Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion 4. Carbonaceous chondrites are grouped according to distinctive compositions thought to reflect the type of parent body from which they originated. These C chondrite groups are now each named with a standard two-letter CX designation, where C stands for "carbonaceous" other types of chondrites do not begin with this letter plus a capital letter in the spot X , which is very often the first letter of the name of a prominent meteorite-often the first to be discovered-in the group. Such meteorites are often named for the place where they fell, thus giving no clue as to the physical nature of the group.
Most of the organic carbon in CI and CM carbonaceous chondrites is an insoluble complex material. That is similar to the description for kerogen. A kerogen-like material is also in the ALH Martian meteorite an achondrite. The CM meteorite Murchison has over 70 extraterrestrial amino acids and other compounds including carboxylic acidshydroxy carboxylic acids, sulphonic and phosphonic acids, aliphatic, aromatic and polar hydrocarbonsfullerenesheterocyclescarbonyl compounds, alcoholsamines and amides.
From Wikipedia, the free encyclopedia. Main article: CM chondrite. Bibcode : Metic. Richard The Cambridge Encyclopedia of Meteorites. Cambridge: Cambridge University Press. Bada Proceedings of the National Academy of Sciences. Bibcode : PNAS Origins of Life and Evolution of the Biosphere. Bibcode : OLEB Astronomy Picture of the Day.
Retrieved Astrophysical Journal. Bibcode : ApJ Meteorites and meteoritics. Table 2 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 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.
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.
In the early afternoon of August 24, 79 CE, Mt Vesuvius erupted violently, sending hot ash flows speeding down its flanks. 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. Both studies detected, in a few of the flows, deviations from atmospheric isotopic composition, most often in the form of excess 40 Ar.
Carbon dating meteorites
The majority of flows, however, had no detectable excess 40 Ar and thus gave correct ages as expected. Of the handful of flows that did contain excess 40 Ar, only a few did so in significant amounts. Note, however, that even an error of 0. Austin has documented excess 40 Ar in the dacite flow from Mount St Helens, but the amounts are insufficient to produce significant errors in all but the youngest rocks.
Thus any potential error due to excess 40 Ar was eliminated by the use of this technique, which was not available when the studies by Dalrymple and Krummenacher were done. Thus the large majority of historic lava flows that have been studied either give correct ages, as expected, or have quantities of excess radiogenic 40 Ar that would be insignificant in all but the youngest rocks.
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. I thank Chris Stassen and 2 anonymous reviewers for their thoughtful comments, which led to important improvements in the manuscript.
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Teaching Resources. Community Outreach Resources. Coronavirus Resources. Browse articles by topic. DIYSci Activities. About NCSE. In five specimens were taken from this dome at five different locations and subjected to conventional Potassium-Argon dating.
What carbon dating meteorites something also think
The results indicated ages of less than one half to almost three million years old, all from eleven year old rock. Click on photo for high resolution We know when this dome formed. When we date rock of known age we test the claims and we see obvious failures. But, when we date rock of unknown age, we are assured that the results are accurate. Plaisted Radiometric Dating. How radiometric dating works in general.
Why methods in general are inaccurate. Why K-Ar dating is inaccurate. The branching ratio problem. Why older dates would be found lower in the geologic column especially for K-Ar dating.
Do different methods agree with each other on the geologic column?
Possible other sources of correlation. Anomalies of radiometric dating. Why a low anomaly percentage is meaningless. The biostrategraphic limits issue. Preponderance of K-Ar dating. Excuses for anomalies. Need for a double-blind test. Possible changes in the decay rate. Atlantic sea floor dating. Dating Meteorites.
Gentry's radiohaloes in coalified wood. Carbon 14 dating. Tree ring chronologies. Coral dating. Evidence for catastrophe in the geologic column. Rates of erosion. Reliability of creationist sources. Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years.
We are told that these methods are accurate to a few percent, and that there are many different methods. We are told that of all the radiometric dates that are measured, only a few percent are anomalous.
