2. SIR MORTIMER WHEELER
“new archaeology” excavated urban centres layer by layer
“The important thing is that the archaeologist
must know his dates and how to use them;
recorded dates where they are valid and
unwritten dates where geological or physical
or chemical or botanical science can win
them from the earth.”
3. RELATIVE /ABSOLUTE
• RELATIVE TECHNIQUES
• Stratigraphy and Seriation
• Typology and Cross Dating
• Fluorine
• Obsidian Hydration
• Pollen Analyses
• ABSOLUTE TECHNIQUES
• Radio Carbon Dating
• Potassium Argon Dating
• Thermoluminescence
• Electron Spin Resonance
• Dendrochronology
4. RELATIVE DATING TECHNIQUES
• One of the most fundamental principles of archaeology is the Law of
Superposition.
• The law states that strata that are younger will be deposited on top
of strata that are older, given normal conditions of deposition.
• This law is the guiding principle of stratigraphy, or the study of
geological or soil layers.
• Stratigraphy is still the single best method that archaeologists have
for determining the relative ages of archaeological materials.
5. RELATIVE DATING
• Relative dating is an invaluable tool, but does not tell us WHEN an event
occurred, just the ORDER in which events occurred. The oldest technique
for establishing the actual ages of deposits is to use artifacts of a known
age.
• These can be coins with minting dates stamped on them, writings with
dates included, or objects that we know were only manufactured during
a certain time.
7. STRATIGRAPHY
•Stratigraphy is the study of strata, or layers.
• Specifically, stratigraphy refers to the application of
the Law of Superposition to soil and geological
strata containing archaeological materials in order
to determine the relative ages of layers.
•In addition, stratigraphy can tell us much about the
processes affecting the deposition of soils, and the
condition of sites and artifacts
9. SERIATION
• This technique places assemblages of artefacts into relative order.
Petrie used sequence dating to work back from the earliest historical
phases of Egypt into pre-dynastic Neolithic times, using groups of
contemporary artefacts deposited together at a single time in graves.
Seriation was developed in the USA to place in order finds from
strata or other kinds of assemblages such as potsherds collected
from the surface of sites.
10. Petrie’s system of Seriation or Sequence Dating was developed in 1899.
The system emphasises the relation of one find to another rather than an
exact date of manufacture. Nine hundred graves were selected from
almost 4000 excavated
11. CROSS DATING
• Cross-dating is a technique used to take advantage of consistencies
in stratigraphy between parts of a site or different sites, and objects
or strata with a known relative chronology.
• A specialized form of cross-dating, using animal and plant fossils, is
known as biostratigraphy.
12. FLUORINE DATING
• Fluorine is an element that is found in most ground water around the world. It can be
used as a relative dating technique.
• Skeletal remains buried in the earth are subject to a wide range of chemical changes. One
of these changes can occur when percolating ground water comes into contact with the
remains. The ground water inundates the bone remains with a solution of minerals drawn
from local soils. This can cause a change in the mineral composition of the bone. Hydroxyl
ions are displaced with a form of soluble fluorides. These ions form fluorapatite which is
markedly less soluble. Over time, more and more fluorides are accumulated. The rate
varies depending on the specific condition in the soil of the area and increases with age.
• Fluorine dating is chiefly of value in determining whether bone implements or human
skeletal remains found in association with other bones were buried at the same time. It
was fluorine dating that was instrumental in the debunking of Piltdown Man.
13. Potassium Argon Dating
• The Potassium-Argon (K-Ar) dating method is the measurement of the accumulation of
argon in a mineral. In contrast to a dating method such as C14 dating which measures the
disappearance of a substance, K-Ar dating measure the accumulation of argon in a
substance from the decomposition of potassium.
• This is relatively easy because argon, being an inert gas, usually does not leech out of a
mineral and is easy to measure in small samples. The actual date is comprised of the time it
has been formed from molten/heated minerals.
• This method, therefore, is not very useful when dating the time a human bone has been in
the ground, but it does help in giving the time of many of the artifacts that are often times
found alongside burials.
