# Introduction to Paleoanthropology/Dating Techniques


of reconstructing how anatomical and behavioral characteristics of early
hominids evolved. \_\_toc\_\_ Researchers who are interested in knowing
the age of particular hominid fossils and/or artifacts have options that
fall into two basic categories:

-   Relative dating methods
-   Chronometric dating methods

## Relative dating methods

Relative dating methods allow one to determine if an object is earlier
than, later than, or contemporary with some other object. It does not,
however, allow one to independently assign an accurate estimation of the
age of an object as expressed in years. The most common relative dating
method is stratigraphy. Other methods include fluorine dating, nitrogen
dating, association with bones of extinct fauna, association with
certain pollen profiles, association with geological features such as
beaches, terraces and river meanders, and the establishment of cultural
seriations. Cultural seriations are based on typologies, in which
artifacts that are numerous across a wide variety of sites and over
time, like pottery or stone tools. If archaeologists know how pottery
styles, glazes, and techniques have changed over time they can date
sites based on the ratio of different kinds of pottery. This also works
with stone tools which are found abundantly at different sites and
across long periods of time.

### Principle of stratigraphy

Stratigraphic dating is based on the principle of depositional
superposition of layers of sediments called strata. This principle
presumes that the oldest layer of a stratigraphic sequence will be on
the bottom and the most recent, or youngest, will be on the top. The
earliest-known hominids in East Africa are often found in very specific
stratigraphic contexts that have implications for their relative dating.
These strata are often most visible in canyons or gorges which are good
sites to find and identify fossils. Understanding the geologic history
of an area and the different strata is important to interpreting and
understanding archaeological findings.

## Chronometric dating methods

The majority of chronometric dating methods are radiometric, which means
they involve measuring the radioactive decay of a certain chemical
isotope. They are called chronometric because they allow one to make a
very accurate scientific estimate of the date of an object as expressed
in years. They do not, however, give \"absolute\" dates because they
merely provide a statistical probability that a given date falls within
a certain range of age expressed in years. Chronometric methods include
radiocarbon, potassium-argon, fission-track, and thermoluminescence.

The most commonly used chronometic method is radiocarbon analysis. It
measures the decay of radioactive carbon (14C) that has been absorbed
from the atmosphere by a plant or animal prior to its death. Once the
organism dies, the Carbon-14 begins to decay at an extremely predictable
rate. Radioactive carbon has a half-life of approximately 5,730 years
which means that every 5,730 years, half of the carbon-14 will have
decayed. This number is usually written as a range, with plus or minus
40 years (1 standard deviation of error) and the theoretical absolute
limit of this method is 80,000 years ago, although the practical limit
is close to 50,000 years ago. Because the pool of radioactive carbon in
the atmosphere (a result of bombardment of nitrogen by neutrons from
cosmic radiation) has not been constant through time, calibration curves
based on dendrochronology (tree ring dating) and glacial ice cores, are
now used to adjust radiocarbon years to calendrical years.

The development of Atomic Absorption Mass Spectrometry in recent years,
a technique that allows one to count the individual atoms of 14C
remaining in a sample instead of measuring the radioactive decay of the
14C, has considerably broadened the applicability of radiocarbon dating
because it is now possible to date much smaller samples, as small as a
grain of rice, for example.

Dendrochronology is another archaeological dating technique in which
tree rings are used to date pieces of wood to the exact year in which
they were cut down. In areas in which scientists have tree rings
sequences that reach back thousands of years, they can examine the
patterns of rings in the wood and determine when the wood was cut down.
This works better in temperate areas that have more distinct growing
seasons (and thus rings) and relatively long-lived tree species to
provide a baseline.

## Methods of dating in archaeology

Techniques of recovery include:

-   Surveys
-   Excavations

Types of archaeological remains include:

-   Perishable: plant remains, animal bones, wooden artifacts, basketry,
    and other easily degradable objects
-   Nonperishable materials: stone tools, pottery, rocks used for
    structures.

Data collection and analysis is oriented to answer questions of
subsistence, mobility or settlement patterns, and economy.

## Methods in physical anthropology

Data collections based on study of hard tissues (bones and teeth),
usually the only remains left of earlier populations, which include:

-   Identification of bones/Which part of skeleton is represented?
-   Measurement of the cranium and other elements of a skeleton.
    Carefully defined landmarks are established on the cranium, as well
    as on the long bones, to facilitate standardization of measurements.
-   Superficial examination of bone for any marks (for instance,
    cutmarks)
-   Further examination using specific techniques:
    -   X-ray to identify evidence of disease and trauma in bones
    -   DNA extraction to determine genetic affiliations

