As someone who has studied radioactivity in detail, I have always been a bit amused by the assertion that radioactive dating is a precise way to determine the age of an object. This false notion is often promoted when radioactive dates are listed with utterly unrealistic error bars. In this report , for example, we are told that using one radioactive dating technique, a lunar rock sample is 4, million years old, plus or minus 23 million years old. Of course, that error estimate is complete nonsense. It refers to one specific source of error - the uncertainty in the measurement of the amounts of various atoms used in the analysis.
And even if the date is one or two geologic periods earlier, it may well be close enough to be accepted as non-spurious. If one does not know the geologic period of a rock by other means, then of course one is likely to date it to find out, and then of course the date agrees with the geologic period and this will not be seen as anomalous.
So it is difficult to know what would be a reasonable test for whether radiometric dating is reliable or not. The percentage of published dates that are considered as anomalous has little bearing on the question. The biostrategraphic limits issue The issue about igneous bodies may need additional clarification. If a lava flow lies above geologic period A and below B, then allowable ages are anything at least as large as A and no larger than B.
This is called the biostratigraphic limit of the flow. Now, according to Woodmorappe's citations, many lava flows have no such limits at all, and most of them have large limits. For example, a flow lying on precambrian rock with nothing on top would have no limits on its dates. And such flows often have a large internal scatter of dates, but these dates are not considered as anomalies because of the unrestricted biostratigraphic limit.
Other flows with wide biostratigraphic limits have weak restrictions on allowable dates. This is one reason why just reporting the percentage of anomalies has little meaning.
John W. Thus these ages, though they generally have a considerable scatter, are not considered as anomalies. He cites another reference that most igneous bodies have wide biostrategraphic limits.
Thus just by chance, many dates will be considered within the acceptable ranges. Again, the percentage of anomalies means nothing for the reliability of radiometric dating.
Now, igneous bodies can be of two types, extrusive and intrusive. Extrusive bodies are lava that is deposited on the surface. These cool quickly and have small crystals and form basalt. Intrusive bodies are deposited in the spaces between other rocks. These cool more slowly and have larger crystals, often forming granite. Both of these tend on the average to have wide biostrategraphic limits, meaning that a large spread of ages will be regarded as non-anomalous. And if we recall that most radiometric dating is done of igneous bodies, one sees that the percentage of anomalies is meaningless.
Thus we really need some evidence that the different methods agree with each other.
To make the case even stronger, "Many discrepant results from intrusives are rationalized away immediately by accepting the dates but reinterpreting the biostrategraphic bracket," according to John Woodmorappe.
This of course means that the result is no longer anomalous, because the geologic period has been modified to fit the date. Finally, the fact that the great majority of dates are from one method means that the general but not universal agreement of K-Ar dating with itself is sufficient to explain the small percentange of anomalies if it is small.
Preponderance of K-Ar dating Now, the point about agreement is that whatever figure is given about how often ages agree with the expected age, is consistent with the fact that there is no agreement at all between K-Ar and other methods, since so many measurements are done using K-Ar dating. And one of the strongest arguments for the validity of radiometric dating is that the methods agree. So when one combines all of the above figures, the statement that there are only 10 percent anomalies or 5 percent or whatever, does not have any meaning any more.
This statement is made so often as evidence for the reliability of radiometric dating, that the simple evidence that it has no meaning, is astounding to me. I don't object to having some hard evidence that there are real agreements between different methods on the geologic column, if someone can provide it.
The precambrian rock is less interesting because it could have a radiometric age older than life, but this is less likely for the rest of the geologic column. It's not surprising that K-Ar dates often agree with the assumed dates of their geological periods, since the dates of the geological periods were largely inferred from K-Ar dating. By the way, Ar-Ar dating and K-Ar dating are essentially the same method, so between the two of them we obtain a large fraction of the dates being used.
Before the discovery of radioactivity in the late nineteenth century, a geological time scale had been developed on the basis of estimates for the rates of geological processes such as erosion and sedimentation, with the assumption that these rates had always been essentially uniform. On the basis of being unacceptably old, many geologists of the time rejected these early twentieth century determinations of rock age from the ratio of daughter to radioactive parent large.