This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points.
Since there doesn't seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.
However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old. If these dates are correct, this calls the Biblical account of a recent creation of life into question. After study and discussion of this question, I now believe that the claimed accuracy of radiometric dating methods is a result of a great misunderstanding of the data, and that the various methods hardly ever agree with each other, and often do not agree with the assumed ages of the rocks in which they are found.
I believe that there is a great need for this information to be made known, so I am making this article available in the hopes that it will enlighten others who are considering these questions.
Even the creationist accounts that I have read do not adequately treat these issues. At the start, let me clarify that my main concern is not the age of the earth, the moon, or the solar system, but rather the age of life, that is, how long has life existed on earth.
Many dating methods seem to give about the same ages on meteorites. Thus radiometric dating methods appear to give evidence that the earth and meteorites are old, if one accepts the fact that decay rates have been constant. However, there may be other explanations for this apparent age. Perhaps the earth was made from older pre-existing matter, or perhaps decay rates were briefly faster for some reason. When one considers the power of God, one sees that any such conclusions are to some extent tentative.
I believe that life was recently created. I also believe that the evidence indicates that the earth has recently undergone a violent catastrophe. Geologic time is divided up into periods, beginning with the Precambrian, followed by the Cambrian and a number of others, leading up to the present.
Some fossils are found in Precambrian rocks, but most of them are found in Cambrian and later periods. We can assume that the Precambrian rocks already existed when life began, and so the ages of the Precambrian rocks are not necessarily related to the question of how long life has existed on earth.
The Cambrian period is conventionally assumed to have begun about million years ago. Since Cambrian and later rocks are largely sedimentary and igneous volcanic rocks are found in Cambrian and later strata, if these rocks are really million years old, then life must also be at least million years old.
Therefore, my main concern is with rocks of the Cambrian periods and later.
Atlantic sea floor dating. Dating Meteorites. Conclusion. Gentry's radiohaloes in coalified wood. Carbon 14 dating. Tree ring chronologies. Coral dating. Varves. Evidence for catastrophe in the geologic column. Rates of erosion. Reliability of creationist sources. The Radiometric Dating Game. Carbon dating meteorites. Most estimates of the time of meteorites from the moon rocks from the frequency of iron meteorites are. Martian meteorite that have not immediately follow that they can go no. The oldest minerals, , moon rocks. Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion (%) of meteorite falls. Some famous carbonaceous chondrites are: Allende, Murchison, Orgueil, Ivuna, Murray, Tagish Lake, and Sutter's MillType: Chondrite.
How radiometric dating works in general Radioactive elements decay gradually into other elements. The original element is called the parent, and the result of the decay process is called the daughter element. Assuming we start out with pure parent, as time passes, more and more daughter will be produced.
By measuring the ratio of daughter to parent, we can measure how old the sample is. A ratio of zero means an age of zero. A higher ratio means an older age. A ratio of infinity that is, all daughter and no parent means an age of essentially infinity.
Each radioactive element has a half-life, which tells how long it takes for half of the element to decay. For potassium 40, the half-life is about 1.
In general, in one half-life, half of the parent will have decayed. Potassium 40 K40 decays to argon 40, which is an inert gas, and to calcium.
Potassium is present in most geological materials, making potassium-argon dating highly useful if it really works. Uranium decays to lead by a complex series of steps. Rubidium decays to strontium. When it is stated that these methods are accurate to one or two percent, it does not mean that the computed age is within one or two percent of the correct age.
It just means that there is enough accuracy in the measurements to compute t to one or two percentage points of accuracy, where t is the time required to obtain the observed ratio of daughter to parent, assuming no initial daughter product was present at the beginning, and no daughter or parent entered or left the system.
