Sean D. Pitman M.D.
© July 2008
Table of Contents
History of Radiometric Dating
the time that Darwin's On the Origin of Species was published, the
earth was "scientifically" determined to be 100 million years old. By
1932, it was found to be 1.6 billion years old. In 1947, science firmly
established that the earth was 3.4 billion years old. Finally in 1976, it was
discovered that the earth is "really" 4.6 billion years old… What
The study of geology grew out of field studies associated with mining and engineering during the sixteenth to nineteenth centuries. In these early studies the order of sedimentary rocks and structures were used to date geologic time periods and events in a relative way. At first, the use of “key” diagnostic fossils was used to compare different areas of the geologic column. Although there were attempts to make relative age estimates, no direct dating method was available until the twentieth century.
Following the discovery of radioactivity by Becquerel (1896), the possibility of using this phenomenon as a means for determining the age of uranium-bearing minerals was demonstrated by Rutherford (1906). In his study Rutherford measured the U and He (He is an intermediate decay product of U) contents of uranium-bearing minerals to calculate an age. One year later Boltwood (1907) developed the chemical U-Pb method. These first “geochronology studies” yielded the first “absolute ages” from geologic material, which seemed to indicate that parts of the Earth's crust were hundreds of millions of years old. (Boltwood's ages have since been revised).
During this same period of time Thomson (1905), Campbell and Wood (1906) demonstrated that potassium was radioactive and emitted beta-particles. The first isotopes of potassium (39K and 41K) were reported by Aston (1921). Kohlhorster (1930) reported that potassium also emitted gamma radiation. Following theoretical arguments by Klemperer, Newman and Walke (1935) on the existence of 40K, which radioactively decayed to 40Ca by beta-emission, Nier (1935) discovered 40K and reported a value of 8600 for the 39K/40K ratio. Newman and Walke also suggested the possibility that 40K could decay to 40Ar. However, it was Von Weizsacker's (1937) argument, based on the abundance of argon in the Earth's atmosphere relative to the other noble gases (He, Ne, Kr, and Xe), that 40K also decayed to 40Ar by electron capture. As a test, Von Weizsacker suggested looking for excess 40Ar in older K-bearing rocks. By combining Von Weizsacker’s argon abundance arguments with Kohlhorster’s observation that potassium emitted gamma-radiation, Bramley (1937) presented strong evidence that potassium underwent dual decay. Thompson and Rowlands (1943), using a cloud chamber, confirmed that 40Ar was the decay product of 40K undergoing electron capture. The absolute confirmation that 40Ar was the decay product of 40K came when Aldrich and Nier (1948) measured significantly increased 40Ar/36Ar ratios on argon extracted from potassium-rich minerals relative to the atmospheric 40Ar/36Ar ratio. The rapid development of the K-Ar dating method soon followed.
The 40Ar/39Ar variation of K-Ar dating grew out of iodine-xenon dating studies of meteorites by Jeffery and Reynolds (1961). In these studies the isotopic ratios of all the noble gases (He, Ne, Ar, Kr, and Xe) of neutron-irradiated meteorites were measured. This led to the discovery of 39Ar, which is derived from 39K by Merrihue (1965). The first 40Ar/39Ar dating results were presented in a paper by Merrihue and Turner (1966). Further development of the 40Ar/39Ar method by Mitchell, (1968), Brereton, (1970), and Turner, (1971) evaluated the interfering argon isotopes derived from potassium and calcium (36ArCa, 39ArCa, and 40ArK) and determination of the respective correction factors [ (36Ar/37Ar)Ca, (39Ar/37Ar)Ca, and (40Ar/39Ar)K]. The first applications of the 40Ar/39Ar dating method of terrestrial rocks compared total fusion 40Ar/39Ar ages with conventional K-Ar ages (Mitchell, 1968; Dunham et al., 1968; York and Berger, 1970; Dalrymple and Lanphere, 1971).
It is felt that the 40Ar/39Ar dating method offers a significant advantage over the conventional 40K/40Ar dating technique for several reasons. However, the most significant advantage of the 40Ar/39Ar dating method over the conventional 40K/40Ar method is the ability to step-heat samples to higher and higher temperatures until the sample is fused, and calculate and ages for each step. The 40Ar/39Ar step-heating method provides information on the internal distribution of potassium relative to argon. The first 40Ar/39Ar step-heating studies of terrestrial samples were by Fitch (1969), Miller (1970), York (1971), Lanphere and Dalrymple (1971), and Brereton (1972).1
Dating rocks by radioactive timekeepers is simple in theory, but almost all of the different methods (except for the isochron methods - see below) rely on these few basic assumptions: 21
Beginning Conditions Known
Beginning Ratio of Daughter to Parent Isotope Known (zero date problem)
Constant Decay Rate
No Leaching or Addition of Parent or Daughter Isotopes
All Assumptions Valid for Billions of Years
There is also a difficulty in measuring precisely very small amounts of the various isotopes
There is, of course, one radiometric dating method that appears to overcome the vital "zero date problem". The isochron dating method theoretically overcomes the need to know the initial ratio of parent and daughter isotopes. It will be covered in more detail below. For now, we will look at those methods that do fall under the above assumptions.
Interweaving the relative time scale with the atomic time scale poses certain problems because only certain types of rocks, chiefly the igneous variety, can be dated directly by radiometric methods; but these rocks do not ordinarily contain fossils. Igneous rocks are those such as granite and basalt, which crystallize from molten material called "magma". There is even some valid question as to if granite could be formed from magma at all since this has never, to my knowledge, been observed or duplicated in the lab. Radio-halos from rapidly decaying radioactive isotopes in granite seem to indicate that the granites were formed almost instantly.
Potassium - Argon and Argon - Argon dating are based on the current understanding that radioactive Potassium-40 decays to the stable form, Argon-40 with a half-life of approximately 1.25 billion years. The same principle holds true for the other isotope dating methods.
Radioactive decay occurs at a constant exponential or geometric rate. The rate of decay is proportional to the number of parent atoms present. There are some circumstances that can affect this rate such as magnetic fluctuations etc... But in general, this seems to be a constant.
If one starts with an originally pure sample of “parent element,” then the proportion of parent to daughter tells us the number of half-lives, which has been used to find the supposed age of igneous rocks. For example, if there are equal amounts of parent and daughter isotopes, then one half-life has passed. If there are three times as many daughter isotopes as parent, then two half-lives have passed, and so on.
Most minerals, which contain radioactive isotopes, are in igneous rocks. The majority of scientists today assume that the dates they give indicate the time the magma cooled. This also assumes that there was no initial daughter isotopes contained in the magma at the time of cooling. The assumption is that at least a great majority of the isotope present was the parent isotope. This parent isotope then degraded to the daughter isotope over time. Consider the following statement by Dalrymple, a well-known geologist:
“The K-Ar method is the only decay scheme that can be used with little or no concern for the initial presence of the daughter isotope. This is because 40Ar is an inert gas that does not combine chemically with any other element and so escapes easily from rocks when they are heated. Thus, while a rock is molten, the 40Ar formed by the decay of 40K escapes from the liquid.” 2
So, according to Dalrymple, K-Ar or Ar-Ar are the only methods that have little or no concern for the presence of initial daughter isotopes. This means that all the other radioisotope-dating methods (excepting isochron methods) are brought into serious question. The reason for this is because unless the initial ratio of parent to daughter isotope is known, the current ratio would be worthless as a means of determining elapsed time. A rock cannot be said to be millions or billions of years old if there is no way of knowing what the original composition of the rock was at the time that it was formed. The assumption for the K-Ar method is that all argon escapes at the time of rock formation because argon is a gas while potassium is not. Likewise, the other non-isochron dating methods, such as uranium-lead, also fall short because who is to say when the "zero date" was when there was only parent isotope and no daughter? Because of this problem, it might be a significant error to simply assume that all original isotopes present in a given rock were parent isotopes.
"The primary assumption upon which K-Ar model-age dating is based assumes zero 40Ar in the mineral phases of a rock when it solidifies. This assumption has been shown to be faulty." CEN Tech. J., Vol. 10, No. 3, p:342 1996
Lets now consider how fossils are dated with many of these methods, such as the potassium-argon method. The mineralized fossils themselves are not directly datable by radiometric techniques. The sedimentary rock that buried them is also not datable. If there is some igneous rock fragments in that sedimentary rock layer, these fragments are dated, most commonly, by the 40K/40Ar dating method described above. It is assumed then that the fossil is as old as the igneous rock fragment that it is buried with. Aside from the zero-date problems noted above, one might consider the possibility that the fossil might not be as old as the sediment that buried it in the first place. For example, lets say that my pet dog dies. I decide to bury it in the back yard. Is the dog as old as the dirt that I buried it in? Likewise, who is to say that some fossils were not buried in sedimentary material that was weathered from significantly more ancient formations?
Potassium-Argon and Argon-Argon Dating
Since Potassium-Argon and Argon-Argon dating techniques are the most common and are considered, even by geologists, to be among the most accurate of all the radioisotope dating methods, lets consider these in particular detail.
Argon is a noble gas. The main isotopes of argon in terrestrial systems are 40Ar (99.6%), 36Ar (0.337%), and 38Ar (0.063%). Naturally occurring 40K decays to stable 40Ar (11.2%) by electron capture and by positron emission, and decays to stable 40Ca (88.8%) by negatron emission; 40K has a half-life of 1.25 billion years.
