DATING METHODS AND PRINCIPLES (RADIOMETRY, ELECTRON
SPIN RESONANCE, THERMOLUMINISCENCE AND
PALEOMAGNETISM)
BY
DIDI CHEKWUBE NNAMDI
PAU-UI-0704
DEPARTMENT OF PETROLEUM GEOSCIENCES
PAULESI, IBADAN, NIGERIA
DATE: 28-07-2022
PRESENTATION OUTLINE
• INTRODUCTION
• TYPES OF DATING
• APPLICATION OF DATING
• SIGNIFICANCE
• CONCLUSION
INTRODUCTION
• How Old Is the Earth?
• How Can We Determine
Earth’s Geologic History?
• How Can We Determine the
Age of Geologic Events?
THE EARTH
TYPES OF DATING
• Two Primary Means of Dating Rocks
1) Relative Dating Relative Dating
• Determines the temporal order of rock forming events
• Does not give numeric ages
• Use of stratigraphic principles and fossils
• Cheap Cheap
2) Absolute Dating Absolute Dating
• Determines the numeric age of rock forming events
• Only appropriate for ages of igneous rocks and minerals
• Primary method is the radiometric technique
• Used in conjunction with stratigraphic principles and fossils
• Expensive
Relative Versus Absolute Dating
Relative Dating
• Stratigraphic principles
• Fossil Succession
• Emphasis on Sed Rocks
Absolute Dating
• Radio-Isotopic techniques
• Emphasis on Igneous Rocks
SOURCE: Ray Rector
How Can We Figure Out the Age Sequence of Geologic Events?
The Stratigraphic Principles
1. Superposition - Oldest layer occurs at base of a layered sequence and is
overlain by progressively younger rock layers.
2. Cross-Cutting Relations - If a body or discontinuity cuts across a rock structure,
it must have formed after that stratum.
3. Law of Inclusions - Rock fragments (in another rock) must be older than the rock
containing the fragments.
4. Law of Fossil Succession - Unique fossil groups were succeeded by other fossil
groups through time.
5. Original Horizontality - All sedimentary rocks are originally deposited
horizontally. Sedimentary rocks that are no longer horizontal have been tilted from
their original position.
6. Lateral Continuity - Sedimentary and volcanic rocks are laterally continuous
over large areas.
The Stratigraphic Principles
Principle of Superposition
Principle of Fossil Succession
Principle of Cross-Cutting Relations
Principle of Inclusions
Index Fossils
1) Narrow time range
2) Worldwide distribution
3) Preserve in a wide range of depositional settings
4) Very Abundant
Index fossils
Original horizontality
Principle of Lateral Continuity
Principle of Unconformities
Q?
ABSOLUTE DATING
Absolute dating is usually based on the physical, chemical, and
life properties of the materials.
RADIOMETRY,
ELECTRON SPIN RESONANCE,
THERMOLUMINISCENCE,
OPTICAL STIMULATING LUMINESCENCE,
PALEOMAGNETISM
ABSOLUTE DATING
Name of Method
Age Range of Application Material Dated
Methodology
Radiocarbon
1 - 70,000 years
Organic material such as
bones, wood, charcoal,
shells
Radioactive decay of 14C
in organic matter after
removal from bioshpere
K-Ar dating
1,000 - billion of years
Potassium-bearing
minerals and glasses
Radioactive decay of 40K
in rocks and minerals
Uranium-Lead
10,000 - billion of years
Uranium-bearing
minerals
Radioactive decay of
uranium to lead via two
separate decay chains
ABSOLUTE DATING
Name of Method
Age Range of Application
Material Dated
Methodology
Uranium series
1,000 - 500,000 years
Uranium-bearing minerals, Radioactive decay of 234U
corals, shells, teeth, CaCO3 to 230Th
Fission track
1,000 - billion of years
Uranium-bearing minerals
and glasses
Measurement of damage
tracks in glass and minerals
from the radioactive decay
of 238U
Luminescence (optically or
thermally stimulated)
1,000 - 1,000,000 years
Quartz, feldspar, stone
tools, pottery
Burial or heating age based
on the accumulation of
radiation-induced damage
to electron sitting in
mineral lattices
ABSOLUTE DATING
Name of Method
Age Range of Application
Material Dated
Methodology
Electron Spin Resonance
(ESR)
1,000 - 3,000,000 years
Uranium-bearing materials
in which uranium has been
absorbed from outside
sources
Burial age based on
abundance of radiationinduced paramagnetic
centers in mineral lattices
Cosmogenic Nuclides
1,000 - 5,000,000 years
Typically quartz or olivine
from volcanic or
sedimentary rocks
Radioactive decay of
