ANTH 235, CHRONOMETRY
“Time I am, the great destroyer of worlds…” – Sri Krisna to
Pandava Arjuna at Kurukshetra, Bhagavad-Gita 11.32
See: http://en.wikipedia.org/wiki/Kurukshetra_war
“Before we can do anything, we must control our data
across space and time” – David Hurst Thomas
To simply describe the sequence of past events, all we
really need to know is the age relationship of different
objects. (That is, X is older than Y; Y is older than Z, etc.)
But, to address processual questions, which try to explain
change, it is necessary to know more.
relative time: In relative time, we only know if something
is younger or older than something else, but we do not
know how much older or younger.
“absolute” time: In “absolute” or chronometric time, we
speak in terms of the ages of objects or events. “Absolute”
dates are thus always accompanied by a unit designator,
such as years Anno Domini (AD), Before Christ (BC),
Before the Common Era (BCE), Before Present (BP), etc.
ESSENTIAL CHRONOMETRIC ABBREVIATIONS:
 BP = Before Present (by convention AD 1950)
 BCE = Before the Common Era, preferred over BC
(Before Christ) or ACN (ante Christum natum)
 CE = Common Era; preferred over AD (Anno Domini,
“In the year of the Lord,” itself a contraction of Anno
Domini Nostri Jesu Christi, “in the year of our Lord Jesus
Christ”)
 KYBP = Kilo Years Before Present (also KA, Kiloyears
Ago and KYA or KYR, Kilo Years Ago)
 MYA = Mega (or Millions of) Years Ago (also MA,
Megayears Ago; MYBP and MYR, Megayears Before
Present)
ADDITIONAL EXPLANATORY NOTES:
 BP, BC, BCE, and CE are always written after the date
(e.g., 2500 BCE).
 AD is always written before the date (e.g., AD 2004).
 RCYBP refers to “radiocarbon years before present.”
Since radiocarbon years  calendar years, a calibration
curve is used to establish the relationship between the two
scales.
 Some authors consider some of these abbreviations case
sensitive (e.g., “bp” indicates an uncalibrated date while
“BP” represents a calibrated date).
 Archaeological dates are often reported in the Islamic
world as BH (Before the Hejira) or AH (After the Hejira),
referencing the Prophet Muhammad’s departure from
Mecca in September, 622 CE.
RELATIVE DATING TECHNIQUES:
stratigraphy: an interpretive science
 Is it possible to determine which ceramic vessel is later: 4, 5,
or 6? If so, which one?
 Is it possible to determine which vessel is earlier: 1, 2, 6, or 7?
If so, which one?
 In what order were the burials interred, from oldest to
youngest?
 Which is older, burial Y or vessel 3?
 Was the wall built before or after burial Y was interred?
seriation (two types): based on observable changes in
artifacts through time
 stylistic seriation
 frequency seriation
Stylistic seriation is based on a technique called sequence
dating developed first by Sir Flinders Petrie through his
excavations of Pre-Dynastic clay pots at Diospolis Parva,
Upper Egypt in 1898-1899.
See: http://www.digitalegypt.ucl.ac.uk/pottery/seqdates.html
Flinders Petrie’s sequence dating of Pre-Dynastic clay vessels from
Diospolis Parva, Upper Egypt
The arrangement of artifact types in a sequence is based on two simple ideas:
first, products of a given period and place have a distinctive style or design; and
second, that changes in style are gradual, or “evolutionary.” Gradual changes in
design are evident in this history of the automobile (top row)* and of the
prehistoric European axe (bottom row: 1, stone; 2-5, bronze). However, the rate
of change (a century for the automobile; millennia for the axe) has to be deduced
from “absolute” or chronometric dating methods, like radiocarbon (14C), etc.
*who knew that the pinnacle of automotive technology was a mid-1970s Citroën DS?
Death’s Head pattern tombstone from Colonial New England
Cherub pattern tombstone from Colonial New England
Urn-and-Willow pattern tombstone from Colonial New England
James Deetz’s seriation of Colonial New England tombstones
Whether tombstones or corporate logos, the principles of seriation are the same.
cross-dating: establishing relative or absolute age by
comparison to a known sequence
“ABSOLUTE” OR CHRONOMETRIC DATING:
age range or time depth: at what age ranges is it feasible to
use particular dating methods
Accuracy is a measure of systematic error and refers to the
“closeness” of a chronometric estimate to the true value.
Precision is a measure of random error and refers to how
often we arrive at the same answer on repeated “tries” or
measurements.
Resolution is closely related to precision and refers to the
shortest interval of time by which two assays can be
distinguished.
direct vs. indirect dating methods
calendrics
The Mexica Sun Stone or “Aztec Calendar,” ca. 1450 CE, Mexico
(Carved basalt, 3.6 meters in diameter)
dendrochronology: tree-ring dating, the most accurate of
all chronometric dating techniques
Radiometric “absolute” dating techniques:
half-life: the length of time necessary for one-half of the
radioactive atoms of a particular isotope to decay.
radiocarbon or 14C dating: possibly the single most
important technological achievement in archaeology, ever.
Half-life of 14C is about 5730 years. The technique is
useful from about 50,000 years ago to the present. Time is
measured in years BP (before present), which is defined as
1950 CE by convention.
K/Ar or potassium/argon dating: based on the
radioactive decay of potassium to argon. Due to the long
half-life of the 40K isotope (1.31 billion years!), this
technique is useful for dating really old things (200,000
years), but only in volcanic environments.
The “dating gap”: radiocarbon dating can be taken back
to about 50,000 years ago reliably, and K/Ar can only be
used before about 200,000 years ago.
Thermoluminescence (TL), electron spin resonance
(ESR), and optically stimulated luminescence (OSL) can
partially fill the “dating gap”
Collecting samples for thermoluminescence (TL) dating
problems of association can be found for any dating
technique, even calendrics
PRACTICAL CONSIDERATIONS:
Relative and absolute dating each have associated costs and
benefits:
 relative dating is free, fast, and reliable, BUT unscaled
 “absolute” dating is expensive, slow, and less reliable,
BUT scaled
 relative dating can be performed in the field, on the spot.
“Absolute” cannot (except calendrics)
 relative dating generally can only be used regionally
 “absolute” dating can be applied globally
Thus, one approach is not better than the other is.
Relative and “absolute” dating are complementary in that
they provide independent means of assessing age.
Archaeologists serve their interests best by using relative
and “absolute” techniques together.