Absolute dating methods in Archaeology

1. ABSOLUTE DATING METHODS
Presented By
BINOD KUMAR SAHU
PG22HT-062
PG 1st SEMESTER
SCHOOL OF HISTORY
GANGADHAR MEHER UNIVERSITY, AMRUTA VIHAR,
SAMBALPUR, 768004
ODISHA
PRESENTATION ON

2.  Archaeological scientists have two primary ways of telling the age
of artefacts and the sites from which they came: relative dating and
absolute dating
 Relative dating fixes a time frame in relation to other strata or
material and not in absolute dates in numbers.
 It can only define the antiquity in terms of older or younger than
something else and makes it possible to arrange a series of things
in proper chronological order.
Relative Dating is when you give the age of a rock or fossil compared to another
rock or fossil.
Example: Rock A is OLDER than Rock B.
An actual age in years is not determined
 Absolute dating methods provide the precise age of a fossil,
artifact or a rock in years.
 These are obviously more useful methods than the relative dating
methods.
ABSOLUTE DATING

3. Absolute Dating Method:
The various dating methods like:
 TL Dating
 Radio Carbon Dating / C14 Dating
 Potassium Argon Dating
 Dendrochronology
 Fission-track dating
 Uranium series method
 Electron spin resonance

7. Radiocarbon Dating
 Radiocarbon dating also referred to as carbon dating or carbon-14 dating
 Radiocarbon dating is a method of determining the age of an object by using the
properties of radiocarbon, a radioactive isotope of carbon.
 The method was invented by Willard Libby in the late 1940s and soon became a
standard tool for archaeologists. It depends on the fact that radiocarbon, often
abbreviated as 14 C, is constantly being created in the atmosphere by the
interaction of cosmic rays with atmospheric nitrogen.

8. Radiocarbon Dating
 Carbon dating is a widely-used method to establish the age of organic materials,
things that were once living.
 Living things have carbon in them in various forms.
 The dating method is based on the fact that Carbon-14 (C-14) is radioactive, and
decays at a well-known rate.
I. C-14 is an isotope of carbon with an atomic mass of 14.
II. The most abundant isotope of carbon in the atmosphere is C-12.
III. A very small amount of C-14 is also present. The ratio of C-12 to C-14 in the
atmosphere is almost static, and is known.
 The Carbon Dating method cannot be used to determine the age of non-living
things like rocks, for example.
 Also, the age of things that are more than 40,000-50,000 years old cannot be
arrived at through carbon dating.
 This is because after 8-10 cycles of half-lives, the amount of C-14 becomes almost
very small and is almost undetectable.

9. Radiocarbon Dating
 Because plants and animals get their carbon from the atmosphere,
they too acquire C-12 and C-14 in roughly the same proportion as is
available in the atmosphere.
 Plants get their carbon through photosynthesis; animals get it
mainly through food.
 When they die, their interactions with the atmosphere stops.
 While C-12 is stable, the radioactive C-14 reduces to one half of
itself in about 5,730 years — known as its ‘half-life’.
 The changing ratio of C-12 to C-14 in the remains of a plant or
animal after it dies can be measured and can be used to deduce the
approximate time when the organism died.

15. THERMOLUMINESCENCEDATING

16. THERMOLUMINESCENCE DATING
 This method is helpful in dating the ancient clay objects like the pottery , bricks and
the ceramics.
 All clays contain crystalline constituents and also traces of radio active materials
the decay of which leads to the accumulation of energy as a constant rate within the
materials.
 This accumulated energy is released as a flash of light when the clay material is
heated to a very high temperature. This phenomenon is called thermoluminescence.
 The amount of light thus emitted is measured by sensitive photo electric equipment.
 When pottery is made and fired, the accumulated radiation in the clay is released as
thermoluminescence.
 This method involves the measurement of the decay of the radio-active particles in
baked clay by calculating the amount of damages to the crystal structure of the
material.
 Therefore if one takes a sample of pottery and measures the amount of
thermoluminescence light emitted in heating, it should be possible to relate this to
the time that has elapsed since the pottery was originally fired.

18. Potassium
Argon Dating

19.  Potassium-Argon (K-Ar) dating method, developed by the scientists at the
University of California in 1950, is based upon decay of the radioactive of a rare
isotope of potassium ( 40K) into argon (40Ar) gas.
 The decay takes place at known rate. The half-life of 40K is 1.31 billion years.
 This method can only be used with the rocks that contained no argon gas when
they are formed.
 Obviously, this makes the scientist to choose volcanic rocks. When the rock is
super heated like volcano, all the accumulated gases would be released into the
atmosphere. This sets the atomic clock to zero.
 When the rocks solidify again, radioactive potassium proceeds to decay into
argon.
 The argon build-up takes place in the rock at a fixed rate. So, the samples
collected from volcanic flow are heated at a high temperature and the
accumulated argon that is being released is measured.
 The date is determined based on the amount of argon gas that had accumulated
through radioactive decay.
Potassium Argon Dating

20. Dendrochronology
 Dendrochronology is the scientific method of dating based on the analysis of patterns
of tree ring variations. It is also known as tree ring dating.
 It is an approach based on counting the annual growth rings observable in the cross-
sections of cut trees.
 The method was devised in 1929 by A. E. Douglas, an astronomer at the University of
Arizona, who intended to use it for studying climatic variations
 It is common knowledge that a tree adds one ring of new wood each year between the
existing wood and the bark
 By counting the number of rings one can estimate the age of the tree when it was
felled.
 The annual growth rings are not of the same width. During years of favorable climate
(wet years) the rings are broad; during years of unfavorable climate (during drought)
they are narrow, since the trees grow less.
 It is this variation and unique nature of patterning of seasonal rainfall, depicted in
patterns of tree ring thickness variations, which makes dendrochronology possible.
 The rings are more visible in temperate zones, where the seasons differ more
markedly. This method may not be applicable in areas showing little seasonal
variations in rainfall, such as tropical areas.

27. THANK YOU