Radioisotope dating problems

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radioisotope dating problems

The fatal flaw with radioactive dating methods by Tas Walker This is the But the basic concept of radioactive dating, sometimes called radiometric dating, This illustrates the problem with the radioactive dating of geological. One way this is done in many radioactive dating techniques is to use an . The heat problem occurs everywhere there are radioactive isotopes. Radiometric dating or radioactive dating is a technique used to date materials such as rocks or . In uranium–lead dating, the concordia diagram is used which also decreases the problem of nuclide loss. Finally, correlation between different .

radioisotope dating problems

The K-T tektites were ejected into the atmosphere and deposited some distance away. Tektites are easily recognizable and form in no other way, so the discovery of a sedimentary bed the Beloc Formation in Haiti that contained tektites and that, from fossil evidence, coincided with the K-T boundary provided an obvious candidate for dating.

Scientists from the US Geological Survey were the first to obtain radiometric ages for the tektites and laboratories in Berkeley, Stanford, Canada, and France soon followed suit.

radioisotope dating problems

The results from all of the laboratories were remarkably consistent with the measured ages ranging only from Similar tektites were also found in Mexico, and the Berkeley lab found that they were the same age as the Haiti tektites. The K-T boundary is recorded in numerous sedimentary beds around the world. Numerous thin beds of volcanic ash occur within these coals just centimeters above the K-T boundary, and some of these ash beds contain minerals that can be dated radiometrically.

Since both the ash beds and the tektites occur either at or very near the K-T boundary, as determined by diagnostic fossils, the tektites and the ash beds should be very nearly the same age, and they are Table 2.

There are several important things to note about these results. First, the Cretaceous and Tertiary periods were defined by geologists in the early s. The boundary between these periods the K-T boundary is marked by an abrupt change in fossils found in sedimentary rocks worldwide. Its exact location in the stratigraphic column at any locality has nothing to do with radiometric dating — it is located by careful study of the fossils and the rocks that contain them, and nothing more.

Furthermore, the dating was done in 6 different laboratories and the materials were collected from 5 different locations in the Western Hemisphere. And yet the results are the same within analytical error.

These flows buried and destroyed Pompeii and other nearby Roman cities. We know the exact day of this eruption because Pliny the Younger carefully recorded the event. They separated sanidine crystals from a sample of one of the ash flows. Incremental heating experiments on 12 samples of sanidine yielded 46 data points that resulted in an isochron age of 94 years.

The actual age of the flow in was years. Is this just a coincidence? No — it is the result of extremely careful analyses using a technique that works. This is not the only dating study to be done on an historic lava flow. Two extensive studies done more than 25 years ago involved analyzing the isotopic composition of argon in such flows to determine if the source of the argon was atmospheric, as must be assumed in K-Ar dating Dalrymple26 flows; Krummenacher19 flows.

Note, however, that even an error of 0. Summary In this short paper I have briefly described 4 examples of radiometric dating studies where there is both internal and independent evidence that the results have yielded valid ages for significant geologic events. It is these studies, and the many more like them documented in the scientific literature, that the creationists need to address before they can discredit radiometric dating.

Their odds of success are near zero. Even if against all odds they should succeed, it still would not prove that the Earth is young. Only when young-earth creationists produce convincing quantitative, scientific evidence that the earth is young will they be worth listening to on this important scientific matter.

Acknowledgments I thank Chris Stassen and 2 anonymous reviewers for their thoughtful comments, which led to important improvements in the manuscript. T Rex and the Crater of Doom. Alvarez W, Asaro, F. Arndts R, Overn W. Excess argon within mineral concentrates from the new dacite lava dome at Mount St Helens volcano.

How old is the earth? A reply to scientific creationism. Awbrey F, Thwaites WM, editors. The Age of the Earth. Stanford, Stanford University Press, US Geological Survey Bulletin The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created.

It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration. Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron.

This can reduce the problem of contamination. In uranium—lead datingthe concordia diagram is used which also decreases the problem of nuclide loss. Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3. The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate.

How Carbon Dating Works

This normally involves isotope-ratio mass spectrometry. For instance, carbon has a half-life of 5, years. After an organism has been dead for 60, years, so little carbon is left that accurate dating cannot be established. On the other hand, the concentration of carbon falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. Closure temperature If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusionsetting the isotopic "clock" to zero.

