Radiocarbon dating can easily establish that humans have been on the earth for (C) dating is one of the most reliable of all the radiometric dating methods. . the gropings and guesses of authors of the early sixties in an effort to debunk. Radiocarbon dating is a key tool archaeologists use to determine the age of plants and objects made with organic material. But new research.
Rubidium-strontium dating[ edit ] This is based on the decay of rubidium isotopes to strontium isotopes, and can be used to date rocks or to relate organisms to the rocks on which they formed.
It suffers from the problem that rubidium and strontium are very mobile and may easily enter rocks at a much later date to that of formation. One problem is that potassium is also highly mobile and may move into older rocks. Due to the long half-life of uranium it is not suitable for short time periods, such as most archaeological purposes, but it can date the oldest rocks on earth. This leaves out important information which would tell you how precise is the dating result.
Carbon dating has an interesting limitation in that the ratio of regular carbon to carbon in the air is not constant and therefore any date must be calibrated using dendrochronology.
Another limitation is that carbon can only tell you when something was last alive, not when it was used. A limitation with all forms of radiometric dating is that they depend on the presence of certain elements in the substance to be dated. Carbon dating works on organic matter, all of which contains carbon.
However it is less useful for dating metal or other inorganic objects. Most rocks contain uranium, allowing uranium-lead and similar methods to date them. Other elements used for dating, such as rubidium, occur in some minerals but not others, restricting usefulness.
Carbon decays almost completely within , years of the organism dying, and many fossils and rock strata are hundreds of times older than that. To date older fossils, other methods are used, such as potassium-argon or argon-argon dating.
Other forms of dating based on reactive minerals like rubidium or potassium can date older finds including fossils, but have the limitation that it is easy for ions to move into rocks post-formation so that care must be taken to consider geology and other factors.
Radiometric dating and YEC[ edit ] See the main article on this topic: Young Earth creationism Radiometric dating — through processes similar to those outlined in the example problem above — frequently reveals that rocks, fossils , etc. The oldest rock so far dated is a zircon crystal that formed 4. They tie themselves in logical knots trying to reconcile the results of radiometric dating with the unwavering belief that the Earth was created ex nihilo about 6, to 10, years ago.
Creationists often blame contamination Indeed, special creationists have for many years held that where science and their religion conflict, it is a matter of science having to catch up with scripture, not the other way around. This is frequently because the selected technique is used outside of its appropriate range, for example on very recent lavas.
In attempting to date Mt. Helens, creationists attempted discredit the discipline through dishonest practices. Ultimately these "creation scientists" were forced to admit that even for methods they accepted as sound, the age of the Earth would be vastly greater than the 6, they set out to prove.
Is radioactive decay constant? An enormous amount of research shows that in the lab decay rates are constant over time and wherever you are. Faced with this, creationists say that you can't extrapolate from this to deduce they are correct over billions of years.
A few experiments have found small variations in decay rates, at least for some forms of decay and some isotopes. While it may require further investigation to see if this is a real phenomenon, even the biggest positive results do not offer anything like a variation that would allow the truth of young earth creationism.
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As lava rises through the crust, it will heat up surrounding rock. Lead has a low melting point, so it will melt early and enter the magma. This will cause an apparent large age. Uranium has a much higher melting point. It will enter later, probably due to melting of materials in which it is embedded.
This will tend to lower the ages. Mechanisms that can create isochrons giving meaningless ages: Geologists attempt to estimate the initial concentration of daughter product by a clever device called an isochron. Let me make some general comments about isochrons. The idea of isochrons is that one has a parent element, P, a daughter element, D, and another isotope, N, of the daughter that is not generated by decay. One would assume that initially, the concentration of N and D in different locations are proportional, since their chemical properties are very similar.
Note that this assumption implies a thorough mixing and melting of the magma, which would also mix in the parent substances as well. Then we require some process to preferentially concentrate the parent substances in certain places.
Radioactive decay would generate a concentration of D proportional to P. By taking enough measurements of the concentrations of P, D, and N, we can solve for c1 and c2, and from c1 we can determine the radiometric age of the sample. Otherwise, the system is degenerate. Thus we need to have an uneven distribution of D relative to N at the start.
If these ratios are observed to obey such a linear relationship in a series of rocks, then an age can be computed from them. The bigger c1 is, the older the rock is. That is, the more daughter product relative to parent product, the greater the age.
Thus we have the same general situation as with simiple parent-to-daughter computations, more daughter product implies an older age. This is a very clever idea. However, there are some problems with it. First, in order to have a meaningful isochron, it is necessary to have an unusual chain of events. Initially, one has to have a uniform ratio of lead isotopes in the magma. Usually the concentration of uranium and thorium varies in different places in rock.