• If you were to take a piece of everyday rock, the K-Ar method would give you the date that
piece of rock was "reset" by the changing of it's chemical structure. Many things can and do
change the structure of rocks. Heating, weathering and many kinds of alterations will reset
this time.
• Therefore, archaeologists can determine relatively accurately how long ago a heat treated
projectile point was made, or a piece of pottery was last used to cook food.
14. POTASSIUM ARGON DATING
• Potassium-Argon Dating Potassium-Argon dating is the only viable
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.
15. POLLEN DATING
PALYNOLOGY
• Each year seed-bearing plants release large numbers of pollen grains.
This process results in a "rain" of pollen that falls over many types of
environments. Pollen that ends up in lake beds or peat bogs is the
most likely to be preserved, but pollen may also become fossilized in
arid conditions if the soil is acidic or cool. Scientists can develop a
pollen chronology, or calendar, by noting which species of pollen
were deposited earlier in time, that is, residue in deeper sediment or
rock layers, than others
16. Value of Pollen Dating
•pollen dating provides relative dates beyond the
limits of radiocarbon (40,000 years), and can be
used in some places where radiocarbon dates are
unobtainable.
•Pollen dating was crucial in the dating of Ice Man
and the Shroud of Turin
17. Weakness of Relative Dating
• The potential flaws in relative dating are obvious. Simply assuming
that an object is older because it was found at a lower depth in the
record is only subjective science.
• There are many instances of deep holes being dug for rubbish pits or
to locate well water that protrude into the record of older strata
injecting more modern material as they are filled in over time.
• Landslides and slips can completely change the topography of an
entire site burying what was once on top by that which is much
older, hence reversing the strata layers
18.
19. ABSOLUTE DATING
•A more precise and accurate system is known as
absolute dating and can in most circumstances
provide a calendar year to the object. Since 1950
there has been a transformation in the dating
techniques of archaeologists.
• Absolute dating is highly dependant on laboratory
analysis. There are a number of techniques that
have come to archaeology through the nuclear
research efforts during WW2.
20. AWatershed
'The application of the 14C method to archaeological materials is
generally considered to be a watershed event in the history of
archaeology and, in particular, in prehistoric studies “ R E Taylor
21. RADIO CARBON DATING
• Radiocarbon dating uses the biological assumption that all living
things absorb carbon, both ordinary carbon, C12, and radioactive
carbon, C14, into their living tissue.
• At the moment of death the C14 begins to decay at a rate that
scientists already know from other experiments. The missing amount
can then determine how long it took to be lost and therefore date
the object to a precise period.
• C14 dating can only be used on organic matter.
22. LIMITATIONS OF C14 DATING
• First, the size of the archaeological sample is important. Larger samples
are better, because purification and distillation remove some matter.
Although new techniques for working with very small samples have
been developed, like accelerator dating, these are very expensive and
still somewhat experimental.
• Second, great care must be taken in collecting and packing samples to
avoid contamination by more recent carbon. For each sample, clean
trowels should be used, to avoid cross contamination between
samples.
• Third, because the decay rate is logarithmic, radiocarbon dating has
significant upper and lower limits. It is not very accurate for fairly
recent deposits
23. AMS radiocarbon dating is a form of radiocarbon dating that is more
precise and requires less carbon than conventional radiocarbon methods
24. DENDROCHRONOLOGY
• Dendrochronology is another traditional technique for establishing
the abolute date of events. This is also called Tree-Ring Dating.
• Tree-Ring dating is based on the principle that the growth rings on
certain species of trees reflect variations in seasonal and annual
rainfall. Trees from the same species, growing in the same area or
environment will be exposed to the same conditions, and hence their
growth rings will match at the point where their lifecycles overlap.
25.
26. Weaknesses in Dendrochronolgy
• In some areas of the world, particularly in the tropics, the species
available do not have sufficiently distinct seasonal patterns that they can
be used.
• Where the right species are available, the wood must be well enough
preserved that the rings are readable. In addition, there must be at least
30 intact rings on any one sample.
• There also must be an existing master strip for that area and species.
