Carbon Dating Articles

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Introduction

Archaeologists believe Egypt's large pyramids are the work of the Old
Kingdom society that rose to prominence in the Nile Valley after 3000
B.C. Historical analysis tells us that the Egyptians built the Giza
Pyramids in a span of 85 years between 2589 and 2504 BC.

Interest in Egyptian chronology is widespread in both popular and
scholarly circles. We wanted to use science to test the accepted
historical dates of several Old Kingdom monuments.
Previous estimates

One radioactive, or unstable, carbon isotope is C14, which decays over
time and therefore provides scientists with a kind of clock for
measuring the age of organic material.

The earliest experiments in radiocarbon dating were done on ancient
material from Egypt. Willard F. Libby's team obtained acacia wood from
the 3rd Dynasty Step Pyramid of Djoser to test a hypothesis they had
developed.

Libby reasoned that since the half-life of C14 was 5568 years, the
Djoser sample's C14 concentration should be about 50% of the
concentration found in living wood (for further details, see Arnold
and Libby, 1949). The results proved their hypothesis correct.

Subsequent work with radiocarbon testing raised questions about the
fluctuation of atmospheric C14 over time. Scientists have developed
calibration techniques to adjust for these fluctuations.
1984
Collecting samples from pyramid.
Project members collect samples.

In 1984 we conducted radiocarbon dating on material from Egyptian Old
Kingdom monuments (financed by friends and supporters of the Edgar
Cayce Foundation). We then compared our results with the mid-point
dates of the kings to whom the monuments belonged (Cambridge Ancient
History, 3rd ed.).

The average radiocarbon dates were 374 years earlier than expected.

In spite of this discrepancy, the radiocarbon dates confirmed that the
Great Pyramid belonged to the historical era studied by Egyptologists.
1994-1995

In 1994-1995 the David H. Koch Foundation supported us for another
round of radiocarbon dating.

We broadened our sampling to include material from:

* The 1st Dynasty tombs at Saqqara (2920-2770 BC).
* The Djoser pyramid (2630-2611 BC).
* The Giza Pyramids (2551-2472BC).
* A selection of 5th Dynasty pyramids (2465-2323 BC).
* A selection of 6th Dynasty pyramids (2323-2150 BC).
* A selection of Middle Kingdom pyramids (2040-1640 BC).

We also took samples from our Giza Plateau Mapping Project Lost City
excavations (4th Dynasty), where we discovered two largely intact
bakeries in 1991. Ancient baking left deposits of ash and charcoal,
which are very useful for dating.

The 1995 set of radiocarbon dates tended to be 100 to 200 years older
than the Cambridge Ancient History dates, which was about 200 years
younger than our 1984 dates.
Comparison 1984/1995

The number of dates from the two projects was only large enough to
allow for statistical comparisons for the pyramids of Djoser, Khufu,
Khafre, and Menkaure.

There are two striking results.

First, there are significant discrepancies between the 1984 and 1995
dates for Khufu and Khafre, but not for Djoser and Menkaure.

Second, the 1995 dates vary widely even for a single monument. For
Khufu's Great Pyramid, they scatter over a range of about 400 years.
Date agreements

We have fair agreement for the 1st Dynasty tombs at North Saqqara
between our historical dates, previous radiocarbon dates, and our
radiocarbon dates on reed material.

We also have fair agreement between our radiocarbon dates and
historical dates for the Middle Kingdom. Eight calibrated dates on
straw from the pyramid of Senwosret II (1897-1878 BC) ranged from 103
years older to 78 years younger than the historical dates for his reign.

Four of the Senwosret II dates were only off by 30, 24, 14, and three
years. Significantly, the older date was on charcoal (see "old-wood
problem" below).

Test results from Middle Kingdom pyramid (Senwosret II).
Middle Kingdom results.
The old-wood problem

Ancient Egypt's population was restricted to the narrow confines of
the Nile Valley with, we assume, a sparse cover of trees. It is likely
that, by the pyramid age, the Egyptians had been intensively
exploiting wood for fuel for a long time.

Because of the scarcity and expense of wood, the Egyptians would reuse
pieces of wood as much as possible. Some of this recycled wood was
burned, for example, in mortar preparation. If a piece of wood was
already centuries old when it was burned, radiocarbon dates of the
resulting charcoal would be centuries older than the mortar for which
it was burned.

We thought that it was unlikely that the pyramid builders consistently
used centuries-old wood as fuel in preparing mortar. The 1984 results
left us with too little data to conclude that the historical
chronology of the Old Kingdom was wrong by nearly 400 years, but we
considered this at least a possibility.

Alternatively, if our radiocarbon estimations were in error for some
reason, we had to assume that many other dates obtained from Egyptian
materials were also suspect. This prompted the second, larger, 1995 study.
Old Kingdom problem

If the Middle Kingdom radiocarbon dates are good, why are the Old
Kingdom radiocarbon dates from pyramids so problematic?

The pyramid builders often reused old cultural material, possibly out
of expedience or to make a conscious connection between their pharaoh
and his predecessors.

