Evolution And History

116 CHAPTER 5 | Field Methods in Archaeology and Paleoanthropology

Dating Method Time Period Method’s Process Drawbacks

Stratigraphy Relative only Based on the law of superposition,

which states that lower layers or strata

are older than higher layers

Site specific; natural forces, such

as earthquakes, and human activity,

such as burials, disturb stratigraphic

relationships

Fluorine analysis Relative only Compares the amount of fluorine

from surrounding soil absorbed by

specimens after deposition

Site specific

Faunal and floral

series

Relative only Sequencing remains into relative

chronological order based on an

evolutionary sequence established in

another region with reliable absolute

dates; called palynology when done

with pollen grains

Dependent upon known relationships

established elsewhere

Seriation Relative only Sequencing cultural remains into

relative chronological order based on

stylistic features

Dependent upon known relationships

established elsewhere

Dendrochronology About 3,000 years BP

maximum

Compares tree-growth rings preserved

in a site with a tree of known age

Requires ancient trees of known age

Radiocarbon Accurate

less than

50,000 years BP

Compares the ratio of radioactive

carbon 14 (^14 C) (with a half-life of

5,730 years) to stable carbon 12 (^12 C)

in organic material

Increasingly inaccurate when

assessing remains from more than

50,000 years ago

Potassium argon

(K-Ar)

More than

200,000 years BP

Compares the amount of radioactive

potassium (^40 K) (with a half-life of

1.3 billion years) to stable argon (^40 Ar)

Requires volcanic ash; requires cross-

checking due to contamination from

atmospheric argon

Amino acid

racemization

40,000–

180,000 years BP

Compares the change in the number

of proteins in a right- versus left-sided

three-dimensional structure

Amino acids leached out from soil

variably cause error

Thermoluminescence Possibly up to

200,000 years BP

Measures the amount of light given

off due to radioactivity when sample

heated to high temperatures

Technique developed for recent

materials such as Greek pottery; not

clear how accurate the dates are for

older remains

Electron spin

resonance

Possibly up to

200,000 years BP

Measures the resonance of trapped

electrons in a magnetic field

Works with tooth enamel—not yet

developed for bone; problems with

accuracy

Fission track Wide range of times Measures the tracks left in crystals

by uranium as it decays; good cross-

check for K-Ar technique

Useful for dating crystals only

Paleomagnetic

reversals

Wide range of times Measures orientation of magnetic

particles in stones and links them to

whether magnetic field of earth pulled

toward the north or south during their

formation

Large periods of normal or reversed

magnetic orientation require dating

by some other method; some smaller

events known to interrupt the

sequence

Uranium series 40,000–

180,000 years BP

Measures the amount of uranium

decaying in cave sites

Large error range

Table 5.1 Absolute and Relative Dating Methods

absence of precise dates, one knows the relative age of
objects in one stratum compared with the ages of those
in other strata. However, defining the stratigraphy of a
given site can be complicated by geologic activities such

as earthquakes that shift the position of stratigraphic

layers.

Another method of relative dating is the fluorine

method. It is based on the fact that the amount of fluo-

rine deposited in bones is proportional to the amount of

time they have been in the earth. The oldest bones contain

the greatest amount of fluorine and vice versa. The fluorine

test is useful in dating bones that cannot be ascribed with

certainty to any particular stratum. A shortcoming of this

fluorine dating In archaeology or paleoanthropology, a tech-

nique for relative dating based on the fact that the amount of

fluorine in bones is proportional to their age.