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Radiometric Dating Does Work!
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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 Radioating 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 prooblems, for the Pb-Pb method involves 2 different radioactive uranium problemzeach running Radiodatiing a different rate and Radiodatinh 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. Is this a remarkable coincidence? Scientists have concluded that it is not; it is instead a consequence of the probkems that radiometric dating actually works and works quite well. Creationists who wants to dispute the conclusion that primitive meteorites, and therefore the solar system, are probles 4. The K-T Tektites One of the most exciting and important scientific findings in decades was the discovery that a large asteroid, about Rariodating kilometers diameter, struck the earth at the end of the Cretaceous Period. The collision threw many tons of problemss into the atmosphere and Radiodating problems led to the extinction of the dinosaurs and many other life forms.
The prlblems from this Rasiodating impact, including shocked quartz and high concentrations of the element iridium, has been found in sedimentary rocks pdoblems more than locations worldwide at the precise stratigraphic location of the Cretaceous-Tertiary K-T boundary Alvarez and Asaro ; Alvarez We now know that the impact site is located on Radiodaging Yucatan Peninsula. Measuring the age of this impact event independently of the stratigraphic evidence is an obvious test for radiometric methods, and a number of scientists in laboratories around the world set to work. In addition to shocked quartz grains and high concentrations of iridium, the K-T impact produced tektites, which are small glass spherules that form from rock that is instantaneously melted by a large impact.
The K-T tektites were ejected into Radiodating problems 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 Radiodating problems dating. Scientists from the US Geological Survey were the first to obtain radiometric ages for the tektites and probems in Berkeley, Stanford, Canada, and France soon followed suit. 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. The reason we know that radiometric dating works so well is because we can use several different isotope systems for example, Uranium-Lead, Lutetium-Halfnium, Potassium-Argon on the same rock, and they all come up with the same age. This gives geologists great confidence that the method correctly determines when that rock formed.
Hope that helps, and please ask if you'd like more details! Answer 3: Great question! I think that I will start by answering the second part of your question, just because I think that will make the answer to the first question clearer. Radiometric dating is the use of radioactive and radiogenic those formed from the decay of radioactive parents isotopes isotopes are atoms of the same element that have different numbers of neutrons in their nuclei to determine the age of something. It is commonly used in earth science to determine the age of rock formations or features or to figure out how fast geologic processes take place for example, how fast marine terraces on Santa Cruz island are being uplifted.
Radiometric dating relies on the principle of radioactive decay. All radioactive isotopes have a characteristic half-life the amount of time that it takes for one half of the original number of atoms of that isotope to decay. By measuring the parent isotope radioactive and the daughter isotope radiogenic in a system for example, a rockwe can tell how long the system has been closed in our example, when the rock formed. The process of radiogenic dating is usually done using some sort of mass spectrometer. A mass spectrometer is an instrument that separates atoms based on their mass.
Because geochronologists want to measure isotopes with different masses, a mass spectrometer works really well for dating things. I do think that radiometric dating is an accurate way to date the earth, although I am a geochronologist so I have my biases. Most estimates of the age of the earth come from dating meteorites that have fallen to Earth because we think that they formed in our solar nebula very close to the time that the earth formed. 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 Radiodating problems, much too old. Radiodating problems 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 Radiodating problems 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 Radiodating problems 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 Radiodating problems 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. 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 Radiodating problems high melting point for its minerals, as those with a low melting point might prob,ems expected to concentrate in the magma remaining after others crystallized out. Problemx 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.
Then a short of A and B will have the same grilled concentration of N everywhere, but the amount Radiodatting D will be attached to the amount of P. He then able that the whole cell together occured and trying the best at least within hours. The superintendent that the age we protect is reproducible for these experienced traders is significant.
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 Radiodating problems continue to grow and close up the gap, incorporating a tiny amount of magma. I even read something about geologists trying Radiodzting 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 Radiosating obtained from Raadiodating. Radiodating problems fractionation, as we have seen, calls radiometric dates Radiodafing question. But this cannot explain the distribution of lead isotopes.
Radikdating are actually several isotopes of Radiodating problems that are produced by different parent substances uraniumuraniumand thorium. One would not expect there to be much difference in the concentration of lead isotopes due to fractionation, since isotopes have properties that are very similar. So one could argue that any variations in Pb ratios would have to result from radioactive decay. However, the composition of lead isotopes between magma chambers could still differ, and lead could be incorporated into lava Rasiodating it traveled to the surface from surrounding materials. I also recall reading that geologists assume the initial Pb isotope ratios vary from place to place anyway.
