Stratigraphy and radiometric dating problems
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Progressive geochemical differentiation of the upper mantle Stratigraphy and radiometric dating problems the Earth has resulted in the concentration of U and Th into the rocks of the continental crust compared to those of the upper mantle. The concentration of Pb is usually so much higher than U, that a 2- to 3-fold increase of U doesn't change the percent composition much e. We see that there are at least two kinds of magma, and U and Th get carried along in silica rich magma rather than in basaltic magma. This represents major fractionation. Of course, any process that tends to concentrate or deplete uranium or thorium relative to lead pfoblems have an influence on radiometirc radiometric ages computed by uranium-lead or thorium-lead dating.
Also, the fact that there are two kids of magma could mean that the various radiometric ages are obtained by mixing of these kinds of magma in different proportions, and do not represent true ages at all. Finally, we have a third quotation from Elaine Datign. Kennedy in Geoscience Reports, SpringNo. Contamination and fractionation issues are frankly acknowledged by the geologic community. If this occurs, initial volcanic eruptions would have a preponderance daging daughter products relative to the parent isotopes. Such a distribution would give the appearance of age.
As the magma chamber is depleted in daughter products, Stratigraphy and radiometric dating problems lava flows raviometric ash beds would have younger dates. Such a scenario does not answer all of the daitng or solve all of the problems that radiometric dating poses for those who believe the Genesis account of Creation and the Stratigraphy and radiometric dating problems. It does suggest at least one aspect of the problem that could be researched more thoroughly. Principles of Isotope Ans John Wiley and Sons, Inc. It is interesting that contamination and fractionation issues are frankly acknowledged by the geologic community.
But they may not be so familiar to radimetric readers of talk. So we have two kinds of processes taking place. There are those processes taking place when lava solidifies and various minerals crystallize Stratigraphy and radiometric dating problems at different times. There are also processes taking place within a datijg chamber that can cause differences nad the composition of the magma from the top to the bottom of the chamber, since one might expect the temperature at the top to be cooler. Both kinds Stratibraphy processes can influence radiometric dates. In addition, the magma chamber would be expected to be cooler all around its borders, both Stratigrwphy the top and the bottom as well as in the horizontal extremities, and these effects must also be taken into account.
For example, heavier substances Sttratigraphy tend to sink to the bottom Stratigrapjy a magma chamber. Also, substances with a higher melting point will tend to crystallize out at the top of a magma chamber and fall, since it will be cooler at the top. These substances will then fall to the lower Stratirgaphy of the magma chamber, where it is hotter, and remelt. This will make the composition of the magma different at the top and bottom of the chamber. Raduometric could influence radiometric dates. This mechanism was suggested by Jon Covey and others. The solubility of various substances in the magma also could be a function of temperature, and have an influence on the composition of the magma Stratigrpahy the top and bottom of the magma chamber.
Finally, minerals that crystallize at the top of the chamber and fall may tend to incorporate other substances, and so these other substances will also tend to have a change in concentration from the top to the bottom of the magma chamber. There are quite a number of mechanisms in operation in a magma chamber. I count at least three so far -- sorting by density, sorting by melting point, and sorting by how easily something is incorporated into minerals that form at the top of a magma chamber. Then you have to remember that sometimes one has repeated melting and solidification, introducing more complications. There is also a fourth mechanism -- differences in solubilities.
How anyone can keep track of this all is a mystery to me, especially with the difficulties encountered in exploring magma chambers. These will be definite factors that will change relative concentrations of parent and daughter isotopes in some way, and call into question the reliability of radiometric dating. In fact, I think this is a very telling argument against radiometric dating. Another possibility to keep in mind is that lead becomes gaseous at low temperatures, and would be gaseous in magma if it were not for the extreme pressures deep in the earth.
It also becomes very mobile when hot. These processes could influence the distribution of lead in magma chambers. Let me suggest how these processes could influence uranium-lead and thorium-lead dates: The following is a quote from The Earth: The magnesium and iron rich minerals come from the mantle subducted oceanic plateswhile granite comes from continental sediments crustal rock. The mantle part solidifies first, and is rich in magnesium, iron, and calcium. So it is reasonable to expect that initially, the magma is rich in iron, magnesium, and calcium and poor in uranium, thorium, sodium, and potassium. Later on the magma is poor in iron, magnesium, and calcium and rich in uranium, thorium, sodium, and potassium.
It doesn't say which class lead is in. But lead is a metal, and to me it looks more likely that lead would concentrate along with the iron. If this is so, the magma would initially be poor in thorium and uranium and rich in lead, and as it cooled it would become rich in thorium and uranium and poor in lead. Thus its radiometric age would tend to decrease rapidly with time, and lava emitted later would tend to look younger. Another point is that of time. Suppose that the uranium does come to the top by whatever reason. Perhaps magma that is uranium rich tends to be lighter than other magma. Or maybe the uranium poor rocks crystallize out first and the remaining magma is enriched in uranium.
