DATING METHODS

1
DATING METHODS
One of the most important questions asked about
any ancient object is just how old it really
is. There are a number of scientific techniques
which can be used to date antiquities

• DENDROCHRONOLOGY
• RADIOCARBON DATING
• POTASSIUM ARGON DATING
• LUMINESCENCE DATING
• ESR DATING
• FISSION TRACK DATING
• PROTEIN AND AMINO ACID DIAGENESIS DATING
• OBSIDIAN HYDRATIAN DATING
• ARCHEOMAGNETIC DATING
• SURFACE DATING USING ROCK VANISH

2
 TARIHLENDIRME YÖNTEMLERI Organik veya inorganik
materiyalleri Radyokarbon (C-14),
Dendrokronoloji-Tree ring dating, Elektron Spin
Rezonans (ESR), Termolüminesans (TL) ve OSL gibi
arkeometrinin en önemli uygulamalari arasinda
sayilabilecek yöntemlerle tarihlendirmek
mümkündür.   Potasyum Argon Metodu (KA)
Radyoaktif olan (potasyumun) radyoaktif olmayan
Argon40 gazina dönüsmesine dayanir. Özellikle
jeolojik tabakalar içinde bulunan fosil
kalintilarina uygulanir. 100.000 yili askin
volkanik kayalara da uygulanmaktadir.   Radyokarbo
n Metodu (C-14) 1955' te Amerika'da Chicago
Üniversitesi'nde W. Libby ve arkadaslari bu
metodu uygulamislardir. Bu tarihten itibaren en
geçerli, en yaygin tarihlendirme metodudur.
Özellikle tarih öncesi arkeolojide kullanilir.
Tüm organik maddelerde bulunan radyoaktif
karbonun, bunlarin canliliklarini
kaybetmelerinden sonra belirli bir tempoda
azaldigi gözlenmistir. Bu oran bilindiginden,
bulunan organic maddenin yasi, bu gözönünde
tutularak bulunur. Ölçülere göre yaklasik olarak
organik maddelerin ömürlerinin yarisi boyunca
yilda 5568 karbon kaybettikleri anlasilmistir.
Sakincali yani tam dogru netice
vermemesidir.Nedeni de atmosferin her zaman ayni
miktarda karbon ihtiva etmemesidir.   Dendrokrono
loji Amerikali A.E. Douglass tarafindan bulunan,
agaç gövdelerinin enine kesitinde görülen yillik
halka tabakalarinin incelenmesine dayanan
tarihlendirme yöntemidir. Agaçlar her yil
gövdesinde yeni bir halka olusturur. Bu halka bol
yagisli yillarda kalin, az yagisli yillarda ince
olur. Douglass eski evlerde kullanilan
agaçlardan özel bir teknikle kesit alarak,
üzerlerindeki halkalari sayip yapilarin tarihini
saptamayi basarmistir.   Termolüminesans Metodu
Tas, keramik, cam gibi kristal yapiya sahip
maddelerin yas tayininde kullanilir.
3
DENDROCHRONOLOGY
Dendrochronology or tree-ring dating is the
method of scientific dating based on the analysis
of tree-ring growth patterns. This technique was
invented and developed during the 20th century
originally by A. E. Douglass,the founder of the
Laboratory of Tree-Ring Research at the
University of Arizona. The technique can date
wood to exact calendar years.
Visible rings result from the change in growth
speed through the seasons of the year, thus one
ring usually marks the passage of one year in the
life of the tree.
4
Radiocarbon dating is a radiometric dating
method that uses the naturally occurring isotope
isotope carbon-14 (14C) to determine the age of
carbonaceous materials up to about 60,000
years The technique of radiocarbon dating was
discovered by Willard Libby and his colleagues
in 1949 during his tenure as a professor at the
University of Chicago. Probably the best known
and most frequently used is radiocarbon or 14C
dating. Radiocarbon dating can only be applied
to organisms that were once alive and is a means
of determining how long ago they died.
Radiocarbon dating is possible because of the
existence in nature of a tiny amount of 14C, or
radiocarbon, a radioactive isotope of carbon.
  By measuring how much 14C remains in
ancient organic materials, it is possible to
calculate how long ago they died. To do this
requires extensive chemical processing, carried
out in laboratories To convert the carbon in the
ancient objects to a form in which the very low
level radioactivity can be measured. Most
radiocarbon dating is carried out on bone or
charcoal, as these are the organics that most
frequently survive from the past, but many other
materials can also be dated using this technique.

5
RADIOCARBON DATING

• Carbon has two stable,
  nonradioactive isotopes carbon-12 (12C), and
  carbon-13 (13C).
• In addition, there are trace
  amounts of the unstable isotope
• carbon-14(14C) on Earth.
• Carbon-14 has a half-life of
  5730 years and would have long ago vanished from
  Earth were it not for the unremitting cosmic ray
  impacts on nitrogen in the Earth's atmosphere,
  which create more of the isotope.