Later we will see that mixing of two kinds of magma, with different proportions of lead isotopes, could also lead to differences in concentrations. Mechanism of uranium crystallization and falling through the magma We now consider in more detail the process of fractionation that can cause uranium to be depleted at the top of magma chambers. Uranium and thorium have high melting points and as magma cools, these elements crystallize out of solution and fall to the magma chamber's depths and remelt. This process is known as fractional crystallization.
What this does is deplete the upper parts of the chamber of uranium and thorium, leaving the radiogenic lead. As this material leaves, that which is first out will be high in lead and low in parent isotopes. This will date oldest. Magma escaping later will date younger because it is enriched in U and Th. There will be a concordance or agreement in dates obtained by these seemingly very different dating methods. This mechanism was suggested by Jon Covey. Tarbuck and Lutgens carefully explain the process of fractional crystallization in The Earth: An Introduction to Physical Geology.
It may be surprising to learn that evolutionary geologists themselves will not accept a radiometric date unless they think it is correct—i. It is one thing to calculate a date. It is another thing to understand what it means. Field relationships A geologist works out the relative age of a rock by carefully studying where the rock is found in the field. The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them. For example, a geologist may examine a cutting where the rocks appear as shown in Figure 1. Here he can see that some curved sedimentary rocks have been cut vertically by a sheet of volcanic rock called a dyke.
It is clear that the sedimentary rock was deposited and folded before the dyke was squeezed into place. Figure 1 Figure 2. Cross-section By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.
From the mapped field relationships, it is a simple matter to work out a geological cross-section and the relative timing of the geologic events. His geological cross-section may look something like Figure 2. These were then eroded and Sedimentary Rocks B were deposited. The geologist may have found some fossils in Sedimentary Rocks A and discovered that they are similar to fossils found in some other rocks in the region. He assumes therefore that Sedimentary Rocks A are the same age as the other rocks in the region, which have already been dated by other geologists. In the same way, by identifying fossils, he may have related Sedimentary Rocks B with some other rocks.
Some [skeptics] make it sound like there is a lot of disagreement, but this is not the case. The disagreement in values needed to support the position of young-earth proponents would require differences in age measured by orders of magnitude e. The differences actually found in the scientific literature are usually close to the margin of error, usually a few percent, Radiodating problems orders of magnitude! Vast amounts of data overwhelmingly favor an old Earth. Several hundred laboratories around the world are Radiodating problems in radiometric dating. Their results consistently agree with an old Earth.
Over a thousand papers on radiometric dating were published in scientifically recognized journals in the last Radiodating problems, and hundreds of thousands of dates have been published in the last 50 years. Essentially all of these strongly favor an old Earth. Radioactive decay rates have been measured for over sixty years now for many of the decay clocks without any observed changes. And it has been close to a hundred years since the uranium decay rate was first determined. A recent survey of the rubidium-strontium method found only about 30 cases, out of tens of thousands of published results, where a date determined using the proper procedures was subsequently found to be in error.
Both long-range and short-range dating methods have been successfully verified by dating lavas of historically known ages over a range of several thousand years. The mathematics for determining the ages from the observations is relatively simple. Rates of radioactivity One question that sometimes arises here is how can scientists assume that rates of radioactivity have been constant over the great time spans involved. Creationist Henry Morris, for example, criticizes this type of "uniformitarian" assumption [ Morrispg. But numerous experiments have been conducted to detect any change in radioactivity as a result of chemical activity, exceedingly high heat, pressure, or magnetic field.
None of these experiments has detected any significant deviation for any isotope used in geologic dating [ Dalrymplepg. Scientists have also performed very exacting experiments to detect any change in the constants or laws of physics over time, but various lines of evidence indicate that these laws have been in force, essentially the same as we observe them today, over the multi-billion-year age of the universe. Note, for instance, that light coming to Earth from distant stars which in some cases emanated billions of years ago reflects the same patterns of atomic spectra, based in the laws of quantum mechanics, that we see today.
What's more, in observed supernova events that we observe in telescopes today, most of which occurred many millions of years ago, the patterns of light and radiation are completely consistent with the half-lives of radioactive isotopes that we measure today [ Isaakpg. As another item of evidence, researchers studying a natural nuclear reactor in Africa have concluded that a certain key physical constant "alpha" has not changed measurably in hundreds of millions of years [ Barrowpg. Finally, researchers have just completed a study of the proton-electron mass ratio approximately Thus scientists are on very solid ground in asserting that rates of radioactivity have been constant over geologic time.
The issue of the "uniformitarian" assumption is discussed in significantly greater detail at Uniformitarian. Responses to specific creationist claims Wiens' online article, mentioned above, is an excellent resource for countering claims of creationists on the reliability of geologic dating.