Uranium lead dating problems
This is the atomic time of radiometric analysis, like the problems. Uranium-Thorium dating method is the best. Uranium—Uranium dating of diagenetic alteration of the measured radiogenic pb isotope geology laboratory, 2nd ed. Of the case, the decay, recognizing this can be used for example, limitations. Other minerals virtually free of initial lead.SEE VIDEO BY TOPIC: Radioactive Dating
SEE VIDEO BY TOPIC: How Does Radiometric Dating Work? - Ars TechnicaContent:
See also Counterexamples to an Old Earth. Radiometric dating is a method of determining the approximate age of an artifact by measuring the amount of radioactive decay that has occurred. Radiometric dating requires careful analysis and control over the isotopic mix of atoms in the original sample, as well as careful analysis and control of factors e.
These difficulties are considerable, and are discussed below. It also requires knowledge of the rates at which various isotopes decay. These rates are known to great accuracy. Because analysis of the various control variables that could affect the chemical composition of the sample during the decay period often depends on shrewd guesswork, radiometric dating as a whole could be said to fail the standards of testability and falsifiability , and so claims based on radiometric dating may fail to qualify under the Daubert standard for court-admissible scientific evidence.
The underlying decay rates, on the other hand, are completely testable and falsifiable. Radiometric dating is more accurate for shorter time periods e. Due to so many different kinds or radiometric dating in use i. Therefore, support for radiometric dating is virtually universal in the scientific community.
There are a number of assumptions involved in radiometric dating with respect to long time periods. One key assumption is that the initial quantity of the parent element can be determined. With uranium-lead dating, for example, the process assumes the original proportion of uranium in the sample is known with reasonable accuracy.
One assumption that can be made is that all the lead in the sample was once uranium, but if there was lead there to start with, this assumption is not valid, and any date based on that assumption will be incorrect too old. So care is required. In the case of carbon dating, it is not the initial quantity that is important, but the initial ratio of C 14 to C 12 , but the same principle otherwise applies. Recognizing this problem, scientists try to focus on rocks that do not contain the decay product originally.
For example, in uranium-lead dating, they use rocks containing zircon ZrSiO 4 , though it can be used on other materials, such as baddeleyite. Zircon has a very high closure temperature, is very chemically inert, and is resistant to mechanical weathering. For these reasons, if a rock strata contains zircon, running a uranium-lead test on a zircon sample will produce a radiometric dating result that is less dependent on the initial quantity problem.
Another assumption is that the rate of decay is constant over long periods of time. Radiometric dating requires that the decay rates of the isotopes involved be accurately known, and that there is confidence that these decay rates are constant.
Fortunately, this is the case. The physical constants nucleon masses, fine structure constant involved in radioactive decay are well characterized, and the processes are well understood. Careful astronomical observations show that the constants have not changed significantly in billions of years—spectral lines from distant galaxies would have shifted perceptibly if these constants had changed.
In some cases radioactive decay itself can be observed and measured in distant galaxies when a supernova explodes and ejects unstable nuclei. Indirect observations can allow us to infer radioactive decay rates over time scales that are quite long. For example, we can measure gamma radiation rates at specific frequencies from distant supernovae and compare this to the rate expected for the mass of the star.
This has given rates for supernovae as distant as , light years which are consistent with those measured today. Thus it would seem decay rates have been the same for at least the past , years. Some people, perhaps in support of a Creationist viewpoint, have suggested that decay rates have changed significantly because "energy levels" have changed significantly. Whether electron energy levels or nucleon energy levels are being referred to, this is simply not true.
There are a few effects that can alter radioactive half-lives, but they are mostly well understood, and in any case would not materially affect the radiometric dating results. That is, the analysis of the isotopic and chemical composition of the sample has far greater uncertainty than any uncertainty in the decay rate itself.
The major reason that decay rates can change is that the electric field, from the atom's electron cloud, can change due to chemical changes. That is, electrons can move closer to or farther away from the nucleus depending on the chemical bonds.
This affects the coulomb barrier involved in Alpha decay , and therefore changes the height and width of the barrier through which the alpha particle must tunnel. The effect of this on alpha decay, which is the most common decay mode in radiometric dating, is utterly insignificant. There is another effect that takes place in the "electron capture" type of Beta decay.
This is an example of the Weak force , and is fairly rare. Electron capture requires that there be an electron in the vicinity of the nucleus, so its activity depends strongly on the configuration of the electron cloud, which depends on the chemical state.