Most of the argon isotope literature deals with measurement of 40Ar for use in 40K/40Ar dating of rocks. The conventional 40K/40Ar dating method depends on the assumption that the rocks contained no argon at the time of formation and that all the subsequent radiogenic argon (i.e., 40Ar) was quantitatively retained. Minerals are dated by measurement of the concentration of potassium, and the amount of radiogenic 40Ar that has accumulated. The minerals that are best suited for dating include biotite, muscovite, and plutonic/high grade metamorphic hornblende, and volcanic feldspar; whole rock samples from volcanic flows and shallow instrusives can also be dated if they are unaltered (Faure, 1986).
Under some circumstances the requirements for successful 40K/40Ar dating may be violated. For example, if 40Ar is lost by diffusion while the rock cooled, the age-dates represent the time elapsed since the rock cooled sufficiently for diffusive losses to be insignificant. Or, if excess 40Ar is present in the rock, the calculated age-dates are too old. The 40Ar/39Ar method is thought to be able to overcome this problem inherent with the 40K/40Ar method.
The 40Ar/39Ar dating method is based on the formation of 39Ar as a result of the intentional irradiation of K-bearing samples within a nuclear reactor. The bombardment produces various isotopes of Ar, K, Ca, and Cl, but the dominant source of 39Ar is from 39K. Radioactive 39Ar decays back to 39K by beta emission with a half-life of 269 years, but the decay is slow compared to the analysis time and can be ignored (Faure, 1986). The principal “advantage” of 40Ar/39Ar dating is that argon can be released partially by stepwise heating of irradiated samples, producing a spectrum of dates related to the “thermal history of the rock” (understanding that Argon is a gas while Potassium is not).
Because of this, it is much easier to determine a 40K/40Ar ratio and do it in a stepwise fashion with varying amounts of time and heat. This “stepwise” testing is thought to eliminate the errors caused by “extraneous” argon that might have “contaminated” the rock over time either by a loss or a gain of “outside” argon (ie: atmospheric argon). The problem with this theory is that who is to know which step, or average of steps in the process represents the “correct” 40K/40Ar ratio? How is this calibrated? Also, even if the argon-argon dating method does eliminate the "contamination" problem, it does not solve the problem of original argon. Did the clock get reset to zero when the volcano erupted? Or, was there some argon trapped in the rocks originally? Also, the 40Ar/39Ar dating method is not an independent dating method. It must be first calibrated against a sample of "known age". This age of this sample is usually determined by, you guessed it, the 40K/40Ar method.
Recent experiments on volcanoes of known ages have been done using the 40Ar/39Ar dating method, which seem to confirm its accuracy. Recent testing of volcanic material from Mt. Vesuvius was dated accurately with the 40Ar/39Ar method to within seven years of the actual event.3 40Ar/39Ar Dating into the Historical Realm: Calibration Against Pliny the Younger was written by P. R. Renne et. al. and published in Science 277: 1279-1280 (1997). Renne tested Ar-Ar dating by checking it against the 79 A.D. eruption of Vesuvius that destroyed Pompeii. Renne and his team noted that “Analysis of single crystals, for example by laser fusion, can obviate xenocrystic contamination, but single crystals are seldom large enough to yield measurable quantities of 40Ar* through radiogenic ingrowth in the Holocene [i.e. last 12,000 years].” Would Ar-Ar dating methods work such recent material? It apparently did. The testing returned an age of 1925±94 years. The true age was 1918 years. The test was off only 7 years. The conclusions of Renne and his team read as follows:
Thus despite the presence of excess 40Ar, a sample less than 2000 years old can be dated with better than 5% precision, validating 40Ar/39Ar dating as a reliable geochronometer into the late Holocene. These results also demonstrate that excess 40Ar can be identified in volcanic sanidine, and while perhaps negligible in pre-Holocene rocks, it has important consequences for sample at the limit of the method’s applicability. Further improvement in precision of 40Ar/39Ar analysis of historically dated samples may lead to welcome refinements in the ages of neutron fluence monitors, currently a limitation on the accuracy of the 40Ar/39Ar method. Our results also substantiate validity of the 40Ar/39Ar method in establishing the eruptive histories of populated active volcanic regions, where such information is vital to volcanic hazard assessment.
Of note however is that this test was not double blinded, and the number of such tests is not statistically significant as far as scientific analysis is concerned. Although interesting, it is basically a case study report, and as such it has very little scientific weight as far as statistical predictability.
Specific Problems with K-Ar and Ar-Ar Dating
In the first place, I am not primarily concerned with dating meteorites, or Precambrian rocks. What I am more interested in is the fossil-bearing geologic column of Cambrian and later “ages”. Since 40K/40Ar and 40Ar/39Ar dating are most commonly used to "prove" the ancient age of many life forms, I will discuss these dating methods specifically in more detail and show that they, along with the other common methods of isotope dating, are to be highly questioned. I will begin this section with a short discussion from Andrew Snelling, an associate professor of geology in El Cajon, California.
According to the assumptions foundational to potassium-argon (K-Ar) and argon-argon (Ar-Ar) dating of rocks, there should not be any daughter radiogenic argon (40Ar*) in rocks when they form. When measured, all 40Ar* in a rock is assumed to have been produced by in situ radioactive decay of 40K within the rock since it formed. However, it is well established that volcanic rocks (e.g. basalt) contain excess 40Ar*, that is, 40Ar which cannot be attributed to either atmospheric contamination or in situ radioactive decay of 40K. This excess 40Ar* represents primordial Ar carried from source areas in the earth's mantle by the parent magmas, is inherited by the resultant volcanic rocks, and thus has no age significance.
However, are all other rocks in the earth's crust also susceptible to "contamination" by excess 40Ar* emanating from the mantle? If so, then the K-Ar and Ar-Ar "dating" of crustal rocks would be similarly questionable.
When muscovite (a common mineral in crustal rocks) is heated to 740°-860°C under high Ar pressures for periods of 3 to 10.5 hours it absorbs significant quantities of Ar, producing K-Ar "ages" of up to 5 billion years, and the absorbed Ar is indistinguishable from radiogenic argon (40Ar*). In other experiments muscovite was synthesized from a colloidal gel under similar temperatures and Ar pressures, the resultant muscovite retaining up to 0.5 wt% Ar at 640°C and a vapor pressure of 4,000 atmospheres. This is approximately 2,500 times as much Ar as is found in natural muscovite. Thus under certain conditions Ar can be incorporated into minerals which are supposed to exclude Ar when they crystallize.
Because it is known that excess 40Ar* is carried from the mantle by plumes of mafic magmas up into the earth's crust, it is equally likely that much of the excess 40Ar* in crustal rocks could be primordial 40Ar. Thus, we have no way of knowing if any of the 40Ar* measured in crustal rocks has any age significance. Additional to the primordial 40Ar from the mantle is 40Ar* released from minerals and rocks during diagenesis and metamorphism, so that there is continual migration and circulation of both primordial 40Ar and 40Ar* in the crust which is reflected in their presence in CO2-rich natural gases. Therefore, when samples of crustal rocks are analyzed for K-Ar and Ar-Ar "dating," one can never be sure that whatever 40Ar* is in the rocks is from in situ radioactive decay of 40K since their formation, or if some or all of it came from the mantle or from other crustal rocks and minerals. Thus all K-Ar and Ar-Ar "dates" of crustal rocks are questionable, as well as fossil "dates" calibrated by them.19
In summary, many scientists assume that since argon is a gas, all of it should have escaped from the lava before it cooled. Therefore, all the 40Ar in the rock should be the result of decay from potassium. Based on the measured potassium, argon, and the decay rate, they calculate an age. That is why it does not matter how long the magma was in the volcano before it erupted. They believe that when the volcano erupts, all the 40Ar escapes, and the atomic clock gets reset to zero.
If all the argon escaped from hot lava of volcanoes that erupted long ago, then all the argon should escape from the hot lava of volcanoes that erupt in modern times too. But modern lava does have 40Ar in it. This is known as the "excess argon problem". Scientists are well aware of this problem and use various calibration methods to "correct" for this problem. However, how are these calibration methods established? Upon what basis are they validated?
"Another issue affecting the ultimate precision and accuracy of the 40Ar/39Ar technique is the uncertainty in the decay constants for 40K. This uncertainty results from 1) the branched decay scheme of 40K and 2) the long half-life of 40K (1.25 billion years)." 49
Some suggest that the 40Ar/39Ar dating method, in particular, helps to solve the contamination problem because the sample is step heated and excess argon can be detected once the data is plotted. This might be true, if the sample weren't evenly contaminated. Beyond this, 40Ar/39Ar is not an independent dating technique, but must first be calibrated against a sample of "known age" before it can be used.