Would this cause trouble for our explanation? Not necessarily. It depends how fast it happened. Some information from the book Uranium Geochemistry, Mineralogy, Geology provided by Jon Covey gives us evidence that fractionation processes are making radiometric dates much, much too old. The half life of U is 4. Thus radium is decaying 3 million times as fast as U At equilibrium, which should be attained inyears for this decay series, we should expect to have 3 million times as much U as radium to equalize the amount of daughter produced. Cortini says geologists discovered that ten times more Ra than the equilibrium value was present in rocks from Vesuvius.
They found similar excess radium at Mount St. Helens, Vulcanello, and Lipari and other volcanic sites. The only place where radioactive equilibrium of the U series exists in zero age lavas is in Hawiian rocks. We need to consider the implications of this for radiometric dating. How is this excess of radium being produced? This radium cannot be the result of decay of uranium, since there is far too much of it. Either it is the result of an unknown decay process, or it is the result of fractionation which is greatly increasing the concentration of radium or greatly decreasing the concentration of uranium.
Thus only a small fraction of the radium present in the lava at most 10 percent is the result of decay of the uranium in the lava. This is interesting because both radium and lead are daughter products of uranium. If similar fractionation processes are operating for lead, this would mean that only a small fraction of the lead is the result of decay from the parent uranium, implying that the U-Pb radiometric dates are much, much too old. Cortini, in an article appearing in the Journal of Volcanology and Geothermal Research also suggests this possibility. He says: By analogy with the behaviour of Ra, Th and U it can be suggested that Pb, owing to its large mobility, was also fed to the magma by fluids.
This can and must be tested. The open-system behaviour of Pb, if true, would have dramatic consequences On the other hand, even if such a process is not operating for lead, the extra radium will decay rapidly to lead, and so in either case we have much too much lead in the lava and radiometric dates that are much, much too ancient! It is also a convincing proof that some kind of drastic fractionation is taking place, or else an unknown process is responsible. He says this is inexplicable in a closed-system framework and certainly invalidates the Th dating method. And it is also possible that something similar is happening in the U decay chain, invalidating U based radiometric dates as well.
In fact, U and Th both have isotopes of radium in their decay chains with half lives of a week or two, and 6. Any process that is concentrating one isotope of radium will probably concentrate the others as well and invalidate these dating methods, too. Radium has a low melting point degrees K which may account for its concentration at the top of magma chambers. What radiometric dating needs to do to show its reliability is to demonstrate that no such fractionation could take place. Can this be done? With so many unknowns I don't think so. How Uranium and Thorium are preferentially incorporated in various minerals I now give evidences that uranium and thorium are incorporated into some minerals more than others.
This is not necessarily a problem for radiometric dating, because it can be taken into account. But as we saw above, processes that take place within magma chambers involving crystallization could result in a different concentration of uranium and thorium at the top of a magma chamber than at the bottom. This can happen because different minerals incorporate different amounts of uranium and thorium, and these different minerals also have different melting points and different densities.
Dating Stratigraphy and problems radiometric
If minerals that crystallize at the top of a magma chamber radiometrkc fall, tend to incorporate a lot of uranium, this will tend to deplete uranium at the top of radiomettic magma chamber, and make the magma there look older. Concerning the distribution of Strztigraphy and daughter isotopes in various substances, there are appreciable differences. Faure shows that in granite U is 4. Some process is causing the differences in the ratios of these magmatic dqting. Depending on their oxidation state, anv to Faure, SStratigraphy minerals can be very soluble in water while thorium compounds are, generally, very insoluble.
These elements also show preferences for the minerals in which they are incorporated, so that they will tend to be "dissolved" in certain mineral "solutions" preferentially to one another. More U is found in carbonate rocks, while Th has a very strong preference for granites in comparison. I saw a reference that uranium reacts strongly, and is never found pure in nature. So the question is what the melting points of its oxides or salts would be, I suppose. I also saw a statement that uranium is abundant in the crust, but never found in high concentrations. To me this indicates a high melting point for its minerals, as those with a low melting point might be expected to concentrate in the magma remaining after others crystallized out.
Such a high melting point would imply fractionation in the magma. Thorium is close to uranium in the periodic table, so it may have similar properties, and similar remarks may apply to it. It turns out that uranium in magma is typically found in the form of uranium dioxide, with a melting point of degrees centrigrade. The result? The results are therefore highly consistent given the analytical uncertainties in any measurement.
Eberth and Braman described the vertebrate paleontology and sedimentology of the Judith River Formation, a dinosaur-bearing unit that occurs stratigraphically below the Baculites reesidei zone the Judith River Formation is below the Bearpaw Formation. It should therefore be older than the results from Baadsgaard et al. An ash bed near the top of the Judith River Fm. Again, this is compatible with the age determined for the Baculites reesidei zone and its relative stratigraphic position, and even with the relative position of the two samples within the same formation. How do these dates compare to the then current geological time scale?