This will, over the assumed millions of years, produce uneven concentrations of lead isotopes. To even this out, one has to have a thorough mixing of the magma. Even this is problematical, unless the magma is very hot, and no external material enters. Now, after the magma is thoroughly mixed, the uranium and thorium will also be thoroughly mixed.
What has to happen next to get an isochron is that the uranium or thorium has to concentrate relative to the lead isotopes, more in some places than others. So this implies some kind of chemical fractionation. Then the system has to remain closed for a long time. This chemical fractionation will most likely arise by some minerals incorporating more or less uranium or thorium relative to lead. Anyway, to me it seems unlikely that this chain of events would occur.
Another problem with isochrons is that they can occur by mixing and other processes that result in isochrons yielding meaningless ages. Sometimes, according to Faure, what seems to be an isochron is actually a mixing line, a leftover from differentiation in the magma.
Fractionation followed by mixing can create isochrons giving too old ages, without any fractionation of daughter isotopes taking place. To get an isochron with a false age, all you need is 1 too much daughter element, due to some kind of fractionation and 2 mixing of this with something else that fractionated differently.
Since fractionation and mixing are so common, we should expect to find isochrons often. How they correlate with the expected ages of their geologic period is an interesting question. There are at least some outstanding anomalies. Faure states that chemical fractionation produces "fictitious isochrons whose slopes have no time significance. As an example, he uses Pliocene to Recent lava flows and from lava flows in historical times to illustrate the problem.
He says, these flows should have slopes approaching zero less than 1 million years , but they instead appear to be much older million years. Steve Austin has found lava rocks on the Uinkeret Plateau at Grand Canyon with fictitious isochrons dating at 1.
Then a mixing of A and B will have the same fixed concentration of N everywhere, but the amount of D will be proportional to the amount of P. This produces an isochron yielding the same age as sample A. This is a reasonable scenario, since N is a non-radiogenic isotope not produced by decay such as lead , and it can be assumed to have similar concentrations in many magmas.
Magma from the ocean floor has little U and little U and probably little lead byproducts lead and lead Magma from melted continental material probably has more of both U and U and lead and lead Thus we can get an isochron by mixing, that has the age of the younger-looking continental crust.
The age will not even depend on how much crust is incorporated, as long as it is non-zero. However, if the crust is enriched in lead or impoverished in uranium before the mixing, then the age of the isochron will be increased. If the reverse happens before mixing, the age of the isochron will be decreased. Any process that enriches or impoverishes part of the magma in lead or uranium before such a mixing will have a similar effect.
So all of the scenarios given before can also yield spurious isochrons. I hope that this discussion will dispel the idea that there is something magical about isochrons that prevents spurious dates from being obtained by enrichment or depletion of parent or daughter elements as one would expect by common sense reasoning. So all the mechanisms mentioned earlier are capable of producing isochrons with ages that are too old, or that decrease rapidly with time. The conclusion is the same, radiometric dating is in trouble.
I now describe this mixing in more detail. Suppose P p is the concentration of parent at a point p in a rock. The point p specifies x,y, and z co-ordinates. Let D p be the concentration of daughter at the point p. Let N p be the concentration of some non-radiogenic not generated by radioactive decay isotope of D at point p.
Suppose this rock is obtained by mixing of two other rocks, A and B. Suppose that A has a for the sake of argument, uniform concentration of P1 of parent, D1 of daughter, and N1 of non-radiogenic isotope of the daughter. Thus P1, D1, and N1 are numbers between 0 and 1 whose sum adds to less than 1.
Suppose B has concentrations P2, D2, and N2. Let r p be the fraction of A at any given point p in the mixture. So the usual methods for augmenting and depleting parent and daughter substances still work to influence the age of this isochron. More daughter product means an older age, and less daughter product relative to parent means a younger age.
In fact, more is true. Any isochron whatever with a positive age and a constant concentration of N can be constructed by such a mixing. It is only necessary to choose r p and P1, N1, and N2 so as to make P p and D p agree with the observed values, and there is enough freedom to do this. Anyway, to sum up, there are many processes that can produce a rock or magma A having a spurious parent-to-daughter ratio.
Then from mixing, one can produce an isochron having a spurious age. This shows that computed radiometric ages, even isochrons, do not have any necessary relation to true geologic ages. Mixing can produce isochrons giving false ages.
But anyway, let's suppose we only consider isochrons for which mixing cannot be detected. How do their ages agree with the assumed ages of their geologic periods? As far as I know, it's anyone's guess, but I'd appreciate more information on this.
