The Horse, the Wheel, and Language
David W. Anthony
Published by Princeton University Press
Anthony, W..
The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World.
Princeton: Princeton University Press, 2010.
Project MUSE., https://muse.jhu.edu/.
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Appendix
Author’s Note on Radiocarbon Dates
All dates in this book are given as BCE (Before the Common Era) and
CE (Common Era), the international equivalent of BC and AD.
All BCE dates in this book are based on calibrated radiocarbon dates.
Radiocarbon dates measure the time that has passed since an organic substance
(commonly wood or bone) died, by counting the amount of 14
C that
remains in it. Early radiocarbon scientists thought that the concentration of
14
C in the atmosphere, and therefore in all living things, was a constant, and
they also knew that the decay rate was a constant; these two factors established
the basis for determining how long the 14
C in a dead organic substance
had been decaying. But later investigations showed that the concentration of
14
C in the atmosphere varied, probably with sunspot activity. Organisms
that lived at different times had different amounts of 14
C in their tissues, so
the baseline for counting the amount of 14
C in the tissues moved up and
down with time. This up-and-down variation in 14
C concentrations has been
measured in tree rings of known age taken from oaks and bristlecone pines
in Europe and North America. The tree-ring sequence is used to calibrate
radiocarbon dates or, more precisely, to convert raw radiocarbon dates into
real dates by correcting for the initial variation in 14
C concentrations as measured
in a continuous sequence of annual tree rings. Uncalibrated radiocarbon
dates are given here with the designation BP (before present); calibrated
dates are given as BCE. Calibrated dates are “real” dates, measured in “real”
years. The program used to convert BP to BCE dates is OxCal, which is accessible
free for anyone at the website of the Oxford Radiocarbon Accelerator
Unit.
Another kind of calibration seems to be necessary for radiocarbon dates
taken on human bones, if the humans ate a lot of fish. It has long been recognized
that in salt-water seas, organic substances like shell or fish bones absorb
old carbon that is in solution in the water, which makes radiocarbon
dates on shell and fish come out too old. This is called the “reservoir effect”
because seas act as a reservoir of old carbon. Recent studies have indicated
that the same problem can affect organisms that lived in fresh water, and
most important among these were fish. Fish absorb old carbon in solution
in fresh water, and people who eat a lot of fish will digest that old carbon
0 60 120 180 240 300 360 420 480 540
+ + + + + + + +- +
8 16 24 32 38 46 54 62 70
8 9 10 11 12 13 14 15 16 17
number of
years to
subtract
from BP date
% 15 N in
human bone
Figure A1. A proposed linear correlation between the % of 15
N in dared human
bone (bottom) and the number of radiocarbon years that should be subtracked
from radiocarbon dares (top) before they are calibrated.
and use it to build their bones. Radiocarbon dates on their bones will come
out too old. Dates measured on charcoal or the bones of horses and sheep
are not affected, because wood and grazing animals do not absorb carbon
directly from water like fish do, and they do not eat fish. Dates on human
bone can come out centuries older than dates measured on animal bone or
charcoal taken from the same grave (this is how the problem was recognized)
if the human ate a lot of fish. The size of the error depends on how much
fish the human ate and how much old carbon was in solution in the groundwater
where he or she went fishing. Old carbon content in groundwater
seems to vary from region to region, although the amount of regional variation
is not at all well understood at this time. The amount of fish in the diet
can be estimated on the basis of 15
N levels in bone. Fish have much higher
percentages of 15
N in their tissues than does any other animal, so humans
with high 15
N in their bones probably ate a lot of fish. High 15
N in human
bones is a signal that radiocarbon dates from those bones probably will yield
ages that are too old.
Research to correct for reservoir effects in the steppes is just beginning
as I write this, so I cannot solve the problem. But many of the radiocarbon
dates from steppe archaeology are from cemeteries, and the dated material
often is human bone. Widespread tests of the 15
N in human bone from
many different steppe cemeteries, from Kazakhstan to Ukraine, indicate
that fish was a very important part of most ancient steppe diets, often accounting
for 50% of the meat consumed. Because I did not want to introduce
dates that were probably wrong, I used an approach discussed by
Bonsall, Cook, and others, and described by them as preliminary and
speculative. They studied five graves in the lower Danube valley where
468 Appendix
Note on Radiocarbon Dates 469
human bone and animal bone in the same grave yielded different ages (see
chapter 7 for references). Data from these graves suggested a correction
method. The average level of 15
N in the human skeletons (15.1%) was
equated with an average radiocarbon error (425±55) that should be subtracted
prior to calibrating those dates. These averages could be placed on a
scale between the known minimum and maximum levels of 15
N found in
human bone, and, speculatively, a given level of 15
N could be equated with
an average error in radiocarbon years. The scale shown in figure A.1 was
constructed in this way. It seems to yield results that solve some longproblematic
dating offsets in steppe chronology (see ch. 9, notes 4, 16, and
22; and ch. 12, note 30). When I use it—when dates are based principally
on human bone—I warn readers in the text. Whatever errors it introduces
probably are smaller than those caused by ignoring the problem. All the
radiocarbon dates listed in the tables in this book are regular BP and calibrated
BCE dates, without any correction for the reservoir effect.
Figure A.1 shows the correction scale I used to revise dates that were
measured from human bone in regions where I knew the average 15
N levels
in human bone. The top number is the number of years that should be
Table A.1
The average 13
C and 15
N% in human bone from seventy−two individuals excavated
from graves in the Samara oblast, by time period.
Time Period Sample Size C13 N15
Years to
Subtract
MESOLITHIC 5 −20.6 13.5 −330±42
NEOLITHIC 8 −22.3 11.8 −228±30
EARLY ENEOL 6 −20.9 14.8 −408±52
LATE ENEOL 6 −21.0 13.1 −306±39
EBA 11 −18.7 11.7 −222±30
MBA 11 −19.0 12.0 −240±32
POTAPOVKA 9 −19.1 11.3 −198±26
EARLY LBA 7 −19.1 11.4 −204±27
LATE LBA 9 −18.9 11.2 −192±26
subtracted from the BP radiocarbon date; the bottom number is the 15
N
level associated with specific subtraction numbers.
Table A.1, based on our own studies in the Samara oblast, shows the
average 15
N content in human bone for different periods, taken from measurements
on seventy-two individuals.
470 Appendix