cosmic-ray generated
nuclides in surficial
environments
Magnetostratigraphy
20,000 - billion of years
Sedimentary and volcanic
rocks
Measurement of ancient
polarity of the earth's
magnetic field recorded in
a stratigraphic succession
ABSOLUTE DATING
Name of Method
Age Range of Application
Material Dated
Methodology
100 - billions of years
Volcanic ejecta
Uses chemistry and age of
volcanic deposits to
ephrochronology
establish links between
distant stratigraphic
successions
ABSOLUTE DATING
GENERAL WORKING PRINCIPLE FOR
• Thermoluminescence,
• Optical stimulating luminescence and
• Electron spin resonance
RADIOACTIVE DECAY
(RADIOCATIVE ELEMENT)
RADITAION
EXCEPTION RANGE
Applicable to materials that are
up to about 100,000 years old
ABSOPTION (NON
RADIOACTIVE ELEMENTS)
EXCEPTION RANGE
No accumulation of electron when the
rock or fossil is older than 100,000 years
because the trap is full
ELECTRON DISPLACEMENT
TRAP OR IMPERFECTION
ELECTRON ACCUMULATION
AGE
RADIOMETRY
RADIOCARBON DATING
RADIOCARBON DATING
• Once an organism dies, it ceases to obtain more 14C
• 14C decays reducing the concentration within organism after death
• 14C decays by beta emission, emission of an electron and a neutron
changing into a proton, thus reverting back into nitrogen
14C
---> 14N + ß + neutrino
The emitted beta particles (ß) are what is counted in Libby's "gas
proportional“ method of 14C dating
RADIOCARBON DATING
Determining the Starting Amount
Two types of carbon used in the dating process: 12C and 14C
•
12C
•
When an organism is alive it has the same ratio (12C to 14C) that is found
in the atmosphere (1-trillion to 100-trillion)
is a stable isotope (it does not decay)
Same ratio
Different
ratio
RADIOCARBON DATING
The C-14 dating method relies on measuring the
amount of 14C in the material
Two Things Need to Know to determine
how many half-lives have expired
1. How fast it decays (measured in half-lives). This
is known (5,730 years --> Cambridge half life).
2. The starting amount of C-14 in the fossil.
A Critical Detail
RADIOCARBON DATING
How the 12C / 14C Ratio Works
PALEOMAGNETISM
The Earth is like a gigantic magnet.
It has a magnetic north and south pole and its magnetic field is
everywhere.
Magnetic needle in a compass points toward magnetic north,
Small magnetic minerals that occur naturally in rocks point toward
magnetic north, approximately parallel to the Earth's magnetic field.
Because of this, magnetic minerals in rocks are excellent recorders of
the orientation, or polarity, of the Earth's magnetic field.
PALEOMAGNETISM CONT’D
ORIGIN OF THE EARTH’S MAGNETISM
• Core
• Core current
MAGNETIC POLARITY DEPENDENT
• Core current direction
• Mantle current direction
MAGNETIC POLARITY
magnetic north marries geographical north
• REVERSE POLARITY: Magnetic north marries geographical south
PALEOMAGNETISM CONT’D
What is paleomagnetism method? Radiometric dates and
measurements of the ancient magnetic polarity in volcanic and
sedimentary rocks
Geologists have been able to determine precisely when magnetic
reversals occurred in the past.
Combined observations of this type have led to the development
of the geomagnetic polarity time scale (GPTS)
The GPTS is divided into periods of normal polarity and reversed
polarity.
PALEOMAGNETISM CONT’D
• Earth’s magnetic field:
earth’s magnetic field that any
earth’s magnetic material
aligns to
• Geomagnetic polarity time
scale (GPTS): Black bands
indicate times of normal
polarity and white bands
indicate times of reversed
polarity.
CONCLUSION
Using a variety of methods, geologists are able to determine the
age of geological materials to answer the question: "how old is
this fossil?"
Relative dating methods are used to describe a sequence of
events. These methods use the principles of stratigraphy to
place events recorded in rocks from oldest to youngest.
Absolute dating methods determine how much time has passed
since rocks formed by measuring the radioactive decay of
isotopes or the effects of radiation on the crystal structure of
minerals. Paleomagnetism measures the ancient orientation of
the Earth's magnetic field to help determine the age of rocks.
THANK YOU