Byincreased confidence in radioisotope dating techniques and the demands of evolution theory for vast amounts of time led to the establishment of an expanded geological time scale.
The construction of this time scale was based on about radioisotope ages that were selected because of their agreement with the presumed fossil and geological sequences found in the rocks.
Igneous rocks are particularly suited to K-Ar dating. The crucial determiners are therefore volcanic extrusive igneous rocks that are interbedded with sediments, and intrusive igneous rocks that penetrate sediments. This verifies what I said about almost all of the dates used to define correct ages for geologic periods being K-Ar dates. Also, the uncertainty in the branching ratio of potassium decay might mean that there is a fudge factor in K-Ar ages of up to a third, and that the occasional agreements between K-Ar ages and other ages are open to question.
So the point is that there is now no reason to believe that radiometric dating is valid on the geologic column. I mentioned the presence of excess argon 40 in a sample as a problem leading to artificially old K-Ar dates.
Henke states in a reply to me, concerning the problem of detecting excess argon. It is possible that such isochrons are not often done. One cannot always use an isochron, since many minerals may have about the same K and Ar40 concentrations, and there may be some fractionation of argon among the minerals. It's not clear to me if this three dimensional plot always works, and how often it is used. I was not able to find any mention of it in Faure or Dickin It is true that by using additional isotopes if they are sufficiently abundant and do not fractionateone can often detect mixings of multiple sources.
My point was that the usual mixing test can only detect two sources. But since these multiple mixing tests are more difficult and expensive, they may not be done very often.
One also has to know which isotopes to examine. I was suprised that Dalrymple said nothing about mixings invalidating isochrons. Dalrymple goes to great lengths to explain this away, but I think this figure is very telling, and find his explanations unconvincing.
It is also remarkable that we have a test for mixing, which is commonly cited in support of the accuracy of radiometric dating, but when it gives contrary results, it is simply ignored. It is a fundamental assumption of the mantle isochron model that neither isotope nor elemental ratios are perturbed during magma ascent through the crust.
However, it is now generally accepted that this assumption is not upheld with sufficient reliability to attribute age significance to erupted isochrons. Dickin suggests that mixings may contribute to such isochrons. It seems reasonable, then, that mixings may be affecting all Rb-Sr isochrons in igneous rock. Your hypothetical example in "More Bad News for Radiometric Dating" is often hard to follow, but it is clearly invalid.
This example is given to show that a mixing of three sources cannot be detected by the usual two sources test. It is not intended to be natural, but to demonstrate a mathematical fact. There is a lot of flexibility in the design of such examples, as I indicate, and it is reasonable to assume that some of these examples would be natural. It's the responsibility of the geologist to show that such mixings have not occurred. To really understand what's going on you have to sample the recent works of many different authors.
How date rocks, Geological dating, how we know age of deposits, radiometric dating, carbon, isotope
You have to follow arguments between experts on different issues and see where they go. Overall, the geologic time scale is in great shape.
Yes, scientists are still making minor adjustments. However, it's clear from StrahlerDalrympleetc. The problem with this approach is that it leaves ample room for the exercise of subjective judgment and evolutionary assumptions.
Also, Dalrymple says essentially nothing about the phanerozoic, and thus gives little evidence of the accuracy of the conventional dating scheme on fossil-bearing rocks. I treated this issue of percentage of anomalies in considerable detail in my original "Radiometric Dating Game" article.
It is interesting that Woodmorappe gives a number of cases in which standard geological tests are ignored. For example, dates may be accepted even when there is evidence of weathering, and rejected when there is not. There may be evidence of heating, but the date may be accepted, and there may be no such evidence, but a hypothetical heating event is assumed anyway. If geological tests are not being applied consistently, one wonders what value they have.
Let me clarify the problem with excess argon.
Errors in dating fossils
It gives the diffusion equation for argon escaping from a rock as it cools. The rate of diffusion is proportional to the gradient of argon concentration, and increases rapidly with temperature.
