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The following are quotes added to my Unclassified Quotes database in June 2007. The date format is dd/mm/yy. See copyright conditions at end.
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2/06/2007 "The baboon marker In the late 1970s G.J. Todaro published a series of papers which, if accepted, would revolutionise common assumptions about human evolution as radically as they had been upset by the papers of Sarich and Wilson in the 1960s. Sarich and Wilson had suggested that the accepted wisdom was wrong about the timing of human emergence-it was far more recent than generally believed. After long debate and resistance their arguments were accepted as valid. Todaro proposed, even more startlingly, that the conventional wisdom was wrong about the place. His ideas were greeted with a professional silence that has persisted to this day. His 1980 paper was entitled 'Evidence using viral gene sequences suggesting an Asian origin of man' [Todaro, G.J., "Evidence using viral gene sequences suggesting an Asian origin of man," in Konigsson, L.K., ed., "Current Arguments on Early Man," Pergamon Press: Oxford, 1980, pp.252- 260] and I discussed his conclusions in the last chapter of The Scars of Evolution. To summarise it briefly: He presented strong evidence that at one period of prehistory the direct ancestors of Homo sapiens were not present on the mainland of Africa. An endogenous virus, spontaneously arising in baboons and not harmful to them, was so damaging when it crossed the species barrier that all primates native to Africa carry a retrovirus, which protected their ancestors from the baboon infection when it was at its most virulent. Homo, unlike the chimp and the gorilla, does not carry the retrovirus. That indicates that Homo's ancestors were elsewhere when the baboon plague first broke out. 'Elsewhere' means not on the continental mass of Africa at all. The evidence suggests that the virus was airborne. It affected the galagos; in the forest canopy as well as the gorillas on the forest floor and the monkeys in the trees and on the savannah. The Congo river was wide enough to prevent interbreeding between the chimpanzees on either side of it and lead to the species differentiation between the common chimpanzee and the bonobo. But it was not wide enough to prevent the spread of the baboon virus which affected primates throughout the whole continent. Microbiology cannot tell us specifically when this event occurred. Todaro himself hypothesised that it happened quite late, and that the human race must be descended from a strain that had emigrated to Asia prior to the baboon plague, and that their descendants moved back again when the danger was over. Although we cannot date the baboon plague precisely, we can date it relative to other evolutionary events. For instance, it must have happened subsequent to the ape/ hominid split. If it had happened in the days of the last common ancestor, then either apes and humans would both have the 'baboon marker' (the retrovirus), or both of them would lack it." (Morgan, E., "The Aquatic Ape Hypothesis," , Souvenir Press: London, Reprint, 2001, pp.168-170. Emphasis original) 1/06/2007 "The Case for Intelligent Design A good place to begin is with the acknowledgment by Richard Dawkins that `Biology is the study of complicated things that give the appearance of having been designed for a purpose.' More precisely, all living organisms are characterized by immense amounts of genetic information that enable them to function. Dawkins puts it vividly: `Physics books may be complicated, but ... the objects and phenomena that a physics book describes are simpler than a single cell in the body of its author. And the author consists of trillions of those cells, many of them different from each other, organized with intricate architecture and precision-engineering into a working machine capable of writing a book.... Each nucleus ... contains a digitally coded database larger, in information content, that all 30 volumes of the Encyclopedia Britannica put together. And this figure is for each cell, not all the cells of the body put together.' [Dawkins, R., "The Blind Watchmaker," W.W. Norton: New York NY, 1986, pp.2-317-18. Emphasis in original] In short, the very complex processes of the cell must be directed by some information-rich entity that can be likened to a computer program. As I explained in chapter two, the information that directs the life processes-like any other meaningful text-needs to be complex, aperiodic and specified. The first requirement means that a very long string of letters or symbols is required. The second means that the order of the letters is not directed by physical or chemical laws, which by their nature produce only simply repeating patterns (such as printing `ABC' over and over again until the printer runs out of paper). The third requirement means that not just any order will do but only the precise order required to produce the encyclopedia, or the computer operating program, or the array of cellular proteins coded for in the DNA nucleotides. Genuinely creative evolution thus requires a mechanism capable of creating immense amounts of complex specified aperiodic genetic information. Random mutation is not such a mechanism, nor is natural selection, nor is any physical or chemical law. Laws produce simple repetitive order, and chance produces meaningless disorder. When combined, law and chance work against each other to prevent the emergence of a meaningful sequence. In all human experience, only intelligent agency can write an encyclopedia or computer program, or produce complex specified aperiodic information in any form. Therefore, the information necessarily present in organisms points to the conclusion that they are products of intelligent design." (Johnson, P.E.*, "The Wedge of Truth: Splitting the Foundations of Naturalism," Intervarsity Press: Downers Grove IL, 2000, pp.126-127. Emphasis original) 1/06/2007 "That is why the classic `monkeys at a typewriter' illustration oversimplifies the problem. Even if a random choice of letters could produce a specified text in a finite period of time, the fixed arrangement of letters on the keyboard would cause some letters (for example `G' `H' `J' and `K') to appear together very frequently, producing recurrent nonsense sequences like `hjk:' In addition, crucial information (i.e., the English alphabet) is built into the situation by the keyboard. Give the monkey paper and pencil and he produces only meaningless squiggles instead of letters. Invention of the alphabet required human intelligence." (Johnson, P.E.*, "The Wedge of Truth: Splitting the Foundations of Naturalism," Intervarsity Press: Downers Grove IL, 2000, p.127) 1/06/2007 "The concept of intelligent design does not rule out `evolution' in the sense of variation or diversification. Many examples of variation within the type occur, and humans by selective breeding produce impressive varieties of dogs and roses. (Selective breeding is itself a form of intelligent design, however, because the breeders employ purposeful intelligence and protect the overspecialized breeds from the natural selection that would otherwise eliminate them.) These uncontroversial examples of what is commonly termed `microevolution' involve no increases in genetic information and hence are not creative in the important sense. Reference to intelligent causes is indispensable not to account for mere change but to account for the creation of new complex genetic information. One convenient way of expressing this distinction is to say that the standard examples of microevolution are all of horizontal evolution, while the grand creative process should be called vertical evolution. Whatever the terminology, the essential point is that something besides mere `change' is required to create new complex organs, and that something must be capable of a task equivalent to writing a computer operating program or an encyclopedia. Unless biologists can provide a testable mechanism capable of doing the job, then the correct scientific conclusion is that biological creation is an unsolved mystery. Calling the mystery `evolution' provides only the illusion of an explanation unless there is a specific theory available to explain how the required transformations are possible. Neo-Darwinism is specific enough, but it doesn't fit the facts, and its mechanism has no real creative power." (Johnson, P.E.*, "The Wedge of Truth: Splitting the Foundations of Naturalism," Intervarsity Press: Downers Grove IL, 2000, pp.127-128. Emphasis original) 1/06/2007 "A wise proverb warns that "it isn't what you don't know that gets you in trouble, it is what you do know that isn't so:" Often the first step toward true understanding is to eliminate false concepts that merely conceal our ignorance by, for example, encouraging the belief that cyclical variations in finch beaks illustrates how birds came into existence in the first place. Science should never fear honest intellectual tools such as precise use of terms, unbiased investigation of evidence and refusal to accept unjustified extrapolations. If use of those tools leads to the undermining of a cherished theory, then that is a gain and not a loss for the advance of knowledge-even if it leaves scientists bewildered for a time. If no true answer is available, it is not an advance in knowledge to embrace a false answer." (Johnson, P.E.*, "The Wedge of Truth: Splitting the Foundations of Naturalism," Intervarsity Press: Downers Grove IL, 2000, pp.128. Emphasis original) 1/06/2007 "Finally, intelligent design theorists need to explain why the vast majority of evolutionary scientists refuse to consider evidence of intelligent design in biology, scornfully dismissing the entire concept as `religion' rather than `science:' This is because they identify science with naturalism, meaning that only `natural' (i.e., material or physical) forces may play a role in the history of life.' Where the designer is itself some natural entity, such as a human being, evidence for design is welcome. Space aliens are also permissible entities, and so Carl Sagan's Search for Extra-Terrestrial Intelligence (SETI) radio telescopes scan the sky for signals, which they could identify as products of intelligence by precisely the same methods which intelligent design theory applies to biology. The difference is that scientific naturalists want to find evidence for extraterrestrial life, in part because they would count it as evidence that natural laws produce life wherever favorable conditions exist and hence as clinching the case for naturalism. They don't want to find evidence for what they think of as an `interfering' God, meaning a God who does not leave everything to law and chance. Hence they will refuse to see evidence of design that is staring them in the face until they are reassured that the designer is something whose existence they are willing to recognize." (Johnson, P.E.*, "The Wedge of Truth: Splitting the Foundations of Naturalism," Intervarsity Press: Downers Grove IL, 2000, p.129. Emphasis original) 4/06/2007 "The origin of life The first question on this subject should perhaps be `Did life originate at all or has it in some sense always existed?' This unfortunately is one of those great questions, like the origin of the universe, that we cannot handle yet. Looking at the problem from the point of view of terrestrial life we may ask four questions. 1. Did life arrive on the planet by migration from some other body? 2. Was life produced on earth by some `life force' operating outside the laws controlling matter as defined by physics? 