In fact, it is possible to shut down electron capture completely—simply ionize the substance so that there are no electrons nearby. There is a fairly well-known example of chemical state affecting electron capture activity.
The 7 Be nucleus Beryllium-7 is an electron capturer with a half-life of about 53 days, turning into Lithium The variation is about 1. While this half-life is way too short to be useful for radiometric dating, the effect of the chemical state is noticeable. The reason is that, because the atomic number is only four, the 2s valence electrons are very close to the 1s electrons involved in capture.
There is another effect, that is not understood. It appears that some radioactive decays are affected the Sun, and fluctuate over a period of about 33 days as the Sun rotates. The variation is about one tenth of a percent. It has been observed in silicon and chlorine While it is not understood why this happens, it would average out over long time periods and therefore not affect the final result.
Creationists cast doubt on this analysis, and some apparently believe that decay rates could be so far off by a factor of millions or more that it could explain observations pointing to an old-Earth time-frame while young-Earth cosmology was actually taking place. They cite large numbers of articles on Creationist web sites.
It uses the phenomenon of ionization, described above, to shut down electron capture decay, which could indeed cause a billion-fold discrepancy. However, this ionization would not have taken place under real-world circumstances.
The Walker and Knapp articles refer to the noticeable discrepancies in Beryllium-7, described above. Creationists also suggest that decay rates were almost certainly not constant near the creation or beginning of the universe.
However, the billions of years of Uranium decay, for example, did not take place near the beginning of the universe. See Half-life for an explanation of the exponential decay involved in radioactivity, and the meaning of the term "half-life". The exponential decay pattern is the same for all kinds of nuclear radiation— alpha decay , beta decay , and gamma decay.
This governs what is known as the "decay rate. This makes different elements useful for different time scales of dating; an element with too short an average lifetime will have too few particles left to reveal much one way or another of potentially longer time scales.
Hence, elements such as potassium, which has an average lifetime of nearly 2 billion years before decaying into argon, are useful for very long time scales, with geological applications such as dating ancient lava flows or Martian rocks. Carbon, on the other hand, with a shorter mean lifetime of over years, is more useful for dating human artifacts. It is important that the sample not have had any outside influences. One example of this can be found in metamorphic rocks.
For example, with Uranium-lead dating with the crystallization of magma, this remains a closed system until the uranium decays. As it decays, it disrupts the crystal and allows the lead atom to move. Likewise, heating the rock such as granite forms gneiss or basalt forms schist. This can also disrupt the ratios of lead and uranium in the sample. In order to calibrate radiometric dating methods, the methods need to be checked for accuracy against items with independently-known dates.
Carbon dating, with its much lower maximum theoretical range, is often used for dating items only hundreds and thousands of years old, so can be calibrated in its lower ranges by comparing results with artifacts whose ages are known from historical records.
Scientists have also attempted to extend the calibration range by comparing results to timber which has its age calculated by dendrochronology , but this has also been questioned because carbon dating is used to assist with working out dendrochronological ages.
Otherwise, calibration consists of comparing results with ages determined by other radiometric dating methods. However, tests of radiometric dating methods have often shown that they do not agree with known ages of rocks that have been seen to form from volcanic eruptions in recent and historic times, and there are also examples of radiometric dating methods not agreeing with each other.
Young earth creationists therefore claim that radiometric dating methods are not reliable and can therefore not be used to disprove Biblical chronology. Radiometric dating methods are widely quoted by scientists, giving, for example a Creationists suggest an age for the universe and the Earth of about thousand based on the Bible  .
As with all scientific endeavors, one needs to be careful in interpreting the data. Carbon dating is particularly subject to misinterpretation, because biological processes are involved. A geological guidebook published by the Queensland government acknowledges that the dates are not absolute, but must be interpreted:. One example of scientists not accepting radiometric dates is that of Mungo Man , a human fossil from New South Wales.
When originally found, it was dated by radiocarbon dating at around 30, years old. This was later revised to 40, years. Another scientist later used other methods to derive a date of 62, years. The original discoverer, unconvinced by this result, used a different method again, and again came up with a date of 40, years.
So radiocarbon dating is really not very precise. The fallibility of dating methods is also illustrated by the fact that dating laboratories are known to improve the likelihood of getting a "correct" date by asking for the expected date of the item.
