We have all seen forensic scientists in TV shows, but how do they really work? What is the science behind their work? The course aims to explain the scientific principles and techniques behind the work of forensic scientists and will be illustrated with numerous case studies from Singapore and around the world. Some questions which we will attempt to address include: How did forensics come about? What is the role of forensics in police work? Can these methods be used in non-criminal areas? Blood. What is it? How can traces of blood be found and used in evidence? Is DNA chemistry really so powerful? What happens (biologically and chemically) if someone tries to poison me? What happens if I try to poison myself? How can we tell how long someone has been dead? What if they have been dead for a really long time? Can a little piece of a carpet fluff, or a single hair, convict someone? Was Emperor Napoleon murdered by the perfidious British, or killed by his wallpaper? *For Nanyang Technological University (NTU) students, please be noted that this course will no longer be eligible for credit transfer.
Week 3A - 5 Analysis of Skeletal Remains II
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Del curso dictado por Nanyang Technological University, Singapore
Introduction to Forensic Science
458 calificaciones
De la lección
Time of Death; Blood
Conoce a los instructores
Roderick BatesAssociate Professor
Division of Chemistry & Biological Chemistry | School of Physical & Mathematical Sciences
[MUSIC]
What if the human remains that have been found are really old?
What technique can we use for dating them?
The answer is a technique called carbon-14 dating.
Now, the element carbon is ubiquitous in living organisms,
it's the basis of all life on Earth.
Now, carbon comes in three forms.
By far, the most common is carbon-12,
this is the isotope carbon-12.
So in carbon-12, the nucleus of the atom is made up
of 6 protons and 6 neutrons, and it's a quite stable nucleus.
A very small amount of carbon is carbon-13,
and in carbon-13, the nucleus of the atom
is made up of six protons and seven neutrons,
and again, this is a perfectly stable atom.
But there's a small amount of carbon-14,
and in carbon-14, the nucleus is made up of six protons and eight neutrons
and this is an unstable nucleus.
That means carbon-14 is radioactive.
And if you have a sample of carbon which contains 12, 13, and 14,
gradually, slowly over time, that carbon-14 will decay and disappear.
Now, radioactive decay occurs at a very fixed and regular rate,
and for carbon-14, we know what the rate is and
we measure that the rate by the so-called half-life.
A half-life is the time it takes for half
the atoms in your sample to undergo radioactive decay.
For carbon-14, that is just over 5000 years,
so in 5000 years, half your carbon-14 will disappear.
In another 5000 years you'll be down to a quarter, and another 5000
years down to an eighth, and so on and so on and so on.
Now, how can we use this for dating?
The key assumption is, the amount of carbon dioxide
which is carbon-14 in the atmosphere is approximately constant.
The carbon-14 is produced by the
bombardment of the atmosphere by cosmic rays.
As long as the bombardment by cosmic rays is constant,
then the formation of carbon-14 is going to be constant.
Now where does the carbon-14 go?
It's present in the atmosphere in carbon dioxide.
So whenever a plant absorbs some carbon dioxide
from the air, it absorbs that amount of carbon-14,
and that carbon-14 will then make its way through the food
chain and end up in herbivorous animals, carnivorous
animals, us, anything made of wood, et cetera.
So we continually intake small amounts of carbon-14 from the
diet, and of course, we give out carbon-14 when we breathe,
which means it reaches a steady state.
So in a living organism, the amount of
carbon-14 is at a steady state during life,
but of course when you die, all this stops.
But the decay of carbon-14 through radioactive processes doesn't stop.
So after death, the amount of carbon-14 drops with
radioactive decay at a very nice and fixed mathematical rate.
So Willard Libby, who won the Nobel Prize
in 1960, developed this as a dating method
and he was able to calibrate it against historical objects,
so we can have a great deal of confidence in this method.
The limitation on carbon-14 is that the object you're studying must be
more than a few centuries old, more than, say, 400 years old.
And the reason for that is very simple,
because if something is only 100 or 200 years old, the amount
of carbon-14 that is decayed is too small for us to measure accurately.
So if something is 500 years old, then we can get a good measurement; if
something is 10,000 years old, we can also get a good measurement.
Future archaeologists are going to have a problem,
and that is because the assumption of the carbon-14
in the atmosphere being constant has now broken down,
and this is due to testing of atomic bombs
in the atmosphere back in the 50s and the 60s.
