3 - 5 - Week 3A - 5 Analysis of Skeletal Remains II (11 37), kryminalistyka, introduction to forensic science
[ Pobierz całość w formacie PDF ]
[MUSIC]What if the human remains that have beenfound are really old?What technique can we use for dating them?The answer is a technique called carbon-14dating.Now, the element carbon is ubiquitous inliving 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 atomis made upof 6 protons and 6 neutrons, and it's aquite stable nucleus.A very small amount of carbon iscarbon-13,and in carbon-13, the nucleus of the atomis made up of six protons and sevenneutrons,and again, this is a perfectly stableatom.But there's a small amount of carbon-14,and in carbon-14, the nucleus is made up ofsix protons and eight neutronsand this is an unstable nucleus.That means carbon-14 is radioactive.And if you have a sample of carbon whichcontains 12, 13, and 14,gradually, slowly over time, that carbon-14will decay and disappear.Now, radioactive decay occurs at a veryfixed and regular rate,and for carbon-14, we know what the rate isandwe measure that the rate by the so-calledhalf-life.A half-life is the time it takes for halfthe atoms in your sample to undergoradioactive decay.For carbon-14, that is just over 5000years,so in 5000 years, half your carbon-14 willdisappear.In another 5000 years you'll be down to aquarter, and another 5000years down to an eighth, and so on and soon and so on.Now, how can we use this for dating?The key assumption is, the amount ofcarbon dioxidewhich is carbon-14 in the atmosphere isapproximately constant.The carbon-14 is produced by thebombardment of the atmosphere by cosmicrays.As long as the bombardment by cosmic raysis constant,then the formation of carbon-14 is goingto be constant.Now where does the carbon-14 go?It's present in the atmosphere in carbondioxide.So, whenever a plant absorbs some carbondioxidefrom the air, it absorbs that amount ofcarbon-14,and that carbon-14 will then make its waythrough the foodchain and end up in herbivorous animals,carnivorousanimals, us, anything made of wood, etcetera.So we continually intake small amounts ofcarbon-14 from thediet, and of course, we give outcarbon-14 when we breathe,which means it reaches a steady state.So in a living organism, the amount ofcarbon-14 is at a steady state duringlife,but of course when you die, all thisstops.But, the decay of carbon-14 throughradioactive processes doesn't stop.So after death, the amount of carbon-14drops withradioactive decay at a very nice and fixedmathematical rate.So Willard Libby, who won the Nobel Prizein 1960, developed this as a datingmethodand he was able to calibrate it againsthistorical objects,so we can have a great deal of confidencein this method.The limitation on carbon-14 is that theobject you're studying must bemore 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 200years old, the amountof carbon-14 that is decayed is too smallfor us to measure accurately.So if something is 500 years old, then wecan get a good measurement; ifsomething is 10,000 years old, we can alsoget a good measurement.Future archaeologists are going to have aproblem,and that is because the assumption of thecarbon-14in the atmosphere being constant has nowbroken down,and this is due to testing of atomic bombsin the atmosphere back in the 50s and the60s.Those atomic bomb explosions produced allsorts of isotopes including carbon-14.And you can see on the graph here thatprior to atom bombtesting, the carbon-14 level was nice andsteady, and then it jumps upto a big spike because of atom bombtesting, and is slowly droppingaway, but it's going to take some time forit to get back to normal.What's this got to do with forensicscience?We're talking about things here that havebeen dead for centuries and centuries.Well, let's look at the story of PeterReyn-Bardt.It was suspected that Peter Reyn-Bardtmurdered his wife Malika back in 1960,but there was no evidence.More to the point, there was no body, herbody was neverfound.It was suspected that Reyn-Bardt hadburiedher body in this place called Lindow Moss,and this is a peat bog on the edge ofManchester.Now, peat is formed when the vegetation ofthe bog is compressed.And traditionally in Northern Europe, peathasbeen used for centuries, particularly forfuel.If the peat is dug out, it's cut up anddug out and dried, it can then be burnedas fuel.So, in 1983, a man was doing just that. Hewas peat cutting when he found a skullfragment. An examinationof the skull fragment showed it still hadtissue attached, evenbrain tissue, which of course indicates itmust be quite recent.So this was handed to the police, thepolice went to Reyn-Bardt,confronted him with the fact that theyfound this fragment, Reyn-Bardtconfessed and he was convicted of murderand sent to prison.Then someone had the idea of sendingthat fragment to Oxford University forcarbon-14 dating,and when the results came back, it musthave been quite a surpriseto Peter Reyn-Bardt because it turned outto be nearly 2,000 years old.It wasn't from his wife after all.But what is surprising is that it's 2,000years old, but it still contains tissue.How can tissue survive that period