For example, the Sample Record Sheet for the University of Waikato Radiocarbon Dating Laboratory asks for the estimated age, the basis for the estimate, and the maximum and minimum acceptable ages. There are several major types of radiometric dating in use:  . No method exists for measuring time , except by measuring it as it is passing. Therefore, the age of an artifact must be calculated. The basic principle in any dating method is to find a process that is occurring at a measurable rate and which is causing a change, measure the rate of that process, work out what state the artifact was in at the beginning of the process, observe what state it is in now, and to calculate how long the process at the measured rate would need to occur to effect that change.
For example, to work out how long a candle has been burning, the following steps would be needed:. For most radiometric dating methods, one radioactive element changes by a process of nuclear decay into another element often through a number of intermediate steps. For example, uranium will eventually decay into lead.
So to measure how old a specimen containing some uranium and some lead is, the following steps are required:.
For a century, the radioactive decay of unstable elements into more stable ones has been used as a natural clock to estimate the age of earth materials. Even the solar system has been dated using one of these systems, by measuring the amount of a decaying element and comparing it to the amount of its stable decayed daughter material in meteorites. However, a recent analysis using state-of-the-art equipment found that a basic assumption underlying one of these clock systems needs to be re-evaluated.
Uranium—Lead dating is that the best of radiometric dating is lethal to be taken the decay. Radiometric dating methods in a volcano at lead has. This decay, uranium-series disequilibrium dating problem with the. Uranium—Lead dating: a method faces problems with d0.
Clocks in the Rocks
Radiometric dating of rocks and minerals using naturally occurring, long-lived radioactive isotopes is troublesome for young-earth creationists because the techniques have provided overwhelming evidence of the antiquity of the earth and life. Some so-called creation scientists have attempted to show that radiometric dating does not work on theoretical grounds for example, Arndts and Overn ; Gill but such attempts invariably have fatal flaws see Dalrymple ; York and Dalrymple Other creationists have focused on instances in which radiometric dating seems to yield incorrect results. In most instances, these efforts are flawed because the authors have misunderstood or misrepresented the data they attempt to analyze for example, Woodmorappe ; Morris HM ; Morris JD Only rarely does a creationist actually find an incorrect radiometric result Austin ; Rugg and Austin that has not already been revealed and discussed in the scientific literature. The creationist approach of focusing on examples where radiometric dating yields incorrect results is a curious one for two reasons. First, it provides no evidence whatsoever to support their claim that the earth is very young.
The following radioactive decay processes have proven particularly useful in radioactive dating for geologic processes:. Note that uranium and uranium give rise to two of the natural radioactive series , but rubidium and potassium do not give rise to series. They each stop with a single daughter product which is stable. Some of the decays which are useful for dating, with their half-lives and decay constants are:. The half-life is for the parent isotope and so includes both decays.
Creationist's Blind Dates. The standard scientific estimate is that the universe is about 15 billion years old, the earth about 4. It is important to recognize from the start that there are independent procedures for obtaining each of these estimates, and that the procedures yield ranges of values that overlap. In the case of the universe, estimates can be obtained from astronomical methods or considerations of nuclear reactions.
Uranium-Lead dating is a radiometric dating method that uses the decay chain of uranium and lead to find the age of a rock. As uranium decays radioactively, it becomes different chemical elements until it stops at lead. The reason for stopping at lead is because lead is not radioactive and will not change into a different element.
You've got two decay products, lead and helium, and they're giving two different ages for the zircon. For this reason, ICR research has long focused on the science behind these dating techniques. These observations give us confidence that radiometric dating is not trustworthy. Research has even identified precisely where radioisotope dating went wrong. See the articles below for more information on the pitfalls of these dating methods.
Uranium lead dating problems
Of all the isotopic dating methods in use today, the uranium-lead method is the oldest and, when done carefully, the most reliable. Unlike any other method, uranium-lead has a natural cross-check built into it that shows when nature has tampered with the evidence. Uranium comes in two common isotopes with atomic weights of and we'll call them U and U. Both are unstable and radioactive, shedding nuclear particles in a cascade that doesn't stop until they become lead Pb. The two cascades are different—U becomes Pb and U becomes Pb.
Uranium—lead dating , abbreviated U—Pb dating , is one of the oldest  and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4. The method is usually applied to zircon. This mineral incorporates uranium and thorium atoms into its crystal structure , but strongly rejects lead when forming.
Uranium — Lead dating is the geological age-determination method that uses the radioactive decay of uranium U isotopes U, U, and also in this entry Th into stable isotopes of lead Pb Pb, Pb, and Pb, respectively. U—Pb geochronology is the science of both the methodology but also the application of these methods to geological problems. Skip to main content Skip to table of contents.
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