For isochrons, which we will discuss later, the conditions are different. If these conditions are not satisfied, the error can be arbitrarily large. In order to use these methods, we have to start out with a system in which no daughter element is present, or else know how much daugher element was present initially so that it can be subtracted out. We also need to know that no parent or daughter has entered or left the system in the meantime. Radiometric dating is commonly used on igneous rocks lavaand on some sedimentary minerals.
But fossils can generally not be dated directly.
The use of 14C in meteorite dating is solely based on its production by cosmic rays (and for terrestrial samples, with its production in the atmosphere). 26Al and some other nuclides not mentioned are also used in this way. Thus, although "extinct", these nuclides are present in meteorites, but produced by a more recent process. Oct 03, A formula to calculate how old a sample is by carbon dating is: t = [ ln (Nf/No) / ] x t1/2. t = [ ln (N f /N o) / ] x t 1/2. where ln is the natural logarithm, N f /N o is the percent of carbon in the sample compared to the amount in living tissue, and t 1/2 is the half-life of carbon (5, years). So, if you had a fossil that had 10 percent carbon compared to.
When lava is hot, argon escapes, so it is generally assumed that no argon is present when lava cools. Thus we can date lava by K-Ar dating to determine its age. As for the other methods, some minerals when they form exclude daughter products. Zircons exclude lead, for example, so U-Pb dating can be applied to zircon to determine the time since lava cooled.
Micas exclude strontium, so Rb-Sr dating can be used on micas to determine the length of time since the mica formed. In rubidium-strontium dating, micas exclude strontium when they form, but accept much rubidium. In uranium-lead U-Pb dating of zircon, the zircon is found to exclude initial lead almost completely. Thus one would know that any strontium that is present had to come from the parent rubidium, so by computing the ratio and knowing the half life, one can compute the age.
In general, when lava cools, various minerals crystallize out at different temperatures, and these minerals preferentially include and exclude various elements in their crystal structures.
So one obtains a series of minerals crystallizing out of the lava. Thus the composition of the lava continues to change, and later minerals can form having significantly different compositions than earlier ones. Lava that cools on the surface of the earth is called extrusive. This type of lava cools quickly, leaving little time for crystals to form, and forms basalt.
Lava that cools underground cools much more slowly, and can form large crystals. This type of lava typically forms granite or quartz. Why methods in general are inaccurate I admit this is a very beautiful theory. This would seem to imply that the problem of radiometric dating has been solved, and that there are no anomalies. So if we take a lava flow and date several minerals for which one knows the daughter element is excluded, we should always get the exact same date, and it should agree with the accepted age of the geological period.
Is this true? I doubt it very much. If the radiometric dating problem has been solved in this manner, then why do we need isochrons, which are claimed to be more accurate?
The same question could be asked in general of minerals that are thought to yield good dates. Mica is thought to exclude Sr, so it should yield good Rb-Sr dates.
But are dates from mica always accepted, and do they always agree with the age of their geologic period? I suspect not.
Indeed, there are a number of conditions on the reliability of radiometric dating. For example, for K-Ar dating, we have the following requirements:. There must have been no incorporation of Ar40 into the mineral at the time of crystallization or a leak of Ar40 from the mineral following crystallization.
The earth is supposed to be nearly 5 billion years old, and some of these methods seem to verify ancient dates for many of earth's igneous rocks. The answer is that these methods, are far from infallible and are based on three arbitrary assumptions a constant rate of decay, an isolated system in which no parent or daughter element can be added or lost, and a known amount of the daughter element present initially. Heating and deformation of rocks can cause these atoms to migrate, and water percolating through the rocks can transport these substances and redeposit them.
These processes correspond to changing the setting of the clock hands. Not infrequently such resetting of the radiometric clocks is assumed in order to explain disagreements between different measurements of rock ages. It is known that neutrinos interact with atomic nucleii, so a larger density of neutrinos could have sped up radioactive decay and made matter look old in a hurry.
