Chemistry
Carbon Dating
Carbon dating is a method used to determine the age of organic materials by measuring the decay of carbon-14, a radioactive isotope of carbon. This technique is based on the principle that living organisms absorb carbon-14 from the atmosphere and that the amount of carbon-14 in the remains of an organism can be used to estimate its age.
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11 Key excerpts on "Carbon Dating"
eBook - ePub- D.C. Creagh, D.A. Bradley(Authors)
- 2000(Publication Date)
- Elsevier Science(Publisher)
It is now fifty years since Willard Libby and his co-workers developed the radioCarbon Dating technique. In the intervening years it has become established as the premier method for dating prehistory in the Holocene and Late Pleistocene periods. In addition, there have been significant advances in routine analysis, methodology and instrumentation, while our understanding of the sources of error in archaeological dating has increased. In this chapter, we outline the basis of the method and tackle some of the significant developments. We then consider the basis for archaeological radioCarbon Dating and illustrate its use with some archaeological case studies.2 The method
The underlying principles of radioCarbon Dating are well known. Carbon is essential for life on Earth, it is the building block of plants and animals. There are three principal isotopes of carbon on Earth; 12 C (98.89% of the global carbon budget), 13 C (1.11%) and 14 C (0.00000000010%). Each are identical chemically, but 14 C is unstable, or radioactive, because it contains extra neutrons in its nucleus. 14 C is created in the upper atmosphere through the action of cosmic rays, which impact the Earth, forming thermal neutrons. A secondary effect of this production is an impact upon the isotope 14 N that results in the emission of a proton and a particle of 14 C:Very soon after production, 14 C is oxidised and becomes 14 C-labelled CO2 (i.e. 14 CO2 ). This 14 CO2 enters plant and animal lifeways via photosynthesis and exchange with Surface Ocean water. 14 C is eventually incorporated within all living organisms throughout the biosphere (Figure 1 ).Figure 1 Pathways of 14 C in nature. Figures in brackets represent 12 C contents in million million tonnes within each of the selected reservoirs[6 ].The 14 C concentration of a plant or animal is maintained in equilibrium during its lifetime with the level of atmospheric 14 C. As soon as the organism dies, decaying 14 C is no longer replaced and a state of increasing disequilibrium begins. As 14
- Kliti Grice(Author)
- 2014(Publication Date)
- Royal Society of Chemistry(Publisher)
14 C content approximately like that of the atmosphere.RadioCarbon Dating, therefore, is essentially any method that measures the residual radioactivity from 14 C. In short, the radiocarbon age indicates when the organism was last alive and in equilibrium with the environment in which it lived, and also the 14 C production rate at the time when it was alive.9.3 Measurement
Probably all organic compounds can be used for radioCarbon Dating, as well as some inorganic materials like shell aragonite, coral, and speleothem carbonate. Inorganic carbon sources are valid where the carbonate, oxalate, or other mineral formation involves carbon capture where the 14 C was in equilibrium with the atmosphere. Materials such as water containing dissolved carbon or carbon compounds in suspension can also be dated. Since carbon is abundant in the biosphere and geosphere a certain amount of physical and chemical pretreatment in required to remove possible contaminants or to select particular fractions before they are analysed for their radiocarbon content.The main techniques used to measure 14 C from a sample are gas proportional counting, liquid scintillation counting, and accelerator mass spectrometry (AMS). Radiocarbon decays by emitting beta particles and conventional radioCarbon Dating is based on counting the number of beta particle emissions which have the energy signature of a beta emission from carbon. For gas proportional counting the carbon in the sample is converted to pure carbon dioxide gas, and the beta emissions in the gas are counted.Conventional counting is a radiometric dating technique that counts the beta particles emitted by a given sample. Beta particles are products of radiocarbon decay. In this method, the carbon sample is first converted to carbon dioxide gas before measurement in gas proportional counters takes place.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- The English Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter-3 Dating Techniques Archaeological science has particular value when it can provide absolute dates for archaeological strata and artifacts. Some of the most important dating techniques include: • radioCarbon Dating — especially for dating organic materials • dendrochronology — for dating trees; also very important for calibrating radiocarbon dates • thermoluminescence dating — for dating inorganic material (including ceramics) • optically stimulated luminescence (OSL)/optical dating — for absolutely dating and relatively profiling buried land-surfaces in vertical and horizontal stratigraphic sections, most often by measuring photons discharged from grains of quartz within sedimentary bodies (although this technique can also measure feldspars, complications caused by internally-induced dose-rates often favour the use of quartz-based analyzes in archaeological applications) • electron spin resonance, as used (for example) in dating teeth • potassium-argon dating — for dating (for example) fossilized hominid remains RadioCarbon Dating RadioCarbon Dating (sometimes simply known as Carbon Dating ) is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 ( 14 C) to estimate the age of carbonaceous materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years Before Present (BP), Present being defined as 1950 CE. Such raw ages can be calibrated to give calendar dates. One of the most frequent uses of radioCarbon Dating is to estimate the age of organic remains from archaeological sites. When plants fix atmospheric carbon dioxide (CO 2 ) into organic material during photosynthesis they incorporate a quantity of 14 C that approximately matches the level of this isotope in the atmosphere (a small difference occurs because of isotope fractionation, but this is corrected after laboratory analysis).