There is an absolute limit on how far back in the past we can date things
with tree rings. Although bristle cone pine trees can live to 9,000 years,
this is a very rare phenomenon. As we try to push our matching of
archaeological specimens beyond the range for which we have good
control data, our confidence in the derived dates diminishes
27. LIMITATIONS
• Fourth, the ratio of C-14 to C-12 in the atmosphere is not constant.
Although it was originally thought that there has always been about
the same ratio, radiocarbon samples taken and cross dated using
other techniques like dendrochronology have shown that the ratio of
C-14 to C-12 has varied significantly during the history of the Earth.
• Finally, although radiocarbon dating is the most common and widely
used chronometric technique in archaeology today, it is not
infallable. In general, single dates should not be trusted. Whenever
possible multiple samples should be collected and dated from
associated strata
28. Obsidian Hydration
• Developed in 1960, Obsidian Hydration Analysis (OHA) is an inexpensive technique
archaeologists and geoarchaeologists use to find the age of a site they have excavated.
This method is most often used as a means of relative dating , but an absolute date may
also be estimated in some circumstances
• Obsidian was a common rock used in stone tool making. Obsidian is used mainly because
of its availability in prehistoric tool making and its unique quality of rehydrating itself after
a fracture
• When obsidian is newly exposed to the atmosphere, its surface begins to absorb water
from the air, which gradually seeps into the interior of the stone. Several factors can affect
the obsidian's water absorption, including soil type, climate, time and geochemistry.
• When viewed under a microscope, the layer permeated by moisture (known as a "rind")
becomes visible as a rim when the rind reaches a width of 0.5 microns (a micron being one
millionth of a meter). The greater the rind thickness, the greater the age of the exposed
obsidian.
29. The actual measurement of hydration involves using light
transmission to determine the amount of hydration, and
therefore the relative age of the sample. The prepared
slides are observed by means of a microscope to
determine the amount of light transmission.
30. Electron Spin Resonance
• Electron Spin Resonance Dating falls into the group of dating methods that uses
radiation exposure to date many materials found at archaeological sites. It is also
known as a Radiometric Dating Method.
• This technique is mostly used to date minerals.It has been used to date such
things as sedimentary quartz, fossilized teeth, flint, and calcium carbonate in
limestone, coral and egg shells.
• This method works by using radiation to cause electrons to separate from the
atoms. These electrons then become trapped in the crystal lattice of minerals.
This changes the magnetic field of the material at a rate that is predictable,
allowing it to be used to date an item. It can be used to date when
mineralization, sedimentation, or the last heating of minerals took place. It is
often used to date quartz from meteorite strikes, and places where earthquake
activity has taken place
31. THERMOLUMINESCENCE
• Artefacts that are made from crystalline
materials can be dated using
luminescence analysis. Crystalline
minerals when subjected to intense heat
will burn with differing colours of flame.
• Mostly used to date pottery the method
is very effective but costly.
• The greatest problem with dating an
object from antiquity is that nearly every
absolute dating process requires the
destruction of at least a piece of the
object in conducting the analysis. There
are relatively few dating laboratories and
having an artefact dated can be an
expensive exercise especially if the
artefact is not of great value itself.
32. Limitations to Thermoluminescence
• Thermoluminescence dating is in its developmental stages. Except for
doing simple authenticity tests of art objects, thermoluminescence
dating is not generally accurate enough for archaeological standards.
• There are many factors which have to be taken into account and each
of these factors has its own random error. This, combined with poorly
understood measurement errors, make the accuracy of
thermoluminescence dating only about 15% accurate for a single sample
and 7 to 10% accurate for a suite of samples in a single context.
• Thermoluminescence dating is used for rocks, minerals and pottery. It
dates items between the years 300-10,000B.P.
33. Uranium Disequilibrium
• Uranium-Thorium dating is an absolute dating technique which uses the
properties of the radio-active half-life of Uranium-238 and Thorium-230.
• Uranium-Thorium dating was first used on fossil bones in 1956,
however, it had been used for dating wood before this. This dating
technique has been used effectively on marine sediment, bone, wood,
coral, stone and soil. One of the benefits of uranium-thorium dating is
that the sample sizes can be less than 20 grams, in fact bone samples
can be 3-5 grams for an accurate date