I believe that the same considerations apply to concordia and discordia, but am not as familiar with them. It's interesting that isochrons depend on chemical fractionation for their validity.
They assume that initially the magma was well mixed to assure an even concentration of lead isotopes, but that uranium or thorium were unevenly distributed initially. So this assumes at the start that chemical fractionation is operating. But these same chemical fractionation processes call radiometric dating into question. The relative concentrations of lead isotopes are measured in the vicinity of a rock.
The amount of radiogenic lead is measured by seeing how the lead in the rock differs in isotope composition from the lead around the rock. This is actually a good argument. But, is this test always done? How often is it done? And what does one mean by the vicinity of the rock?
How big is a vicinity? One could say that some of the radiogenic lead has diffused into neighboring rocks, too. Some of the neighboring rocks may have uranium and thorium as well although this can be factored in in an isochron-type manner. Furthermore, I believe that mixing can also invalidate this test, since it is essentially an isochron.
Finally, if one only considers U-Pb and Th-Pb dates for which this test is done, and for which mixing cannot be detected. The above two-source mixing scenario is limited, because it can only produce isochrons having a fixed concentration of N p. To produce isochrons having a variable N p , a mixing of three sources would suffice. This could produce an arbitrary isochron, so this mixing could not be detected.
Also, it seems unrealistic to say that a geologist would discard any isochron with a constant value of N p , as it seems to be a very natural condition at least for whole rock isochrons , and not necessarily to indicate mixing. I now show that the mixing of three sources can produce an isochron that could not be detected by the mixing test.
First let me note that there is a lot more going on than just mixing. There can also be fractionation that might treat the parent and daughter products identically, and thus preserve the isochron, while changing the concentrations so as to cause the mixing test to fail. It is not even necessary for the fractionation to treat parent and daughter equally, as long as it has the same preference for one over the other in all minerals examined; this will also preserve the isochron.
Now, suppose we have an arbitrary isochron with concentrations of parent, daughter, and non-radiogenic isotope of the daughter as P p , D p , and N p at point p. Suppose that the rock is then diluted with another source which does not contain any of D, P, or N. Then these concentrations would be reduced by a factor of say r' p at point p, and so the new concentrations would be P p r' p , D p r' p , and N p r' p at point p.
Now, earlier I stated that an arbitrary isochron with a fixed concentration of N p could be obtained by mixing of two sources, both having a fixed concentration of N p. With mixing from a third source as indicated above, we obtain an isochron with a variable concentration of N p , and in fact an arbitrary isochron can be obtained in this manner.
So we see that it is actually not much harder to get an isochron yielding a given age than it is to get a single rock yielding a given age. This can happen by mixing scenarios as indicated above. Thus all of our scenarios for producing spurious parent-to-daughter ratios can be extended to yield spurious isochrons. The condition that one of the sources have no P, D, or N is fairly natural, I think, because of the various fractionations that can produce very different kinds of magma, and because of crustal materials of various kinds melting and entering the magma.
In fact, considering all of the processes going on in magma, it would seem that such mixing processes and pseudo-isochrons would be guaranteed to occur. Even if one of the sources has only tiny amounts of P, D, and N, it would still produce a reasonably good isochron as indicated above, and this isochron could not be detected by the mixing test. I now give a more natural three-source mixing scenario that can produce an arbitrary isochron, which could not be detected by a mixing test.
P2 and P3 are small, since some rocks will have little parent substance. Suppose also that N2 and N3 differ significantly.
Such mixings can produce arbitrary isochrons, so these cannot be detected by any mixing test. Also, if P1 is reduced by fractionation prior to mixing, this will make the age larger. If P1 is increased, it will make the age smaller. If P1 is not changed, the age will at least have geological significance.
But it could be measuring the apparent age of the ocean floor or crustal material rather than the time of the lava flow. I believe that the above shows the 3 source mixing to be natural and likely.
We now show in more detail that we can get an arbitrary isochron by a mixing of three sources. Thus such mixings cannot be detected by a mixing test. Assume D3, P3, and N3 in source 3, all zero. One can get this mixing to work with smaller concentrations, too. All the rest of the mixing comes from source 3. Thus we produce the desired isochron. So this is a valid mixing, and we are done.
We can get more realistic mixings of three sources with the same result by choosing the sources to be linear combinations of sources 1, 2, and 3 above, with more natural concentrations of D, P, and N. The rest of the mixing comes from source 3. This mixing is more realistic because P1, N1, D2, and N2 are not so large. I did see in one reference the statement that some parent-to-daughter ratio yielded more accurate dates than isochrons.