Suppose the partial pressure of argon 40 in the environment is p. Suppose the partial pressure of argon 40 in lava or magma is initially at least p, as it cools. Then the partial pressure of argon 40 in the magma will never decrease below p; excess argon 40 will remain dissolved in the lava or magma as it cools.
This argon 40 will then be trapped within the resulting rocks and lead to artificially old K-Ar dates. Now, the problem with this is that this excess argon 40 will probably be deposited as single atoms of argon distributed evenly within the sample. This makes it very difficult or even theoretically impossible to distinguish this excess argon 40 from argon generated by radioactive decay. This will make the sample appear artificially old right away.
Even if crystals exclude argon as they form, argon will rapidly diffuse into them as the lava cools, by the diffusion equation mentioned above. A similar problem can occur if the excess argon 40 dissolved within lava or magma is not able to escape, due to rapid cooling or subsequent deposits of sediment or other lava on top.
It is possible that in some cases an isochron might be able to detect such initial argon 40, but this can only happen if the potassium concentration varies significantly within the sample. It is not clear to me, also, how often such a test for initial argon 40 is performed.
And of course, such isochrons can be falsified by mixings or other problems. There are spectrum tests for adsorbed argon involving Ar-Ar dating; basically, one can see whether the argon 40 is concentrated near the surface of the sample or near the interior. The former would indicated adsorbed argon 40, which would not give a true age. However, this test would not indicate excess argon 40 present during cooling.
Faure p. It seems reasonable to me that this is a uniform problem with K-Ar dating. To me the geological evidence suggests catastrophic conditions and rapid formation of the sedimentary layers in the past.
Thus the lava might have been covered before the excess argon was able to escape. Or the lava might have cooled quickly, due to rainfall. It only needs to cool to about degrees centigrade or less to trap most of the argon, at least for biotite. As I mentioned before, one sometimes finds significant argon 40 in a rock and no potassium at all, as mentioned in Snelling's article. This shows that excess argon is entering these rocks by some means, and calls K-Ar dating into question.
Join. And errors in dating fossils were not mistaken
Excess argon could even cause different minerals in a given formation to yield similar K-Ar ages, since they all might have similar concentrations of K, approximately equal to its abundance in the earth's crust, and similar concentrations of argon 40, due to the partial pressure of argon 40 being similar during cooling.
Even sedimentary minerals might have a similar K-Ar age for the same reason. Also, lava magma that cooled within the earth is likely to have artificially old K-Ar ages, since the enclosed excess argon 40 might have a more difficult time escaping. One sedimentary mineral of particular importance for K-Ar dating is glaucony.
The following message from a talk. For example, Plaisted's "explanation" for the correlation of isotopic age with vertical position in the geologic column is essentially that excess argon would have existed in lavas in greater quantity early in the Flood, and decreased as it was outgassed over time.
Had Plaisted actually bothered to look at the data e. Glaucony did not come from a "magma chamber," so Plaisted's explanation cannot possibly cover the majority of ages on the younger parts of the column. Of the or so "anomalous" dates in Woodmorappe94 Woodmorappe is clearly misusing illite and glauconite dates to simply pad his list. The fact that glauconies are unreliable is significant, since they provide such a large part of the dates for the mesozoic-cenozoic parts of the geological column.
Glauconies are formed in seawater from a variety of materials, and incorporate potassium from the seawater Faure,p. The process of their formation gives a ready mechanism for their K-Ar ages, namely, the incorporation of argon 40 as well as potassium from the seawater. We can assume that as a result of a global catastrophe, the oceans were highly enriched in argon 40 in the past, and that the concentration of argon 40 gradually decreased over time, due to its diffusion into the atmosphere and due to a smaller amount being released into the seawater.
Therefore older glauconies would absorb more argon 40 from the seawater, resulting in old K-Ar dates for lower strata which become progressively younger for higher strata. Another factor in this direction is that older glauconies have more time to absorb argon Some minerals contain argon 40 but no potassium, so this indicates excess argon 40, which in the presence of potassium leads to artificially old dates.