3. Do the laws that control the matter of the universe contain factors, besides the known laws of physics, which dictated the necessity for life to begin (and presumably also to evolve)? 4. Can we show that life may have arisen by the operation of forces known to operate in the terrestrial physical world? Over all of these there also of course lies the question whether life originated once only and on the earth, or once, or more often, elsewhere. In the present state of knowledge none of these possibilities can be excluded (see Calvin 1969) [Calvin, M., "Chemical Evolution: Molecular Evolution Towards the Origin of Living Systems on the Earth and Elsewhere," Clarendon Press: Oxford, 1969]. It has been alleged that micro-organisms are found in meteorites arriving from space. The possibility that these are in fact the result of terrestrial contamination has not been excluded and some hold it impossible that organisms could survive within a meteorite. This question remains to be resolved. The answer to the problem of the origin of life on earth may still be that it came from outer space, but probably most scientists regard this as unlikely." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.367-368. Emphasis original) 4/06/2007 "Similarly it is not excluded that God or some vital force so manipulated the materials of the early earth that they acquired the property we have called information storage and that controlled systems thus began. Once they had begun, it is easier to see how they proceeded to evolve and there is nowadays little doubt that the processes of homeostasis have continued since then without further intervention. The laws of the physical world will adequately account for the behaviour of organisms, provided that their conduct is controlled by the pre-existing order in an information store. It is the origin of the latter that is in question, and it cannot at present be excluded that it was the result of the operation of an outside agency. The uniformitarian assumptions of science would of course be opposed to such an explanation, but this is not enough to disprove it. The fact that the operation of the agency would seem to be limited in time somehow suggests that some other solution is correct. It certainly alters the emotional appeal of a deity to consider him as intervening only to make the first DNA. Indeed, such an interventionist view may well be thought blasphemous by those who would wish to understand more of the Deity than is possible by thinking only of a being who was simply an initiator." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, p.368) 4/06/2007 "This brings us to the third possibility, perhaps the most elusive. Since physics has been revolutionized several times in the last few centuries it can hardly be held that we yet `know its laws'. But we do know something about the operation of some of them, at least within certain limits. The qualification is important because we are not yet able to apply even the laws that we do know to complex systems such as organisms. The question whether other laws that are yet beyond our ken are in operation has not therefore much meaning. The view that it is possible to understand the origin and subsequent course of life by the operation of what may be called well-tried physical laws is therefore the only one that can be fully submitted to rational examination. As we shall see, this does not by any means imply that we have sufficient knowledge to compel its complete acceptance. In these matters it is important that we should both humbly acknowledge our ignorance and firmly assert our knowledge. The latter is much greater today than even 10 years ago and this provides a further warning that any conclusions reached are provisional and are likely to be changed before long." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.368-369. Emphasis original) 4/06/2007 "The origin of organic molecules It is very widely supposed that life originated in the sea, whose composition in early stages of the earth's history is therefore of prime importance. Some, however, have argued that life may have originated on the land surface which `provides innumerable environmental niches, such as crevices in dust particles and rocks' which `may have provided ideal conditions for the abiogenic synthesis of organic compounds. Drying in such niches would permit high concentrations of chemicals to occur, and would thus favour chemical reactions when they were wet' (Hinton 1968). The fact that life can be reduced to a purely morphological state by drying (p. 287) certainly removes some difficulties to this view. But it seems more likely that only a fluid medium could provide the continuity necessary to reach the present level of metabolic sophistication in a reasonable time. `Equally only large moving bodies of water could meet the spatial requirement that materials of all kinds should be continuously available and brought together for interaction' (Needham in Hinton 1968). In any case biogenesis must have taken place in water and made use of materials dissolved in it from the atmosphere. Probably some concentrating mechanism for bringing the substances together must be assumed (p. 371)." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, p.369. Emphasis original) 4/06/2007 "The question of the origin of life is clearly closely related to that of the origin of organic materials. Until relatively recently it was generally held that all the more complex organic molecules were products of life itself. Deposits of hydrocarbons such as oil and coal, for example, which are known to be formed from plant decay, are still often held to be wholly so formed. There is, however, some evidence that such substances are quite widespread in the universe and are of abiogenic origin. The evidence is of two sorts. First, the analysis of meteorites shows that some may contain much more organic matter than can be explained by contamination. Secondly, numerous studies have now shown that a whole range of organic molecules can be produced from quite simple carbon- and nitrogen-containing compounds, given a suitable supply of energy, say, by electrical sparking or ultraviolet radiation. The question of the probable composition of the earth's early atmosphere is therefore crucial. Fortunately there is in the main agreement that there was no oxygen and that reducing conditions prevailed. This is fundamental, because in the presence of oxygen electrical discharges, for example, will produce combustion, whereas reducing conditions allow synthesis. In the early atmosphere there was probably methane, ammonia, water, carbon monoxide, and carbon dioxide. The first three, incidentally, make up the atmosphere of Jupiter." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, p.369-370) 4/06/2007 "Oxygen probably appeared only as a result of the action of organisms. The earliest photosynthesis may have served simply as an excretory process. Further developments then made it into the prime synthetic process that it is today. But in the meantime the oxygen produced revolutionized life. Some of it, converted to ozone, shielded the earth from ultraviolet radiation. This radiation may previously have been essential as a source of energy and then of mutation, but complex systems could develop only when their instructional systems were not disturbed by ultraviolet radiation. It is not clear whether it is anything but chance that the nucleotide molecules absorb very strongly in this region of the spectrum. The other equally important influence of oxygen was of course to allow organisms to obtain large concentrations of energy by respiration. ... But we must remember that these are only the late products of evolution. The earlier syntheses must have obtained their energy directly from outside sources or by some anaerobic process. We have thus some reason to believe that the early atmosphere of reducing gases later became changed, as a result of the influence of life itself." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.369-370) 4/06/2007 "The time-scale of these events is, however, very speculative. Oparin suggests that the ocean and primitive (presumably reducing) atmosphere were formed 3 x 109 years ago and that oxygen began to accumulate at about 2-1.8 x 109 years, giving the present atmosphere only at 3 x 109 years ago. These figures will doubtless eventually be made more precise. We still have almost no data from records in the rocks of the earliest stages of the origin of life. The earliest known organisms lived about 3 x 109 years ago (p. 406). But we can say much more about it than was possible even 20 years ago, because laboratory experiments have shown that quite complex organic molecules can be produced from the simple gases that are likely to have been present in the early atmosphere. Miller has shown that mixtures of methane, ammonia, hydrogen, and water vapour subjected to silent electric discharge produce a wide variety of amino-acids (Bernal 1967). Pavlovskaya and Pasynskii (1959) produced these from water, formaldehyde, and ammonium chloride under the influence of ultraviolet light. Other compounds that have been made by Oro and Kimball (1961 and 1962) include phosphocreatine, porphyrins, and purines and pyrimidines, bases that are similar to those found in nucleic acids. Oro has also synthesized the pentoses (ribose and desoxyribose). By electron bombardment a wide variety is obtained, including adenine and hydrogen cyanide, which is a possible agent for polymerization (Calvin 1969). Schramm (1965) has obtained high-molecular-weight peptides and polynucleotides. It is therefore probable that protein-like and nucleic acidlike polymers were formed under the conditions of the early earth. But as Schramm himself points out, they would have had a random arrangement of monomers in their chains. The problem is to discover how the specific sequences, with their adaptive properties, arose." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, p.370) 4/06/2007 "Another interesting feature of these artificial products is that they include both the right- and left-handed optically rotating isomers. It has long been recognized that one of the striking features of living chemistry has been the preponderance of one or other forms, never of both. Thus amino-acids are all of the l- rotatory form, as are the amino-acids in the earliest bacterial remains of 3000 million years ago. But sugars are all of the d-form. It is clear that this uniformity is an important, perhaps essential, feature, if large molecules are to be built, for example spirals such as DNA. Moreover, the various parts of the biosphere all `feed' upon each other, in a manner that would be impossible if different species had different symmetry. This perhaps provides evidence that life on this planet began only once - or at least that the descendants of all lines but one have failed to survive. But this still does not tell us how this particular selection of isomers, one of the most fundamental of all the selections, was accomplished. One suggestion is that these early molecules were formed not in a random environment but in one already occupied by asymmetric quartz and other crystals. Bernal suggested many years ago that some form of absorption on to clays or other minerals would provide for the concentration of the early organic products, preventing reverse reactions." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, p.370) 4/06/2007 "In any case there is little doubt that given the composition of the early atmosphere and the availability of energy from ultraviolet sources, radioactivity, or electrical sparking, many of the simpler molecules necessary for life would have been produced. We have some direct evidence from finding such molecules in extraterrestrial bodies that this did actually occur. Thus Calvin and Vaughn (1960) found a substance like cytosine in a meteorite. This raises the further controversial question of the possible presence of bacteria and other forms of life on meteorites. The compounds found in carbonaceous meteorites are similar to those formed by synthetic processes from ammonia and other gases as described above. This suggests that such early stages of biopoiesis were not confined to the earth. Indeed, there is reason on statistical grounds to think that the conditions necessary for life must occur not infrequently in planetary systems throughout the universe. There appears, however, to be no other suitable planet in our own solar system. The difficulty of establishing `communication' with inhabitants of other solar systems is obviously enormous because of the times involved for signalling, but attempts are being made." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.371-372) 4/06/2007 "The origin of a self-maintaining system The presence on the early earth of types of molecules essential for life, in some form of fundamental broth, is thus not difficult to accept. A much greater problem is to understand how, even given these substances, the specific giant molecules such as information-carrying nucleotides and enzymatic proteins were formed. It is still more difficult to imagine how their actions became so adjusted as to produce self-maintaining and self-replicating systems. Haldane (1965) focused the problem by considering what might have been the probability of formation of the simplest self-replicating system. He considered four stages. 1. A probiotic soup of amino-acids, ribose, four purine and pyrimidine bases, and a source of high-energy phosphate. 2. Formation of nucleotides, probably at first RNA. 3. Combination of amino-acids with ATP. 4. Coupling of these to make a peptide. Haldane therefore suggested that the first organism included only one enzyme, a non-specific phosphokinase, able to organize the various energy transfers needed for such a sequence of changes to the materials of the probiotic soup. This one protein would be specified by one `gene' of RNA. Haldane noted that ribonuclease is the smallest known enzyme, containing 124 amino-acid residues ... This would require 540 bits of information to be specified (assuming equal base-frequencies) and it could certainly not appear spontaneously like the compounds already considered in the experiments of Miller and others. Haldane therefore considered a simpler protoenzyme requiring, say, 100 bits of information. But this is still one of 1.3 x 1030 chances. That is to say, if one `trial' were made each minute for 108 years there would have to be 1017 simultaneous trials. The earth simply is not big enough to house them! By reducing the number to 60 bits and using only 15 amino-acids the probability becomes perhaps just conceivable, but even so, would such a molecule be 'adequate'? We have not really faced the question of how it would control itself. [Haldane, J.B.S., "Data Needed for a Blueprint of the First Organism," in Fox, S.W., ed., "The Origins of Prebiological Systems and of Their Molecular Matrices," Proceedings of a Conference Conducted at Wakulla Springs, Florida, Oct. 2730, 1963, Academic Press: New York NY, 1965, pp.11-15] In his last discussion of the subject, shortly before his death, Haldane seemed not to be able to see a solution to this problem. It is indeed most formidable and must be attacked if we are not to be simply lulled by the evidence of the synthesis of molecules of moderate complexity. Dixon and Webb (1958), in a similar discussion, calculate that even if the earth had been wholly made of amino- acids and these rearranged themselves at random ten times a second there would have been little chance of forming one molecule of the simple protein insulin. [Dixon, M. & Webb, E.C., "Enzymes," Longman: London, 1958]" (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.372-373. Emphasis original) 4/06/2007 "It may be, however, that we take rather too rigorous a view of the problem by considering enzymes as we know them today. The properties of an enzyme seem to depend largely on features of a small part of it, the active site... Much of the rest of the protein may be irrelevant forerformance of crude syntheses. There is some evidenre simpler because they did not need to be very effective to `compete' with what was there before (Bernal 1960). One kind of solution to this problem is that already mentioned by Bernal, namely in effect that the probabilities of certain configurations were increased by the crystal lattices in clays with which they were associated. This is an appealing argument, but it requires more particular suggestions so that the probabilities can be calculated. An extension of this view suggests that the clay particles were not simply sites where organic molecules could interact but were actually the first organisms. Crystals can be said to contain information in their defects, specifically in silicates by the substitution of silicon atoms by others, such as aluminium. Such crystals are very stable and might have an information content, by weight, half that of DNA. Moreover, in growth they replicate their defects. Conditions can be imagined in which certain patterns would be selected. In particular, any configuration that tended to keep the clay particle in a clay-synthesizing environment would survive. This suggests how the first `inorganic' organisms may have provided the templates for carbon-containing organisms, as it were a second origin of life. Organic materials may have made mixed two-dimensional crystals with the clays, by which the probability of growth of the latter was increased. The information in the silicate layers could be imposed upon the organic layers and so simple polymers, proteins, and nucleotides be produced. Such mixed organisms can be imagined to have evolved gradually into the carbon-containing ones that we know. This hypothesis cannot perhaps be taken very literally, but it shows how calculations that claim to demonstrate the improbability of the spontaneous origin of life omit known natural processes that may have been decisive." (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.373-374) 4/06/2007 "Another useful line of reasoning on this problem stems from the possibility that after a long period of nonbiological syntheses a very abundant supply of organic materials was available: Simple instruction- controlled systems could therefore readily be built up but would then proceed to deplete the raw materials. As these disappeared those systems with instructional molecules adequate to replace them by synthesis would continue (Horowicz in Bryson and Vogel 1965) [Bryson, V. & Vogel, H.J., "Evolving genes and Proteins: A Symposium Held at the Institute of Microbiology of Rutgers University, 1964," Academic Press: New York NY, 1965]. The genome would thus gradually have grown in complexity. This would explain the present situation in which many genes must work together to produce an enzyme. It is difficult to see how each separate mutation could have come to have value unless the final product was available throughout. This `Garden of Eden' hypothesis has considerable attraction, but it still leaves vague the question of the origin of the first instructional molecules, unless the non-biological syntheses had in effect already produced them, which begs the question" (Young, J.Z., "An Introduction to the Study of Man," Clarendon Press: Oxford UK, 1971, pp.374) 11/06/2007 "carbon dating (radiocarbon dating) A method of estimating the ages of archaeological specimens of biological origin. As a result of cosmic radiation a small number of atmospheric nitrogen nuclei are continuously being transformed by neutron bombardment into radioactive nuclei of carbon-14: 14/7N n -> 14/6C p Some of these radiocarbon atoms find their way into living trees and other plants in the form of carbon dioxide, as a result of photosynthesis. When the tree is cut down photosynthesis stops and the ratio of radiocarbon atoms to stable carbon atoms begins to fall as the radiocarbon decays. The ratio 14C/12C in the specimen can be measured and enables the time that has elapsed since the tree was cut down to be calculated. The method has been shown to give consistent results for specimens up to some 40 000 years old, though its accuracy depends upon assumptions concerning the past intensity of the cosmic radiation. The technique was developed by William F. Libby (1908-80) and his coworkers in 1946-47." (Daintith, J., ed., "Oxford Dictionary of Chemistry," , Oxford University Press: Oxford UK, Fourth edition, 2000, p.104. Emphasis original) 11/06/2007 "radiocarbon an unstable, or radioactive, ISOTOPE of carbon with atomic mass 14 that is produced in the atmosphere and assimilated into living plants and animals in equilibrium with the atmospheric 14C content. Radiocarbon is the basis for RADIOCARBON DATING, the method most frequently used by archaeologists. 14C has a HALF-LIFE of 5730 years; it was originally calculated by Willard F. LIBBY, to be 5568 years and this value is utilized in calculating radiocarbon ages. radiocarbon dating a RADIOMETRIC DATING technique for determining the age of late QUATERNARY carbon-bearing materials, including wood and plant remains, bone, PEAT and calcium carbonate shell. The method is based on the radioactive decay of the 14C ISOTOPE in the sample to nitrogen, with the release of ß particles that is initiated when an organism dies and ceases to exchange 14C with the atmosphere. After death the 14C content is a function of time and is determined by counting ß particles with either a proportional gas counter or a liquid scintillation counter for a period of time. The method yields reliable ages back to about 50 000 bp and under extreme conditions to about 75 000 bp. radiometric dating or radiometric assay dating using a method based on the decay of radioactive ISOTOPES and yielding absolute age estimations, usually reported with a standard error. These methods include RADIOCARBON DATING, URANIUM SERIES DATING arid POTASSIUM- ARGON DATING." (Bahn, P., ed., "Collins Dictionary of Archaeology," HarperCollins: Glasgow UK, Ninth printing, 1992, p.422. Emphasis original) 11/06/2007 "accelerator mass spectrometry (AMS) a RADIOCARBON-DATING method that utilizes an accelerator mass spectrometer to determine the actual numbers of 14C atoms present in a sample, rather than the relatively small numbers of 14C atoms that decay radioactively during the measurement time of the conventional ß-counting method. Both methods have about the same dating age limit of about 50 000 bp. The greatest advantage of the AMS method is the sample size requirement of only 1 mg of carbon, and in some cases, as little as 100 µg of carbon. A second advantage is that actual measurement time takes about an hour, whereas conventional ß-counting can take days. The cost of AMS analysis is a drawback and, if enough sample is available, the finest conventional counters can achieve a slightly greater precision. In addition to dating standard materials such as charcoal, bones and other organic residues of occupation, the AMS method allows dating of individual seeds, textiles and artifacts without totally destroying the sample." (Bahn, P., ed., "Collins Dictionary of Archaeology," HarperCollins: Glasgow UK, Ninth printing, 1992, p.4. Emphasis original) 11/06/2007 "radiocarbon dating A method used to determine the age of organic materials up to about 40 000-70 000 years old. It relies on the fact that the 14C isotope of carbon is unstable and decays, emitting beta rays, to 14N, with a half-life of about 5700 