Those atomic bomb explosions produced all sorts of isotopes including carbon-14.
And you can see on the graph here that prior to atom bomb
testing, the carbon-14 level was nice and steady, and then it jumps up
to a big spike because of atom bomb testing, and is slowly dropping
away, but it's going to take some time for it to get back to normal.
What's this got to do with forensic science?
We're talking about things here that have been dead for centuries and centuries.
Well, let's look at the story of Peter Reyn-Bardt.
It was suspected that Peter Reyn-Bardt murdered his wife Malika back in 1960,
but there was no evidence.
More to the point, there was no body, her body was never
found.
It was suspected that Reyn-Bardt had buried
her body in this place called Lindow Moss,
and this is a peat bog on the edge of Manchester.
Now, peat is formed when the vegetation of the bog is compressed.
And traditionally in Northern Europe, peat has
been used for centuries, particularly for fuel.
If the peat is dug out, it's cut up and
dug out and dried, it can then be burned as fuel.
So, in 1983, a man was doing just that. He
was peat cutting when he found a skull fragment. An examination
of the skull fragment showed it still had tissue attached, even
brain tissue, which of course indicates it must be quite recent.
So this was handed to the police, the police went to Reyn-Bardt,
confronted him with the fact that they found this fragment, Reyn-Bardt
confessed and he was convicted of murder and sent to prison.
Then someone had the idea of sending
that fragment to Oxford University for carbon-14 dating,
and when the results came back, it must have been quite a surprise
to Peter Reyn-Bardt because it turned out to be nearly 2,000 years old.
It wasn't from his wife after all.
But what is surprising is that it's 2,000 years old, but it still contains tissue.
How can tissue survive that period of time?
And the answer comes in the very unusual chemistry of the peat bog.
So on the left there is Lindow Moss. It's a peat bog, and as
I said, peat is formed by the compression of this vegetable matter in the swamp,
and the vegetable matter, as it breaks down, releases chemicals into the water.
Most particularly, it releases tannins, and this is why
the water on peat bogs is often a brown colour.
It's the same chemicals that make tea brown,
and in fact they taste about the same too.
So the peat bogs are acidic, and
also these tannins have antibacterial properties, and
that means that the microorganisms which are
responsible for the tissue breakdown can't grow.
Their growth is inhibited by these natural antibiotics, the tannins.
Now, it's not true for all peat bogs.
On the left there you have Lindow Moss where
that skull fragment was found, on the right is Dartmoor.
Dartmoor should be well known to all of us because quite a few of the Sherlock
Holmes stories are set on Dartmoor, most famously "The Hound of the Baskervilles".
The Dartmoor chemistry is quite different.
Dartmoor has 20,000 archaeological sites,
and that's one in the picture.
Many of those archaeological sites are graves.
That one is a grave;
the depression in the centre of that stone circle is where the body was buried.
And yet, there's been almost no human remains found on Dartmoor.
The chemistry there is a little bit different,
the human remains dissolved away.
Now, peat and peat bogs are not restricted to England, they're spread all
across Northern Europe, Northern Germany and especially Denmark.
And as people have been cutting the peat for fuel
and for other reasons, they've been finding bodies in the bog.
And these bodies, typically, are extremely well preserved
and they date back to about 2,000 years ago.
And they are from the Celts,
the Celts were the people living in this part of Europe
at that time, and they, it is believed, practiced human sacrifice.
And what they would do is they would ritually kill
the person involved and then drop their body in the bog.
What they didn't know is that body would be preserved for thousands of years.
So, here's one of them.
Here's Grauballe Man, he was found in Denmark.
And you can see remarkable preservation;
that may be his original hair colour,
it's not his original skin colour,
that is a result of the tannins.
And typically, what used to happen when bodies such as
Grauballe Man were found by the peat cutters, they looked
so well preserved that the peat cutters would assume this
was a murder case, and they would call the local police.
The local police would come and they would take a look, and then
they would call the University and a
professor specializing in this would come over.
And in fact, in Denmark, they have a museum dedicated to these people.
One bog person has been found in Lindow Moss, where Reyn-Bart is
believed to have buried the remains of his wife. This is Lindow Man,
and if you happen to be in London, you can
go to the British museum and take a look at him.
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