6
This 14C isotope is produced in the upper
atmosphere by the action of cosmic rays on 14N.
This 14C combines with oxygen to produce carbon
dioxide (CO2) and is taken in by plants during
photosynthesis. From plants this 14C is absorbed
into the tissues of every living thing via the
food chain. Since it is radioactive, it is
unstable and decays away at a known rate. While
any plant or animal is alive the 14C lost by
radioactive decay is constantly replaced through
the food chain, but when that organism dies, no
more 14C is taken in, and the amount present in
the tissues goes down. (from Aitken 1990)
                                             
7
POTASSIUM ARGON DATING
Potassium-Argon Dating is the only technique
for dating very old archaeological materials.
Geologists have used this method to date rocks
as much as 4 billion years old. It is based on
the fact that some of the radioactive isotope of
Potassium, Potassium-40 (K-40) ,decays to the gas
Argon as Argon-40 (Ar-40). By comparing the
proportion of K-40 to Ar-40 in a sample of
volcanic rock, and knowing the decay rate of
K-40, the date that the rock formed can be
determined.   
8
In principle all the materials containing quartz
or feldspars and submitted to heating to several
hundreds of degrees centigrate can be dated by
this way
9
LUMINESCENCE DATING
Materials with suitable luminescence properties
can be dated because at some point in the past
traps are emptied of their charge by sufficient
exposure to heat or light.
Subsequently, traps become refilled because of
continued ionization by radioactivity and a
latent luminescence signal steadily accumulates

Optical dating is method of determining how long
ago minerals were last exposed to daylight, It is
useful to geologists and archaeologists who want
to know when such an event occurred. Time clock
become zero for a sediment of earthquake line,or
sediment of loess.
Thermo luminescence dating is method of
determining how long ago minerals heated to
800-1000C degrees then when heated time clock
become zero (for making pottery or baked brick)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
In phosphorescence the energy difference between
the excited state and the meta stable state is
generally so small that detrapping occurs by
lattice vibra- tions at ambient temperature, i.e.
no external supply of energy is
required. However, in TL and OSL the energy
difference between the excited state and the meta
stable state is so large that external energy
must be applied to detrap the electrons. In TL
the luminescence emission is accelerated
by thermal stimulation whereas in OSL the
luminescence emission is accelerated by optical
stimulation.
25
LUMINESCENCE DATING

• As far as dating is concerned, the phenomenon
  of luminescence can be subdivided according to
  the kind of energy supply during stimulation into
• thermoluminescence (TL,
  stimulated by heat)
• optical stimulated luminescence (OSL, stimulated
  by visible light)
• infrared stimulated luminescence (IRSL,
  stimulated by infrared light)

ELSEC 9010 osl device
26
Basic Concepts in Luminescence Luminescence is a
generic term for the electromagnetic radiation
(usually in the form of visible light) emitted as
a consequence of an atomic or molecular
non-thermal excitation. Thus, luminescence is
often described as cold light to distinguish it
from incandescent light emission, which occurs
when a material is excited thermally. Luminescent
materials are able to absorb energy, store part
of it and convert it into light these materials
usually have a crystalline structure.
27
Luminescence can broadly be categorised as either
Fluorescence or phospho-rescence. Fluorescence
the light emission resulting from the relaxation
of an electron from an excited state to the
ground state (possibly through a metastable state
from which transition to the ground state is
allowed). The delay between the absorption of
energy resulting in the excited state and the
emission is determined by the life time of the
excited state.The life time can be as short as
picoseconds and as long as milliseconds in
special cases. Photoluminescence, cathodo
luminescence, chemi-luminescence, bioluminescence
and triboluminescence are all examples of
different fluorescence processes with different
means of excitation(i.e. photons, electrons,
chemical energy, biochemical and mechanical
energy, respectively) Phosphorescence the
relaxation back to the ground state is delayed by
a relaxation to the ground state is not
permitted. These meta stable states function as
electron traps, and energy must be supplied to
detrap (release) the electrons back to the
excited state from where they can relax to the
ground state (McKinlay, 1981). The return to the
ground state is thus delayed for period of time
the length of which depends on the life time of
the electron in the meta stable state.
The two types of luminescence are distinguished
by the atomic mechanisms whereby the light is
emitted.
28
How stimulation occurs

• With optical dating,the signal is obtained
  by exposure to a beam of blue /green light or
  infrared radiation.
• Optically-stimulated luminescence(OSL) is
  commonly used , also it is calling as Photon
  stimulated luminescence (PSL) and
  Photoluminescence(PL)