years. Plants incorporate 14CO2 into their tissues during photosynthesis but when they die the concentration of 14C starts to fall at a rate related to the half-life. By comparing a specimen of unknown age with a sample of zero age, the age of the specimen may be calculated by measuring the amount of 14C using a mass spectrometer. The method assumes that the 14C: 12C ratio in the atmosphere has always remained constant. Certain discrepancies between age determinations based on radiocarbon dating and dendrochronology show there have been systematic variations in this ratio." (Bailey, J., ed., "The Penguin Dictionary of Plant Sciences," , Penguin: London, New edition, 1999, pp.393-394. Emphasis original) 11/06/2007 "radiocarbon dating (14C dating) A dating method for organic material that is applicable to about the last 70 000 years. It relies on the assumed constancy over time of atmospheric 14C:12C ratios (now known not to be valid), and the known rate of decay of radioactive carbon, of which half is lost in a period (the `half-life') of every 5730 ± 30 years. (The earlier `Libby standard', 5568 years, is still widely used.) In principle, since plants and animals exchange carbon dioxide with the atmosphere constantly, the 14C content of their bodies when alive is a function of the radiocarbon content of the atmosphere. When an organism dies, this exchange ceases and the radiocarbon fixed in the organism decays at the known half-life rate. Comparison of residual 14C activity in fossil organic material with modern standards enables the age of the samples to be calculated. Since the method was first devised it has been realized that the atmospheric 14C content varies, as the cosmic-ray bombardment of the outer atmosphere that generates the 14C varies. Correction for these fluctuations is possible for about the last 8000 years by reference to the 14C contents of long tree-ring series, e.g. those for bristlecone pine ( Pinus longaeva)." (Allaby, A. & Allaby, M., eds, "Oxford Dictionary of Earth Sciences," , Oxford University Press: Oxford UK, Second edition, 1999, pp.448-449. Emphasis original) 11/06/2007 "carbon-14 or radiocarbon n. a radioactive isotope of carbon, 14C, having a mass number of 14 and a half-life of 5730 ± 40 years. It occurs m nature as the result of reaction between atmospheric nitrogen, 14N, and neutrons produced by cosmic-ray collisions. Carbon-14 is used in dating substances directly or indirectly associated with the carbon cycle, provided they are not over 50 000 years old. carbon-14 dating, see DATING METHODS. carbonaceous, adj. (of rock sediment or other or containing carbon, or resembling it in some aspect. ... The CARBON-14 (radiocarbon) method is often used to date materials and events that are relatively recent; it is particularly valuable for use on materials less than 50000 years old, as this time span is too brief for the more slowly disintegrating elements to produce measurable amounts of daughter products. The radiocarbon method has been widely used in dating archaeological finds, and provides the best dating for the Holocene and Pleistocene. The method is based on the assumption that the isotope ratio of carbon in the cells of living things is identical with that in air because of the balance between photosynthesis and respiration. Although several sources of error are introduced into this method, such as the inconstant supply of 14C, both in time and latitude, it has proved to be enormously useful." (Lapidus, D.F. & Winstanley, I., eds., "Collins Dictionary of Geology," , HarperCollins: London, Revised, 1990, pp.89, 150-151. Emphasis original) 11/06/2007 "radiometric dating Methods employed to measure the amount of an isotope produced by radioactive decay, or the amount of the radioisotope itself. By assuming that the proportion of the radioactive isotope to the stable isotope is the same now as when the sediment was laid down, and that no subsequent addition or dilution has occurred, the proportion of the radioactive isotope or its product remaining today is a function of the time that it has had to decay at its constant known rate (the half-life). Carbon-14 is the most commonly used radiometric dating technique in Quaternary palaeoecology, as it has a suitable decay rate (half-life = 5,568 years), which allows dating to be made back to c. 40,000 yr BP. Accelerator mass spectrometry (AMS) has provided further analytical improvements in the 14C method, since samples containing 1 mg of less of elemental carbon can be analysed. Previous methods have required nearly 1,000 times that amount. Dating of recent materials using 14C is difficult because of the relatively large errors in the measurements, and the large amounts of 14C-deficient carbon that have been introduced into the atmosphere through burning of fossil fuels since the industrial revolution." (Thain, M. & Hickman, M., "The Penguin Dictionary of Biology," , Penguin: London, Tenth Edition, 2000, pp.438-439. Emphasis original) 11/06/2007 "Carbon-14 (radiocarbon) is the most widely used method for dating samples less than 50,000 years old. All living things absorb carbon, including the isotope carbon-14, from the atmosphere or ocean, either directly or by eating plants. When a plant or animal is growing, the ratio of carbon-14 to other forms of carbon in its new growth reflects the source from which the carbon is absorbed. After the organism dies, the carbon-14 decays radioactively, and the proportion declines. By measuring the amount of carbon-14 in an organism's remains it is possible to estimate how long ago it was formed. However, this is only reliable if we know the original proportion of carbon-14. Evidence from tree rings has demonstrated that the quantity of carbon-14 in the atmosphere has not always been constant." (Luntz, S., "Recalibrating the carbon-14 clock," Australasian Science, July 2000) 13/06/2007 "Radiometric dating In atoms of a radioactive element the nuclei undergo spontaneous decay to a more stable form, with the emission of radiation and various energetic particles. The rate of radioactive decay is expressed by the half-life, that is, the time taken for half of the parent atoms to decay to the daughter atoms. Half-lives of radioactive isotopes vary from fractions of a second to thousands of millions of years. For example in carbon-14 (14C), which has a half-life of 5730 ± 40 years, half of the 14C atoms in a given sample will have decayed in 5730 years, half of the remainder in the next 5730 years, and so on; the level of radioactivity approaches closer and closer to zero but never completely disappears. Because radioactive decay involves only the nuclei of the atoms it is entirely independent of external factors such as temperature and pressure. ... The important assumption made is that the original proportions of these isotopes in the sample are known. ... Whenever possible radiometric dates are cross-checked by applying more than one dating method to the sample. ... Carbon-14 atoms are continuously produced in the earth's upper atmosphere by collision of neutrons (produced by cosmic rays) with nitrogen atoms. They are rapidly oxidised to carbon dioxide (14CO2), and probably become distributed throughout the atmosphere, oceans and all living organisms within a few years. The 14C content of living organisms is, with rare exceptions, in equilibrium with that of the atmosphere, but after death the 14C content of the bodies decreases steadily due to radioactive decay with a half-life of 5730 years. To determine the age of a sample containing carbon it is necessary to measure the proportion of the radioactive 14C to stable isotopes of carbon, and to know the proportion of these isotopes in living organisms. The method assumes that the 14C content of the atmosphere has remained constant for at least the past 50000 years. However, radiocarbon assays of samples of wood from the long-lived bristle-cone pine, dated absolutely by dendrochronology, show deviations of as much as several hundred years when the age calculated by the radiocarbon methods is compared with the dendrochronological age. This phenomenon probably reflects periods of increased 14C content in the atmosphere, resulting from a higher influx of cosmic rays. The more recent part of the radiocarbon time scale can thus be recalibrated by means of dendrochronology." (Friday, A. & Ingram, D.S., eds, "The Cambridge Encyclopedia of Life Sciences," Cambridge University Press: Cambridge UK, 1985, p.304. Emphasis original) 13/06/2007 "Radiocarbon Dating Among the radiometric dating methods ... the one based on 14C (also known as radiocarbon) is unique for two reasons. The first is that the half-life of 14C is short by comparison with the half- lives of 40K, 117 Rb, and the isotopes of thorium and uranium. The second reason is that the number of daughter atoms cannot be measured. Radiocarbon is continuously created in the atmosphere through bombardment of nitrogen-14 (14N) by neutrons created by cosmic radiation ... . 14C, with a half-life of 5730 years, decays back to 14N by ß decay. The 14C mixes with 12C and 13C and diffuses rapidly through the atmosphere, hydrosphere, and biosphere. Because the rates of mixing and exchange are rapid compared with the half-life, the proportion of 14C is nearly constant throughout the atmosphere. As long as the production rate remains constant, the radioactivity of natural carbon remains constant because the rate of production balances the rate of decay. While an organism is alive, it will continuously take in carbon from the atmosphere and so will contain the balanced proportion of 14C. However, at death the balance is upset, because replenishment by life processes such as feeding, breathing, and photosynthesis ceases. The 14C in dead tissues continuously decreases by radioactive decay. The analysis for the radiocarbon date of a sample involves only a determination of the radioactivity level of the 14C it contains. This is done by measuring the particles emitted as a result of radioactive decay. The daughter isotope, 14N, cannot be measured successfully because it leaks away and because of atmospheric contamination." (Skinner, B.J. & Porter, S.C., "The Dynamic Earth: An Introduction to Physical Geology," , Wiley: New York NY, Third edition, 1995, pp.181,183. Emphasis original) 13/06/2007 "Because of its application to organisms (by dating fossil wood, charcoal, peat, bone, and shell material) and its short half-life, radiocarbon has proved to be enormously valuable in establishing dates for prehistoric human remains and for recently extinct animals. In this way it is of extreme importance in archaeology. It is also of great value in dating the most recent part of geologic history, particularly the latest glacial age. For example, the dates of many samples of wood taken from trees overrun by the advance of the latest great ice sheet and buried in the rock debris thus deposited show that the ice reached its greatest extent in the Ohio-Indiana-Illinois region about 18,000 to 21,000 years ago. It is even possible to date young ice, such as that in the Greenland Ice Sheet, directly. As the ice forms, bubbles of air are trapped in it. The carbon dioxide in the air bubbles can be liberated in the laboratory and dated, providing an age for the time of ice formation." (Skinner, B.J. & Porter, S.C., "The Dynamic Earth: An Introduction to Physical Geology," , Wiley: New York NY, Third edition, 1995, p.183. Emphasis original) 13/06/2007 "Carbon 14 dating, or radiocarbon dating, is the best known of all radiometric techniques-but because the half-life of carbon 14 is only 5730 years, this technique can be used only on materials that are less than about 70,000 years old. Most of the materials dated by