Mount etna rock dating examples

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The equipment in use at the time at the lab employed by Dr. Austin, Geocron Laboratorieswas of a type sensitive enough to only detect higher concentrations of argon gas. Geocron clearly stated that their equipment was only capable of accurate results when the sample contained a concentration of argon high enough to be consistent with 2, years or older.

And so, by any standard, it was scientifically meaningless for Dr. Austin to apply Geocron's potassium-argon dating to his sample of dacite known to be only six years old. But let's ask the obvious question. If there wasn't yet enough argon in the rock to be detectable, and the equipment that was used was not sensitive enough to detect any argon, how was enough argon found that such old results were returned?

There are two possible reasons that the old dates were returned. The first has to do with the reason Geocron's equipment was considered useful only for high concentrations of argon. There would always be a certain amount of argon inside the mass spectrometer left over from previous experiments. If the sample being tested is old enough to have significant argon, this leftover contamination would be statistically insignificant; so this was OK for Geocron's normal purposes.

But for a sample with little or no argon, it would produce a falsely old result. This was undoubtedly a factor in Dr. The second possibility is that so-called "excess argon" could have become trapped in the Mount St.

This is where we find the bulk of the confusing complexity in Austin's paper and in those of his critics. The papers all go into great detail describing the various ways that argon-containing compounds can be incorporated into magma.

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These include the occlusion of xenoliths and xenocrysts, which are basically contaminants from existing old rocks that get mixed in with the magma; and phenocrysts, which are crystals of all sorts of different minerals that form inside the rock in different ways depending on how quickly the magma cools.

Page after page of chemical compositions, mineral breakdowns, charts and graphs, and all sorts of discussion of practically every last molecule found in the Mount St. Summarizing both arguments, Dr. Austin claims that xenoliths and xenocrysts were completely removed from the samples before testing, and that the wrong results are due to phenocrysts, which form to varying degrees in all magma, and thus effectively cast doubt on all potassium-argon testing done throughout the world.

It's important to note that his arguments are cogent and are based on sound geology, and are often mischaracterized by skeptics. He did not simply use the wrong kind of radiometric dating as an ignorant blunder. He was deliberately trying to illustrate that even a brand-new rock would show an ancient age, even when potassium-argon dating was properly used.

Austin's critics charge that he ignored the probable likelihood that the limitations of Geochron's equipment accounts for the results, just as Geochron warned. They also charge that he likely did not remove all the xenoliths and xenocrysts from his samples. However, neither possibility can be known for sure. Certainly there is no doubt that the test was far outside the useful parameters of potassium-argon dating, but whereas critics say this invalidates the results, Austin concludes that his results certify that the test is universally useless.

If we allow both sides to have their say, and do not bring a bias preconditioning us to accept whatever one side says and to look only for flaws in the other side, a fair conclusion to make is that both sides make valid points. Austin does indeed identify a real potential weakness in potassium-argon dating.

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However he is wrong that his phenocrysts constitute a fatal flaw in potassium-argon dating previously unknown to geology. In fact, the implications of phenocrysts were already well understood. Yes they are one of the variables, and yes, in some samples they do push the error bars. However, the errors they introduce are in the range of a standard deviation, they are not nearly adequate to explain errors as gross as three or more orders of magnitude, which would be necessary to explain the discrepancy between the measured age of rocks and the Biblical age of the Earth.

Such variables are also a principal reason that geologists never rely on just one dating method, with no checks or balances. That would be pretty reckless. For most rocks, multiple types of radiometric dating are appropriate; and in practice, multiple samples would always be tested, not just one like Austin used.

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In combination, these tests give a far more complete and accurate picture of a rock's true age than just a single potassium-argon test could. In addition, stratigraphic and paleomagnetic data can often contribute to the picture as well.

From many decades of such experience, geologists have excellent data that guides proper usage of each of these tools, and they don't include gross misuse of potassium-argon dating. What Austin did was to exploit a known caveat in radiometric dating; dramatically illustrate it with a high-profile test using the public's favorite volcano, Mount St.