Some more quotes from the same source:. In the lead-uranium systems both uranium and lead can migrate easily in some rocks, and lead volatilizes and escapes as a vapor at relatively low temperatures. It has been suggested that free neutrons could transform Pb first to Pb and then to Pb, thus tending to reset the clocks and throw thorium-lead and uranium-lead clocks completely off, even to the point of wiping out geological time.
Furthermore, there is still disagreement of 15 percent between the two preferred values for the U decay constant.
Potassium volatilizes easily, is easily leached by water, and can migrate through the rocks under certain conditions. Furthermore, the value of the decay constant is still disputed, although the scientific community seems to be approaching agreement. Historically, the decay constants used for the various radiometric dating systems have been adjusted to obtain agreement between the results obtained.
Argon, the daughter substance, makes up about one percent of the atmosphere, which is therefore a possible source of contamination. However, since it is possible for argon to be formed in the rocks by cosmic radiation, the correction may also be in error. Argon from the environment may be trapped in magma by pressure and rapid cooling to give very high erroneous age results. Rubidium parent atoms can be leached out of the rock by water or volatilized by heat.
All of these special problems as well as others can produce contradictory and erroneous results for the various radiometric dating systems. So we have a number of mechanisms that can introduce errors in radiometric dates. Heating can cause argon to leave a rock and make it look younger.
In general, if lava was heated after the initial flow, it can yield an age that is too young. If the minerals in the lava did not melt with the lava, one can obtain an age that is too old. Leaching can also occur; this involves water circulating in rock that can cause parent and daughter elements to enter or leave the rock and change the radiometric age. Thus it is easy to rationalize any date that is obtained.
If a date is too old, one can say that the mineral did not melt with the lava. Maybe it got included from surrounding rock as the lava flowed upward.
If the date is too young, one can say that there was a later heating event. One can also hypothesize that leaching occurred. But then it is claimed that we can detect leaching and heating.
But how can we know that this claim is true, without knowing the history of rocks and knowing whether they have in fact experienced later heating or leaching? The problems are compounded because many of the parent and daughter substances are mobile, to some extent.
I believe that all parent substances are water soluble, and many of the daughter products as well. A few sources have said that Sr is mobile in rock to some extent. This could cause trouble for Rb-Sr dating. In fact, some sources say that Sr and Ar have similar mobilities in rock, and Ar is very mobile. Especially the gaseous radioactive decay byproducts such as argon, radon, and helium are mobile in rock.
So if a rock has tiny cracks permitting gas to enter or escape or permitting the flow of water, the radiometric ages could be changed substantially even without the rock ever melting or mixing. Now, there is probably not much argon in a rock to start with. So the loss of a tiny amount of argon can have significant effects over long time periods. A loss of argon would make the rock look younger.
In a similar way, argon could enter the rock from the air or from surrounding rocks and make it look older. And this can also happen by water flowing through the rock through tiny cracks, dissolving parent and daughter elements.
Consider, that carbon dating meteorites not
It would be difficult to measure the tiny changes in concentration that would suffice to make large changes in the radiometric ages over long time periods. I also question the assertion that argon, for example, is excluded from certain minerals when they crystallize and never enters later on. Geologists often say that ages that are too old are due to excess argon. So it must be possible for that excess argon to get in, even though the crystal is supposed to exclude it.
Here is one such reference, although this is to a mineral that does not exclude argon:. In a few cases, argon ages older than that of the Earth which violate local relative age patterns have even been determined for the mineral biotite. Such situations occur mainly where old rocks have been locally heated, which released argon into pore spaces at the same time that new minerals grew. Under favourable circumstances the isochron method may be helpful, but tests by other techniques may be required.
For example, the rubidium-strontium method would give a valid isotopic age of the biotite sample with inherited argon. Another problem is that the crystal structure typically has imperfections and impurities. For example, different kinds of quartz have different colors due to various impurities that are included but not part of the repetitive unit of the quartz crystal. So even if the crystal excludes the daughter element, it could be present in impurities.