this method are of biological origin, and many of these consist of wood. Despite its limitations, radiocarbon dating is of great value for dating materials from the latter part of the Pleistocene Epoch-an interval so recent that most other radioactive materials found in its sediments have not decayed sufficiently for their products to be measured accurately. Fortunately, the useful range of carbon 14 extends back far enough to encompass the entire time interval during which modern humans have existed-as well as the interval during which glaciers most recently withdrew from North America and Europe at the close of the recent Ice Age (Pleistocene Epoch). Thus, radiocarbon dating plays a valuable role in the study of human culture, sometimes being used to date materials that are no more than a few hundred years old." (Stanley, S.M., "Earth and Life Through Time," , W.H. Freeman & Co: New York NY, Second edition, 1989, p.116. Emphasis original) 13/06/2007 "Carbon 14 is a rare isotope of carbon that forms in the upper atmosphere, about 16 kilometers (~10 miles) above the earth's surface, as a result of the bombardment of nitrogen by cosmic rays. Both carbon 14 and the stable isotope carbon 12 are assimilated by plants, which turn them into tissue. Once a plant dies, however, carbon is no longer incorporated in its tissues, and the carbon 14 that was present when the plant died decays back into nitrogen 14. Thus, the percentage of carbon 14 in the tissues of plants declines in relation to the percentage of carbon 12, and the ratio of the two can be used to determine when the tissue died. A basic assumption in radiometric dating is that the rate of carbon 14 production has been constant during the past 70,000 years and that the ratio of carbon 14 to carbon 12 in the atmosphere has also remained constant. Although no major errors have resulted from this assumption, some minor errors have been noted. As an example, wood used by the ancient Egyptians at times that are well documented in historical records have yielded radiometric dates that are slightly too early. Such errors, which exceed 10 percent for material 5000 years old, apparently result from minor changes in the rate of carbon 14 production in the upper atmosphere." (Stanley, S.M., "Earth and Life Through Time," , W.H. Freeman & Co: New York NY, Second edition, 1989, p.116) 13/06/2007 "Atoms of the same element that have differing numbers of neutrons in their nuclei are called isotopes. Carbon, for example, always has six protons but may have six, seven, or eight neutrons. Carbon is therefore said to possess three isotopes which are respectively termed carbon-12, carbon-13, and carbon-14, based on the total number of particles in their atomic nuclei (the mass number). ... In 1896, Henri Bequerel discovered that not all isotopes are stable. Instead, some are radioactive and spontaneously break down to more stable isotopes through the release of energy and particles. Through the loss or gain of protons, the breakdown of a radioactive parent isotope produces a stable daughter isotope of a new element. Carbon-12 and carbon-13, for example, are stable isotopes but carbon-14, the basis of radiocarbon dating, is radioactive and decays by the spontaneous breakdown of one neutron to a proton and an electron (which is ejected). The daughter; now with seven protons rather than six, is nitrogen, and the specific isotope, now with seven neutrons instead of eight, is nitrogen-14. This form of radioactive decay involving the ejection of an electron is called beta particle emission. Two other forms of decay involve either alpha particle emission (the ejection of two protons and two neutrons) or electron capture and the conversion of a proton in the nucleus to a neutron ... . In each case, the number of protons in the atomic nucleus (the atomic number) changes and so a different element is produced. (Murphy, B. & Nance, D., "Earth Science Today," Brooks/Cole-Wadsworth: Pacific Grove CA, 1998, p.72. Emphasis original) 13/06/2007 "Radiocarbon Dating Prior to 1950, archaeologists, anthropologists, and geologists could make only educated guesses as to the ages of plant and animal remains, artifacts, and ice-laid sediment deposits of the late Ice Age and the Holocene Epoch that has followed. Other radiometric methods we have described cannot be applied to such young organic compounds and sedimentary materials. About 1950, there came a great scientific breakthrough when a new radiometric method was developed by Willard F. Libby of the Institute for Nuclear Studies of the University of Chicago. His work won him a Nobel prize. Libby's method made use of a radioisotope of carbon, carbon-14, that originates in the earth's upper atmosphere. At levels above 16 km, atoms of ordinary nitrogen (nitrogen-14) are subject to bombardment by neutrons created by highly energetic cosmic particles (cosmic rays) penetrating the atmosphere from outer space. Upon being struck, an atom of nitrogen-14 absorbs the impacting neutron and emits a proton. The nitrogen atom is thus transformed into carbon-14, which quickly combines with oxygen to form carbon dioxide (C02) . Carbon-14 is radioactive and decays back to nitrogen-14 by emitting beta particles. The half-life of carbon-14 is 5730 ± 40 years. The rate of production of carbon-14 in the upper atmosphere is first assumed to be constant. If so, atmospheric carbon dioxide that is taken up by plants and animals will contain a fixed proportion of carbon- 14 relative to the total amount of ordinary carbon (carbon-12). From an initial point in time marked by the death of the organism, the proportion of carbon-14 in the organic structure declines steadily, following the exponential curve of decline. By making precision measurements of the extremely small amounts of carbon- 14 in a sample of organic matter, the age in years of that matter can be estimated to within a fairly small percentage of error. There are about one trillion (10^12) atoms of C-12 to one of C-14. The very short half-Life of carbon-14 makes it an excellent tool for age determinations in the last few tens of thousands of years. On the other hand, the uncertainty of measurement increases at such a rate that the present limit of usefulness is about -40,000 y." (Strahler, A.N., "Science and Earth History: The Evolution/Creation Controversy," , Prometheus Books: Amherst NY, 1999, Second edition, p.155. Emphasis original) 13/06/2007 "Dendrochronology and Carbon-14 Ages As the years passed, discrepancies began to appear in the radiocarbon dates when they were compared with dates arrived at by other means. An alternate method of dating makes use of tree rings exposed in a sample cut at right angles to the tree trunk. Each growth ring represents one calendar year, and the age of a tree is obtained by simply counting the rings. A given tree trunk shows distinctive sequences of wide and narrow rings that are controlled by variations in climate from year to year. Trees whose life spans overlapped in time can be correlated by matching the distinctive ring sequences. In this way, logs and timbers used in ancient dwellings can be dated accurately. The method of precise tree-ring dating is called dendrochronology, developed by an American astronomer, A. E. Douglass, and extended by a number of collaborators and successors. Another approach has been to count the growth rings of long-lived species of trees and compare the ring counts with carbon-14 dates of the same wood. One tree in particular, the bristlecone pine (Pinus aristata), has an extremely long life span, some specimens living to an age of just over 5000 years. The trunks of dead bristlecone pines could also be used for tree-ring analysis, and this made possible the extension of the total chronology to about 9000 years. ... By the early 1970s, the carbon-14 ages had been obtained for the same tree rings used to establish the dendrochronology to -7300 y. Assuming that the tree-ring count gave an absolute age, it was clear that the C-14 age was subject to an error that first decreased with time to zero, then increased to a small maximum, again decreased to zero, and then again increased to reach a large error. ... The tree-ring age (dendrochronological age) is subtracted from the C-14 age. Between 1700 and 1500 A.D. (-300 to -500 y.) the C-14 ages run 50 to 100 years too low, but with considerable irregularity in trend. By about 1300 A.D. (-700 y.) the two sets of ages agree. Then the C-14 ages gradually give ages too large by some 200 to 400 years. This trend then reverses and by about 400 B.C. (-2400 y.) the two ages are again in agreement. From this point on, the C-14 ages begin to develop an error in which they are too small. The error increases steadily to about -6000 y., when the discrepancy amounts to about 700 years. The trend then reverses, but here the information runs out. The smooth curve on the graph has been fitted to the observed data, but the deviations from the individual observations are small throughout much of the time-span, so that the reliability of the cycle shown is high. The C-14 ages are calculated from the observed ratio of C-14 to ordinary carbon, C-12. Therefore a plot of the C-14/C-12 ratio against time should give a similar but inverse curve, showing the same cycle. ... It extends farther back in time because it uses samples from-rings in trunks of dead trees. The curve shown is a sine wave fitted to the individual observations, which fluctuate with a short-period cycle that may be an effect of the sunspot cycle. The long period shown by the sine curve is on the order of 6,000 years from maximum to minimum (12,000 y. per full cycle). ... What might be the cause of the 12,000-year cycle of variation in ratio of carbon-14 to carbon-12? Variation in the dipole field strength of the earth's magnetic field seems like a good candidate for the cause of the cycle. We can reason that when the dipole field increases, the magnetosphere is strengthened and is more effective in shielding the upper atmosphere from cosmic rays, and, under those conditions, C-14 is produced at a lower rate. When the dipole field weakens, increased bombardment by cosmic rays leads to a higher rate of production of C-14. (Strahler, A.N., "Science and Earth History: The Evolution/Creation Controversy," , Prometheus Books: Amherst NY, 1999, Second edition, pp.155-156. Emphasis original) 13/06/2007 "Radiocarbon Dating Radiocarbon dating, developed by physicists J. R. Arnold and W. F. Libby in 1949, is the best known of all chronometric methods. Cosmic radiation produces neutrons that enter the earth's atmosphere and react with nitrogen to produce the carbon isotope carbon-14 (14C, or radiocarbon), which has eight rather than the usual six neutrons in its nucleus. With these additional neutrons, the nucleus is unstable and is subject to radioactive decay. Arnold and Libby calculated that it took 5568 years for half of the 14C in any sample to decay, the so-called half-life of 14C. (The half-life is now more accurately measured at 5730 years.) The 14C isotope is believed to behave just like ordinary carbon (12C) from a chemical standpoint. Together with 12C it enters into the carbon dioxide of the atmosphere. Because living vegetation builds up its own organic matter by photosynthesis and by using atmospheric carbon dioxide, the ratio of 14C to 12C in living vegetation and the animals that eat it is equal to that in the atmosphere. As soon as an organism dies, no further radiocarbon is incorporated into it. The radiocarbon present in the dead organism will continue to disintegrate, so that after 5,730 years half the original amount will be left; after about 11,400 years, a quarter; and so on. Thus, measuring the amount of 14C