The temperature at which this happens is known as the closure temperature or blocking temperature and is specific to a particular material and isotopic system.

These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace. As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.

This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature.

The age that can be calculated by radiometric dating is thus the time at which the rock or mineral cooled to closure temperature. This field is known as thermochronology or thermochronometry. The age is calculated from the slope of the isochron line and the original composition from the intercept of the isochron with the y-axis. The equation is most conveniently expressed in terms of the measured quantity N t rather than the constant initial value No.

The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature. This is well-established for most isotopic systems.

Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition. Modern dating methods[ edit ] Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth.

In the century since then the techniques have been greatly improved and expanded. The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization. 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 relative concentrations of different atoms in the beams.

Uranium—lead dating method[ edit ] Main article: Uranium—lead dating A concordia diagram as used in uranium—lead datingwith data from the Pfunze BeltZimbabwe.

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.

Such a large variety of igneous rocks exists that it is logical to assume an equally large variety of magmas must also exist. However, geologists have found that various eruptive stages of the same volcano often extrude lavas exhibiting somewhat different mineral compositions, particularly if an extensive period of time separated the eruptions.

Evidence of this type led them to look into the possibility that a single magma might produce rocks of varying mineral content. A pioneering investigation into the crystallization of magma was carried out by N.

  • Scientist Realizes Important Flaw in Radioactive Dating

Bowen in the first quarter of this century. Bowen discovered that as magma cools in the laboratory, certain minerals crystallize first. At successively lower temperature, other minerals begin to crystallize as shown in Figure 3.

Radiometric dating

As the crystallization process continues, the composition of the melt liquid portion of a magma, excluding any solid material continually changes. For example, at the stage when about 50 percent of the magma has solidified, the melt will be greatly depleted in iron, magnesium, and calcium, because these elements are found in the earliest formed minerals. But at the same time, it will be enriched in the elements contained in the later forming minerals, namely sodium and potassium.

Further, the silicon content of the melt becomes enriched toward the latter stages of crystallization. Bowen also demonstrated that if a mineral remained in the melt after it had crystallized, it would react with the remaining melt and produce the next mineral in the sequence shown in Figure 3.

For this reason, this arrangement of minerals became known as Bowen's reaction series. On the upper left branch of this reaction series, olivine, the first mineral to form, Ml] react with the remaining melt to become pyroxene. This reaction will continue until the last mineral in the series, biotite mica, is formed. This left branch is called a discontinuous reaction series because each mineral has a different crystalline structure. Recall that olivine is composed of a single tetrahedra and that the other minerals in this sequence are composed of single chains, double chains, and sheet structures, respectively.

Ordinarily, these reactions are not complete so that various amounts of each of these minerals may exist at any given time. The right branch of the reaction series is a continuum in which the earliest formed calcium-rich feldspar crystals react with the sodium ions contained in the melt to become progressively more sodium rich. Oftentimes the rate of cooling occurs rapidly enough to prohibit the complete transformation of calcium-rich feldspar into sodium-rich feldspar.

In these instances, the feldspar crystals will have calcium-rich interiors surrounded by zones that are progressively richer in sodium. During the last stage of crystallization, after most of the magma has solidified, the remaining melt will form the minerals quartz, muscovite mica, and potassium feldspar. Although these minerals crystallize in the order shown, this sequence is not a true reaction series. Bowen demonstrated that minerals crystallize from magma in a systematic fashion.

But how does Bowen's reaction series account for the great diversity of igneous rocks? It appears that at one or more stages in the crystallization process, a separation of the solid and liquid components of a magma frequently occurs.

This can happen, for example, if the earlier formed minerals are heavier than the liquid portion and settle to the bottom of the magma chamber as shown in Figure 3. This settling is thought to occur frequently with the dark silicates, such as olivine.

When the remaining melt crystallizes, either in place or in a new location if it migrates out of the chamber, it will form a rock with a chemical composition much different from the original magma Figure 3. In many instances the melt which has migrated from the initial magma chamber will undergo further segregation. As crystallization progresses in the " new" magma, the solid particles may accumulate into rocklike masses surrounded by pockets of the still molten material.

