the Egyptian rulers to create the full chronology. ‘The results’, he explained, ‘were broadly in line with previous estimates. But the radiocarbon dating pinpoints some periods as being earlier than previously thought. Djoser, one of the best-known pharaohs of the Old Kingdom, was found to have ruled from between 2691 and 2625 BCE, about 50–100 years earlier than some scholars previously thought. The study also suggested that the start of the New Kingdom might have been a few decades earlier, at somewhere between 1570 and 1544 BC.’

Going forward, with techniques and methodology vindicated by the results, there are exciting further possibilities for study. Professor Ramsey says: ‘This time, despite the generosity of the museums, we were limited in terms of the material we could use. I’m sure that there is further material to be studied that will allow future projects to look more closely at other periods – for example, ones before the Old Kingdom. It should also be possible with more material to get even greater precision for the Old, Middle and new Kingdoms we studied this time – maybe as close as an exact decade.’