Can not errors in dating fossils not doubt
Many historical volcanoes give K-Ar dates that are much too old, even if the reasons for this are understood. Finally, I want to comment on the circumstances of the interchange with Dr. During most of our interchange, I was not aware that it would be published on talk.
Now it has been web-immortalized on a radiometric dating web page. I was not informed that this exchange had been posted there. In addition, the complete exchange was not posted, but only a portion of it. I do thank Tim Thomson for the courteous and professional manner in which he has interacted with me, and that he has included the rest of my exchange with Dr.
Excuses for anomalies Another issue is that sometimes the geologic periods of rocks are revised to agree with the ages computed. This also makes data about percentages of anomalies less meaningful.
It sometimes seems that reasons can always be found for bad dates, especially on the geologic column.
If a rock gives a too old date, one says there is excess argon. If it gives a too young date, one says that it was heated recently, or cannot hold its argon. How do we know that maybe all the rocks have excess argon? It looks like geologists are taking the "majority view" of K-Ar dating, but there is no necessary reason why the majority of rocks should give the right date.
The relationship of a radioisotope age with real-time must be based on an interpretation. A discussion of rubidium-strontium ages in the Isotope Geoscience Section of the journal, Chemical Geology, specifically states that a radioisotope age determination "does not certainly define a valid age information for a geological system. Any interpretation will reflect the interpreters presuppositions bias.
Need for a double-blind test Concerning the need for a double blind test, it would seem that there are many places where human judgment could influence the distribution of measured radiometric dates. It could increase the percentage of anomalies, if they were regarded as more interesting. It could decrease them, if they were regarded as flukes. Human judgment could determine whether points were collinear enough to form an isochron.
It could determine whether a point can justifiably be tossed out and the remaining points used as an isochron. It could determine whether one should accept simple parent-to-daughter K-Ar ratios or whether some treatment needs to be applied first to get better ages.
It could influence whether a spectrum is considered as flat, whether a rock is considered to have undergone leaching or heating, whether a rock is porous or not, or whether a sample has been disturbed in some way.
Since one of the main reasons for accepting radiometric dates at least I keep hearing it is that they agree with each other, I think that geologists have an obligation to show that they do agree, specifically on the geologic column. Since we do not know whether or how much human judgment is influencing radiometric dating, a double blind study is most reasonable. And it should not be restricted to just one or two well-behaved places, but should be as comprehensive as possible.
Possible changes in the decay rate The following information was sent to me by e-mail:. Radiometric dating is predicated on the assumption that throughout the earth's history radioactive decay rates of the various elements have remained constant.
Is this a warranted assumption? Has every radioactive nuclide proceeded on a rigid course of decay at a constant rate? This has been challenged by studies involving Carbon C At the temperature or pressure, collisions with stray cosmic rays or the emanations of other atoms may cause changes other than those of normal disintegration.
It seems very possible that spontaneous disintegration of radioactive elements are related to the action of cosmic rays and the rate of disintegration varying from century to century according to the intensity of the rays. The evidence for a strongly increasing change in the cosmic ray influx is most favorable especially in light of the decay of the earth's magnetic field. Most geochronologists maintain that pleochroic haloes give evidence that decay constants have not changed.
Crystals of biotite, for example, and other minerals in igneous or metamorphic rocks commonly enclose minute specks of minerals containing uranium or thorium.
The a- alpha particles emitted at high velocity by the disintegrating nuclides interact, because of their charge, with electrons of surrounding atoms which slow them down until they finally come to rest in the host material at a distance from their source that depends on their initial kinetic energy and the density and composition of the host. Where they finally stop to produce lattice distortions and defects there generally occurs discoloring or darkening.
Each of the 8 a-particles emitted during the disintegration of U to Pb produces a dark ring in biotite. Each ring has its own characteristic radius in a given mineral in this case biotite.
This radius measures the kinetic energy, hence the probability of emission of the corresponding a-particle and also the half-life of the parent nuclide according to the Geiger-Nuttall law. The Geiger-Nuttall law is an empirical relation between half-life of the a-emitter and the range in air of the emitted a-particles.