oftime?And the answer comes in the very unusualchemistry of the peat bog.So on the left there is Lindow Moss. It's apeat bog, and asI said, peat is formed by the compressionof 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 whythe water on peat bogs is often a browncolour.It's the same chemicals that make teabrown,and in fact they taste about the same too.So the peat bogs are acidic, andalso these tannins have antibacterialproperties, andthat means that the microorganisms whichareresponsible for the tissue breakdown can'tgrow.Their growth is inhibited by these naturalantibiotics, the tannins.Now, it's not true for all peat bogs.On the left there you have Lindow Mosswherethat skull fragment was found, on theright is Dartmoor.Dartmoor should be well known to all ofus because quite a few of the SherlockHolmes stories are set on Dartmoor, mostfamously "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 aregraves.That one is a grave;the depression in the centre of that stonecircle is where the body was buried.And yet, there's been almost no humanremains found on Dartmoor.The chemistry there is a little bitdifferent,the human remains dissolved away.Now, peat and peat bogs are not restrictedto England, they're spread allacross Northern Europe, Northern Germanyand especially Denmark.And as people have been cutting the peatfor fueland for other reasons, they've beenfinding bodies in the bog.And these bodies, typically, are extremelywell preservedand they date back to about 2,000 yearsago.And they are from the Celts,the Celts were the people living in thispart of Europeat that time, and they, it is believed,practiced human sacrifice.And what they would do is they wouldritually killthe person involved and then drop theirbody in the bog.What they didn't know is that body wouldbe preserved for thousands of years.So, here's one of them.Here's Grauballe Man, he was found inDenmark.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 whenbodies such asGrauballe Man were found by the peatcutters, they lookedso well preserved that the peat cutterswould assume thiswas a murder case, and they would call thelocal police.The local police would come and they wouldtake a look, and thenthey would call the University and aprofessor specializing in this would comeover.And in fact, in Denmark, they have a museumdedicated to these people.One bog person has been found in LindowMoss, where Reyn-Bart isbelieved to have buried the remains of hiswife. This is Lindow Man,and if you happen to be in London, you cango to the British museum and take a lookat him.[BLANK_AUDIO] [ Pobierz całość w formacie PDF ]
zanotowane.pl doc.pisz.pl pdf.pisz.pl charloteee.keep.pl
[MUSIC]What if the human remains that have beenfound are really old?What technique can we use for dating them?The answer is a technique called carbon-14dating.Now, the element carbon is ubiquitous inliving 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 atomis made upof 6 protons and 6 neutrons, and it's aquite stable nucleus.A very small amount of carbon iscarbon-13,and in carbon-13, the nucleus of the atomis made up of six protons and sevenneutrons,and again, this is a perfectly stableatom.But there's a small amount of carbon-14,and in carbon-14, the nucleus is made up ofsix protons and eight neutronsand this is an unstable nucleus.That means carbon-14 is radioactive.And if you have a sample of carbon whichcontains 12, 13, and 14,gradually, slowly over time, that carbon-14will decay and disappear.Now, radioactive decay occurs at a veryfixed and regular rate,and for carbon-14, we know what the rate isandwe measure that the rate by the so-calledhalf-life.A half-life is the time it takes for halfthe atoms in your sample to undergoradioactive decay.For carbon-14, that is just over 5000years,so in 5000 years, half your carbon-14 willdisappear.In another 5000 years you'll be down to aquarter, and another 5000years down to an eighth, and so on and soon and so on.Now, how can we use this for dating?The key assumption is, the amount ofcarbon dioxidewhich is carbon-14 in the atmosphere isapproximately constant.The carbon-14 is produced by thebombardment of the atmosphere by cosmicrays.As long as the bombardment by cosmic raysis constant,then the formation of carbon-14 is goingto be constant.Now where does the carbon-14 go?It's present in the atmosphere in carbondioxide.So, whenever a plant absorbs some carbondioxidefrom the air, it absorbs that amount ofcarbon-14,and that carbon-14 will then make its waythrough the foodchain and end up in herbivorous animals,carnivorousanimals, us, anything made of wood, etcetera.So we continually intake small amounts ofcarbon-14 from thediet, and of course, we give outcarbon-14 when we breathe,which means it reaches a steady state.So in a living organism, the amount ofcarbon-14 is at a steady state duringlife,but of course when you die, all thisstops.But, the decay of carbon-14 throughradioactive processes doesn't stop.So after death, the amount of carbon-14drops withradioactive decay at a very nice and fixedmathematical rate.So Willard Libby, who won the Nobel Prizein 1960, developed this as a datingmethodand