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How old is that mummy, anyway?

Plain old seeds and woven baskets from Egyptian archaeological sites are helping scientists date the reigns of mighty pharaohs more precisely.

Figuring out the dates for 3,000 years of pharaonic history can sometimes be as much an art as a science. Scholars have to draw upon textual references and inscriptions, then match them up with ancient astronomical observations and chronologies from other cultures (which kept better records).

Traditional carbon-dating techniques tend to give age estimates within a range of 100 to 200 years for the pharaonic time frame, which the researchers behind the latest study say are "too imprecise" to resolve key questions about Egyptian chronology. However, Oxford University's Christopher Bronk Ramsey and his colleagues said their new method narrows that window to decades or years.

"For the first time, radiocarbon dating has become precise enough to constrain the history of ancient Egypt to very specific dates," Bronk Ramsey said in a news release from the journal Science, which published the findings in this week's issue. "I think scholars and scientists will be glad to hear that our small team of researchers has independently corroborated a century of scholarship in just three years."

How did they do it? They went to museums around the world - from Stockholm and Berlin, Paris and Brussels, London and New York - and were able to snag samples from different eras in Egyptian history. Egypt itself was out of bounds, because of restrictions on the export of antiquities. Mummies and their wrappings were ruled out as well, because the mummification process might have scrambled up the samples. The researchers also stayed away from charcoal and wood, because that material might have come from an earlier age.

The perfect samples turned out to be short-lived plant material - seeds, baskets, textiles, plant stems and fruit, which were harvested and used during a short period of time. The material also had to be linked to a particular pharaoh's reign. Even this type of material is highly valued by researchers, and museum curators needed some convincing to part with it. "Fortunately, we only needed samples that were about the same size as a grain of wheat," Bronk Ramsey said.

More than 200 samples were analyzed at the Oxford Radiocarbon Accelerator Unit, and the carbon-14 decay dates were mapped against the chronologies for 37 pharaohs, starting with Djoser in the Old Kingdom and also including Khufu (whose tomb was placed in the Great Pyramid of Giza), Hatshepsut (one of Egypt's best-known female pharaohs), King Tut and Rameses II (widely thought to be the Pharaoh of the Book of Exodus ... or was that Amenhotep II?).

Some of the samples were excluded because they came back with dates that were hundreds or even thousands of years off, most likely due to contamination. But for the most part, the samples matched up well with the stories that scholars have slaved over. Egyptologist Ian Shaw's highly respected timeline of pharaonic reigns was used to fill out the gaps in the chronology.

The researchers say a few events may have occurred somewhat earlier than previously estimated on the basis of historical accounts: For example, the beginning of Djoser's reign was pegged at sometime between 2691 and 2625 B.C. The commonly accepted historical date is 2630 B.C., which is on the late side of that time window. As Nature's Richard Lovett points out, archaeologists have debated whether Egypt's New Kingdom (which includes Tut and his relatives) began in 1550 B.C. or 1539 B.C., and whether the Middle Kingdom began in 2055 B.C. or 2039 B.C. In both cases, the radiocarbon results favor the earlier dates.

But the interpretation of the radiocarbon results can get complex, as Bronk Ramsey explained in this e-mail exchange:

Cosmic Log: Because the slight discrepancy in dates seems to be systemic (consistently earlier based on radiocarbon data), what might the explanation be? Might there be a systemic factor in the carbon-dating process that puts the top of the curve consistently earlier, or are there selections of key dates (based on astronomical or other dating techniques) that throw things off systemically?

Bronk Ramsey: It depends on exactly what you mean here. Are you referring to the fact that the radiocarbon chronology is earlier than some of the historical chronologies? If so, I'd point out that the chronology is very similar to the consensus published by Shaw and for the New Kingdom. Our results for, e.g., Tutankhamun are both very precise and just where you would expect them to be.

If you are referring (as I suspect) to the fact that the radiocarbon dates lie, on average, just above the calibration curve in our fits, this is an issue that we investigated in some detail. This effect is also seen for material from the last few centuries (plant specimens taken by botanists in the 18th and 19th centuries). The reason for this is, we think, due to the fact that the amount of radiocarbon in the atmosphere varies in a regular way during the year. There is less in the winter and more in the summer. In Egypt, the plants in the Nile Valley tend to grow in the winter, when the floods come, and this means that the radiocarbon ratio is slightly lower than for plants in, for example, Northern Europe where the calibration data comes from. The effect of this is that the dates in Egypt are on average about 20 years older.

Q: Do you see any results that might actually lead to an archaeological reinterpretation? For example, are there some historical events (Akhenaten, Tut and the biblical Exodus) that take on a different context? In the past, there’s been a debate over exactly which pharaoh was the pharaoh mentioned in the Bible. Could this chronology shed any light on such questions?

A: I don't think so - as the chronology and exact nature of these events are hotly debated anyway. For the New Kingdom, our chronology is very similar to many of those derived from purely historical information. We do put the start of the New Kingdom at the early end of most widely accepted estimates - but still well after the radiocarbon-based date for the eruption of Santorini. For the Old Kingdom, our chronology also supports the previous early chronologies and seems to rule out other possibilities.

Q: Were there any specimens that showed evidence of being fakes or modern-era reproductions?

A: Some material did indeed turn out to be contemporary with the excavations themselves (19th or early 20th century) - and so were either inadvertently or intentionally added at that stage. There were no very modern samples.

Bronk Ramsey's reference to Santorini is of interest because that eruption (which may have given rise to the legends about Atlantis) is used as a guidepost to chronologies all over the ancient world. The researchers behind the latest study hope that their radiocarbon techniques can be used as a similar guidepost. Theoretically, you could take samples from the foodstuffs or woven goods that were found alongside an unidentified mummy and figure out where it fit in the Egyptian chronology.

In a commentary that was also published in Science, Hendrik Bruins of the Ben-Gurion University of the Negev says the latest findings highlight a "vexing time difference" in estimates for the date of the Santorini eruption. The radiocarbon readings suggest that the eruption occurred around 1627 to 1600 B.C., while the accepted archaeological and historical record places the eruption around 1500 B.C., during the New Kingdom era.

"Major problems exist here in relation to the Santorini eruption between archaeological dating, radiocarbon dating and association between archaeological strata in the field and Egyptian historical chronology," Bruins said in a news release. Those problems will have to be resolved through further testing of ancient samples, not only from Egypt but from other archaeological sites in the region, Bruins said.

Isn't it typical that when one mystery about the ancient world is seemingly solved, another mystery immediately pops up?

More mysteries from Egypt:


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