If the radii of these haloes from the same nuclide vary, this would imply that the decay rates have varied and would invalidate these series as being actual clocks. Are the radii in the rocks constant in size or are there variable sizes? Most of the early studies of pleochroic haloes were made by Joly and Henderson. Joly concluded that the decay rates have varied on the basis of his finding a variation of the radii for rocks of alleged geological ages.
This rather damaging result was explained away saying that enough evidence of correct radii for defferent geologic periods and sufficient variation in the same period have been obtained that one is forced to look for a different explanation of such variations as were observed by Joly.
"Direct Dating of Cretaceous-Jurassic Fossils (and Other Evidences for Human-Dinosaur Coexistence)" ( Twin Cities Creation Conference). In this paper, the authors describe in detail the measures taken to ensure that no other source of carbon contamination was present inside or outside the bones. Apr 03, In beta decay, a neutron turns into a proton by emitting a beta particle, which is an electron (click for credit) As someone who has studied radioactivity in detail, I have always been a bit amused by the assertion that radioactive dating is a precise way to determine the age of an object. Sep 16, None of these methods can be used directly on fossils or the sedimentary rock in which fossils are found. All radiometric dating (with the exception of carbon dating) must be done on igneous rocks (rocks solidified from a molten state such as lava). These radiometric "clocks" begin keeping time when the molten rock solidifies.
Measurements were later made in an excellent collection of samples with haloes. It was found that the extent of the haloes around the inclusions varies over a wide range, even with the same nuclear material in the same matrix, but all sizes fall into definite groups.
The measurements are, in microns, 5,7,10,17,20,23,27, and More recent studies have been made by Robert V.
Gentry also finds a variation in the haloes leading him to conclude that the decay constants have not been constant in time. Gentry points out an argument for an instantaneous creation of the earth. He noted form his studies of haloes: "It thus appears that short half-life nuclides of either polonium, bismuth, or lead were incorporated into halo nuclei at the time of mica crystallization and significantly enough existed without the parent nuclides of the uranium series.
For the Po half-life of 3 minutes only a matter of minutes could elapse between the formation of the Po and subsequent crystallization of the mica; otherwise the Po would have decayed, and no ring would be visible.
The occurrence of these halo types is quite widespread, one or more types having been observed in the micas from Canada Pre-CambrianSweden, and Japan.
So, then, careful scientists have measured variations in halo radii and their measurements indicate a variation in decay rates. The radioactive series then would have no value as time clocks. This would knock our C, potassium-argon, and uranium-lead dating measurements into a cocked hat!
The age of prehistoric artifacts, the age of the earth, and that of the universe would be thrown into doubt. Flint, "Radiocarbon Dating," in Science, February 8,p. This is significant because it is known that neutrinos do interact with the nucleii of atoms, and it is also believed that much of the energy of supernovae is carried away by neutrinos. Isochrons Isochrons are an attempt to avoid the need for an absence of daughter element initially in computing radiometric ages.
The idea is that one has a parent element, X, a daughter element, Y, and another isotope, Z, of the daughter that is not generated by decay. One would assume that initially, the concentration of Z and Y are proportional, since their chemical properties are very similar. Radioactive decay would generate a concentration of Y proportional to X.
So we would obtain an equation of the form. By taking enough measurements of the concentrations of X, Y, and Z, we can solve for c1 and c2, and from c1 we can determine the radiometric age of the sample.
If the concentration of K varies in a rock, that it is unlikely for the concentration of added argon 40 to vary in a way that will yield an isochron. But if the concentration of K does not vary, then one can still get an isochron if the concentration of the non-radiogenic isotope Ar36 of the daughter product varies.
So let's call an isochron a "super-isochron" if the concentration of the parent element varies from one sample to another. Let's call it a "wimpy isochron" otherwise.
Above errors in dating fossils join. And
The question is, what percentage of isochrons are super-isochrons, and how do their dates agree with the conventional dates for their geologic period? I would think that it may be rare to have a super-isochron.