It is very likely that some of this melt will be squeezed from the mixture into the cracks which develop in the surrounding rock. This process will generate an igneous rock of yet another composition. The process involving the segregation of minerals by differential crystallization an separation is called fractional crystallization.

At any stage in the crystallization process the melt might be separated from the solid portion of the magma. Consequently, fractional crystallization can produce igneous rocks having a wide range of compositions.

Bowen successfully demonstrated that through fractional crystallization one magma can generate several different igneous rocks. However, more recent work has indicated that this process cannot account for the relative quantities of the various rock types known to exist.

Although more than one rock type can be generated from a single magma, apparently other mechanisms also exist to generate magmas of quite varied chemical compositions. We will examine some of these mechanisms at the end of the next chapter.

Illustration of how the earliest formed minerals can be separated from a magma by settling. The remaining melt could migrate to a number of different locations and, upon further crystallization, generate rocks having a composition much different from the parent magma.

So we see that many varieties of minerals are produced from the same magma by the different processes of crystallization, and these different minerals may have very different compositions. It is possible that the ratio of daughter to parent substances for radiometric dating could differ in the different minerals.

Clearly, it is important to have a good understanding of these processes in order to evaluate the reliability of radiometric dating.

Another quotation about fractionation follows: Faure discusses fractional crystallization relating to U and Th in his book p. These values may be taken as an indication of the very low abundance of these elements in the mantle and crust of the Earth.

radioisotope dating problems

In the course of partial melting and fractional crystallization of magma, U and Th are concentrated in the liquid phase and become incorporated into the more silica-rich products. For that reason, igneous rocks of granitic composition are strongly enriched in U and Th compared to rocks of basaltic or ultramafic composition. Progressive geochemical differentiation of the upper mantle of 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.

More Bad News for Radiometric Dating

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 would have an influence on the 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 G. 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 of 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, subsequent lava flows and ash beds would have younger dates. Such a scenario does not answer all of the questions or solve all of the problems that radiometric dating poses for those who believe the Genesis account of Creation and the Flood. It does suggest at least one aspect of the problem that could be researched more thoroughly. Principles of Isotope Geology: 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 the 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 out at different times. There are also processes taking place within a magma chamber that can cause differences in 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 of processes can influence radiometric dates. In addition, the magma chamber would be expected to be cooler all around its borders, both at 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 will tend to sink to the bottom of 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 portion 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. This 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 at 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? 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.

Radiometric Dating Does Work!

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?

Radiometric dating - Wikipedia

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. 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.

If minerals that crystallize at the top of a magma chamber and fall, tend to incorporate a lot of uranium, this will tend to deplete uranium at the top of the magma chamber, and make the magma there look older.

Concerning the distribution of parent 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 rocks. Depending on their oxidation state, according to Faure, uranium 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. This high melting point suggests that uranium would crystallize and fall to the bottom of magma chambers. Geologists are aware of the problem of initial concentration of daughter elements, and attempt to take it into account.

U-Pb dating attempts to get around the lack of information about initial daughter concentrations by the choice of minerals that are dated. For example, zircons are thought to accept little lead but much uranium. Thus geologists assume that the lead in zircons resulted from radioactive decay. But I don't know how they can be sure how much lead zircons accept, and even they admit that zircons accept some lead. Lead could easily reside in impurities and imperfections in the crystal structure.

Also, John Woodmorappe's paper has some examples of anomalies involving zircons. It is known that the crystal structure of zircons does not accept much lead. However, it is unrealistic to expect a pure crystal to form in nature.

Perfect crystals are very rare. In reality, I would expect that crystal growth would be blocked locally by various things, possibly particles in the way. Then the surrounding crystal surface would continue to grow and close up the gap, incorporating a tiny amount of magma.

I even read something about geologists trying to choose crystals without impurities by visual examination when doing radiometric dating. Thus we can assume that zircons would incorporate some lead in their impurities, potentially invalidating uranium-lead dates obtained from zircons.

Chemical fractionation, as we have seen, calls radiometric dates into question. But this cannot explain the distribution of lead isotopes. There are actually several isotopes of lead that are produced by different parent substances uraniumuraniumand thorium.