Thus crystals, as they form, may have tiny imperfections that accept parent and daughter products in the same ratios as they occur in the lava, so one can inherit ages from the lava into minerals in this way.
It is also possible that parent and daughter elements could be present in boundaries between regular crystal domains. I don't know how we can be sure that a crystal will exclude argon or other daughter substances except by growing it in the laboratory under many conditions.
There can also be argon or other daughter products added from the air or from other rocks. One could say that we can detect whether the daughter is embedded in the crystal structure or not. But this would require an atom by atom analysis, which I do not believe is practical. Why K-Ar dating is inaccurate Since K-Ar potassium-argon dating is one of the most prevalent techniques, some special commentary about it is in order.
Potassium is about 2. Argon is about 3. This is about one ten millionth of the mass of the rock, a very tiny percentage. And yet, with a large amount of argon in the air and also filtering up from rocks below, and with excess argon in lava, with argon and potassium water soluble, and argon mobile in rock, we are still expecting this wisp of argon to tell us how old the rock is! The percentage of Ar40 is even less for younger rocks. For example, it would be about one in million for rocks in the vicinity of 57 million years old.
To get one part in 10 million of argon in a rock in a thousand years, we would only need to get one part in 10 billion entering the rock each year.
This would be less than one part in a trillion entering the rock each day, on the average. This would suffice to give a rock having an average concentration of potassium, a computed potassium-argon age of over million years!
We can also consider the average abundance of argon in the crust. This implies a radiometric age of over 4 billion years. So a rock can get a very old radiometric age just by having average amounts of potassium and argon.
It seems reasonable to me that the large radiometric ages are simply a consequence of mixing, and not related to ages at all, at least not necessarily the ages of the rocks themselves. The fact that not all of the argon is retained would account for smaller amounts of argon near the surface, as I will explain below. This could happen because of properties of the magma chambers, or because of argon being given off by some rocks and absorbed by others.
I don't see how one can possibly know that there are no tiny cracks in rocks that would permit water and gas to circulate. The rates of exchange that would mess up the dates are very tiny. It seems to me to be a certainty that water and gas will enter rocks through tiny cracks and invalidate almost all radiometric ages. Let me illustrate the circulation patterns of argon in the earth's crust. About 2. So argon is being produced throughout the earth's crust, and in the magma, all the time.
In fact, it probably rises to the top of the magma, artificially increasing its concentration there. Now, some rocks in the crust are believed not to hold their argon, so this argon will enter the spaces between the rocks. Leaching also occurs, releasing argon from rocks. Heating of rocks can also release argon. Argon is released from lava as it cools, and probably filters up into the crust from the magma below, along with helium and other radioactive decay products. All of this argon is being produced and entering the air and water in between the rocks, and gradually filtering up to the atmosphere.
But we know that rocks absorb argon, because correction factors are applied for this when using K-Ar dating. So this argon that is being produced will leave some rocks and enter others. The partial pressure of argon should be largest deepest in the earth, and decrease towards the surface. This would result in larger K-Ar ages lower down, but lower ages nearer the surface. So this confirms that argon can travel from rock to rock when one rock is heated. Now, argon is very soluble in magma, which can hold a lot of it:.
After the material was quenched, the researchers measured up to 0. They noted, 'The solubility of Ar in the minerals is surprisingly high'. I note that this concentration of argon, if it were retained in the rock, would suffice to give it a geological age well over nillion years, assuming an average concentration of potassium. This is from a paper by Austin available at ICR. This paper also discusses Mount St.
Helens K-Ar dating, and historic lava flows and their excess argon. So magma holds tremendous amounts of argon. Now, consider an intrusive flow, which cools within the earth. All its argon will either remain inside and give an old age to the flow, or will travel through surrounding rock, where it can be absorbed by other rocks.
So magma should have at least 20 times as much argon as a rock million years old by K-Ar dating. In fact, the argon in the magma may well be even higher, as it may concentrate near the top. This amount of argon is enough to raise 20 times the volume of magma to a K-Ar age of million years, and probably times the volume of the magam to an age of 57 million years.