If one is dealing with minerals that exclude parent or daughter, then one cannot get an isochron at all. If one is dealing with minerals that do not exclude parent and daughter elements, then most likely the parent element will be evenly distributed everywhere, and one will have a wimpy isochron that cannot detect added daughter product, and thus may give unreliable ages.
Whole rock isochrons may also tend to be wimpy, for the same reason. Even super isochrons can yield ages that are too old, due to mixings, however. False K-Ar isochrons can be produced if a lava flow starts out with a lot of excess Ar40 which becomes well mixed, along with potassium.
Then while cooling or afterwards, a mixture of Ar36 and Ar40 can enter the rock, more in some places than others. Other isotopes of argon would work as well. I believe that this will produce a good K-Ar isochron, but the age calculated will be meaningless. There is another way that false isochrons can be produced. For a wimpy isochron, say a K-Ar isochron, we can assume that initially there is a uniform concentration of K everywhere, and concentrations of Ar40 and Ar36 that form an isochron.
Then a lot of Ar40 enters, uniformly, through cracks in the rock or heating. This will retain the isochron property, but will make the isochron look too old. My reasoning was that if the lava is thoroughly mixed, then the concentration of parent material should be fairly constant.
If the concentration of parent substance is not constant, it could indicate that the lava is not thoroughly mixed. Or it could have other explanations. If the lava is not thoroughly mixed, it is possible to obtain an isochron from the mixing of two different sources, in which case the radiometric age is inherited from the sources, and does not necessarily yield the age of the flow.
Someone pointed out to me that many Rb-Sr isochrons are super isochrons. I find this information very interesting, and thank him for it. I'd be curious to know which strata they occur in, as my main interest is the geologic column of Cambrian and above.
If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. Sometimes multiple index fossils can be used. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between and million years. May 31, According to carbon dating of fossil animals and plants, the spreading and receding of great ice sheets lagged behind orbital changes by several thousand years, a .
My impression is that these are not on this part of the geologic column. And how well do the dates correlate with others for the same formation? There are also mixing scenarios that can produce even super isochrons having invalid ages.
And geologists admit in any event that isochrons can sometimes give false ages. Here is a mixing scenario for false isochrons. Consider this possibility: There are two sources of lava, A and B. Suppose these mix together so that at point 0 we have only A, at point 1 we have only B, and in between we have varying concentrations. Half way between there is a mixture of half A and half B, for example. Suppose X is a parent substance, Y is its daughter, and Z is a non-radiogenic isotope of the daughter.
Suppose A has a little X and lots of Y and not much Z, all uniformly distributed, and B has some mixture of Y and Z, all uniformly distributed.
Then this varying mixture of A and B, with all A at 0 and all B at 1, produces a good isochron. There is no way this mixture can be distinguished from a similar case in which A has lots of X and little Y, and B is the same as before, and a lot of time passes. It is claimed that mixing can often be detected. If this is so, then the question remains, for super isochrons on the geologic column which can be shown not to be caused by mixing, how do they correlate with other methods, and with the expected dates for their geologic period?
My understanding is that isochrons measure the time since a rock was last well mixed. For a lava flow, this could be the time of the flow. Or it could be that several flows all come from the same well-mixed magma, and might yield a joint isochron giving the time of the flow. It seems to me that a single lava flow might not mix well, and thus the age obtained would be that of the magma and not the time of the flow.
So this points out another problem with interpretation of isochrons. I'm also curious to know how much of the geologic column is datable by super isochrons for which no mixing can be shown. Atlantic sea floor dating One often hears about K-Ar dates of the Atlantic Ocean bottom which increase from zero at the mid-Atlantic ridge to about million years at the edges.
When fossil A is found in rock strata below a rock layer containing fossil B, fossil A can generally be dated as older, relative to fossil B. That is relative dating. But relative dating doesn't yield actual age; that is what absolute dating attempts to do. "Absolute dating complements relative dating by . The guide describes a number of radiometric methods and states that for 'suitable specimens the errors involved in radiometric dating usually amount to several percent of the age result. Thus a result of two hundred million years is expected to be quite close (within, say, 4 million) to the true age.'. Evolution places severe demands upon fossils used to support it. A fossil in an evolutionary sequence must have both the proper morphology (shape) to fit that sequence and an appropriate date to justify its position in that sequence. Since the morphology of a fossil cannot be changed, it is obvious that the dating is the more subjective element of the two items.