"Once an accurate and precise age is determined for the primary standard, other minerals can be dated relative to it by the 40Ar/39Ar method. . . However, while it is often easy to determine the age of the primary standard by the K/Ar method, it is difficult for different dating laboratories to agree on the final age. Likewise, because of heterogeneity problems with the MMhb-1 sample, the K/Ar ages are not always reproducible. This imprecision (and inaccuracy) is transferred to the secondary minerals used daily by the 40Ar/39Ar technique." 49
Fission Track Dating
track dating is a radioisotopic dating method that depends on the tendency of
uranium (Uranium-238) to undergo spontaneous fission as well as the usual decay
process. The large amount of energy released in the fission process ejects the
two nuclear fragments into the surrounding material, causing damage paths called
fission tracks. The number of these tracks, generally 10-20 µ in length, is a
function of the initial uranium content of the sample and of time. These
tracks can be made visible under light microscopy by etching with an acid
solution so they can then be counted.
usefulness of this as a dating technique stems from the tendency of some
materials to lose their fission-track records when heated, thus producing
samples that contain fission-tracks produced since they last cooled down. The
useful age range of this technique is thought to range from 100 years to 100
million years before present (BP), although error estimates are difficult to
assess and rarely given. Generally it is thought to be most useful for dating in
the window between 30,000 and 100,000 years BP.
problem with fission-track dating is that the rates of spontaneous fission are
very slow, requiring the presence of a significant amount of uranium in a sample
to produce useful numbers of tracks over time. Additionally, variations in
uranium content within a sample can lead to large variations in fission track
counts in different sections of the same sample.42
of such potential errors, most forms of fission track dating use a form of
calibration or "comparison of spontaneous and induced fission track density
against a standard of known age. The principle involved is no different from
that used in many methods of analytical chemistry, where comparison to a
standard eliminates some of the more poorly controlled variables. In the zeta
method, the dose, cross section, and spontaneous fission decay constant, and
uranium isotope ratio are combined into a single constant." 43
course, this means that the fission track dating method is not an independent
method of radiometric dating, but is dependent upon the reliability of other
dating methods. The reason for this
is also at least partly due to the fact that the actual rate of fission track
production. Some experts suggest using a rate constant of 6.85x10-17
yr-1 while others recommend using a rate of 8.46x10-17 yr-1
(G. A. Wagner, Letters to Nature, June 16, 1977). This
difference might not seem like much, but when it comes to dates of over one or
two million years, this difference amounts to about 25-30% in the estimated age
value. In other words, the actual rate of fission track production isn't really
known, nor is it known if this rate can be affected by various concentrations of
or other physical factors. For
example, all fission reactions produce neutrons. What happens if fission from
some other radioactive element, like U235
or some other radioisotope, produces tracks?
Might not these trackways be easily confused with those created by
fission of U238?
human element is also important here. Fission trackways have to be manually
counted. This is problematic since
interpreting what is and what is not a true trackway isn't easy.
Geologists themselves recognize the problem of mistaking non-trackway
imperfections as fission tracks. "Microlites
and vesicles in the glass etch out in much the same way as tracks."45
Of course, there are ways
to avoid some of these potential pitfalls. For
example, it is recommended that one choose samples with as few vesicles and
microlites as possible. But, how is one to do this if they are so easily
confused with true trackways? Fortunately, there are a few other
"hints". True tracks are straight, never curved. They also tend to
show characteristic ends that demonstrate "younging" of the etched
track. True tracks are thought to form randomly and have a random orientation.
Therefore, trackways that show a distribution pattern tend not to be
trusted as being "true". Certain
color and size patterns within a certain range are also used as helpful hints.
Yet, even with all these hints in place, it has been shown that different
people count the same trackways differently - up to 20% differently.44
Add up the human error with the error of fission track rate and we
are suddenly up to a range of error of 50% or so.
is yet another reason why calibration with other dating techniques is used in
fission track dating. It just isn't very reliable or accurate by itself.
And, it gets even worse. Fairly recently, Raymond Jonckheere and Gunther
Wagner (American Minerologist, 2000) published results showing that there are
two kinds of real fission trackways that had "not been identified
previously." The first type of
trackway identified is a "stable" track and the second type is
produced through fluid inclusions. As it turns out, the "stable tracks do
not shorten significantly even when heated to temperatures well above those
normally sufficient for complete annealing of fission tracks."
Of course, this means that the "age" of the sample would not
represent the time since the last thermal episode as previously thought.
The tracks through fluid are also interesting. They are "excessively
long". This is because a
fission fragment traveling through a fluid inclusion does so without appreciable
energy loss. Such features, if undetected, "can distort the
temperature-time paths constructed on the basis of confined fission-track-length
measurements." Again, the
authors propose measures to avoid such pitfalls, but this just adds to the
complexity of this dating "method" and calls into question the dates
obtained before the publication of this paper (i.e., 2000).46
problems have resulted in several interesting contradictions, despite
calibration. For example, Naeser and
Fleischer (Harvard University) showed that, depending upon the calibration
method chosen, the calculated age of a given rock (from Cerro de Mercado, Mexico
in this case) could be different from each other by a factor
of "sixty or more" - -
"which give geologically unreasonable ages.
In addition, published data concerning the length of fission tracks and
the annealing of minerals imply that the basic assumptions used in an
alternative procedure, the length reduction-correction method, are also invalid
for many crystal types and must be approached with caution unless individually
justified for a particular mineral." [emphasis added] 47
Now that's pretty significant -
being off by a factor of sixty or
more?! No wonder the authors
recommend only going with results that do not provide "geologically
example of this sort of aberrancy comes in the form of glass globs known as
"tektites". Tektites are
thought to be produced when a meteor impacts the Earth.
When the massive impact creates a lot of heat, which melts the rocks of
the Earth and send them hurtling through the atmosphere at incredible speed.
As these fragments travel through the atmosphere, they become superheated
and malleable as they melt to a read-hot glow, and are formed and shaped as they
fly along. It is thought that the
date of the impact can be dated by using various radiometric dating methods to
date the tektites. For example, Australian tektites (known as australites) show
K-Ar and fission track ages clustering around 700,000 years.
The problem is that their stratigraphic ages show a far different
Gill, of the National Museum of Victoria, Melbourne, while working the Port
Campbell area of western Victoria uncovered 14 australite samples in situ
above the hardpan soil zone. This zone had been previously dated by the
radiocarbon method at seven locales, the oldest dating at only 7,300 radiocarbon
years (Gill 1965). Charcoal from the same level as that containing specimen 9
yielded a radiocarbon age of 5,700 years. The possibility of transport from an
older source area was investigated and ruled out. Since the "Port Campbell
australites include the best preserved tektites in the world ... any movement of
the australites that has occurred ... has been gentle and has not covered a
great distance" (Gill 1965). Aboriginal implements have been discovered in
association with the australites. A fission-track age of 800,000 years and a K-Ar
age of 610,000 years for these same australites unavoidably clashes with the
obvious stratigraphic and archaeological interpretation of just a few thousand
"Hence, geological evidence from the Australian mainland is at variance, both as to infall frequency and age, with K-Ar and fission-track dating" (Lovering et al. 1972). Commenting on the above findings by Lovering and his associates, the editors of the book, Tektites, state that, "in this paper they have built an incontrovertible case for the geologically young age of australite arrival on earth" (Barnes and Barnes 1973, p. 214).
is problematic. The argument that
various radiometric dating methods agree with each other isn't necessarily true.
Here we have the K-Ar and fission track dating methods agreeing with each other,
but disagreeing dramatically with the radiocarbon and historical dating methods.
These findings suggest that, at least as far as tektites are concerned,
the complete loss of 40Ar
(and therefore the resetting of the radiometric clock) may not be valid (Clark
et al. 1966). It has also been shown that different parts of the same tektite
have significantly different K-Ar ages (McDougall and Lovering, 1969).
This finding suggests a real disconnect when it comes to the reliability
of at least two of the most commonly used radiometric dating techniques.48
short, it seems like fission track dating is tenuous a best - even when given
every benefit of the doubt. It is
just too subjective and too open to pitfalls in interpretation to be used as any
sort of independent measure of estimating elapsed time.
Circular Calibration Methods
There is a methodological problem connected with the manner in which geologists
infer the argon-retention abilities of different minerals. Concerning the
suitability of different minerals for K-Ar dating, Faure (1986, p. 72) writes
"The minerals beryl, cordierite, pyroxene, and tourmaline frequently
contain excess 40Ar, while hornblende, feldspar, phlogopite, biotite, and
sodalite contain such excess 40Ar only rarely ... ." And how is this known?
By comparing the K-Ar dates yielded by such minerals with the expected ones.
Thus the correctness of the geologic time scale is assumed in deciding which
minerals are suitable for dating. For example, concerning the use of glauconies
for K-Ar dating, Faure (1986, p. 78) writes, "The results have been
confusing because only the most highly evolved glauconies have yielded dates
that are compatible with the biostrategraphic ages of their host rocks whereas
many others have yielded lower dates. Therefore, K-Ar dates of 'glauconite' have
often been regarded as minimum dates that underestimate the depositional age of
their host." All of the choices are made in order to obtain dates that are
more in agreement with each other.
There is a methodological problem connected with the manner in which geologists infer the argon-retention abilities of different minerals. Concerning the suitability of different minerals for K-Ar dating, Faure (1986, p. 72) writes "The minerals beryl, cordierite, pyroxene, and tourmaline frequently contain excess 40Ar, while hornblende, feldspar, phlogopite, biotite, and sodalite contain such excess 40Ar only rarely ... ." And how is this known? By comparing the K-Ar dates yielded by such minerals with the expected ones. Thus the correctness of the geologic time scale is assumed in deciding which minerals are suitable for dating. For example, concerning the use of glauconies for K-Ar dating, Faure (1986, p. 78) writes, "The results have been confusing because only the most highly evolved glauconies have yielded dates that are compatible with the biostrategraphic ages of their host rocks whereas many others have yielded lower dates. Therefore, K-Ar dates of 'glauconite' have often been regarded as minimum dates that underestimate the depositional age of their host." All of the choices are made in order to obtain dates that are more in agreement with each other.
It is also interesting that Faure (1986, pp. 345-6) mentions that fission track dating is calibrated (the "zeta calibration") using rocks of "known" ages. However, if these "known" ages are incorrect, then fission track dating that is based on these ages is also incorrect. Thus fission track dating is not an independent test that helps to verify the accuracy of other tests. The result is that radiometric dating in general is in danger of being based on circular reasoning.25
Examples of Problems with Radiometric Dating Techniques
work early work on 26 historic lava flows showed that many of them had excess
argon and were not set to zero at the eruption of the volcano.