29
Optically stimulated luminescence relies on the
same basic concepts as TL, but in OSL the
stimulation energy is supplied by photons instead
of heat. Thus, the physical principles of OSL are
closely related to those of TL. How- ever, it is
not clear that the same defect centres are
involved in both processes in any one material
(McKeever, 2001). OSL has several advantages over
TL. When dealing with unheated materials (i.e.
materials zeroed by light ex- posure) the most
important of these advantages are that in OSL
only the trapping levels most sensitive to light
are sampled that is the charge popula- tion most
eectively zeroed. In many samples, it is
believed that 99 of the initial OSL signal
originates from the 325 C TL peak in quartz
(Murray and Wintle, 1999). Another advantage of
OSL over TL is that stimulation can be performed
at room temperature (although some advantages may
be obtained at slightly elevated temperatures),
which means that thermal quenching is not made
worse by heating.
30
Trap mechanism
Trap mechanism, namely the time-dependent
accumulation of electrons and holes in the
crystal lattice of certain common minerals
(trap). The minerals are acting as natural
radiation dosimeters. When a mineral is formed or
reset, all electrons are in the ground state.
Naturally occurring radioactive isotopes (U, Th,
and K) emit a variety of rays which ionize atoms.
Negatively charged electrons are knocked off
atoms in the ground state (valence band) and
transferred to a higher energy state (conduction
band) positively charged holes remain near the
valence band.
Trap schematic
The trapped electrons and holes forms
luminescence centres which can be stimulated. For
the measurement of a luminescence signal, the
trapped electrons have to be either thermally (by
heating) or optically (by light exposure)
activated. The electrons return to the conduction
band and most of them will recombine with the
holes. If such holes are luminescence centres,
light emission (luminescence) is observed.
31
Zeroing a trap

• Figure show the basic principles of the dating
  process. A zeroing event resets any previously
  stored trapped electrons - this resetting may be
  heating, exposure to sunlight or mineral
  formation. After zeroing, new electrons and holes
  are trapped as a result of natural radiation

32
References

• Chronometric Dating in Archaelogy (Edited by
  R.E.Taylor and Martin j.Aitken)
• Archaeological dating using physical
  phenomena(M.J. Aitken)

33
Electron spin resonance
34
ESR DATING

• Electron spin resonance (ESR) was proposed
  as a dating method by Zeller as early as 1967,
  but its practical application began with the work
  of Ikeya in 1975.Study based on carbonate
  materials, bones, and quartz

ESR-dating is a powerful tool to date the time of
mineralization, sedimentation or last heating of
minerals. The dating method has the same
dosimetric basis as TL/OSL, but in contrast to
these methods only paramagnetic centers are
detected with ESR. As the measurement does not
destroy the centers however, it can be repeated
several times.
Figure 1 Created by ionising radiation, point
defects accumulate predictably in enamel.
Imperfections in the crystal lattice exist
between the valence and conduction bands,
trapping free radicals
35
FISSION TRACK DATING

• Fission track dating is a radiometric dating
  technique based on analyses of the damage trails,
  or tracks, left by fission fragments in certain
  uranium bearing minerals and glasses.
• Uranium-238 undergoes spontaneous fission decay
  at a known rate. The fragments emitted by this
  fission process leave trails of damage in the
• crystal structure of the minerals enclosing
  the uranium

Fission tracks in an apatite crystal (top) and in
a muscovite mica (bottom).
36
FISSION TRACK DATING

• Etching of polished surfaces of these minerals
  reveals the spontaneous fission tracks for
  counting by optical microscopic means. The number
  of tracks correlates directly with the age of the
  sample and the uranium content

Fission Tracks (FT) are micrometer-sized, linear
damage tracks that occur in insulating minerals
and that are caused by the spontaneous fission of
heavy, unstable nuclides (mostly 238U in natural
minerals). The spontaneous fission of 238U occurs
at a specific rate, described by the decay
constant (l f 8.46 10-17a-1). This implies
that when the uranium concentration (CU) of a
sample is known, the spontaneous FT density (r s
number of tracks/cm2) in that sample is an
indication for the samples age. r s is
determined by counting the tracks under an
optical microscope (at 1250 magnification).
Since FTs are features at an atomic scale, they
require chemical techniques (etching) to make
them observable under the optical microscope. CU
is measured by irradiating the sample in a
nuclear reactor with thermal neutrons
37
PROTEIN AND AMINO ACID DIAGENESIS DATING

• At a widely publicized news conference in August
  of 1972, Dr. Jeffrey Bada of Scripps Institute of
  Oceanography announced the "discovery" of a new
  dating method based on the rate of racemization
  of amino acids in fossil material. He was quoted
  as saying that he had discovered the basis of the
  method in 1968, and that it was so obvious and
  simple he was amazed it hadn't been discovered
  earlier.