This is taken as proof that the continents began separating about million years ago. However, this can be explained by assuming that argon rises to the top of the magma, so magma deeper down looks younger.
The magma deeper down would have come to the surface later, and thus would be nearer to the mid-Atlantic ridge. Or if the continents split quickly, the observed pattern of dates could be explained by a decreasing concentration of Ar40 in the water.
In any event, I don't see how the lava in the center of the Atlantic could have a young age in the conventional view, since it would have cooled rapidly under a lot of water, and would have retained its argon, making it look old.
Dating Meteorites We now make some comments about dating the meteorites. Since I have not had as much time to study this, I will just list some points that must be considered. Many parent to daughter ratios for many meteorites give radiometric ages of about 4. This gives support to an ancient age for the meteorites, assuming constant decay rates. However, in interpreting these results, some facts need to be kept in mind. The first is that these results are not obtained by a simple parent to daughter ratio.
Instead, some estimate of the amount of daughter initially present in the meteorite has to be made in order to compute a radiometric age.
Thus one has a "fudge factor," and in fact, a different fudge factor for each method. So one has to be sure that these fudge factors are properly used, and not simply adjusted in order to obtain an agreement among the dates. The importance of this is underlined by the fact that these same fudge factors are used to estimate uranium and thorium dates on earth. Thus the estimate of initial concentrations of lead isotopes could also affect the 4. We noted above that there also seems to be a fudge-factor built into potassium-argon dating, namely, the branching ratio estimate.
Remarkable, errors in dating fossils share your opinion
This causes the correlation between K-Ar dates and other dates on meteorites to come into question, as well. Now, at least for uranium-lead dating, a kind of isochron has been observed among five meteorites containing uranium and a number which do not, which gives a rational basis for assuming how much daughter product was present initially.
The obvious question to ask in regards to this is how the meteorites were chosen for this isochron, and whether there are other meteorites and other bodies from the solar system that do not fit.
If so, this calls this interpretation into question.
In addition, there is just one point on this isochron for all of the meteorites that do not contain uranium. Is this obtained by averaging, or do they all have exactly the same ratio of lead isotopes? If the former, then this could indicate that the points of this isochron have considerable scatter, further calling the age computation into question.
A point from the earth is also on this isochron. This is from a sedimentary deposit. But since uranium is much more water soluble than lead, it seems questionable to use this point as reprsenting the ratio of lead isotopes on earth, since it may be impoverished or enriched in uranium. In addition, if other sediments yield different ratios of isotopes, why was only this one chosen? Another question that needs to be asked is whether this isochron could have been produced by some kind of a mixing process, since such processes can produce isochrons not representing a true age.
It also needs to be determined whether the daughter products for methods other than uranium-lead dating also yield isochrons among the different meteorites. The above discussion concerns dating techniques based on simple parent to daughter ratios. There are other dating techniques such as isochrons and discordia which avoid the need to estimate initial daughter product concentrations. Therefore, it should be determined how many correlations remain in meteorite dating when only such techniques are applied.
Of course, in the traditional view, the matter out of which the solar system was formed would have been very old at the start, in any event, and so the radiometric ages obtained from meteorites or from the earth do not necessarily tell us anything about the age of the solar system or the age of the earth.
My point is not to refute the meteorite dating, since it may be sound, assuming a constant decay rate. However, on seeing the lack of evidence for large-scale evolution, the many problems with radiometric dating on the geologic column, and the many plausible evidences for catastrophe which often seem to be interpreted away by science, I have become somewhat skeptical of any area of science having to do with origins, and so have come to question even the assumptions behind the dating of the meteorites.