Beneath the 3rd Dynasty pyramid of pharaoh Djoser, early explorers
found more than 40,000 stone vessels. These vessels included
inscriptions of most of the kings of the 1st and 2nd Dynasties, but
Djoser's name occurred only once. Did Djoser gather and reuse vases
that were already 200 years old from tombs at North Saqqara?

In the 12th Dynasty, Amenemhet I (1991-1962 BC) left clear evidence of
this kind of recycling. He took pieces of Old Kingdom tomb chapels and
pyramid temples (including those of the Giza Pyramids) and dumped them
into the core of his pyramid at Lisht.

Test results from 5th Dynasty pyramid (Sahure).
5th Dynasty results.

Three of the eight radiocarbon dates from samples taken at our
excavation at the Lost City are almost direct hits on Menkaure's
historical dates: 2532- 2504 BC. The other five range from 350 to 100
years older.

Our radiocarbon results from the Lost City site suggest that the dates
on charcoal scatter widely, like those from the pyramids, with many
dates older than the historical estimate. The inhabitants were very
likely recycling their own settlement debris during the 85 or so years
that they were building pyramids.
Conclusions

It may have been premature to dismiss the old wood problem in our 1984
study. Radiocarbon dating can only tell us when a tree died, not when
it was last used. Wood may lay around for centuries before being
burned, especially in a dry climate like Egypt.

Also, any living forest or stand of trees will have old trees and very
young shoots. Any individual tree will have old parts (the inner
rings) and very young parts (the outer rings and small branches).

Do our radiocarbon dates reflect the Old Kingdom deforestation of Egypt?

Did the pyramid builders exploit whatever wood they could harvest?

Or did they have to scavenge for wood to burn tons of gypsum for
mortar, to forge copper chisels, and to bake bread for thousands of
assembled laborers?

The giant stone pyramids in the early Old Kingdom may mark a major
depletion of Egypt's exploitable wood. This may be the reason for the
wide scatter and history-unfriendly radiocarbon dating results from
the Old Kingdom.

While the multiple old-wood effects make it difficult to obtain
pinpoint age estimates of pyramids, the David H. Koch Pyramids
Radiocarbon Project now has us thinking about forest ecologies, site
formation processes, and ancient industry and its environmental
impact—in sum, the society and economy that left the Egyptian pyramids
as hallmarks for all later humanity.

The David H. Koch Pyramids Radiocarbon Project was a collaborative
effort of Shawki Nakhla and Zahi Hawass, The Egyptian Supreme Council
of Antiquities; Georges Bonani and Willy Wölfli, Institüt für
Mittelenergiephysik, Eidgenossische Technische Hochschule; Herbert
Haas, Desert Research Institute; Mark Lehner, The Oriental Institute
and the Harvard Semitic Museum; Robert Wenke, University of
Washington; John Nolan, University of Chicago; and Wilma Wetterstrom,
Harvard Botanical Museum. The project was administered by Ancient
Egypt Research Associates, Inc.

See also:
Bonani G, Haas H, Hawass Z, Lehner M, Nakhla S, Nolan J, Wenke R,
Wölfli W. "Radiocarbon Dates of Old and Middle Kingdom Monuments in
Egypt," Radiocarbon 43, No. 3 (2001), 1297-1320(2

Dating the Pyramids Volume 52 Number 5, September/October 1999
by members of the David H. Koch Pyramids Radiocarbon Project

[image] Robert Wenke, John Nolan, and Ala'a Amran collect and log
samples for radiocarbon dating from the pyramid of Menkaure at Giza.
Pyramid of Khafre is in background. (Mark Lehner) [LARGER IMAGE]

It was an odd sensation climbing over the Great Pyramid, looking for
minute flecks of charcoal or other datable material, loaded down with
cameras, scales, notebooks, and forms with entries for sample number,
site, monument, area, feature, material (charcoal, reed, wood, etc.),
matrix (gypsum mortar, mud brick, etc.), date, time, notes on details,
extracted by, logged by, photograph numbers, and sketches. It was 1984
and the Edgar Cayce Foundation, named for an early twentieth-century
psychic who claimed that the Sphinx and Khufu's Great Pyramid were
built in 10,500 B.C., was paying for the analysis of our samples. Old
friends and supporters of the deceased psychic had visited Giza in the
early 1980s and several of them were willing to put their beliefs to
the test by radiocarbon dating the Great Pyramid. Archaeologists
believe it is the work of the Old Kingdom Dynasty 4 society that rose
to prominence in the Nile Valley from ca. 3000 B.C. and built the Giza
Pyramids in a span of 85 years between 2589 and 2504 B.C.

1984 Results. The 1984 radiocarbon dates from monuments spanning
Dynasty 3 (Djoser) to late Dynasty 5 (Unas), averaged 374 years older
than the Cambridge Ancient History dates of the kings with whom the
pyramids are identified. In spite of this discrepancy, the radiocarbon
dates confirmed that the Great Pyramid belonged to the historical era
studied by Egyptologists. In dealing with the 374-year discrepancy, we
had to consider the old wood problem. In 1984 we thought it was
unlikely that the pyramid builders consistently used centuries-old
Egyptian wood as fuel in preparing mortar. Ancient Egypt's population
was compressed in the narrow confines of the Nile Valley with a tree
cover, we assumed, that was sparse compared to less arid lands. We
expected that by the pyramid age the Egyptians had been intensively
exploiting wood for fuel for a long time and that old trees had been
harvested long before. The 1984 results left us with too little data
to conclude that the historical chronology of the Old Kingdom was in
error by nearly 400 years, but we considered this at least a
possibility. Alternatively, if our radiocarbon age estimations were in
error for some reason, we had to assume that many other dates obtained
from Egyptian materials were also suspect. This prompted a second,
larger study.