The following is the data from these tests: 5
Hualalai basalt, Hawaii (AD 1800-1801) 1.05 to 1.19 million years
Mt. Etna basalt, Sicily (122 BC) 100,000 years
Mt. Etna basalt, Sicily (AD 1972) 150,000 years
Mt. Lassen plagioclase, California (AD 1915) 130,000 years
Sunset Crater basalt, Arizona (AD 1064-1065) 210,000 to 220,000 years
Glass Mountain (BP 130-390) 130,000 years in the future
Mt. Mihara (AD 1951) 70,000 years in the future
Sakurajima (AD 1946) 200,000 years in the future
Dalrymple comments on such findings by saying, "With the exception of the Hualalai flow, the amounts of excess 40Ar and 36Ar found in the flows with anomalous 40Ar/36Ar ratios were too small to cause serious errors in potassium-argon dating of rocks a few million years or older. However, these anomalous 40Ar/36Ar ratios could be a problem in dating very young rocks. If the present data are representative, argon of slightly anomalous composition can be expected in approximately one out of three volcanic rocks."
Dalrymple may have a point. It seems like rocks dating within one or two million years cannot be accurately dated by K-Ar techniques just because of the relatively wide ranges of error. However, can rocks that are tens or hundreds of millions of years be more accurately dated? Perhaps, if these rocks were in fact closed systems and were not subject to contamination by external argon.
also have found that excess 40Ar is trapped in the minerals within
lava flows.7, 8, 9 Several instances have been reported of
phenocrysts with K-Ar "ages" 1-7 millions years greater than that of
the whole rock, and one K-Ar "date" on olivine phenocrysts in a recent
(<13,000 year old) basalt was greater than 110 Ma.10 Laboratory
experiments have tested the solubility of argon in synthetic basalt melts and
their constituent minerals, with olivine retaining 0.34 ppm 40Ar.11,
12 It was concluded that the
argon is held primarily in lattice vacancy defects within the minerals.
The obvious conclusion most investigators have reached is that the excess 40Ar had to be present in the molten lavas when extruded, which then did not completely degas as they cooled, the excess 40Ar becoming trapped in constituent minerals and the rock fabrics themselves. However, from whence comes the excess 40Ar, that is, 40Ar which cannot be attributed to atmospheric argon or in situ radioactive decay of 40K? It is not simply "magmatic" argon? Funkhouser and Naughton found that the excess 40Ar in the 1800-1801 Hualalai flow, Hawaii, resided in fluid and gaseous inclusions in olivine, plagioclase, and pyroxene in ultramafic xenoliths in the basalt, and was sufficient to yield "ages" of 2.6 Ma to 2960 Ma.13 Thus, since the ultramafic xenoliths and the basaltic magmas came from the mantle, the excess 40Ar* must initially reside there, to be transported to the earth's surface in the magmas.
Many recent studies confirm the mantle source of excess 40Ar. Hawaiian volcanism is typically cited as resulting from a mantle plume, most investigators now conceding that excess 40Ar in the lavas, including those from the active Loihi and Kilauea volcanoes, is indicative of the mantle source area from which the magmas came. Considerable excess 40Ar measured in ultramafic mantle xenoliths from Kerguelen Archipelago in the southern Indian Ocean likewise is regarded as the mantle source signature of hotspot volcanism.14 Indeed, data from single vesicles in mid-ocean ridge basalt samples dredged from the North Atlantic suggest the excess 40Ar in the upper mantle may be almost double previous estimates, that is, almost 150 times more than the atmospheric content (relative to 36Ar).15 Another study on the same samples indicates the upper mantle content of 40Ar could be even ten times higher.16
Further confirmation comes from diamonds, which form in the mantle and are carried by explosive volcanism into the upper crust and to the surface. When Zashu et al. obtained a K-Ar isochron "age" of 6.0±0.3 Ga for 10 Zaire diamonds, it was obvious excess 40Ar was responsible, because the diamonds could not be older than the earth itself.14 These same diamonds produced 40Ar/39Ar "age" spectra yielding a ~5.7 Ga isochron.17 It was concluded that the 40Ar is an excess component which has no age significance and is found in tiny inclusions of mantle-derived fluid.
The conventional K-Ar dating method was applied to the 1986 dacite flow from the new lava dome at Mount St. Helens, Washington. Porphyritic dacite which solidified on the surface of the lava dome in 1986 gives a whole rock K-Ar 'age' of 0.35 ± 0.05 million years (Ma). Mineral concentrates from the dacite which formed in 1986 give K-Ar 'ages 'from 0.34 ± 0.06 Ma (feldspar-glass concentrate) to 2.8 ± 0.6 Ma (pyroxene concentrate). These dates are, of course, preposterous. The fundamental dating assumption (no radiogenic argon was present when the rock formed) is brought into question. Instead, data from the Mount St. Helens dacite argue that significant "excess" argon was present when the lava solidified in 1986. Phenocrysts of orthopyroxene, hornblende and plagioclase are interpreted to have occluded argon within their mineral structures deep in the magma chamber and to have retained this argon after emplacement and solidification of the dacite. The amount of argon occluded is probably a function of the argon pressure when mineral crystallization occurred at depth and/or the tightness of the mineral structure. Orthopyroxene retains the most argon, followed by hornblende, and finally, plagioclase. The lava dome at Mount St. Helens dates very much older than its true age because phenocryst minerals inherit argon from the magma. The study of this Mount St. Helens dacite brings yet another question to mind: How accurate are K-Ar "ages" from the many other phenocryst-containing lava flows world-wide?18
The Contamination Argument
Potassium is about 2.5% of the earth's crust. About 1/10,000 of potassium is 40K, which decays into 40Ar with a half-life of 1.25 billion years. Actually, only about 1/10th of the40K decays to Argon, and the rest decays to calcium. Argon is about 3.6 x 10-4 % of the earth's crust. We can assume then that the magma is probably about 2.5% potassium and about 0.00025% of the radioactive form, Potassium-40 (40K). Now, Lets say we are trying to date a one billion year old rock. How much of it would be 40K? Starting with 0.00025% as the modern concentration of 40K in magma, we would have to divide by roughly two (About one half-life). This would leave us with a 0.000125% of 40K. Now, about 90% of the decay product is calcium and only about 10% is Ar-40. This gives about 0.0000125% 40Ar in the total make-up of the rock. This is about one ten millionth of the mass of the rock, a very tiny fraction. If the rock weighed one gram, the Ar-40 in the rock would weight one ten millionth of a gram. And yet, with a relatively large amount of argon in the air, argon filtering up from rocks below, excess argon in lava, the fact that argon and potassium are water soluble, and the fact that argon is mobile in rock and is a gas, we are still expecting this wisp of argon gas to tell us how old the rock is? The percentage of 40Ar is even less for younger rocks. For example, it would be about one part in 100 million for rocks in the vicinity of 50-60 million years old. However, to get just one part in 10 million of argon in a rock in a thousand years, we would only need to get one part in 10 billion entering the rock each year. This would be less than one part in a trillion entering the rock each day, on the average. This would suffice to give a rock an average computed potassium-argon age of over a billion years. Some geochronologists believe that a possible cause of excess argon is that argon diffuses into certain minerals progressively with time and pressure. Significant quantities of argon may be introduced into a mineral even at pressures as low as one bar.
We can also consider the average abundance of argon in the crust. If we assume that a rock has 1/400,000 40K, that is, 2.5 x 10-6 40K, and 3.6 x 10-6 40Ar, then eight times this much 40K must have decayed, thus about 28.8 x 10-6 parts of 40K have decayed, so there is less than 1/10 of the original 40K left. This implies a radiometric age of over 4 billion years. So a rock can get a very old radiometric age just by having average amounts of potassium and argon. It seems reasonable to me that the large radiometric ages are simply a consequence of mixing, and not related to ages at all, at least not necessarily the ages of the rocks themselves. The rates of exchange that would mess up “dates” are very small. It seems to me to be a certainty that water and gas will enter most, if not all, volcanic type rocks through tiny openings and invalidate almost all K-Ar ages. Rocks are not sealed off from the environment. Even if magma was set to “zero time” at the eruption of a volcano, over the course of eons of time and exposure to atmospheric and other sources of extraneous argon, it would seem that contamination would be inevitable. This contamination would seem to be more and more of a problem the older the rock became.
Let me illustrate the circulation patterns of argon in the earth's crust. About 2.5 percent of the earth's crust is believed to be potassium, and about 1/10,000 of this is 40K, which decays to 40Ar with a half-life of about 1.25 billion years. So argon is being produced throughout the earth's crust, and in the magma, all the time. In fact, it probably rises to the top of the magma, artificially increasing its concentration there. Now, some rocks in the crust are believed not to hold their argon, so this argon will enter the spaces between the rocks. Leaching also occurs, releasing argon from rocks. Heating of rocks can also release argon. Argon is released from lava as it cools, and probably filters up into the crust from the magma below, along with helium and other radioactive decay products. All of this argon is being produced and entering the air and water in between the rocks, and gradually filtering up to the atmosphere. But, we know that some minerals absorb argon (“correction factors” are applied for this when using K-Ar dating). So this argon that is being produced will leave some rocks and enter others. The various pressures, temperatures, moisture, nature of the materials and a variety of other factors all play together to challenge the validity of K-Ar and/or Ar-Ar dating.
Different Dating Methods Agree
It is often said that a great many dating methods, used on a single specimen, will agree with each other, thus establishing the accuracy of the date given. In reality, the overwhelming majority of measurements on the fossil bearing geologic column are all done using one method, the K-Ar method (Recall that both potassium and argon are water soluble, and argon (a gas) is mobile in rock.)
