Dating and Sampling Archaeological Probing

Dating and Sampling
Archaeological Probing
Dr Aman Kumar Singh

1. Dating and Sampling
Archaeological Probing
Dr. Aman Kumar Singh
[email protected]
Conservation and Heritage Management ,
Delhi Institute of Heritage Research and Management,
New Delhi 110067, India
Archaeological Dating

2. 1
Introduction Archaeology Dating
2
Types, Carbon Dating, Uranium Dating, Absolute, Relative ,
3
Examples
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3. Introduction
Catchment analysis
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4. Examination
Cation-ratio datingDating technique applied to rock varnish on
stone artifacts and petroglyphs, based on differences in the rate
at which cations (positively charged ions) such as K+ and Ca2+
are leached out relative to the less soluble Ti4+. For absolute
dating, a cation leaching curve must be established using inde-
pendently dated rocks from the region of interest. The methodol-
ogy of the technique is not without controversy.
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5. Examination
Absolute Age Dating Radiometric Methods
Absolute age dating is an incredible method scientists use to find
out almost precisely the age of a certain fossil or rock. By mea-
suring how much of a certain radioactive material is remaining in
something, we can accurately determine how long ago it existed.
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6. Examination
Uranium
Uranium contains 92 protons and 146 neutrons, for a combined
total of 238 protons and neutrons. This unstable element gives off
alpha particles (made up of 2 protons and 2 neutrons) to become
more stable.
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7. Examination
Alpha Particle
An alpha particle consists of 2 protons and 2 neutrons. This is
identical to a Helium nucleus, which is also made up of 2 protons
and 2 neutrons.
Thorium
The element now has an atomic number of 234 and it is the ele-
ment thorium. It is composed of a total of 234 protons and neu-
trons (this is also the atomic mass).
Parent and Daughter Atoms
When isotopes decay, we call the atom that was originally present
the parent atom and the atom that it becomes, the daughter prod-
uct. Once we know how long it takes for half of the parent atoms
in a sample to transform into daughter products, we are then able
to measure how old something is by measuring how much parent
and daughter product is left in one sample.
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8. Examination
Potassium
Potassium 40K breaks down into its daughter product Argon 40Ar.
It has a very long half life of 1.251 billion years, which means it
has the ability to help us mark a specific time within the range of
billions of years!
Parent/Daughter Ratio
If we measure the ratio of the parent product, Potassium, to the
daughter product Argon, we can know how much time has passed
since the rock first crystallized until today. This helps us get a bet-
ter idea of how old things are on Earth.
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9. Examination
Carbon
14
Most of the carbon we have inside of our bodies is the stable
atom of Carbon
12
,
but we also have a steady ratio of unstable or radioactive Carbon
14 within us.
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10. Examination
Radiocarbon Dating
Another important isotope we use for dating is Carbon
14
.
Carbon dioxide is essential to life on Earth; plants take it in,
animals eat the plants, and we eat the animals and the plants,
so there are carbon molecules bouncing around everywhere.
Most of the carbon we have inside of our bodies is the stable
atom of Carbon
12
,butwealsohaveasteadyratioofunstableorradioactiveCarbon
14
withinus.
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11. Examination
C
14
Carbon
14
Carbon 14 comes from the stable molecule of Nitrogen 14.
Cosmic rays from the sun send an energetic neutron to hit
stable Nitrogen 14. This neutron turns Nitrogen 14 into
Carbon 14.
Plants absorb Carbon14 Plants absorb Carbon 14 through
the process of photosynthesis, converting light energy
from the sun into food. Animals and people then absorb
Carbon 14 by eating plants.
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12. Examination
Plant absorb C14
Plants absorb Carbon 14 through the process of photosynthesis,
converting light energy from the sun into food. Animals and peo-
ple then absorb Carbon 14 by eating plants.
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13. Examination
Magnesium Dating
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14. Examination
Carbon
14
When plants and animals decay
When plants and animals decay, any radioactive Carbon 14 that
is present sheds protons and neutrons. Over time, the Carbon
14 turns back into its stable daughter product, Nitrogen 14.
Magnetism DatingWhere is the North Pole? Well, obviously it’s
north, right? Well, that is true, today, but North has not always
been north and South has not always been south.
Deep inside the Earth, the Earth’s solid inner core rotates a bit
faster than the liquid outer core and this is thought to create the
Earth’s magnetism. But over time, about every 200,000 years,
the direction of this magnetism has flipped.
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15. Examination
C
14
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16. Examination
title
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17. Examination
Crystallized North
About 800,000 years ago, a compass would point South but still
say North! Minerals inside rocks point to wherever North is at the
time of their crystallization. Knowing the direction of magnetic
poles in certain time periods help determine a rock’s age.
Magnetic Time Scale
The time scale shows how the Earth’s magnetic field has changed
through time. The black bands show when the magnetic field was
normal and pointed north and the white bands indicate when it
was pointing south.
TodayHere, we can see our magnetic field as it is today. This
magnetic field is also responsible for protecting our planet from
the Sun’s harmful rays.
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18. Examination
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19. Examination
Ratio Mass Spectrometer
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20. Examination
The Ratio Mass Spectrometer
The Ratio Mass Spectrometer
We all know that atoms are so small they can’t even be seen with
a microscope. How is it possible then to actually count the ratio
of radioactive to stable atoms when all that makes them distinct
is a few protons or neutrons at best?
Ratio Mass Spectrometer
We use a fancy machine, called the isotope ratio mass spectrom-
eter (IR-MS). It uses ions to charge the sample and then sepa-
rate the different ions by measuring the mass to charge ratio of
the ions.
How Does It Work?It deflects atoms and molecules by mag-
netic fields — provided the atom or molcul is first turned into n
ion. Electrically charged particles are affected by magnetic field
although electrically neutral ones are not.
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21. Examination
Ratio Mass Spectrometer
Ratio Mass Spectrometer
We use a fancy machine, called the isotope ratio mass spectrom-
eter (IR-MS). It uses ions to charge the sample and then sepa-
rate the different ions by measuring the mass to charge ratio of
the ions.
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22. Examination
C
14
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23. Examination
Magnet
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24. Examination
Deflation
If something is moving and you subject it to sideways force, in-
stead of moving in straight line, it will move in curve — deflected
out of its original path by the sideways force.
The Less the Deflection, the Heavier the Particle
If you knew the particle’s speed and the size of the force, you
could calculate the ball’s mass if you knew the curved path it was
deflected through. Less deflection means a heavier ball. The
same principle applies to atomic-sized particles.
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25. Examination
Deflation
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26. Examination
Rock Formation
Figure:
.
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27. Examination
Rock Formation
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