This does not answer my question, which referred at least in part to dates obtained by a simple daughter-to-parent ratio. Dalrymple does say that many ages for meteorites are "model ages," which are computed by making assumptions about initial amounts of daughter product.
Such assumptions are also necessary for the Pb-Pb method of dating. For meteorites, there is a good basis for making such assumptions. Also, Dalrymple gives impressive agreements between different isochron methods on meteorites, which support a roughly 4. Henke refers to this in his second reply:. Dalrymple lists more than just a "small number of meteorites.
Specifically, Figure 6. Table 6. None of these results are only a few thousand years old. For further details, see Dalrymplechapter 6. Other than a true age for the meteorites, this could indicate a mixing process, which does not seem likely, or an increase in decay rates, for which a mechanism would need to be found. However, in order to date the earth, one needs an isochron which includes a point from the earth. This is more difficult, and this is the isochron that I saw on the talk.
Also, many of the meteorite dates I saw in the FAQ were apparently simple daughter-to-parent ratio ages. It is also remarkable that so many different isochron-based dating schemes, even on the same meteorite, often yield roughly the same 4. This is a case where different methods agree without making assumptions about initial amount of daughter product. This either indicates a true age, or a change in the decay constants.
I would like to know how often this is true on the phanerozoic. How often does one have two or three different isochrons on the same system yielding very similar dates? It is also important that the concentrations of parent substances are linearly independent, to preclude mixings. Such a multiple-isochron agreement is fairly convincing, but the failure to find such isochrons likewise casts doubt on the ages obtained.
If radiometric dating is accurate on fossil-bearing rocks, there should be an abundance of such agreements between different isochrons on the same systems, and they should yield the conventionally accepted ages. A change in the decay constants on the phanerozoic seems less likely, since it could radically affect the properties of matter, and be harmful to life.
Another reliable technique mentioned by Dalrymple is the U-Pb concordia-discordia method on zircons, which is valid even for many open systems. This technique requires assumptions about lead and uranium loss, and seems to give good evidence of a reliable date relative to decay constantsespecially when there is agreement with other methods such as isochrons on the same system.
This can often be complicated by the fact that geological forces can cause faulting and tilting of rocks. Absolute Dating Absolute dating is used to determine a precise age of a rock or fossil through radiometric dating methods. This uses radioactive minerals that occur in rocks and fossils almost like a geological clock. So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
The atoms in some chemical elements have different forms, called isotopes. These isotopes break down at a constant rate over time through radioactive decay. By measuring the ratio of the amount of the original parent isotope to the amount of the daughter isotopes that it breaks down into an age can be determined. We define the rate of this radioactive decay in half-lives. If a radioactive isotope is said to have a half-life of 5, years that means after 5, years exactly half of it will have decayed from the parent isotope into the daughter isotopes.
Then after another 5, years half of the remaining parent isotope will have decayed. While people are most familiar with carbon dating, carbon dating is rarely applicable to fossils. Carbon, the radioactive isotope of carbon used in carbon dating has a half-life of years, so it decays too fast. It can only be used to date fossils younger than about 75, years. Potassium on the other hand has a half like of 1. This makes it ideal for dating much older rocks and fossils.
The nucleus of an atom is made up of protons and neutrons. The number of protons in the nucleus define what type of element it is. However, the number of neutrons of an element may vary. Atoms with the same number of protons, but different numbers of neutrons are called isotopes. Some isotopes are stable, while others are unstable. Unstable isotopes undergo a process called radioactive decaywhereby they spontaneously change to elements of a different type.
We can never predict when a specific atom will undergo radioactive decay. However, when considering many atoms, we observe that the decay occurs at an exponential decay rate. Exponential decay means that over a certain period of time, called a half lifehalf of the unstable isotopes in a sample will undergo radioactive decay.
The carbon atom exists as three different isotopes. These are carbon Ccarbon C and carbon C All living organisms maintain an equilibrium of carbon with the atmospheric carbon After an organism dies, it no longer incorporates new carbon into its body.
The carbon present within them undergoes radioactive decay to nitrogen, and decreases from the original equilibrium with carbon The half-life of carbon is years.