"The construction of this time scale was based on about 380 radioisotope ages that were selected because of their agreement with the presumed fossil and geological sequences found in the rocks. Radioisotope ages that did not meet these requirements were rejected on the basis of presumed chemical and/or physical modifications that made the "ages" unreliable indicators of real time. About 85% of the selections were K-Ar date s, 8% rubidium-strontium dates, and 4% uranium-lead dates."
Thus the agreement found between many dates does not necessarily reflect an agreement between different methods, but rather the agreement of the K-Ar method with itself (Especially noting that Dalrymple suggested that only K-Ar dating methods were at all trust worthy). I have seen no good double-blinded research studies that say otherwise. One would think that if this were a good science, then such studies would be done and published, but they are strangely lacking.
Also, specific differences are known and have been known to exist between different dating methods. For example, Isotopic studies of the Cardenas Basalt and associated Proterozoic diabase sills and dikes have produced a geologic mystery. Using the conventional assumptions of radioisotope dating, the Rb-Sr and K-Ar systems should give concordant "ages". However, it has been known for over 20 years that the two systems give discordant "ages", the K-Ar "age" being significantly younger than the Rb-Sr "age".
The "argon reset model" was the first explanation proposed for the discordance. A metamorphic event is supposed to have expelled significant argon from these rocks. The reset model is unable to reconcile the new data, leading to a metamorphic event which is excessively young and inconsistent with the conventional stratigraphic interpretation.
The "argon leakage model" also attempts to explain why these rocks have about half the argon which seems to be required by the Rb-Sr system. The leakage model supposes an incredible improbability. Both the old and new data imply that the rocks leaked argon in nearly exact proportion to the abundance of potassium producing a "leakage isochron", an explanation not supported by a quantity of an appropriate mineral or mesostasis phase. Strong negative correlation between K-Ar model age and K2O in the upper portion of the Cardenas Basalt is not easily explained in a consistent manner. Furthermore, reset and leakage models have difficulty explaining the abundance of initial 36Ar in the rocks, especially the abundance of 36Ar in those rocks which supposedly leaked the most 40Ar.
Three alternatives are suggested to the two argon loss models. The "argon inheritance model" and "argon mixing model" simply propose that argon is positively correlated with potassium from its magma source or produced by a mixing process, and that the linear relationship on a plot of 40Ar versus 40K is an artifact of the magma, not produced by radioisotope decay within these rocks. The inheritance of argon seems to be a better model than is the mixing model. The "change of decay model" goes to the physics of radioisotope decay and proposes a fundamental change in 87Rb and/or 40K decay. All three explanations offered as alternatives to the argon loss models invalidate using the K-Ar system as conventional geochronology would assume. 23
The word "isochron" basically means "same age". Isochron dating is based on the ability to draw a straight line between data points that are thought to have formed at the same time. The slope of this line is used to calculate an age of the sample in isochron radiometric dating. The isochron method of dating is perhaps the most logically sound of all the dating methods - at first approximation. This method seems to have internal measures to weed out those specimens that are not adequate for radiometric evaluation. Also, the various isochron dating systems seem to eliminate the problem of not knowing how much daughter element was present when the rock formed.
Isochron dating is unique in that it goes beyond measurements of parent and daughter isotopes to calculate the age of the sample based on a simple ratio of parent to daughter isotopes and a decay rate constant - plus one other key measurement. What is needed is a measurement of a second isotope of the same element as the daughter isotope. Also, several different measurements are needed from various locations and materials within the specimen. This is different from the normal single point test used with the other "generic" methods. To make the straight line needed for isochron dating each group of measurements (parent - P, daughter - D, daughter isotope - Di) is plotted as a data point on a graph. The X-axis on the graph is the ratio of P to Di. For example, consider the following isochron graph: 21
Obviously, if a line were drawn between these data points on the graph, there would be a very nice straight line with a positive slope. Such a straight line would seem to indicate a strong correlation between the amount of P in each sample and the extent to which the sample is enriched in D relative to Di. Obviously one would expect an increase in the ratio of D as compared with Di over time because P is constantly decaying into D, but not into Di. So, Di stays the same while D increases over time.
But, what if the original rock was homogenous when it was made? What if all the minerals were evenly distributed throughout, atom for atom? What would an isochron of this rock look like? It would look like a single dot on the graph. Why? Because, any testing of any portion of the object would give the same results.
The funny thing is, as rocks cool, different minerals within the rock attract certain atoms more than others. Because of this, certain mineral crystals within a rock will incorporate different elements into their structure based on their chemical differences. However, since isotopes of the same element have the same chemical properties, there will be no preference in the inclusion of any one isotope over any other in any particular crystalline mineral as it forms. Thus, each crystal will have the same D/Di ratio of the original source material. So, when put on an isochron graph, each mineral will have the same Y-value. However, the P element is chemically different from the D/Di element. Therefore, different minerals will select different ratios of P as compared with D/Di. Such variations in P to D/Di ratios in different elements would be plotted on an isochron graph as a straight, flat line (no slope).
Since a perfectly horizontal line is likely obtained from a rock as soon as it solidifies, such a horizontal line is consistent with a "zero age." In this way, even if the daughter element is present initially when the rock is formed, its presence does not necessarily invalidate the clock. Time might still be able to be determined based on changes in the slope of this horizontal line.
As time passes, P decays into D in each sample. That means that P decreases while D increases. This results in a movement of the data points. Each data point moves to the left (decrease in P) and upwards (increase in D). Since radioactive decay proceeds in a proportional manner, the data points with the most P will move the most in a given amount of time. Thus, the data points maintain their linear arrangement over time as the slope between them increases. The degree of slope can then be used to calculate the time since the line was horizontal or "newly formed". The slope created by these points is the age and the intercept is the initial daughter ratio. The scheme is mathematically sound.
The nice thing about isochrons is that they would seem to be able to detect any sort of contamination of the specimen over time. If any data point became contaminated by outside material, it would no longer find itself in such a nice linear pattern. Thus, isochrons do indeed seem to contain somewhat of an internal indicator or control for contamination that indicates the general suitability or unsuitability of a specimen for dating.
So, it is starting to look like isochron dating has solved some of the major problems of other dating methods. However, isochron dating is still based on certain assumptions.
All areas of a given specimen formed at the same time
The specimen was entirely homogenous when it formed (not layered or incompletely mixed)
Limited Contamination (contamination can form straight lines that are misleading)
Isochrons that are based on intra-specimen crystals can be extrapolated to date the whole specimen
Given these assumptions and the above discussion on isochron dating, some interesting problems arise as one considers certain published isochron dates. As it turns out, up to "90%" of all published dates based on isochrons are "whole-rock" isochrons.22
So, what exactly is a whole-rock isochron? Whole-rock isochrons are isochrons that are based, not on intra-rock crystals, but on variations in the non-crystalline portions of a given rock. In other words, sample variations in P are found in different parts of the same rock without being involved with crystalline matrix uptake. This is a problem because the basis of isochron dating is founded on the assumption of original homogeny. If the rock, when it formed, was originally homogenous, then the P element would be equally distributed throughout. Over time, this homogeny would not change. Thus, any such whole-rock variations in P at some later time would mean that the original rock was never homogenous when it formed. Because of this problem, whole-rock isochrons are invalid, representing the original incomplete mixing of two or more sources.
Interestingly enough, whole rock isochrons can be used as a test to see if the sample shows evidence of mixing. If there is a variation in the P values of a whole rock isochron, then any isochron obtained via crystal based studies will be automatically invalid. The P values of various whole-rock samples must all be the same, falling on a single point on the graph. If such whole-rock samples are identical as far as their P values, mixing would still not be ruled out completely, but at least all available tests to detect mixing would have been satisfied. And yet, such whole-rock isochrons are commonly published. For example, many isochrons used to date meteorites are most probably the result of mixing since they are based on whole-rock analysis, not on crystalline analysis.22
There are also methods used to detect the presence of mixing with crystalline isochron analysis. If a certain correlation is present, the isochron may be caused by a mixing. However, even if the correlation is present, it does not mean the isochron is caused by a mixing, and even if the correlation is absent, the isochron could still be caused by a more complex mixing (Woodmorappe, 1999, pp. 69-71). Therefore such tests are of questionable value.25
Interestingly, mainstream scientists are also starting to question the validity of isochron dating. In January of 2005, four geologists from the UK, Wisconsin and California, writing in Geology, wrote:
The determination of accurate and precise isochron ages for igneous rocks requires that the initial isotope ratios of the analyzed minerals are identical at the time of eruption or emplacement. Studies of young volcanic rocks at the mineral scale have shown this assumption to be invalid in many instances. Variations in initial isotope ratios can result in erroneous or imprecise ages. Nevertheless, it is possible for initial isotope ratio variation to be obscured in a statistically acceptable isochron. Independent age determinations and critical appraisal of petrography are needed to evaluate isotope data. If initial isotope ratio variability can be demonstrated, however, it can be used to constrain petrogenetic pathways. . .
[Beyond this, the geologist has to know that the rock had (1) slow diffusion and (2) rapid cooling. But then,] The cooling history will depend on the volume of magma involved and its starting temperature, which in turn is a function of its composition. . .
If the initial variation is systematic (e.g., due to open-system mixing or contamination), then isochrons are generated that can be very good [based on their fit to the graph], but the ages are geologically meaningless.50
In short, isochron dating is not the independent dating method that it was once thought. As with the other dating methods discussed already, isochron dating is also dependent upon "independent age determinations".