still present in plant and animal remains and emitting radiation enables us to determine the time that has elapsed since death. By calculating the difference between the amount of 14C originally present and that now present, and comparing the difference with the known rate of decay, we can compute the time elapsed in years. The amount of 14C in a fresh sample emits particles at a rate of about 15 particles per minute per gram of carbon. A sample with an emission rate of half that amount would be approximately 5730 years old, the time needed for one-half the original radioactive material to disintegrate (the half-life of 14C)." (Fagan, B.M., "Archaeology: A Brief Introduction," , HarperCollins: New York NY, Fourth edition, 1991, pp.67-68. Emphasis original) 13/06/2007 "Radiocarbon samples can be taken from many organic materials, about a handful of charcoal, burned bone, shell, hair, wood, or other organic substance is needed for analysis. This requisite means that few actual artifacts may be dated, because wood and other organic artifacts are rare. But charcoal from hearths is frequently used for dating. The samples themselves are collected with meticulous care from particular stratigraphic contexts so that an exact location, or a specific structure, is dated. The laboratory converts the sample to gas and pumps it into a proportional counter. The beta particle emissions are measured, usually for 24 hours. The results of the count are then converted to an age determination. When a 14C date comes from a laboratory, it bears a statistical plus or minus factor. For example, 3600 ± 200 years (200 years represents one standard deviation) means that chances are two out of three that the correct date is between the span of 3400 and 3800. If we double the deviation, chances are 19 out of 20 that the span 3200 to 4000 is correct. Radiocarbon dates should be recognized for what they are-statistical approximations." (Fagan, B.M., "Archaeology: A Brief Introduction," , HarperCollins: New York NY, Fourth edition, 1991, p.68) 13/06/2007 "The conventional radiocarbon method relies on measurements of a beta ray decay rate to date the sample. A new approach uses accelerator mass spectrometry, which allows radiocarbon dating to be carried out by direct counting of 14C atoms rather than by counting radioactive disintegrations. This has the advantage that one can date even tiny samples, especially ones dating to between 10,000 and 30,000 years ago. The samples required are so small that it is possible, for example, to date an individual tree ring. Accelerator dating is especially useful for dating the amino acids from bone collagen, but one can date almost any material, even tiny wood fragments preserved in the haft sockets of metal spearheads, for example. Another major advantage is the ability to date materials such as charcoal from an artifact associated with a hearth; very often tiny fragments of organic material still adhere to the actual object one wishes to date. This makes it possible, for example, to date an actual corn cob in a Southwestern cave, a much better way of dating early agriculture than by merely using the law of association to link a cob with a dated feature or isolated charcoal sample. At present about one-third of all radiocarbon dates are accelerator-generated dates, which often achieve high precision." (Fagan, B.M., "Archaeology: A Brief Introduction," , HarperCollins: New York NY, Fourth edition, 1991, p.68) 13/06/2007 "The practical limits of radiocarbon dating with beta decay approaches are between 40,000 and 60,000 years. Researchers have tried detecting 14C atoms directly with a particle accelerator, a technique that would extend the limits of radiocarbon dating to as much as 100,000 years, although at present its limits, mainly because of contamination carried into soil by roots, are around 70,000 years." (Fagan, B.M., "Archaeology: A Brief Introduction," , HarperCollins: New York NY, Fourth edition, 1991, p.69) 13/06/2007 "When J. R. Arnold and W. F. Libby first developed radiocarbon dating in the late 1940s, they compared their 14C readings with dates from objects of known age, such as ancient Egyptian boats. These tests enabled them to claim that radiocarbon dates were accurate enough for archaeologists' purposes. But about 25 years later, just when archaeologists thought they at last had an accurate and reliable means for dating the past, some radiocarbon dates for dated tree rings of long-lived California bristlecone pines were published. They turned out to be consistently younger-for trees dating to before 1200 B.C. It turned out that Libby had incorrectly assumed that the concentration of radiocarbon in the atmosphere has remained constant through time, so that prehistoric samples, when they were alive, would contain the same amount of radiocarbon as living things today. But, in fact, changes in the strength of the earth's magnetic field and alternations in solar activity have considerably varied the concentration of radiocarbon in the atmosphere and in living things. Fortunately, however, it is possible to correct 14C dates back to about 4500 B.C. by calibrating them with tree-ring chronologies, for dendrochronology provides absolutely precise dates. ... Calibration of dates earlier than 4500 B.C. is impossible because three-ring chronologies are lacking, but extreme accuracy is less important for earlier periods anyway because time scales are less precise." (Fagan, B.M., "Archaeology: A Brief Introduction," , HarperCollins: New York NY, Fourth edition, 1991, p.69) 13/06/2007 "Despite its chronological and technical limitations, radiocarbon dating is of enormous significance. 14C samples have dated some African hunter-gatherers to more than 50,000 years ago and Paleo-Indian bison kills on the Great Plains to more than 11,000 years ago and they have provided chronologies for the origins of agriculture and civilization in the New World and the Old. Radiocarbon dates provide a means for developing a truly global chronology that can equate major events such as the origins of literate civilizations in such widely separated areas as China and Peru. The prehistory of the world from some 40,000 years ago up to historic times is dated almost entirely by the radiocarbon method. But most `finite' 14C dates earlier than 40,000 years ago (and a lot of younger ones) are, in fact, minimum dates. (Fagan, B.M., "Archaeology: A Brief Introduction," , HarperCollins: New York NY, Fourth edition, 1991, pp.69-70. Emphasis original) 13/06/2007 "WHERE DO WE COME FROM, we humans? Darwin called this `the great subject.' Even five-year-old children sometimes ask this question. That we ask such a question at all is a testament to human consciousness. I somehow doubt that the desert animals around here, including the two bats cruising overhead, spend much time contemplating their origin and destiny." (Calvin, W.H., "The River That Flows Uphill: A Journey from the Big Bang to the Big Brain," Macmillan: New York NY, 1986, p.2. Emphasis original) 13/06/2007 "Though it might be a coincidence, the human brain has been enlarging ever since some crazy fluctuations in the earth's climate started to occur about 2 to 3 million years ago. After many millions of years of a cooling and drying trend, the earth began to build up ice in its northern latitudes, covering as much as 30 percent of the land surface; this was an unusual development because the earth has been without polar ice caps for 99 percent of its history. About every 100,000 years, some of the accumulated ice melts off; then the drift back to ice resumes. This has been going on for several dozen cycles, each icy period pushing the more highly selected frontier population back into competition with tropical populations, each warm period providing an opportunity for the survivors on the frontiers to gradually enjoy a baby boom, then fading into another squeeze-and-expand cycle. During this peculiar 2 to 3 million-year period since the climate began to fluctuate, one species' brain underwent what was, by the standards of evolutionary biology, an extraordinarily rapid growth. For some reason-and the rapidity suggests that it was a compelling one-our brains more than tripled in size. That's 3.6 times larger than the brain that sufficed for the other apes during the same time period. Why? THAT'S PERHAPS THE KEY QUESTION, and it has emerged after millennia of humans sitting out at night under the stars, wondering what life is all about, from whence we came. " (Calvin, W.H., "The River That Flows Uphill: A Journey from the Big Bang to the Big Brain," Macmillan: New York NY, 1986, pp.3-4. Emphasis original) 13/06/2007 "We still don't know why those evolutionary changes occurred, but we're getting close to providing a detailed scenario that would seem to answer that crucial question about brain size-and a few related ones as well. Various experts now know enough to make some educated guesses about how humans happened, to spin some scenarios that fit the facts-if one can get them to talk about it. It usually takes a special setting to get scientists to speculate, off the record, about what isn't yet certain. A long river trip through the Grand Canyon is just the sort of setting in which it might happen. On the river and around the campfire, inundated by the evolutionary stories told by the Grand Canyon itself, will be a good place to discuss these tentative scientific versions of the old creation myths. Our new [anthropological] origin beliefs are in fact surrogate myths, that are themselves part science, part myth... . People clearly want to be free to choose their evolutionary origin stories. Bear this in mind as you read this and other accounts of human evolution. The archaeologist GLYNN LLYWELYN ISAAC (1937-1985)" (Calvin, W.H., "The River That Flows Uphill: A Journey from the Big Bang to the Big Brain," Macmillan: New York NY, 1986, pp.4-5. Emphasis original) 13/06/2007 "The existence of radiocarbon in nature was predicted before it was detected. Nevertheless, this prediction was sufficient for an American scientist called Willard Libby to perceive the basis of a dating method. The theoretical aspects were formulated in the mid 1940s when Libby was Professor of Chemistry at the University of Chicago. In 1946 he published a paper suggesting that radiocarbon might exist in living matter. One year later, a single-page paper appeared in the journal Science in which Ernest Anderson and Libby, together with collaborators in Pennsylvania, summarised the first detection of radiocarbon in material of biological origin [Anderson, E.C., Libby, W.F., et. al., "Radiocarbon From Cosmic Radiation," Science, Vol. 105, 30 May 1947, pp.576-577]. ... These first experiments required enrichment of the radiocarbon in the sample to make it easily detectable. By 1949, when Libby and Anderson (now joined in Chicago by James Arnold) published results of a world-wide assay of radiocarbon [Libby, W.F. , Anderson, E.C. & Arnold, J.R., "Age Determination by Radiocarbon Content: World-Wide Assay of Natural Radiocarbon," Science, Vol. 109, 4 March 1949, pp.227-228], enrichment was no longer necessary. The assay showed the contemporary level of radiocarbon in wood to be the same globally. The paper also contained the first two results of measurements on archaeological samples. The end of 1949 saw the publication of radiocarbon results on several samples of known age [Libby, W.F. & Arnold, J.R., "Age Determinations by Radiocarbon Content: Checks with Samples of Known Age," Science, Vol. 110, 23 December 1949, pp.678-680], and the publication of measurements of unknowns shortly followed. ... A remarkable vision had been turned into an invaluable tool, and for his work on radiocarbon Libby was awarded the Nobel prize for chemistry in 1960." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.9-10) 13/06/2007 "Carbon has three naturally occurring isotopes, that is, atoms of the same atomic number but different atomic weights. These are designated 12C, 13C and 14C in scientific notation, the letter C being the symbol for elemental carbon and the isotopes having atomic weights 12, 13 and 14 respectively. They do not occur equally: carbon consists of 99% of 12C, 1% of 13C, but only about one part. in a million million of modern carbon is 14C. Unlike 12C and 13C, 14C is unstable and therefore radioactive, though only weakly. Hence the name 'radiocarbon' for this isotope which, because of its scientific designation, is also called 'carbon fourteen'. ... The really unusual characteristic of 14C is that it is continually being formed. This occurs in the upper atmosphere (strictly the lower stratosphere and upper troposphere) by the interaction of neutrons produced by cosmic rays with nitrogen atoms. 14C is therefore one of a small number of cosmogenic nuclides. After formation, the 14C atoms rapidly combine with oxygen to form carbon dioxide which is chemically indistinguishable from carbon dioxide containing either of the other carbon isotopes. This carbon dioxide mixes throughout the atmosphere, dissolves in the oceans and, via the photosynthesis process and the food chain, enters all plant and animal life, known collectively as the biosphere. Under certain circumstances, in particular if the production rate is constant, there is a dynamic equilibrium between formation and decay, and therefore a constant 14C concentration in the atmosphere. Thus in principle there is a constant 14C level in all living organisms." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.10) 14/06/2007 "When a plant or animal dies, it ceases to participate in carbon exchange with the biosphere and no longer takes in 14C. Were 14C stable, its concentration would remain constant after death, but since it is not, the level falls at a rate that is determined by the law of radioactive decay. This law relates the number of atoms A left after time t to the initial number A0 at time zero by the equation describing exponential decay ... A term better known in relation to radioactive decay is the half-life, T½ ... half-lives are specific to a particular radioactive atom, and for 14C the best estimate of T½ is 5730 years. For historical reasons, however, the Libby half-life is conventionally used in the calculation of a radiocarbon result ... This 'half-life', being 5568 years, is 3% smaller than the true one ... The constant percentage decrease of 14C with time means that a small change in A results in a proportional change in the age t. Thus if the small change is a loss of 1%, t changes by 8033/200, an increase of about 80 radiocarbon years. ... The decay of a radioactive element follows the exponential decay law. The primary characteristic of exponential decay is that the percentage decrease in number of atoms per unit time is constant; hence after each half-life the number of atoms remaining is halved: if there are A0 atoms to begin with, then after one half-life there will be A0/2 atoms remaining; after two half-lives, A0/4 remain; after three, A0/8 and so on." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.10-11) 14/06/2007 "In principle, therefore, if the number of 14C atoms remaining and the initial, or equilibrium, number can be evaluated by experiment, then the time elapsed since death can be determined. For a bone excavated on an archaeological site this provides an estimate of the time since death of the animal, though it must not be assumed necessarily to date the age of the context (for example, the stratigraphic layer) in which the bone was found." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.12) 14/06/2007 "There are two methods of measurement of 14C. The so-called conventional method detects the activity of the sample, that is, the number of electrons emitted per unit time and weight of sample by the decay of 14C. The other method, accelerator mass spectrometry (AMS), is a very much more recent technique and directly detects the number, or a proportion of the number, of 14C atoms in the sample relative to 13C or 12C atoms. Both perform similar measurements on modern reference standards to establish the initial activity or concentration ratio of 14C." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.12) 14/06/2007 "Datable materials In general, the materials which can be dated by radiocarbon are those which once formed part of the biosphere and are therefore organic. For example, the most commonly preserved sample types occurring on British sites are bone, shell and charcoal, but on some sites or in other areas of the world a different suite of materials might remain. Preservation may be effected by charring, as with charcoal, so that dating of charcoal inclusions in wrought iron and of food residues on, and organic temper in, pottery is feasible. Equally, uncharred wood and other plant remains such as ropes, cloth, reeds and seeds may be well preserved in arid environments or if waterlogged. Certain situations will be detrimental to some types of material. Peat bogs, themselves datable, are acidic and will dissolve bone and shell. Ironically, though, they preserve muscle and other soft tissue otherwise only found in arid environments, such as existed in many of the pyramids. Soft-tissue remains are also datable by radiocarbon, as are many other materials such as antler, horn, tooth, ivory, hair, blood residues, wool, silk, leather, paper, parchment, insects and coral.... Sediments and soils may also be datable, although the sources of carbon within these are many and diverse and such material is rarely dated for archaeological purposes. In some circumstances it may even be possible to date materials that have not been part of the biosphere, if their formation involves incorporation of carbon with a 14C concentration that can be assumed to be in equilibrium with the atmosphere." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.12-13. Emphasis original) 14/06/2007 "Assumptions made in the simplified approach ... at this stage it is perhaps appropriate to review some of the assumptions made, explicitly or implicitly, in setting out the basis of the radiocarbon dating method: o The atmosphere has had the same 14C concentration in the past as now; this in turn assumes constant production, constant and rapid mixing, exchange and transfer rates, as well as constant sizes of reservoirs. o As a corollary of this, the biosphere has the same overall concentration as the atmosphere and therefore it is assumed that there is rapid mixing between these two reservoirs. o The same 14C concentration exists in all parts of the biosphere. o The death of a plant or animal is the point at which it ceases to exchange with the environment. o After ceasing exchange, the 14C concentration in a plant or animal is only affected by radioactive decay." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.14. Emphasis original) 14/06/2007 "None of these assumptions is strictly correct, beyond a rough first approximation. ... the geochemical and geophysical reasons for the breakdown of these assumptions ... can be summarised briefly as: o processes affecting the global concentration of 14C in the atmosphere o source or reservoir effects o alteration effects o contamination. Processes affecting the global concentration are largely production-rate variations, but under some circumstances the size of the atmospheric carbon reservoir has been changed. Source or reservoir effects result from the particular origin of the carbon taken up by an organism; this may have local effects dependent on the prevailing 14C to 12C balance. Alteration effects is the term used here to describe processes, other than radioactive decay, that change the concentration of 14C in an organism relative to that of the atmosphere or other parts of the biosphere. Strictly speaking, contamination could be considered under this heading, but this alters the apparent 14C concentration in the sample rather than the true one by introducing extraneous carbon material." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.14-15) 14/06/2007 "Age at death and time-width of samples The processes outlined above all potentially affect the 14C concentration in a sample submitted for dating ... The one remaining assumption is that time of death and cessation of exchange with the biosphere are contemporary events. If not, then the radiocarbon age of the organism at death is not zero. This is one type of 'age offset'. Others arise from reservoir effects and archaeological depositional processes ... For seeds and grasses, since only a single season of growth is involved, there is no inherent age offset. Bone does not cease to exchange with the biosphere until death, but there is a turnover time of about thirty years for human bone and an equivalently shorter period for animal bone. Hence there is no age offset, but there is a time-width for bone samples. The outstanding example of age at 'death', or more usually felling, is wood. It is well known that trees grow by the addition of rings, usually though not always annually. Once laid down, rings cease to exchange with the biosphere. Hence, if one considers a long-lived tree, say a three-hundred-year-old oak, the innermost heartwood will give a radiocarbon result 300 years older than the sapwood." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.15. Emphasis original) 14/06/2007 "Atmospheric 14C variations ... The assumption of constant 14C concentration was not taken lightly even from the very beginning. In 1949, James Arnold and Willard Libby published a 'curve of knowns' which was a test of the technique, and therefore of the assumption of constant concentration, using known-age samples ranging from about 900 to 4900 years old. Given the experimental conditions then achievable, there was good agreement, at least for this period, between the theoretical and measured 14C activities versus known age. During the 1950s, with advances in techniques for detecting 14C, discrepancies increasingly emerged between radiocarbon ages and historical ages for the Egyptian Old Kingdom. These discrepancies were far from insignificant, the radiocarbon results being several centuries too young. ... Tree rings provided the truly known-age material needed to test the accuracy of the new technique. Dendrochronology, the science of using tree rings for dating ..., had been developed by A.E. Douglass in America in the early part of the twentieth century for research on past climate. By the late 1950s several scientists, notably Hessel de Vries in the Netherlands, were radiocarbon dating rings from trees dated by dendrochronology, and confirming the radiocarbon discrepancy. It therefore became clear that radiocarbon results would need to be calibrated to convert them to calendar ages. Since there is no theoretical way of predicting the correction factor, empirical calibration curves were needed to link radiocarbon 'age' with known age. In the 1960s, a continuous tree-ring sequence stretching back some 5000 years was established by Wesley Ferguson, and the first calibration curve using this was published by Hans Suess. This curve was partly based on a remarkable tree, the bristlecone pine ... Suess's curve confirmed that there are indeed major discrepancies between radiocarbon age and calendar age. This was the first useful calibration curve in that it had a long temporal coverage, radiocarbon error terms in the order of 1%, and used truly known-age material (i.e. tree rings) for the calendar axis. It was also the first of many such curves, and their proliferation prior to 1985 has caused almost as many problems as have been solved. There are now internationally agreed calibration curves for the period back to 2500 BC ..." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.16-17. Emphasis original) 14/06/2007 "Two trends were apparent in Suess's curve. First there is a long-term trend that can be described approximately by a sine wave with a period of about 9000 years. The maximum deviation from true age is about 900 years too recent at the beginning of the fourth millennium BC. On the other hand, in the middle of the first millennium AD, radiocarbon produces ages too old by a century or so ... The second feature takes the form of 'wiggles'. These are superimposed on the main sine wave and are of short calendar duration (a few decades) but can have amplitudes on the radiocarbon axis of a century or so. ... Techniques with higher precision have now been developed and the general validity of these wiggles has been proven by various laboratories ... . So what causes the short-term variations seen in the calibration curve: the wiggles? These are known as the de Vries effect or Suess wiggles and are probably produced by variations in sunspot activity, records for which over the past few centuries show a cycle with period of about 200 years, superimposed on which is a more rapid 11-year cycle. High sunspot activity increases the weak magnetic field that exists between the planets, and at such times there is greater deflection of cosmic rays and hence 14C production decreases." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.17-19) 14/06/2007 "Variations in natural production rate Although the detailed geophysical causes of the trends may not be fully understood, the broad principles are known. The long-term variation correlates reasonably well with fluctuations in the earth's magnetic field strength (the geomagnetic moment). The geomagnetic moment affects 14C production because cosmic rays are charged particles and are therefore deflected by a magnetic field. If the magnetic moment is high, more cosmic rays are deflected away from the earth and production of 14C will fall; if low, the production rises. Whether the moment is high or low, the effect of the magnetic field varies with latitude, but rapid mixing in the atmosphere leads to a uniform 14C concentration globally. However, when the production rate changes, a new equilibrium concentration in the carbon cycle as a whole ... will only be established after a considerable time, owing to the finite, and in some cases long, mixing and exchange rates and the relative sizes of the different reservoirs. The likely timescale for achieving the new equilibrium level throughout is of the order of 10 000 years, although the atmosphere, biosphere and surface oceans require only a few tens of years to adjust to quasi-equilibrium. Quantification of the effect that these natural production rate changes have on 14C concentration is impossible primarily because the sizes of the fluctuations themselves are unknown." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.18. Emphasis original) 14/06/2007 "A more dramatic effect on atmospheric 14C content has come about through-nuclear-weapons testing ... . This is often referred to as the bomb effect. The neutrons produced in turn produce 14C by interaction with 14N, simulating the natural cosmogenic production, albeit in large bursts. Using this artificial injection of 14C to good purpose, radiocarbon scientists have been able to test theories about the mixing rates of 14C through the various carbon reservoirs. They have also shown that once laid down, a tree ring does not exchange 14C with other rings; this is fundamental to the use of dendrochronology to construct a radiocarbon calibration curve." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.19-20) 14/06/2007 "Alteration effects This term is used here to encompass the effects that may change the 14C concentration in a sample, making it either different from that in the atmosphere or different from the value expected purely on the basis of decay. The processes involved are fractionation, recrystallisation of shell carbonate and in situ production. They potentially alter the 14C concentration of the true sample material without any infiltration of extraneous carbon-containing material. Contamination is discussed separately below. Of the alteration effects listed, fractionation is the most important; it applies to every sample dated." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, p.20. Emphasis original) 14/06/2007 "Fractionation Although 12C, 13C and 14C are all carbon isotopes and chemically indistinguishable, in any biological pathway there will be a tendency for the lightest isotope 12C to be preferentially taken up. Similarly 13C will be taken up in preference to 14C. Growing plants and animals (that is, the parts still exchanging with the biosphere) are therefore expected to have a lower 14C level than the atmosphere. If the difference is significant, they will appear to be older than the atmosphere when dated and, since uptake also varies according to species, different parts of the biosphere will appear to have different radiocarbon ages. This differential uptake is referred to as fractionation, and needs to be taken into account if useful radiocarbon results are to emerge. Fortunately, the fact that carbon has three isotopes of which two are stable enables a correction for fractionation to be applied. The principle is to measure the ratio of 13C to 12C in the sample; any shifts in this concentration ratio, sample to sample, indicate fractionation has occurred. To evaluate what the equivalent shifts in 14C concentration ratio would be, it is assumed that the effect for 14C is double that for 13C, reflecting the mass difference relative to 12C. ... The ratio of 13C to 12C can be readily measured in a mass spectrometer with low resolution, since 13C is far more abundant than 14C (1% relative to one part in a million million of 14C in modern carbon). In accelerator mass spectrometry (AMS) dating ..., the ratio can be measured as part of the measurement process." (Bowman, S., "Radiocarbon Dating," Interpreting the Past, British Museum Publications: London, 1990, pp.20-21. Emphasis original) 16/06/2007 "The highlight of the exhibition is Lindow Man. I found him slightly disappointing in that only half of him survived, and he was rather squashed and leathery, and not as impressive as the German and Danish ones. But there are continuing problems over his date. Three sets of radiocarbon dates have been obtained. Firstly there are those obtained by conventional methods from the peat that surrounded him, which has been dated both by Harwell and by the British Museum at dates around 300 BC, and this is the date they are adopting for publication. The other dates are done by the two new super-duper small measurement laboratories at Harwell and at Oxford, which can date minute samples of the body itself, of the hair, bones and skin. However whereas all the Oxford samples come out consistently in the 1st century AD, all the Harwell samples come out consistently in the 5th century AD. At one time they thought that the difference might be due to the differing pre-treatment at the laboratories, so they swapped samples following pre-treatment, but the resulting measurements came out within the respective series for each laboratory. The archaeological world waits with bated breath to see how this problem is resolved." ("The British Museum Exhibition," Current Archaeology, Issue 101, Vol. IX, No. 6, August 1986, p.163) 16/06/2007 "Further attempts to resolve the dating of Lindow Man have been made with the Oxford Accelerator Mass Spectrometer facility using a total of eighteen samples. These form part of the latest date list issued by the Oxford Laboratory and published in Archaeometry (30, Part 1, 1988). One problem, that of a difference in date between Lindow Man and the surrounding peat, still seems to be with us although the gap is closing. Thus the peat gave dates ranging from 2220 ± 80 BP to 2670 ± 80 BP whereas his hair gave a date of 1920 ± 75 BP, a muscle dated to 2125 ± 80 BP and ten samples from the same vertebra with different methods of pretreatment gave dates in the range 1800 ± 80 BP to 2190 ± 100 BP." ("Oxford AMS Dates," Current Archaeology, Issue 110, Vol. X, No. 6, July 1988, p.107) 16/06/2007 "Certainty, it seems, is on the wane. The sun may rise tomorrow on schedule, and the sea sons may pass as they always have. But radioactive decay-the pacemaker of geologic time-can no longer be called precisely `clocklike.' Says geochemist Douglas Hammond of the University of Southern California (USC) in Los Angeles: Everybody always assumes radioactive decay to be totally independent of temperature, pressure, and chemical Some it seems there are some exceptions.' In the 15 September issue of Earth and Planetary Science Letters, geochemist Chih-An Huh of the Institute of Earth Sciences of the Academia Sinica in Taipei reports that the decay rate of beryllium-7 varies, depending on its chemical form. Creationists hoping to trim geologic history to biblical proportions will be disappointed-the variations seen so far are much too small, just a percent or so, to affect Earth's overall time scale. Still, the variability in beryllium decay will prompt those who want to trace out fine divisions in the earliest reaches of time to take a close look at their pacemakers. Theoreticians long ago anticipated some variability of radioactive decay. The decay of beryllium-7, for example, should depend on the density of electrons at the nucleus. That's because it transforms itself into lithium-7 by capturing one of its own electrons, turning one of its protons into a neutron, and emitting a gamma ray. When a change in chemical bonding subtly rearranges the electrons and increases an electron's chance of finding itself at the nucleus, the odds are better that it will be captured and the beryllium will decay. In the last few years, German researchers have demonstrated the converse of this effect: a surge in the decay of rhenium-187, which emits an electron rather than capturing one. When Fritz Bosch and his colleagues at the Gesellschaft fur Schwerionenforschung in Darmstadt, Germany, stripped away all the electrons from rhenium nuclei, something that might happen in a star's harsh interior, its half-life plummeted from 42 billion years to 33 years. But, until now, researchers have detected only tiny variations (or none at all) in the decay rate of beryllium and other atoms under Earth-like conditions. Undismayed, Huh applied the latest technology to the problem. He used an extremely sensitive but stable gamma ray spectrometer to monitor the decay of beryllium-7 (which has a half-life of about 53.3 days) in the form of the hydrated ion, the hydroxide, and the oxide-chemical combinations common in the environment. Thanks to an unprecedented precision of i0.01%, he could see that the half-lives of the three forms were 53.69 days, 53.42 days, and 54.23 days, respectively. The 1.5% range is `probably quite real,' says geochemist Teh-Lung Ku of USC. `Although the idea has been around quite a while, this time [the researchers] will be able to show it more convincingly.'" (Kerr, R.A.., "Tweaking the Clock of Radioactive Decay," Science, Vol. 286, 29 October 1999, pp.882-883, p.882)
* Authors with an asterisk against their name are believed not to be evolutionists. However, lack of an asterisk
does not necessarily mean that an author is an evolutionist.
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Created: 23 December, 2006. Updated: 4 April, 2010.