Really. carbon dating meteorites pity, that now
So one sees that there is a tremendous potential for age increases in this way. It is not necessary for this increase in age to happen all at once; many events of this nature can gradually increase the K-Ar ages of rocks.
In general, older rocks should have more argon because they have been subject to more exposure to such argon, but their true age is not necessarily related to their K-Ar radiometric age. We can also consider that most volcanoes and earthquakes occur at boundaries between plates, so if the lava has flowed before, it is likely to flow again nearby, gradually increasing the age.
I suppose earthquakes could also allow the release of argon from the magma. Other mechanisms include dissolving of rock, releasing its argon, fracturing of rock, with release of argon, argon from cooling lava under water entering the water and entering other rocks, and argon from cooling lave entering subterranean water and being transported to other rock.
There are so many mechanisms that it is hard to know what pattern to expect, and one does not need to rely on any one of them such as more argon in the magma in the past to account for problems in K-Ar dating. Since even rocks with old K-Ar dates still absorb more argon from the atmosphere in short time periods, it follows that rocks should absorb quite a bit of argon over long time periods, especially at higher pressures.
In fact, if a rock can absorb only a ten millionth part of argon, that should be enough to raise its K-Ar age to over million years, assuming an average amounts of potassium. It wouldn't require many internal cracks to allow a ten millionth part of argon to enter. Also, as the rock deforms under pressure, more cracks are likely to form and old ones are likely to close up, providing more opportunity for argon and other gases to enter.
I mentioned a number of possibilities that could cause K-Ar dates to be much older than the true ages of the rocks. Here is another way that K-Ar dates can be too old: If we assume the earth went through a catastrophe recently, then the crustal plates might have been agitated, permitting lava and argon to escape from the magma.
Thus a lot of argon would be filtering up through the crust. As intrusive flows of lava cooled inside the crust, they would have been in an environment highly enriched in argon, and thus would not have gotten rid of much of their argon.
Thus they would have hardened with a lot of argon inside. This would make them appear old. The same goes for extrusive flows on the surface, since argon would be filtering up through the earth and through the lava as it cooled. In areas where tremendous tectonic activity has taken place, highly discordant values for the ages are obtained. The difficulties associated are numerous and listed as follows:. There seems to be a great deal of question regarding the branching ratio for K40 into Ar40 and Ca But the value is not really known.
The observed value is between 0. However, this doesn't remedy the situation and the ages are still too high [low? The geochronologists credit this to "argon leakage". There is far too much Ar40 in the earth for more than a small fraction of it to have been formed by radioactive decay of K This is true even if the earth really is 4.
In the atmosphere of the earth, Ar40 constitutes This is around times the amount that would be generated by radioactive decay over the age of 4. Certainly this is not produced by an influx from outer space. Thus, a large amount of Ar40 was present in the beginning. Since geochronologists assume that errors due to presence of initial Ar40 are small, their results are highly questionable.
Argon diffuses from mineral to mineral with great ease. It leaks out of rocks very readily and can move from down deep in the earth, where the pressure is large, and accumulate in an abnormally large amount in the surface where rock samples for dating are found.
They would all have excess argon due to this movement. This makes them appear older. Rocks from deeper in the crust would show this to a lesser degree. Also, since some rocks hold the Ar40 stronger than others, some rocks will have a large apparent age, others smaller ages, though they may actually be the same age.
If you were to measure Ar40 concentration as function of depth, you would no doubt find more of it near the surface than at deeper points because it migrates more easily from deep in the earth than it does from the earth into the atmosphere.
It is easy to see how the huge ages are being obtained by the KAr40 radiometric clock, since surface and near-surface samples will contain argon due to this diffusion effect. Some geochronologists believe that a possible cause of excess argon is that argon diffuses into mineral progressively with time. Significant quantities of argon may be introduced into a mineral even at pressures as low as one bar.