Isochrons have been touted by the uniformitarians as a fail-safe method for dating rocks, because the data points are supposed to be self-checking (Kenneth Miller used this argument in a debate against Henry Morris years ago.) Now, these geologists, publishing in the premiere geological journal in the world, are telling us that isochrons can look perfect on paper yet give meaningless ages, by orders of magnitude, if the initial conditions are not known, or if the rocks were open systems at some time in the past?!
sounds like what young earth creationists have been complaining about all
along. But then, these geologists put a happy face on the situation.
It’s not all bad news, they say, because if the geologist can know the true
age by another method, he can glean some useful information out of the
errors. The problem is that it is starting to get really difficult to find
a truly independent dating method out of all the various dating methods
Zircons and Uranium-Lead Dating
Uranium-238 has a half-life decay of 4.5 billion years. It gives rise to Thorium-234Thorium-234 has a half-life decay of 24 days. It's daughter product is protactinium-234.Protactinium-234 decays in about one minute. It gives rise to uranium-234.Uranium-234 has a half-life of 233,000 years. It yields Thorium-230.Thorium-230 takes about 83,000 years to decay. It's daughter product is radium-226.Radium-226 decays in 1600 years. It is converted to radon-222.Radon-222 takes 3.8 days to decay into polonium-218.Polonium-218 has the short life of 3 minutes before it is decayed into the next product on our list, lead-214.Lead-214 takes 24 minutes to decay into bismuth-214.Bismuth-214 lives only 20 minutes before becoming polonium-214.Polonium-214 has the short life of 150 microseconds before converting itself to lead-210.Lead-210 yields bismuth-210 in about 22 years.Bismuth-210 then gives rise to polonium-210 in about 5 days.Polonium-210 finally decays into lead-206 which is stable.
"Simple laboratory (Hf) leaching experiments of zircon provide a clear link between enhanced solubility of U234 and radiogenic lead due to alpha-recoil damage (Davis and Krogh submitted; Mattinson 1994). Furthermore, because most upper crustal rocks cooled below annealing temperatures long after their formation, early formed lead rich in Pb207 is locked in annealed sites so that the leachable component is enriched in recently formed Pb206. The isotopic composition of the leachable lead component then depends more on the cooling history and annealing temperatures of each host mineral than on their geological age; and the axiom that Pb isotopes cannot be fractionated in the natural environment, is invalid. . . Although these experiments are based on a strong Hf attack on zircons, we believe, given the widespread U234 anomalies (of several hundred percent) observed in groundwater (Osmond and Cowart 1992), that they apply to the differential mobility of radiogenic Pb isotopes on a local and global scale."33
Also, consider the following excerpt concerning ancient zirons from the Gabbro-Peridotite Complex of the Mar:
"All the grains are characterized by high common Pb content: 206Pb/204Pb ratios are in the interval 18.36-18.66 [usually around 5000]. There was constructed Pb-Pb isochron on the four points of studied zircon with the age corresponding to 3476+/-510 Ma (MSWD=0.4). High error of the age estimation is caused by rather limited variation of 206Pb/204Pb ratio in the studied zircons and a comparatively high error in determination of Pb isotope composition. Zircon age calculations on the base of Upb systematics have been complicated by high share of common Pb and uncertainty of its isotope composition. . . . Common lead was captured in the process of zircon crystallization, perhaps, by mineral and fluid inclusions. But there is a small share of inherited zircon substance with the age of 3.0-3.5 Ga in the composition of the studied zircon. Thus, the discordia itself obtained by us is interpreted as a result of mixture of newly formed young zircon with some share of Archean zircon presented in each studied crystal."34
as well that the "206Pb/204Pb ratio, used for contamination
Also, if errors for individual zircon tests are too
large, these values are simply discarded. Those
"analyses with large errors that can be attributed to the presence of
zoning, cracks and inclusions in the analyzed zircon"
Such data are simply "rejected from the dataset." In addition,
"High uranium content may cause a zircon to become metamict due to
destruction of the crystal lattice by radiation. This enhances the mobility of U
and especially Pb." So, high
uranium content is "also a reason for rejection of some analyses." A
"correction is also applied for common Pb on the basis of the abundance of
204Pb, which was typically 10 ppm in all standards measured and variable in the
So, how confident can one be in zircon dates who's
published 204Pb levels range from very high to very low?
It seems to me that quite often published U-Pb and Pb-Pb dates do in fact
involve fairly significant 204Pb levels.33,37,38
Certainly there are "correction" factors to and methods of
selection are used compensate for this common lead, but how are these calibrated
and how is the reliability of the calibration and selection method determined?
Of course, if the level of 204Pb is too high, the data obtained is not
calibrated, but is simply discarded.39
And, what about the fact that other isotopes of uranium, thorium, as well
as the many lead isotopes move around, in and out of zircon crystals, as a
function of temperature, radiation, and other sorts of factors over time?
Doesn't this mess up the idea that all lead in zircons must be the result
of radioactive decay?
Squashed Polonium Haloes
It is also of interest in regard to radiometric dating that Robert Gentry claims to have found "squashed" polonium haloes as well as embryonic uranium radiohaloes in coal deposits from many geological layers claimed to be hundreds of millions of years old. (See the Oct.15, 1976 issue of Science.) These haloes represent particles of polonium and uranium, which penetrated into the coal at some point and produced a halo by radioactive decay. The fact that they are squashed indicates that part of the decay process began before the material was compressed, so the polonium had to be present before compression. Since coal is relatively incompressible, Gentry concludes that these particles of uranium and polonium must have entered the deposit before it turned to coal. However, there is only a very small amount of lead with the uranium; if the uranium had entered hundreds of millions of years ago, then there should be much more lead. With very little evidence or obvious method of diffusion or other forms of loss the amount of lead present is consistent with an age of thousands rather than millions of years. However, it's just hard to believe, according to conventional geological time scales, that this coal was compressed any time within the past several thousand or even hundred million years.
Some have argued that "radon 222 that results from uranium decay is an inert gas and may have escaped, resulting in little lead being deposited. This would make the observed haloes consistent with an old age for the coal." However, the fact that these uranium haloes are "embryonic (very faint) also argues for a young age. In addition, not all of the radon would be on the surface of the particles of uranium. That which was inside or bordering on coal would likely not be able to escape. Since radon 222 has a half-life of about 4 days, it would not have much time to escape, in any event. Such haloes were also found in shale, with young U/Pb ages as well, and it may be less likely for the radon to escape from shale."40,41
The Paradox of Old Age Without Evidence of Aging
What happens when something is dated as being very old, but shows little or no physical signs of relative aging? For example, consider the Columbia River Basalt Group (CRBG) located in the northwestern part of the United States (eastern Washington, northern Oregon, and western Idaho). This basalt group is rather large covering an area of 163,700 square kilometers and fills a volume of 174,000 cubic kilometers. The vast extent and sheer volume of such individual flows are orders of magnitude larger than anything ever recorded in known human history. Within this group are around 300 individual lava flows each of rather uniform thickness over many kilometers with several extending up to 750 kilometers from their origin. The CRBG is believed to span the Miocene Epoch over a period of 11 million years (from ~17 to 6 million years ago via radiometric dating).26
Now, the problem with the idea that these flows span a period of over 11 million years of deposition is that there is significant physical evidence that the CRBG flows were deposited relatively rapidly with respect to each other and with themselves. The average time between each flow works out to around 36,000 years, but where is the erosion to the individual layers of basalt that one would expect to see after 36,000 years of exposure? The very fact that these flows cover such great distances indicate that the individual flows traveled at a high rate of speed in order to avoid solidification before they covered such huge areas as they did. Also, there are several examples where two or three different flows within the CRBG mix with each other. This suggests that some of the individual flows did not have enough time to solidify before the next flow(s) occurred. If some 36,000 years of time are supposed to separate each of the individual flows where is the evidence of erosion in the form of valleys or gullies cutting into the individual lava flows to be filled in by the next lava flow? There are no beds of basalt boulders that would would expect to be formed over such spans of time between individual flows.
Some have suggested that the rates of erosion on these basalts was so minimal (< 0.5 cm/k.y.) that it would not have resulted in a significant change even after 36,000 years. However, a recent real time study by Riebe et. al. to determine the effects of various climatic conditions on erosion rates of granite showed that erosion rates averaged 4cm per 1,000 years (k.y.) with a range of between 2cm/k.y. and 50cm/k.y. What is especially interesting is that despite ranges in climate involving between 20 to 180 cm/yr of annual precipitation and between 4 to 15 °C the average erosion rates varied by only 2.5 fold across all the sites and were not correlated with climate indicating that climatic variations weakly regulate the rates of granitic erosion.27 Another fairly recent paper, by Lasaga and Rye, from the Yale University Department of Geology and Geophysics, noted that the average erosion rates of basalts from the Columbia River and Idaho regions is "about 4 times as fast as non-basaltic rocks" - to include granite.28 This suggests that one could reasonable expect the erosion rate of basalts to average 16 to 20 cm/k.y. Over the course of 36,000 years this works out to between 6 to 7 meters (19 to 23 feet) of vertical erosion. This is significant erosion and there should be evidence of this sort of erosion if the time gap between flow was really 36,000 years. So, where is this evidence?
