Potassium-argon dating | Define Potassium-argon dating at negeriku.info
a method for estimating the age of a mineral or rock, based on measurement of the rate of decay of radioactive potassium into argon. Measurement of the ratio of these isotopes thus gives the age of the mineral Compare radiocarbon dating, rubidium-strontium dating. As a Creationist, what about all the other radioisotope methods for dating the Yet Potassium-Argon dates, for example, can easily go back to the time Two field examples: the first in the Columbia River Basalts, the second. What dating method did scientists use, and did it really generate reliable results? The field of radiocarbon dating has become a technical one far removed dating are addressed, and corrective, up-to-date scientific creationist thought is.
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.
If the earth were only —10 years old, then surely there should be some scientific evidence to confirm that hypothesis; yet the creationists have produced not a shred of it so far. Where are the data and age calculations that result in a consistent set of ages for all rocks on earth, as well as those from the moon and the meteorites, no greater than 10 years?
Glaringly absent, it seems. Second, it is an approach doomed to failure at the outset. Creationists seem to think that a few examples of incorrect radiometric ages invalidate all of the results of radiometric dating, but such a conclusion is illogical.
Even things that work well do not work well all of the time and under all circumstances. Try, for example, wearing a watch that is not waterproof while swimming. It will probably fail, but what would a reasonable person conclude from that? That watches do not work? A few verified examples of incorrect radiometric ages are simply insufficient to prove that radiometric dating is invalid.
All they indicate is that the methods are not infallible. Those of us who have developed and used dating techniques to solve scientific problems are well aware that the systems are not perfect; we ourselves have provided numerous examples of instances in which the techniques fail.
We often test them under controlled conditions to learn when and why they fail so we will not use them incorrectly. We have even discredited entire techniques. For example, after extensive testing over many years, it was concluded that uranium-helium dating is highly unreliable because the small helium atom diffuses easily out of minerals over geologic time. As a result, this method is not used except in rare and highly specialized applications. These methods provide valuable and valid age data in most instances, although there is a small percentage of cases in which even these generally reliable methods yield incorrect results.
Such failures may be due to laboratory errors mistakes happenunrecognized geologic factors nature sometimes fools usor misapplication of the techniques no one is perfect.
Not only that, they have to show the flaws in those dating studies that provide independent corroborative evidence that radiometric methods work. This is a tall order and the creationists have made no progress so far.
It is rare for a study involving radiometric dating to contain a single determination of age. Usually determinations of age are repeated to avoid laboratory errors, are obtained on more than one rock unit or more than one mineral from a rock unit in order to provide a cross-check, or are evaluated using other geologic information that can be used to test and corroborate the radiometric ages.
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Scientists who use radiometric dating typically use every means at their disposal to check, recheck, and verify their results, and the more important the results the more they are apt to be checked and rechecked by others. As a result, it is nearly impossible to be completely fooled by a good set of radiometric age data collected as part of a well-designed experiment.
The purpose of this paper is to describe briefly a few typical radiometric dating studies, out of hundreds of possible examples documented in the scientific literature, in which the ages are validated by other available information. I have selected four examples from recent literature, mostly studies involving my work and that of a few close colleagues because it was easy to do so.
I could have selected many more examples but then this would have turned into a book rather than the intended short paper. The heat of the impact melted some of the feldspar crystals in the granitic rocks of the impact zone, thereby resetting their internal radiometric clocks.
The impact also created shocked quartz crystals that were blasted into the air and subsequently fell to the west into the inland sea that occupied much of central North America at that time. Today this shocked quartz is found in South Dakota, Colorado, and Nebraska in a thin layer the Crow Creek Member within a thick rock formation known as the Pierre Shale. The Pierre Shale, which is divided into identifiable sedimentary beds called members, also contains abundant fossils of numerous species of ammonites, ancestors of the chambered nautilus.
The fossils, when combined with geologic mapping, allow the various exposed sections of the Pierre Shale to be pieced together in their proper relative positions to form a complete composite section Figure 1. The Pierre Shale also contains volcanic ash that was erupted from volcanoes and then fell into the sea, where it was preserved as thin beds.
There are three important things to note about these results. First, each age is based on numerous measurements; laboratory errors, had there been any, would be readily apparent. Second, ages were measured on two very different minerals, sanidine and biotite, from several of the ash beds. Third, the radiometric ages agree, within analytical error, with the relative positions of the dated ash beds as determined by the geologic mapping and the fossil assemblages; that is, the ages get older from top to bottom as they should.
Finally, the inferred age of the shocked quartz, as determined from the age of the melted feldspar in the Manson impact structure The Ages of Meteorites Meteorites, most of which are fragments of asteroids, are very interesting objects to study because they provide important evidence about the age, composition, and history of the early solar system. There are many types of meteorites. Some are from primitive asteroids whose material is little modified since they formed from the early solar nebula.
Others are from larger asteroids that got hot enough to melt and send lava flows to the surface. A few are even from the Moon and Mars. The most primitive type of meteorites are called chondrites, because they contain little spheres of olivine crystals known as chondrules. Because of their importance, meteorites have been extensively dated radiometrically; the vast majority appear to be 4.
Some meteorites, because of their mineralogy, can be dated by more than one radiometric dating technique, which provides scientists with a powerful check of the validity of the results. The results from three meteorites are shown in Table 1. Many more, plus a discussion of the different types of meteorites and their origins, can be found in Dalrymple There are 3 important things to know about the ages in Table 1.
The first is that each meteorite was dated by more than one laboratory — Allende by 2 laboratories, Guarena by 2 laboratories, and St Severin by four laboratories. This pretty much eliminates any significant laboratory biases or any major analytical mistakes. The second thing is that some of the results have been repeated using the same technique, which is another check against analytical errors.
The third is that all three meteorites were dated by more than one method — two methods each for Allende and Guarena, and four methods for St Severin. This is extremely powerful verification of the validity of both the theory and practice of radiometric dating.
In the case of St Severin, for example, we have 4 different natural clocks actually 5, for the Pb-Pb method involves 2 different radioactive uranium isotopeseach running at a different rate and each using elements that respond to chemical and physical conditions in much different ways. And yet, they all give the same result to within a few percent. 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 decayand 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 forceand 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 7Be nucleus Beryllium-7 is an electron capturer with a half-life of about 53 days, turning into Lithium The variation is about 1.
Potassium-argon dating | negeriku.info
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. 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 decaybeta decayand 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. Outside influences 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. Calibration 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 dendrochronologybut this has also been questioned because carbon dating is used to assist with working out dendrochronological ages.