he was able to calibrate it againsthistorical objects,so we can have a great deal of confidencein this method.The limitation on carbon-14 is that theobject you're studying must bemore 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 200years old, the amountof carbon-14 that is decayed is too smallfor us to measure accurately.So if something is 500 years old, then wecan get a good measurement; ifsomething is 10,000 years old, we can alsoget a good measurement.Future archaeologists are going to have aproblem,and that is because the assumption of thecarbon-14in the atmosphere being constant has nowbroken down,and this is due to testing of atomic bombsin the atmosphere back in the 50s and the60s.Those atomic bomb explosions produced allsorts of isotopes including carbon-14.And you can see on the graph here thatprior to atom bombtesting, the carbon-14 level was nice andsteady, and then it jumps upto a big spike because of atom bombtesting, and is slowly droppingaway, but it's going to take some time forit to get back to normal.What's this got to do with forensicscience?We're talking about things here that havebeen dead for centuries and centuries.Well, let's look at the story of PeterReyn-Bardt.It was suspected that Peter Reyn-Bardtmurdered his wife Malika back in 1960,but there was no evidence.More to the point, there was no body, herbody was neverfound.It was suspected that Reyn-Bardt hadburiedher body in this place called Lindow Moss,and this is a peat bog on the edge ofManchester.Now, peat is formed when the vegetation ofthe bog is compressed.And traditionally in Northern Europe, peathasbeen used for centuries, particularly forfuel.If the peat is dug out, it's cut up anddug out and dried, it can then be burnedas fuel.So, in 1983, a man was doing just that. Hewas peat cutting when he found a skullfragment. An examinationof the skull fragment showed it still hadtissue attached, evenbrain tissue, which of course indicates itmust be quite recent.So this was handed to the police, thepolice went to Reyn-Bardt,confronted him with the fact that theyfound this fragment, Reyn-Bardtconfessed and he was convicted of murderand sent to prison.Then someone had the idea of sendingthat fragment to Oxford University forcarbon-14 dating,and when the results came back, it musthave been quite a surpriseto Peter Reyn-Bardt because it turned outto be nearly 2,000 years old.It wasn't from his wife after all.But what is surprising is that it's 2,000years old, but it still contains tissue.How can tissue survive that period oftime?And the answer comes in the very unusualchemistry of the peat bog.So on the left there is Lindow Moss. It's apeat bog, and asI said, peat is formed by the compressionof 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 whythe water on peat bogs is often a browncolour.It's the same chemicals that make teabrown,and in fact they taste about the same too.So the peat bogs are acidic, andalso these tannins have antibacterialproperties, andthat means that the microorganisms whichareresponsible for the tissue breakdown can'tgrow.Their growth is inhibited by these naturalantibiotics, the tannins.Now, it's not true for all peat bogs.On the left there you have Lindow Mosswherethat skull fragment was found, on theright is Dartmoor.Dartmoor should be well known to all ofus because quite a few of the SherlockHolmes stories are set on Dartmoor, mostfamously "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 aregraves.That one is a grave;the depression in the centre of that stonecircle is where the body was buried.And yet, there's been almost no humanremains found on Dartmoor.The chemistry there is a little bitdifferent,the human remains dissolved away.Now, peat and peat bogs are not restrictedto England, they're spread allacross Northern Europe, Northern Germanyand especially Denmark.And as people have been cutting the peatfor fueland for other reasons, they've beenfinding bodies in the bog.And these bodies, typically, are extremelywell preservedand they date back to about 2,000 yearsago.And they are from the Celts,the Celts were the people living in thispart of Europeat that time, and they, it is believed,practiced human sacrifice.And what they would do is they wouldritually killthe person involved and then drop theirbody in the bog.What they didn't know is that body wouldbe preserved for thousands of years.So, here's one of them.Here's Grauballe Man, he was found inDenmark.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 whenbodies such asGrauballe Man were found by the peatcutters, they lookedso well preserved that the peat cutterswould assume thiswas a murder case, and they would call thelocal police.The local police would come and they wouldtake a look, and thenthey would call the University and aprofessor specializing in this would comeover.And in fact, in Denmark, they have a museumdedicated to these people.One bog person has been found in LindowMoss, where Reyn-Bart isbelieved to have buried the remains of hiswife. This is Lindow Man,and if you happen to be in London, you cango to the British museum and take a lookat him.[BLANK_AUDIO] [ Pobierz całość w formacie PDF ]