The 1995 Project. During 1995 samples were collected from the Dynasty
1 tombs at Saqqara to the Djoser pyramid, the Giza Pyramids, and a
selection of Dynasty 5 and 6 and Middle Kingdom pyramids. Samples were
also taken from our excavations at Giza where two largely intact
bakeries were discovered in 1991. The calibrated dates from the 1995
Old Kingdom pyramid samples tended to be 100 to 200 years older than
the historical dates for the respective kings and about 200 years
younger than our 1984 dates. The number of dates from both 1984 and
1995 was only large enough to allow for statistical comparisons for
the pyramids of Djoser, Khufu, Khafre, and Menkaure. There are two
striking results. First, there are significant discrepancies between
1984 and 1995 dates for Khufu and Khafre, but not for Djoser and
Menkaure. Second, the 1995 dates are scattered, varying widely even
for a single monument. For Khufu, they scatter over a range of about
400 years. By contrast, we have fair agreement between our historical
dates, previous radiocarbon dates, and our radiocarbon dates on reed
for the Dynasty 1 tombs at North Saqqara. We also have fair agreement
between our radiocarbon dates and historical dates for the Middle
Kingdom. Eight calibrated dates on straw from the pyramid of Senwosret
II ranged from 103 years older to 78 years younger than the historical
dates for his reign, with four dates off by only 30, 24, 14, and three
years. Significantly, the older date was on charcoal.

Old Kingdom Problem. If the Middle Kingdom radiocarbon dates are okay,
why are the Old Kingdom ones from pyramids so problematic? The pyramid
builders used older cultural material, whether out of expedience or to
make a conscious connection between their pharaoh and his
predecessors. In galleries under the pyramid of the Dynasty 3 pharaoh
Djoser more than 40,000 stone vessels were found. Inscriptions on them
included most of the kings of Dynasty 1 and 2, but Djoser's name
occurred only once. Perhaps Djoser gathered up the vases from the
200-year-old Archaic tombs at North Saqqara. In Dynasty 12, Amenemhet
I actually took bits and pieces of Old Kingdom tomb chapels and
pyramid temples (including those of the Giza Pyramids) and dumped them
into the core of his pyramid at Lisht.

At Giza, south of the Sphinx, we are excavating remains of facilities
for storage and production of fish, meat, bread, and copper that date
to the middle and end of Dynasty 4, when the pyramids of Khafre and
Menkaure were under construction. Three of the eight dates from
samples taken here are almost direct hits on Menkaure's historical
dates, 2532- 2504 B.C. The other five, however, range from 350 to 100
years older. Our radiocarbon dates from the site suggest that, like
those from the pyramids, the dates on charcoal from the settlement
scatter widely in time with many dates older than the historical
estimate. The pyramid builders were likely recycling their own
settlement debris.

It may have been premature to dismiss the old wood problem in our 1984
study. Do our radiocarbon dates reflect the Old Kingdom deforestation
of Egypt? Did the pyramid builders devour whatever wood they could
harvest or scavenge to roast tons of gypsum for mortar, to forge
copper chisels, and to bake tens of thousands of loaves to feed the
mass of assembled laborers. The giant stone pyramids in the early Old
Kingdom may mark a major consumption of Egypt's wood cover, and
therein lies the reason for the wide scatter, increased antiquity, and
history-unfriendly radiocarbon dating results from the Old Kingdom,
especially from the time of Djoser to Menkaure. In other words, it is
the old-wood effect that haunts our dates and creates a kind of shadow
chronology to the historical dating of the pyramids. It is the shadow
cast by a thousand fires burning old wood.

While the multiple old wood effects make it difficult to obtain
pinpoint age estimates of pyramids, the David H. Koch Pyramids
Radiocarbon Project now has us thinking about forest ecologies, site
formation processes, and ancient industry and its environmental
impact--in sum, the society and economy that left the Egyptian
pyramids as hallmarks for all later humanity.

The David H. Koch Pyramids Radiocarbon Project is a collaborative
effort of Shawki Nakhla and Zahi Hawass, The Egyptian Supreme Council
of Antiquities; Georges Bonani and Willy Wölfli, Institüt für
Mittelenergiephysik, Eidgenossische Technische Hochschule; Herbert
Haas, Desert Research Institute; Mark Lehner, The Oriental Institute
and the Harvard Semitic Museum; Robert Wenke, University of
Washington; John Nolan, University of Chicago; and Wilma Wetterstrom,
Harvard Botanical Museum. The project is administered by Ancient Egypt
Research Associates, Inc.
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© 1999 by the Archaeological Institute of America
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