To me, this suggests the possibility that geologists themselves recognize the problems with isochrons, and are looking for a better method. The impression I have is that geologists are continually looking for new methods, hoping to find something that will avoid problems with existing methods. But then problems also arise with the new methods, and so the search goes on.
Furthermore, here is a brief excerpt from a recent article which also indicates that isochrons often have severe problems. If all of these isochrons indicated mixing, one would think that this would have been mentioned: The geological literature is filled with references to Rb-Sr isochron ages that are questionable, and even impossible.
Woodmorappe , pp. Faure , pp. Zheng , pp. Zheng pp. He comes closest to recognizing the fact that the Sr concentration is a third or confounding variable in the isochron simple linear regression. Snelling discusses numerous false ages in the U-Pb system where isochrons are also used. However, the U-Th-Pb method uses a different procedure that I have not examined and for which I have no data.
Many of the above authors attempt to explain these "fictitious" ages by resorting to the mixing of several sources of magma containing different amounts of Rb, Sr, and Sr immediately before the formation hardens.
Akridge , Armstrong , Arndts , Brown , , Helmick and Baumann all discuss this factor in detail. Anyway, if isochrons producing meaningless ages can be produced by mixing, and this mixing cannot be detected if three or maybe even two, with fractionation sources are involved, and if mixing frequently occurs, and if simple parent-to-daughter dating also has severe problems, as mentioned earlier, then I would conclude that the reliability of radiometric dating is open to serious question.
The many acknowledged anomalies in radiometric dating only add weight to this argument. I would also mention that there are some parent-to-daughter ratios and some isochrons that yield ages in the thousands of years for the geologic column, as one would expect if it is in fact very young. One might question why we do not have more isochrons with negative slopes if so many isochrons were caused by mixing.
This depends on the nature of the samples that mix. It is not necessarily true that one will get the same number of negative as positive slopes. If I have a rock X with lots of uranium and lead daughter isotope, and rock Y with less of both relative to non-radiogenic lead , then one will get an isochron with a positive slope. If rock X has lots of uranium and little daughter product, and rock Y has little uranium and lots of lead daughter product relative to non-radiogenic lead , then one will get a negative slope.
This last case may be very rare because of the relative concentrations of uranium and lead in crustal material and subducted oceanic plates. Another interesting fact is that isochrons can be inherited from magma into minerals.
Earlier, I indicated how crystals can have defects or imperfections in which small amounts of magma can be trapped. This can result in dates being inherited from magma into minerals. This can also result in isochrons being inherited in the same way. So the isochron can be measuring an older age than the time at which the magma solidified. This can happen also if the magma is not thoroughly mixed when it erupts.
If this happens, the isochron can be measuring an age older than the date of the eruption. This is how geologists explain away the old isochron at the top of the Grand Canyon. From my reading, isochrons are generally not done, as they are expensive. Isochrons require more measurements than single parent-to-daughter ratios, so most dates are based on parent-to-daughter ratios. So all of the scenarios given apply to this large class of dates. Another thing to keep in mind is that it is not always possible to do an isochron.
Often one does not get a straight line for the values. This is taken to imply re-melting after the initial solidification, or some other disturbing event. Anyway, this also reduces the number of data points obtained from isochrons. It is an accurate way to date specific geologic events. This is an enormous branch of geochemistry called Geochronology. There are many radiometric clocks and when applied to appropriate materials, the dating can be very accurate. As one example, the first minerals to crystallize condense from the hot cloud of gasses that surrounded the Sun as it first became a star have been dated to plus or minus 2 million years!!
That is pretty accurate!!! Other events on earth can be dated equally well given the right minerals. For example, a problem I have worked on involving the eruption of a volcano at what is now Naples, Italy, occurred years ago with a plus or minus of years. Answer 2: Yes, radiometric dating is a very accurate way to date the Earth.
We know it is accurate because radiometric dating is based on the radioactive decay of unstable isotopes. For example, the element Uranium exists as one of several isotopes, some of which are unstable. When an unstable Uranium U isotope decays, it turns into an isotope of the element Lead Pb. We call the original, unstable isotope Uranium the "parent", and the product of decay Lead the "daughter". From careful physics and chemistry experiments, we know that parents turn into daughters at a very consistent, predictable rate.
For an example of how geologists use radiometric dating, read on: A geologist can pick up a rock from a mountainside somewhere, and bring it back to the lab, and separate out the individual minerals that compose the rock.
They can then look at a single mineral, and using an instrument called a mass spectrometer, they can measure the amount of parent and the amount of daughter in that mineral. The ratio of the parent to daughter then can be used to back-calculate the age of that rock.
Pretty cool! 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.