Amino acids are the "building blocks," or
sub-units, of proteins. About 20 different kinds
of amino acids are found in proteins. All amino
acids in proteins (except glycine) are L-amino
acids. These amino acids spontaneously tend to
slowly change to the D-form. The D-form tends to
revert to the L-form, and eventually an
equilibrium is obtained, as illustrated here for
alanine
38
PROTEIN AND AMINO ACID DIAGENESIS DATING

• The process by which an L-amino acid changes into
  a mixture of the L- and D-forms (or the D-form
  changes into a mixture of the L- and D-forms) is
  called racemization. Racemization is complete
  when equal amounts of the L- and D-forms are
  obtained.

Hare and Mitterer3 measured the rate of
racemization of L-isoleucine to D-alloisoleucine
in modern shell fragments heated in water at high
temperatures and extrapolated these data to lower
temperatures in order to estimate the rate of
racemization of L-isoleucine in fossil shells to
obtain what they believed to be an approximate
age for these fossil shells.
These data are believed to yield the rates at
which L-isoleucine was converted to
Dalloisoleucine in the sediment through
geological time. The extent of conversion of
L-isoleucine to D-alloisoleucine in core sediment
samples from various depths was then determined
and conclusions based on the above rates were
used to estimate the ages of the sediments from
various core depths
39
OBSIDIAN HYDRATIAN DATING

• The obsidian hydration dating method was
  introduced to the archaeological community in
  1960 by Irving Friedman and Robert Smith of the
  U. S. Geological Survey (Friedman and Smith
  1960). The potential of the method in
  archaeological chronologic studies was quickly
  recognized and research concerning the effect of
  different variables on the rate of hydration has
  continued to the present day by Friedman and
  others.

Obsidian hydration rim (between arrows)
40
OBSIDIAN HYDRATIAN DATING

• When a new surface of obsidian is exposed to the
  atmosphere, such as during the manufacture of
  glass tools, water begins to slowly diffuse from
  the surface into the interior of the specimen.
  When this hydrated layer or rind reaches a
  thickness of about 0.5 microns, it becomes
  recognizable as a birefringent rim when observed
  as a thin section under a microscope. Hydration
  rims formed on artifacts can vary in width from
  less than one micron for items from the early
  historic period to nearly 30 microns for early
  sites in Africa (Michels et al. 1983a Origer
  1989).

Once a hydration layer has been measured, it can
be used to determine the relative ages of items
or, in some circumstances, can be converted into
an estimated absolute age. In order to transform
the hydration rim value to a calendar age, the
rate of the diffusion of water into the glass
must be determined or estimated. The hydration
rate is typically established empirically through
the calibration of measured samples recovered in
association with materials whose cultural age is
known or whose age can be radiometrically
determined, usually through radiocarbon dating
methods (Meighan 1976).
41
ARCHEOMAGNETIC DATING
Paleomagnetism is concerned with the history of
the Earth's magnetic field during geologic
time,and applications to geological and
geophysical problems.Archeomagnetism involves the
study of the Earth's magnetic field during
archaelogical time,and the application of
paleomagnetic techniques and principles to
archaeological features and artifacts (Tarling
1983)

• An absolute dating method based on the earth's
  shifting magnetic poles. When clays and other
  rock and soil materials are fired to
  approximately 1300F (700C) and allowed to cool
  in the earth's magnetic field, they retain a weak
  magnetism which is aligned with the position of
  the poles at the time of firing. This allows for
  dating, for example, of when a fire pit was used,
  based on the reconstruction of pole position for
  earlier times.

42
SURFACE DATING USING RACK VANISH

• Rock vanish ,a dark colored,magnesium-,iron-,and
  silica-rich coating that forms on exposed rock
  surfaces over time, especially in arid and
  semi-arid regions,has been used as a chronometric
  dating tool in both archeology and geology.
• The methods most commonly employed are
  cation-ratio dating ,using differential leaching
  of cations in the varnish coating ,and
  accelerator mass spectrometry-based radiocarbon
  dating of organic material contained within or
  trapped beneath the varnish coating.

43
(No Transcript)
44
Some terminology
Chronology is the science of locating events in
time. An arrangement of events from either
earliest to latest or the reverse
45
Archaeological stratigraphy

• In the field of archaeology, soil stratigraphy is
  used to better understand the processes that form
  and protect archaeological sites. The law of
  superposition holds true, and this can help date
  finds or features from each context, as they can
  be placed in sequence and the dates interpolated.
  Phases of activity can also often be seen through
  stratigraphy, especially when a trench or feature
  is viewed in section (profile). As pits and other
  features can be dug down into earlier levels, not
  all material at the same absolute depth is
  necessarily of the same age, but close attention
  has to be paid to the archeological layers.