If such [excessive] ages as mentioned above are obtained for pillow lavas, how are those from deep-sea drilling out in the Atlantic where sea-floor spreading is supposed to be occurring? Potassium is found to be very mobile under leaching conditions. This could move the "ages" to tremendously high values. Ground-water and erosional water movements could produce this effect naturally.
Rocks in areas having a complex geological history have many large discordances. In a single rock there may be mutually contaminating, potassium- bearing minerals. There is some difficulty in determining the decay constants for the KAr40 system. Geochronologists use the branching ratio as a semi-emperical, adjustable constant which they manipulate instead of using an accurate half-life for K A number of recent lava flows within the past few hundred years yield potassium-argon ages in the hundreds of thousands of years range.
This indicates that some excess argon is present. Where is it coming from? And how do we know that it could not be a much larger quantity in other cases? If more excess argon were present, then we could get much older ages.
It is true that an age difference in the hundreds of thousands of years is much too small to account for the observed K-Ar ages. But excess argon is commonly invoked by geologists to explain dates that are too old, so I'm not inventing anything new.
Second, there may have been a lot more more argon in the magma in the past, and with each eruption, the amount decreased. So there would have been a lot more excess argon in the past, leading to older ages. For rocks that are being dated, contamination with atmospheric argon is a persistent problem that is mentioned a number of times. Thus it is clear that argon enters rock easily. It is claimed that we can know if a rock has added argon by its spectrum when heated; different temperatures yield different fractions of argon.
It is claimed that the argon that enters from the atmosphere or other rocks, is less tightly bound to the crystal lattice, and will leave the rock at a lower temperature.
But how do we know what happens over thousands of years? It could be that this argon which is initially loosely bound if it is so initially gradually becomes more tightly bound by random thermal vibrations, until it becomes undetectable by the spectrum technique. The fact that rock is often under high pressure might influence this process, as well. The branching ratio problem We now consider in more detail one of the problems with potassium-argon dating, namely, the branching ratio problem.
Here is some relevant information that was e-mailed to me. There are some very serious objections to using the potassium-argon decay family as a radiometric clock.
Sorry, carbon dating meteorites all became clear
The geochronologist considers the Ca40 of little practical use in radiometric dating since common calcium is such an abundant element and the radiogenic Ca40 has the same atomic mass as common calcium.
Here the actual observed branching ratio is not used, but rather a small ratio is arbitrarily chosen in an effort to match dates obtained method with U-Th-Pb dates. The branching ratio that is often used is 0. Thus we have another source of error for K-Ar dating. Henke criticized some statements in my article taken from Slusher about the branching ratio for potassium.
Slusher asserted that the best known value of the branching ratio was not always used in computing K-Ar radiometric ages. Unfortunately, Dalrymple says nothing about the calculation of the branching ratio. He simply gives the correct value for the K-Ar system. The issue is not just how well this was known in the past, but which value was actually used, and whether dates published in the past have been computed with the most recent value.
Often values for constants are standardized, so that the values actually used may not be the most accurate known. All that Dalrymple says is that his ages were all recomputed using the most accurate values of the constants. This implies that some of them were originally computed using less accurate values, which is similar to Slusher's point.
Dalrymplep. He admits that Slusher's statements about it would have been true in the 's and early 's, but are no longer true. But he didn't say when the correct value for the branching ratio began to be used. Even some figures from Faure, Principles of Isotope Geology, are based on another constant that is 2 or 3 percent too low, according to Dalrymple, and so there may be many ages in the literature that need revision by small amounts.
However, Harland et al imply that nearly the correct value for the branching ratio has been known and used since the mid-fifties. We now consider whether they can explain the observed dates. In general, the dates that are obtained by radiometric methods are in the hundreds of millions of years range. One can understand this by the fact that the clock did not get reset if one accepts the fact that the magma "looks" old, for whatever reason.