eBook - PDFThe Age of Everything
How Science Explores the Past
- Matthew Hedman(Author)
- 2008(Publication Date)
- University of Chicago Press(Publisher)
This research has certainly improved the reliability and accuracy of carbon-14 dating; and it has also had some unex-pected benefits for climatologists and astrophysicists. One by-product of the decades-long effort to refine carbon-14 dating is a detailed record of atmospheric carbon-14 levels over the last 15,000 years. This may not seem like much, but a 1–2% increase in the carbon-14 content of the atmosphere can be the faint echo of a major change in the ocean’s cur-rents or in the sun’s activity. Such changes therefore provide a unique win-dow into the complex, interconnected processes that shape the sun’s surface and the earth’s climate. For example, a shift in atmospheric carbon-14 levels 68 Chapter Five 13,000 years ago provides an important clue to the sequence of dramatic changes that unfolded at the end of the last Ice Age. s e c t i o n 5 . 1 : f r o m r a w t o c a l i b r a t e d d a t e s The standard procedure for extracting chronological information from carbon-14 can be divided into two fundamental tasks: estimate how much carbon-14 the object contained when it was part of a living creature, and determine how much carbon-14 remains in the material today. Since the current carbon-14 content of an object can be measured directly, carbon-14 dating almost always begins by obtaining the isotopic composition of a sample from the artifact. In principle, these data could be reported as a number of carbon-14 atoms in the sample, but in practice dating facilities normally compute a “raw” or “conven-tional” carbon-14 date for the sample. These dates are expressed as a number of years “BP,” which meant “Before Present” when the present was 1950.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 34,300 years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sediments, from which their ratios are measured. The scheme has a range of several hundred thousand years. ____________________ WORLD TECHNOLOGIES ____________________ RadioCarbon Dating method Ale's Stones at Kåseberga, around ten kilometres south east of Ystad, Sweden were dated at 600 CE using the carbon-14 method on organic material found at the site. RadioCarbon Dating , or Carbon Dating , is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 ( 14 C) to determine the age of carbonaceous materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years Before Present (BP), Present being defined as 1950 CE. Such raw ages can be calibrated to give calendar dates. One of the most frequent uses of radioCarbon Dating is to estimate the age of organic remains from archaeological sites. When plants fix atmospheric carbon dioxide (CO 2 ) into organic material during photosynthesis they incorporate a quantity of 14 C that approximately matches the level of this isotope in the atmosphere (a small difference occurs because of isotope fractionation, but this is corrected after laboratory analysis). After plants die or they are consumed by other organisms (for example, by humans or other animals) the 14 C fraction of this organic material declines at a fixed exponential rate due to the radioactive decay of 14 C. Comparing the remaining 14 C fraction of a sample to that expected from atmospheric 14 C allows the age of the sample to be estimated. The technique of radioCarbon Dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949.
eBook - PDFNuclear Physics 2
Radiochronometers and Radiopharmaceuticals
- Ibrahima Sakho(Author)
- 2024(Publication Date)
- Wiley-ISTE(Publisher)
Prerequisites Radioactive decay law; Fission of uranium-238; γ de-excitation; Uranium-235 and uranium-238 decay chain; Law of simple filiation with two bodies; Natural production of carbon-14; Law of accumulation of simple filiation with two bodies; Nuclear spallation reactions; Properties of β − decay; Electron–positron annihilation process. 3.1. Carbon-14 dating Absolute dating (or absolute radio-chronology) aims to quantitatively estimate the age of rock formations, fossil organisms, climatic events, etc. This method is based on the principle of radioactive decay [CHA 21]. 3.1.1. A brief history of radiocarbon-14 dating We give a brief overview of experimental research into the carbon-14 dating method according to Guibert [GUI 18]. Radiochronometer Applications in Dating 65 RadioCarbon Dating is undoubtedly the most popular method in archaeology, and the one that has attracted the most attention worldwide since the 1950s [LIB 49] and Libby’s Nobel Prize in Chemistry in 1960. Everyone is familiar with the principle of the method, to which we will confine ourselves here. It is based on the formation of carbon-14 from nuclear reactions between cosmic rays and nitrogen molecules. The atoms thus formed are immediately incorporated into CO 2 molecules through chemical interaction with ozone. The last 40 years have been marked by several highlights in terms of developments in instrumentation, advances in accuracy and the diversity of datable samples. Technological advances have clearly enabled radiocarbon to develop to the extent we have seen in recent decades. This was due in part to the development of tandem accelerators in the late 1970s, following Muller’s article [MUL 77], which is considered to be the seminal work in the field of direct counting of atoms, rather than beta radioactive decays. The Accelerator Mass Spectrometer (AMS) made it possible to analyze very small quantities of carbon, down to a few milligrams.