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Helens; and sensationalize the results in a paper that introduces nothing new to geologists, but that impresses laypeople with its detailed scientific language. Using science, there are at least three hypotheses that may be purposed to explain why Austin obtained 'dates' ofto 2. Argon gas 'excess' argon was incorporated into the glass and minerals in the dacite as they formed in the parent melt. The argon failed to degas from the minerals before the dacite solidified.

Because all but one of the dates in the above table are below the 2 million year lower dating limit established by Geochron Laboratories, the dates may be nothing more than contamination artifacts from the mass spectrometer at Geochron Laboratories. IF the Geochron mass spectrometer was exceptionally clean on the day that Austin's samples were run that is, IF hypothesis 2 is not a factorthe dates may be approximately accurate.

Even if the absolute values of the dates are highly erroneous, the relative order of the fractions' dates from oldest to youngest may be roughly correct. That is, the various minerals phenocrysts in the dacite may have grown in the parent melt at different times and the entire crystallization process may have taken as much as a few million years.

Additionally, somewhat older xenoliths foreign rocks and xenocrysts foreign minerals, for example, Hyndman,p. Any or all of these hypotheses are possible. Austin strongly argues that steps were taken in his laboratory to protect the samples from contamination and that xenoliths foreign rocks, hypothesis 3 were removed from the samples before analysis.

He also claims that microscopes were used to scan for 'foreign particles' xenocrysts? Of course, he and his assistants may have missed many of the xenocrysts if they were small. Austin clearly ignores the possibility of contamination in the mass spectrometer hypothesis 2 and the possibility that the phenocrysts in his samples may be much older than the AD eruption hypothesis 3.

Austin simply assumes that the first explanation is correct and then he proceeds to use the 'presence' of 'excess argon' in his samples to question the reliability of all K-Ar dates on other rocks and minerals. This is the logical fallacy of composition Copi and Cohen, The validity of either hypothesis 2 or 3 would provide additional evidence that Austin's application of the K-Ar method is flawed and that he has failed to prove that the K-Ar method is universally invalid. In the caption of Figure 4, Austin identifies the grains in the photograph as phenocrysts and microphenocrysts, which is probably generally correct.

Phenocrysts and microscopic phenocrysts microphenocrysts are crystals that grow in a melt magma deep within the Earth. In some cases, the entire melt solidifies before reaching the Earth's surface and an intrusive igneous rock develops Hyndman,p.

Because intrusive rocks solidify deep within the Earth away from cool water and air, volcanic glass is absent and the grains may be fairly large that is, easily reaching lengths of one centimeter or more.

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In other cases, such as Austin's dacite, a partially crystallized melt erupts on the Earth's surface and produces a volcanic rock, which may be a mixture of rapidly quenched volcanic glass and coarser phenocrysts Hyndman,p. Although Austin and Swenson will not admit it, some of the grains in Figure 4 may be xenocrysts rather than phenocrysts. In some cases, the magma may not be hot enough to melt or entirely dissolve the xenocrysts and they may survive after the melt cools.

For even the best mineralogists and petrologists, xenocrysts may be difficult to distinguish from phenocrysts for example, Hyndman,p. As clearly shown in Figure 4 of Austin's essaymany of the mineral grains are zoned. The zoning appears as a series of concentric rings of various shades of gray within the grains see the two obvious examples in the middle of Figure 4.

Zoned crystals also may show Carlsbad twinning, which is typical of feldspars Perkins and Henke,Plate 10; Klein and Hurlbut,p. In thin section and under crossed-polarized light, Carlsbad twinning has a 'half and half' appearance, where one half of the grain is darker than the other half Perkins and Henke,Plate As the sample is rotated on a microscope stage, one twin will darken as the other lightens in crossed-polarized light.

A large grain with very noticeable Carlsbad twinning is located at the top of Figure 4. Well-established laboratory studies Klein and Hurlbut,p. That is, as the magma cools, calcium-rich plagioclases crystallize first, which causes the remaining melt to become depleted in calcium and relatively enriched in sodium. Once temperatures further decline, more sodium-rich plagioclase begins to solidify from the melt and may surround the calcium-rich grains.