Harland et al. Here are the numbers they applied to the geological boundaries in this interval, compared to the numbers in the newer studies: Figure 5. Comparison of newer data with the Harland et al. As you can see, the numbers in the rightmost column are basically compatible. Skeptics of radiometric dating procedures sometimes claim these Stratigraphy and radiometric dating problems should not work reliably, or only infrequently, but clearly the results are similar: Most of the time, the technique works exceedingly well to Stratigraphy and radiometric dating problems first approximation.
However, there are some smaller differences. The date for the Baculites reesidei zone is at least 0. What to do? Well, standard scientific procedure is to collect more data to test the possible explanations -- is it the time scale or the data that are incorrect? Obradovich has measured a large number of high-quality radiometric dates from the Cretaceous Period, and has revised the geological time scale for this interval. Specifically, he proposes an age of This is completely compatible with the data in Baadsgaard et al.
Conclusions Skeptics of conventional geology might think scientists would expect, or at least prefer, every date to be perfectly consistent with the current geological time scale, but realistically, this is not how science works. The age of a particular sample, and a particular geological time scale, only represents the current understanding, and science is a process of refinement of that understanding. In support of this pattern, there is an unmistakable trend of smaller and smaller revisions of the time scale as the dataset gets larger and more precise Harland et al. If something were seriously wrong with the current geologic time scale, one would expect inconsistencies to grow in number and severity, but they do not.
The same trend can be observed for other time periods. Palmer and Harland et al. The latter includes an excellent diagram summarizing comparisons between earlier time scales Harland et al. Sincethere have been still more revisions by other authors, such as Obradovich for the Cretaceous Period, and Gradstein et al. Figure 6. A recent geological time scale, based on Harland et al. This is not uncommon. Besides the papers mentioned here, there are hundreds, if not thousands, of similar papers providing bracketing ranges for fossil occurrences. The synthesis of work like this by thousands of international researchers over many decades is what defines geological time scales in the first place refer to Harland et al.
Although geologists can and do legitimately quibble over the exact age of a particular fossil or formation e. The data do not support such an interpretation. The methods work too well most of the time. In addition, evidence from other aspects of geology e. Prior to the availability of radiometric dating, and even prior to evolutionary theory, the Earth was estimated to be at least hundreds of millions of years old see above. Radiometric dating has simply made the estimates more precise, and extended it into rocks barren of fossils and other stratigraphic tools. The geological time scale and the techniques used to define it are not circular. They rely on the same scientific principles as are used to refine any scientific concept: There are innumerable independent tests that can identify and resolve inconsistencies in the data.
This makes the geological time scale no different from other aspects of scientific study. For potential critics: Refuting the conventional geological time scale is not an exercise in collecting examples of the worst samples possible. A critique of conventional geologic time scale should address the best and most consistent data available, and explain it with an alternative interpretation, because that is the data that actually matters to the current understanding of geologic time. References also refer to " Other sources " Baadsgaard, H.
Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan Campanian-Maastrichtian stage boundary? Canadian Journal of Earth Sciences, v. Baadsgaard, H. Eberth, D. Stratigraphy, sedimentology, and vertebrate paleontology of the Judith River Formation Campanian near Muddy Lake, west-central Saskatchewan.
This aluminum was subsequently bogged by the discovery of hardship in the radiometgic decades of the 19th dump, which was an immobile for source of pitching in Kelvin's complement payers. So the isochron can be plugging an older age than the necessary at which the run recovery. The contain of the u comes from modern 3.
Bulletin of Canadian Petroleum Geology, v. On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the wnd concentrations of different atoms in the beams. Uranium—lead dating method[ edit ] Main article: Radiomstric dating A concordia diagram as used in uranium—lead rqdiometricwith data from the Pfunze Belt Stratigrapgy, Zimbabwe. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event.
This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample. Samarium—neodymium dating method[ edit ] Main article: Samarium—neodymium dating This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable. Potassium—argon dating This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1.
Rubidium—strontium dating method[ edit ] Main article: Rubidium—strontium dating This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples. Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Uranium—thorium dating method[ edit ] Main article: Uranium—thorium dating A relatively short-range dating technique is based on the decay of uranium into thorium, a substance with a half-life of about 80, years.
It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 32, years.
While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured. This grade activity lets students place parts of their own life story into a time line so that they can better understand how geologic time is reconstructed by scientists. Who's on FirstUniversity of California, Berkeley. This grade activity introduces students to the idea of sequencing information in overlapping data sets and the Principle of Superposition, which is a core concept in relative dating. Chapter Geologic Time. Tarbuck Prentice-Hall Publishing. This website is a book chapter about geologic time.
Offers history of age dating, stratigraphic principles, rock correlation, fossil correlations, radiometric dating, and the geologic time scale. The Potassium-Argon dating method has to be calibrated. If it has to be calibrated, it can not be absolute. This goes for all dating methods. Excess daughter isotope 40Ar leads to higher ages than is really the case. 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.