For several other such flows in the United States and elsewhere around the world the time intervals between flows are thought to be even longer - and yet still there is little evidence of the erosion that would be expected after such passages of time. For example, the Lincoln Porphyry of Colorado was originally thought to be a single unit because of the geographic proximity of the outcrops and the mineralogical and chemical similarities throughout the formation. Later, this idea was revised after radiometric dating placed various layers of the Lincoln Porphyry almost 30 million years apart in time. But how can such layers which show little if any evidence of interim erosion have been laid down thousands much less millions of years apart in time? Other examples, such as the Garrawilla Lavas of New South Wales, Australia, are found between the Upper Triassic and Jurassic layers and yet these lavas, over a very large area, grade imperceptibly into lavas which overlie Lower Tertiary sedimentary rock (supposedly laid down over 100 million years later). 26 Robert Kingham noted, concerning this formation, in the 1998 Australian Geologic Survey Organization that that, "Triassic sediments unconformably overlie the Permian sequences. . . The Napperby depositional sequence represents the upper limit of the Gunnedah Basin sequence, with a regional unconformity existing between the Triassic and overlying Jurassic sediments of the Surat Basin north of the Liverpool Ranges. The Gunnedah Basin sequence includes a number of basic intrusions of Mesozoic and Tertiary rocks. These are associated with massive extrusions of the Garrawilla Volcanic complex and the Liverpool, Warrumbungle and Nandewar Ranges."29 Now, isn't it interesting that Tertiary sediments in the Gunnedah Basin sequence, which are thought to be over 100 million years younger, exist between Triassic and Jurassic sediments?
Also, throughout the CRBG and elsewhere are found "pillow lava" and palagonite formations - especially near the periphery of the lava flows. There are a few outcrops where tens of meters of vertical outcrop and hundreds of meters of horizontal outcrop consist entirely of pillow structures. Also, palagonite, with a greenish-yellow appearance produced via the reaction of hot lava coming in contact with water, is found throughout. These features are suggestive of lava flow formation in a very wet or even underwater environment. Certainly pillow lavas indicate underwater deposition, but note that lavas can be extruded subaqeously without the production of pillow structures. The potential to form pillow lava decreases as the volume of extruded lava increases. Thus, the effective contact area between lava and water (where pillow formations can potentially form) becomes proportionately smaller as the volume of lava extruded becomes larger. Other evidences of underwater formation include the finding of fresh water fossils (such as sponge spicules, diatoms, and dinoflagellates) between individual lava flows. Consider some interesting conclusions about these findings by Barnett and Fisk in a 1980 paper published in the journal, Northwest Science:
The Palouse Falls palynoflora reflects reasonably well the regional climatic conditions as evidence by the related floras of the Columbia Plateau. The presence of planktonic forms, aquatic macrophytes, and marsh plants indicates that deposition of the sediments took place in a body of water, probably a pond or lake. This interpretation is supported by the presence of abundant diatoms. The general decrease in aquatic plants and increase in forest elements upward in the section suggest a shallowing or infilling of the pond or lake, perhaps due to increased volcanic activity and erosion of ash from the surrounding region. Supporting this view is the presence of thin bands of lignite near the top of the section, with a 1-10 cm coal layer just underlying the capping basalt." 31
Now, what is interesting here is that these "forest elements" to include large lenses of fossilized wood are widely divergent in the type of preserved wood found. It is interesting that hundreds of species are found all mixed up together ranging from temperate birch and spruce to subtropical Eucalyptus and bald cypress. The petrified logs have been stripped of limbs and bark and are generally found in the pillow complexes of the basaltic flows, implying that water preserved the wood from being completely destroyed by the intense heat of the lava as it buried them.
For Barnett and Fisk to suggest that the finding of such fossil remains suggest the presence of a small pond or lake being filled in by successive flows just doesn't seem to add up. How are such ecologically divergent trees going to get concentrated around an infilling pond or lake? Also, how is a 10cm layer of coal going to be able to form under the "capping basalt"? It is supposed to take very long periods of time, great pressure, heat, and moisture to produce coal. How did this very thin layer of coal form and then be preserved without evidence of any sort of uneven erosion by a relatively thin layer of capping basalt? Also, numerous well-rounded quartzite gravel, cobbles, and boulders locally interbedded within and above the basalt flows.26 How did these quartzite boulders, cobbles, and gravel get transported hundreds of miles by enough water to form tiny ponds and small shallow lakes? Does this make any sense? It seems more likely that huge shortly spaced watery catastrophes were involved in formation of many of these features - concentrating and transporting mats of widely divergent vegetation and inorganic rocks over long distances before they were buried by shortly spaced lava flows traveling rapidly over huge areas.
Lava traveling rapidly under water would experience rapid surface cooling and fracturing of this surface "skin". As it turns out, entablatures and colonnades are a common structural feature of basalts. These features are named by analogy to the respective horizontal and vertical architectural structures. Some have hypothesized that as water cools the outer "skin" of the molten lava a thin crust is rapidly formed. Then, the large temperature gradient between the crust above and the molten lava below creates tensional stresses that crack the crust which allow water to percolate through these cracks to come in contact with more molten lava and form another crust, which then cracks . . . and the cycle of crust formation and cracking continues. In the end, this rapid cyclical cooling process produces a thick slab of rock with columnar jointing.26
One other evidence of fairly rapid cooling is the finding that these basalts contain relatively small crystals. When magma cools, crystals form because the solution is super-saturated with respect to some minerals. If the magma cools quickly, the crystals do not have much time to form, so they are very small. If the magma cools slowly, then the crystals have enough time to grow and become large. For comparison, consider that some granites contain minerals which are up to one meter in diameter! The size of crystals in an igneous rock is thought to be an important indicator of the conditions where the rock formed. A rock with small crystals probably formed at or near the surface and cooled quickly.30
Turrin, A Tutorial on the 40Ar/39Ar
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Broadhurst, M.J. Drake, B.E. Hagee and T.J. Benatowicz,
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Broadhurst, M.J. Drake, B.E. Hagee and T.J. Benatowicz, Solubility
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Valbracht, M. Honda, T. Matsumoto, N. Mattielli, I. McDougall, R. Ragettli
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Primordial Noble Gases in the Earth, Science, 276 pp. 568-571. 1997
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Austin, S. A., Excess Argon within Mineral Concentrates from the New Dacite Lava Dome at Mount St Helens Volcano, Creation Ex Nihilo Technical Journal, Vol. 10, No. 3, 1996, page 355
Stanssen, Chris., Isochron Dating, Sept., 1998. ( http://www.talkorigins.org/faqs/isochron-dating.html )
Overn, W. 1986 "The Truth About Radiometric Dating" Proceedings of the First International Conference on Creationism Vol 1, Creation Science Fellowship, Pittsburgh, Pennsylvania, pp 101-104. ( http://tccsa.freeservers.com/articles/isochrons2.html )
Austin, Steven A., Snelling, Andrew A., Discordant Potassium-Argon Model and Isochron "Ages" for Cardenas Basal (Middle Proterozoic) and Associated Diabase of Eastern Grand Canyon, Arizona, Presented at the Fourth International conference on Creationism, Pittsburgh, PA, August 3-8, 1998. ( http://www.icr.org/research/sa/sa-r03.htm )
Riebe, C., Kirchner, J.W., Granger D.E., Finkel, R.C., "Minimal climatic control on erosion rates in the Sierra Nevada, California", Geology; May 2001; v. 29; no.5; p. 447-450. (http://www.seismo.berkeley.edu/~kirchner/reprints/2001_41_minimal_climatic.pdf)
Lasaga, A.C., Rye, D.M., "Reactive Fluid Flow and Applications to Diagenesis, Mineral Deposits, and Crustal Rocks", Grantee: Yale University, Department of Geophysics, Summer, 1997. (http://www.sc.doe.gov/production/bes/geo/Publications/FY97Summ/yale.htm)
Kingham, Robert, "Geology of the Murray-Darling Basin - simplified Lithostratigraphic Groupings", Australian Geological Survey Organization, Department of Primary Industries and Energy, 1998. (http://www.brs.gov.au/mdbsis/mdbgeol.pdf)
DeLaughter, John, "Cooling Rate and Crystal Size", Accessed December, 2003. (http://www.earth.nwu.edu/people/seth/demos/XTAL/xtal.html)
Barnett, J. and Fisk, L.H., "Palynology and paleoecology of a sedimentary interbed in the Yakima Basalt (Miocene)", Palouse Falls, Washington, (4):259-278, 1980. Northwest Science, p 54.
Raymond C. Jonckheere and Gunther A. Wagner, "On the occurrence of anomalous fission tracks in apatite and titanite," American Mineralogist, Volume 85, pages 1744–1753, 2000 ( Link )
Naeser, C.W., Feischer, R.L., "Age of the apatite at Cerro de Mercado, Mexico: A problem for fission-track annealing corrections," Geophysical Research Letters, (1975) Volume 2, Issue 2, p. 67-70 ( Link )
Johns, Warren H., "Anomalous Ages for Meteorite Impacts and Tektites", Origins 3(2):85-96 (1976). ( Link )
McDougall and Harrison, K/Ar and 40Ar/39Ar Methodology, New Mexico Geochronology Research Laboratory, 1999 ( Link )
Davidson, Charlier, Hora, and Perlroth, “Mineral isochrons and isotopic fingerprinting: Pitfalls and promises,” Geology, (2005) Vol. 33, No. 1, pp. 29–32 (Link)
"Two important assumptions are implicit in this equation: First, that we are dealing with a closed system. And second, that no atoms of the daughter were present in the system when it formed. These assumptions furnish the most serious limitations on the accumulation clock. Rigorously closed systems probably do not exist in nature, but surprisingly, many minerals and rocks satisfy the requirement well enough to be useful for nuclear age determination. The problem is one of judicious geologic selection.", Henry Fall, "ASSUMPTIONS", AGES OF ROCKS, PLANETS & STARS, p.vi.