eBook - PDFRadiocarbon Dating
An Archaeological Perspective
- R Taylor(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
CHAPTER 1 ELEMENTS OF THE RADIOCARBON METHOD 1.1 BASIC PRINCIPLES Carbon-containing compounds are widely distributed in many forms throughout the earth's diverse environments. These materials are cycled through the various carbon reservoirs on different time scales primarily by solar energy. This process includes the operation of two major inter-acting systems: (i) a photosynthetic cycle involving the fixation of at-mospheric carbon dioxide in plant materials, an incorporation of a small portion of this in animal tissue, and subsequent decomposition and (ii) the cycling in the oceans, atmosphere, and major lake systems of various chemical species (carbon dioxide-carbonate-bicarbonate). Various geo-logic processes including the deposition of carbonates in sediments and volcanic activity are also involved in the operation of the carbon cycle (Craig, 1953, 1957). Carbon has three naturally occurring isotopes, two of which are stable ( , 2 C, , 3 C) and one ( , 4 C) which is unstable or radioactive. 1 The natural 1 Over the years, various symbols ( , 4 C, C 1 4 , C-14, Carbon-14) have been used to designate radiocarbon. The current international convention is to use , 4 C as the standard abbreviation. 1 2 1. Elements of the Radiocarbon Method C A t , / 2 = c a . 5700 YEARS Figure 1.1 Basis of radiocarbon method: production, distribution and decay of l 4 C. [After Taylor (1985b).] radioactive isotope of carbon, or radiocarbon, decays with a half-life of about 5700 years. The basis of the 1 4 C dating method can be simply il-lustrated, as in Fig. 1.1, in terms of the production, distribution, and decay of I 4 C. The natural production of 1 4 C is a secondary effect of cosmic-ray bombardment in the upper atmosphere. Following production, it is oxi-dized to form , 4 C 0 2 . In this form, 1 4 C is distributed throughout the earth's atmosphere. Most of it is absorbed in the oceans, while a small percentage becomes part of the terrestrial biosphere.
eBook - PDF- Eileen M. Murphy, Nicki J. Whitehouse(Authors)
- 2007(Publication Date)
- Oxbow Books(Publisher)
RadioCarbon Dating: A Practical Overview Philip Barratt and Paula J. Reimer 1 Abstract Today it would be difficult to imagine archaeology without the availability of radioCarbon Dating. It has revolutionised our ability to provide absolute dates for objects and places, and allows us to compare their place in time with others from around the world. All of this has been made possible simply from measuring the properties of a simple and abundant element – carbon. This paper describes some of the stages in the development of the technique, why it works and how to use it. We especially highlight its role in Ireland, home to one of the world’s leading high-precision radiocarbon laboratories. We aim to provide the user of radioCarbon Dating with the necessary information to obtain optimum results and how best to convey these to a wider audience. Introduction Time is inherently important to us all; we relate to our past and anticipate and plan our futures using concepts of time. The physical world we inhabit changes at scales of minutes to millennia. The environmental archaeologist attempts to describe both the human and environmental record through time in a way that is sensible to the non-specialist. To do this, places and events of the human past need to be set in a chronological context along with the environments they inhabited. This is especially important when investigating the varying impact of people on a landscape that is changing on a range of temporal scales. Since its discovery in the 1940s, radioCarbon Dating has provided archaeologists with a tool that has revolutionised our understanding of the human past (Renfrew 1973). An increasing appreciation of the contribution of environmental and earth science disciplines to archaeology has, in part, been enabled through an improvement of chronological control provided by radioCarbon Dating.