"Certain assumptions presupposes that the concentration of uranium in any specimen has remained constant over the specimen's life...groundwater percolation can leach away a proportion of the uranium present in the rock crystals. The mobility of the uranium is such that as one part of a rock formation is being improvised another part can become abnormally enriched. Such changes can also take place at relatively low temperatures." J.D. Macdougall, “SHIFTY URANIUM”, Scientific American, Vol.235(6):118
"What complicates things for the uranium-lead method is that nonradiogenic lead 204, 206, 207 and 208 also exist naturally, and scientists are not sure what the ratios of nonradiogenic to radiogenic lead were early in the moon's history...The problem of how much lead was around to begin with still remains...If all of the age-dating methods (rubidium-strontium, uranium-lead and potassium-argon) had yielded the same ages, the picture would be neat. But they haven't. The lead ages, for example, have been consistently older...Isotopic ages have been obtained for material from five landing sites on the moon--those of Apollo's 11, 12, 14, 15 and Luna 16; each site has a different age. But in a given site, the ages also vary...Ideally, however, any one basaltic rock from a given site should yield the same isotopic age, regardless of the method used.", Everly Driscoll, "DATING OF MOON SAMPLES: PITFALLS AND PARADOXES", Science News, Vol. 101, p. 12
"Studies of the helium method (2) have shown that low ages based on helium, obtained on common rockforming minerals, do not necessarily reflect diffusive loss of helium from the lattices of those minerals; under ideal conditions, some mineral lattices even appear to retain helium quantitatively for longer than 10 8years." Fanale & Schaeffer, Brookhaven National Laboratory, Science Vol.149, p.312
"There has been in recent years the horrible realization that radiodecay rates are not as constant as previously thought, nor are they immune to environmental influences. And this could mean that the atomic clocks are reset during some global disaster, and events which brought the Mesozoic to a close may not be 65 million years ago but, rather, within the age and memory of man." Frederic B. Jueneman, FAIC, Industrial Research & Development, p.21, Tune 1982
"It is now well known that KAr ages obtained from different minerals in a single rock may be strikingly discordant." Joan C. Engels, “DIFFERENT AGES FROM ONE ROCK”, Journal of Geology, ,Vol.79, p.609
"We suspect that the lack of concordance may result in some part, from the choice of isotope ratios from primitive lead, rather than from lead gain or Uranium loss. It therefore follows that the whole of the classical interpretation of the meteorite, lead isotope data is in doubt and that the radiometric estimates of the age of the earth are placed in jeopardy." Gail, Arden, & Huchenson Oxford, FOUNDATION DECAYS, Nature, Vol.240, p.67.
"The radiogenic argon and helium contents of three basalts erupted into the deep ocean from an active volcano (Kilauea) have been measured. Ages calculated from these measurements increase with sample depth up to 22 million years for lavas deduced to be recent....it is possible to deduce that these lavas are very young, probably less than 200 years old. The samples, in fact, may be very recent...", C.S. Nobel & J.J. Naughton, RECENT LAVA @ 22M, Dept. of Chem, Hawaiian Inst. of Geophysics, Science, Vol.162, p.265
"In conventional interpretation of KAr age data, it is common to discard ages which are substantially too high or too low compared with the rest of the group or with other available data such as the geological time scale. The discrepancies between the rejected and the accepted are arbitrarily attributed to excess or loss of argon." A. HAYATSU, “ARBITRARY”, Dept. of Geophysics, U. of Western Ontario, Canadian Journal Of Earth Science, 16:974.
"In general, dates in the 'correct ball park' are assumed to be correct and are published, but those in disagreement with other data are seldom published nor are the discrepancies fully explained." R. L. MAUGER, E. Carolina U., DISSENTERS EJECTED, Contributions To Geology, Vol.15 (1): 17
"If we assume that (1) a rock contained no Pb206 when it was formed, (2) all Pb206 now in the rock was produced by radioactive decay of u238, (3) the rate of decay has been constant, (4) there has been no differential leaching by water of either element, and (5) no U238 has been transported into the rock from another source, then we might expect our estimate of age to be fairly accurate. Each assumption is a potential variable, the magnitude of which can seldom be ascertained. In cases where the daughter product is a gas, as in the decay of potassium (K40) to the gas argon (Ar 40) it is essential that none of the gas escapes from the rock over long periods of time...It is obvious that radiometric technique may not be the absolute dating methods that they are claimed to be. Age estimates on a given geological stratum by different radiometric methods are often quite different (sometimes by hundreds of millions of years). There is no absolutely reliable long-term radiological clock. The uncertainties inherent in radiometric dating are disturbing to geologists and evolutionists...". W.D. Stansfield, Prof. Biological Science, Cal. Polyt. State U., THE SCIENCE OF EVOLUTION, 1977, p.84.
"The two principle problems have been the uncertainties in the radioactive decay constants of potassium and in the ability of minerals to retain the argon produced by this decay.” G.W. Wetherill, "Radioactivity of Potassium and Geologic Time," in Science, September 20, 1957, p. 545.
"The conventional K-Ar dating method was applied to the 1986 dacite flow from the new lava dome at Mount St. Helens, Washington. Porphyritic dacite, which solidified on the surface of the lava dome in 1986, gives a whole rock K-Ar 'age ' of 0.35 ± 0.05 million years (Ma). Mineral concentrates from the dacite, which formed in 1986, give K-Ar 'ages 'from 0.34 ± 0.06 Ma (feldspar-glass concentrate) to 2.8 ± 0.6 Ma (pyroxene concentrate). These 'ages 'are, of course, preposterous. The fundamental dating assumption ('no radiogenic argon was present when the rock formed ') is questioned by these data. Instead, data from this Mount St. Helens dacite argue that significant 'excess argon 'was present when the lava solidified in 1986." Steven A. Austin, Creation Ex Nihilo Technical Journal Vol. 10 (Part 3) - ISSN 1036 CEN Tech. J, 1996.
"Processes of rock alteration may render a volcanic rock useless for potassium-argon dating . . We have analyzed several devitrified glasses of known age, and all have yielded ages that are too young. Some gave virtually zero ages, although the geologic evidence suggested that devitrification took place shortly after the formation of a deposit." J.F. Evernden, et. al., "K / A Dates and Cenozoic Mannalian Chronology of North America," in American Journal of Science, February 1964, p. 154.
"As much as 80 percent of the potassium in a small sample of an iron meteorite can be removed by distilled water in 4.5 hours." L.A. Rancitelli and D.E. Fisher, "Potassium-Argon Ages of Iron Meteorites," in Planetary Science Abstracts, 48th Annual Meeting of the American Geophysical Union (1967), p. 167.
“Situations for which we have both the carbon-14 and potassium-argon ages for the same event usually indicate that the potassium-argon ‘clock’ did not get set back to zero. Trees buried in an eruption of Mount Rangotito in Auckland Bay area of New Zealand provide a prime example. The carbon-14 age of the buried trees is only 225 years, but some of the overlying volcanic material has a 465,000-year potassium-argon age.” (Harold Coffin, Origin by Design, pp. 400.)
“Lunar soil collected by Apollo 11 gave discordant ages by different methods” Pb207/Pb206, 4.67 billion ; Pb206 / U238, 5.41 billion; Pb207 / U238, 5.41 billion; Pb207 / U235, 4.89 billion; and Pb208 / Th232, 8.2 billion years. Rocks from the same location yielded K / Ar ages of around 2.3 billion years.” (R.E. Kofahl and K.L. Segraves, Creation Explanation (1975), pp. 200, 201.)
"Actually, the method (of comparing lead isotopes to make specimen dating more accurate) is subject to several errors.  Loss of radon 222 raises the lead: lead ratio and the calculated age.  A rather large error may be introduced by the uncertainty in the composition of the original lead. This error may exceed the measured value when dealing with younger uranium minerals containing even small amounts of original lead, as clearly recognized by Holmes when the method was first proposed.  Presence of old radiogenic lead (formed in a prior site of the parent uranium) may cause great error.  Instrumental errors in mass spectrometry may yield consistently high apparent proportions of lead 204 and lead 207.  Re-distribution of elements by renewed hydrothermal activity may be a serious source of error in all-lead methods. Henry Faul, Nuclear Geology (1954), p. 295.
"And what essentially is this actual time scale? On what criteria does it rest? When all is winnowed out and the grain reclaimed from the chaff it is certain that the grain in the product is mainly the paleontologic record [strata dating based on index fossil theories] and highly likely that the physical record [radioactive dating] is the chaff "~*E.M. Spieker, "Mountain-Building Chronology and the Nature of the Geologic Time-Scale," in Bulletin of the American Association of Petroleum Geologists, August 1956, p 1806.
"The two uranium-lead ages often differ from each other markedly, and the thorium-lead age on the same mineral is almost always drastically lower than either of the others. " L.T. Aldrich, "Measurement of Radioactive Ages of Rocks," in Science, May 18, 1956, p.872.
"Most of the ages obtained by the lead:thorium method disagree with the ages of the same minerals computed by other lead methods. The reasons for this disagreement are largely unknown. Henry Faul, Nuclear Geology (1954), p.295.
"The most reasonable age (from among the many conflicting "dates" offered) can be selected only alter careful consideration of independent geochronologic data as well as field, stratigraphic and paleontologic evidence, and the petrographic and paragenetic relations.” L.R. Stief, T.W. Stem and R.N. Eichler, "Algebraic and Graphic Methods for Evaluating Discordant Lead-Isotope Ages," in U.S. Geological Survey Professional Papers, No. 414-E (1963).
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