eBook - PDF- Robert Kelly, David Thomas(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
This 14 C combines with oxygen to form carbon dioxide, and is then dispersed throughout the atmosphere by stratospheric winds. About 98 percent of all 14 C enters the oceans; plants take up much of the rest through photo-synthesis. From plants, radioactive carbon enters herbivores and carnivores—and you. All radioactive isotopes are unstable and break down, or “decay,” over time. Carbon-14 decays through beta emissions (the emission of a negatively charged electron) back into 14 N. The amount a living organism loses through decay is replaced from the environment; so, as long as an organism is alive, its 14 C remains in equilibrium with the atmosphere. Once dead, the organism no longer takes in 14 C, and the amount of 14 C in its body decreases through radioactive decay. But not very quickly. The half-life of 14 C is 5730 years; this means that half the amount of 14 C present in a sample will convert to 14 N every 5730 years. Imagine a piece of wood that contained 100 atoms of 14 C when it died (actually, it would con-tain plenty more, but let’s keep it simple). After 5730 years, 50 of these atoms (more or less) would have decayed into 14 N. After another 5730 years, half of those 50 14 C atoms (that is, 25 atoms, again, more or less) would have converted to 14 N, leaving only 25 14 C atoms. After another 5730 years (a total of 17,190 years), this amount would be halved again to about 12 14 C atoms. After a long time, very few 14 C atoms remain (Figure 6-9). Theoretically, radioCarbon Dating could extend far back in time, but current technology places a practical limit on it: RadioCarbon Dating is good only for organic remains that are younger than about 45,000 years. Radiocarbon dates can be run on anything organic, but some materials are better than others. Charcoal is perhaps the most common material dated. The wood species is identified, and root hairs or other obvious organic contaminants are removed.
- C. Marjorie Aelion, Patrick Höhener, Daniel Hunkeler, Ramon Aravena(Authors)
- 2009(Publication Date)
- CRC Press(Publisher)
Combined Radiocarbon and Stable Carbon Isotope Studies 353 naturally occurring radiocarbon and stable carbon isotopic signature can be mea-sured on the same molecule such as on the CO 2 itself, or a specific contaminant. Combining the CO 2 stable carbon, radiocarbon, and contaminant concentration measurements allow pieces of the biodegradation puzzle to be more precisely deci-phered because these measurements provide complementary information. 11.2 INTRODUCTION TO RADIOCARBON Since the discovery of radioactivity just over 100 years ago by Marie Sklodowska Curie, Pierre Curie, and Henri Becquerel who jointly were awarded the Nobel Prize for physics in 1903, radioisotopes have been used in several scientific fields as dis-parate as medicine and warfare. The initial use of cis -radioisotopes for dating the Earth was theorized soon after its discovery. As early as 1905, scientists including Rutherford, carried out age determinations on uranium-bearing minerals based on the formation of helium. Boltwood used the idea that lead was the end product of the decay of uranium to make age determinations on uranite using U/Pb ratios (Faure 1986). Today the identity of naturally occurring radioactive elements and their decay series are well known, including environmentally important radioisotopes, such as radiocarbon ( 14 C) and tritium ( 3 H). The radioCarbon Dating technique is commonly used and best known in geological and archeological dating, and has provided an accurate and precise method of estimating groundwater age and residence time (Hanshaw et al. 1967; Vogel 1970; Lloyd 1981) within systems of certain age limits. For analyses of great ages, corrections may be required and models may be used to estimate the levels of uncertainties. Naturally occurring radiocarbon is produced in the transitional region of the atmo-sphere between the stratosphere and the troposphere.
- C. Bronk Ramsey, Andrew J. Shortland(Authors)
- 2013(Publication Date)
- Oxbow Books(Publisher)
C HAPTER 4 Sample Selection for RadioCarbon Dating F. Brock and M. W. Dee Author’s Address : F. Brock and M. W. Dee , RLAHA, University of Oxford, Dyson Perrins Building, South Parks Road, Oxford OX1 3QY, UK Obtaining reliable age data using radioCarbon Dating requires a considered sampling strategy. It is first necessary to identify material suitable for dating, taking into account the availability of samples, the suitability of the sample material, and also how a sample is going to date the event in question. Before a sample undergoes chemical pre-treatment in the laboratory, it may have already been subject to processes that have reduced its suitability for dating. Such issues may relate to material use in antiquity, the integrity of the archaeological context, how carefully the object was excavated, or how it has subsequently been stored and preserved. In this chapter, we present a summary of key points to consider when choosing samples for radioCarbon Dating, and also discuss suitable sampling procedures. To demonstrate the issues discussed, we give examples of the sampling strategy applied to the Oxford project. Introduction to Sampling for RadioCarbon Dating A radiocarbon date estimates the time at which a material ceased exchanging carbon with the reservoir in which it lived and grew. It is generally accepted that the death of an organism represents the start of the ‘ticking’ of the radiocarbon clock, the beginning of the decay of the 14 C isotope with the absence of any further replenishment. This is an oversimplification, however, since it ignores the complexities of the growth of certain organisms, such as wood. A further difficulty is the way in which material interacts with the environment after deposition. Material in archaeological sites can be bioturbated, or mixed in other ways with residual or intrusive carbonaceous samples. Samples may become chemically contaminated with carbon of a different age too.
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