This process produces zoning, where the older and more calcium-rich plagioclases are located in the core of the grains and the younger and more sodium-rich plagioclases occupy the rims. Because of their crystalline and chemical differences, the calcium-rich plagioclase cores have somewhat different optical properties than the sodium-rich rims, which produce the noticeable concentric zoning in the grains in Austin's thin section photograph. Besides plagioclase feldspars, chemicals in cooling magmas deep within the Earth may organize into pyroxenes, amphiboles and a large variety of other minerals.

In contrast, any melt that reaches the Earth's surface during an eruption will immediately quench into volcanic glass if it comes into contact with seawater or other surface waters. The quenching process freezes the atoms in place and prevents them from organizing into crystals. In the presence of air, the lava may cool slowly enough that some VERY small minerals may grow.

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The highly disorganized volcanic glass matrix in Austin's Figure 4 appears black or 'isotropic' in crossed-polarized light. Unlike most minerals, which lighten and darken in crossed-polarized light as the microscope stage is rotated, volcanic glass always remains consistently dark under crossed-polarized light.

Furthermore, unlike disorganized and quickly chilled volcanic glass, well-zoned and developed feldspar crystals, such as those shown in Figure 4, don't form overnight. On the basis of the glass and mineral textures and elementary melt chemistry, we know that the zoned plagioclases and other relatively large and well-developed minerals in Austin's dacite must have taken more time to grow than the surrounding glass matrix.

By using high-temperature ovens in undergraduate university laboratories or even crystal-growing kits and kitchen chemicals, a normally intelligent person can verify that coarse crystals take more time to grow than finer-grained materials. Clearly, basic crystal chemistry and physics dictates that zoned and other relatively large phenocrysts grew deep within the Earth and existed before the glass matrix that rapidly formed during the eruption.

Nevertheless, it is clear from Austin's essay that he has failed to incorporate the obviously diverse ages of the phenocrysts and the volcanic glass into his explanation for the origin of the dacite. Similarly, Swenson also fails to comprehend the indisputable history that is associated with the plagioclase zoning and to properly recognize the important age differences between the coarsest phenocrysts and the volcanic glass.

Even when phenocrysts as in Austin's Figure 4 and xenocrysts can be seen with an optical microscope, they can be extremely difficult, if not impossible, to effectively separate from the glass. I've attempted to separate very fined-grained minerals from glass in coal ashes by using magnetic separation and hydrofluoric and other acids. Specifically, Austin admits that most of his fractions are impure when he includes the term 'etc.

Furthermore, Austin's descriptions in the following statements clearly indicate that he FAILED to adequately separate the phenocrysts and possible xenocrysts from the volcanic glass. Because Austin clearly understands the heterogeneous composition of this 'fraction', he should have known that a K-Ar date on this mess would be meaningless.

Again, the mineral textures, as well as the laws of chemistry and physics, dictate that the calcium-rich plagioclase cores grew at higher temperatures before the sodium-rich rims and that glasses only formed once the melt erupted at the surface.

Mafic microphenocrysts within these glassy particles were probably dominated by the strongly magnetic Fe-Ti oxide minerals. The microscopic examination of the 'heavy-magnetic concentrate' also revealed a trace quantity of iron fragments, obviously the magnetic contaminant unavoidably introduced from the milling of the dacite in the iron mortar.

No attempt was made to separate the hornblende from the Fe-Ti oxides, but further finer milling and use of heavy liquids should be considered.

Although the contamination might have seriously affected any iron analyses, K and Ar analyses may not have been affected. The description of another one of Austin's 'fractions' indicates that it is also highly impure: These mafic microphenocrysts and fragments of mafic phenocrysts evidently increased the density of the attached glass particles above the critical density of 2. This sample also had recognizable hornblende, evidently not completely isolated by magnetic separation.

Because it was composed of finer particles meshit contained far fewer mafic particles with attached glass fragments than DOME-IH. This preparation is the purest mineral concentrate. Therefore, instead of dating the ages of the pyroxenes, he probably dated a mixture of mostly pyroxenes along with other minerals and volcanic glass.

Again, a K-Ar date on such an impure 'fraction' would be meaningless and a waste of time and money. That is, Austin is not dating the volcanic glass or the pyroxenes in the dacite, but artificial mixtures, which result from incomplete separations.

Because Austin admits that his separations were impure, how can he, Swenson and other YECs justify their claims that these dacite samples were a fair test of the validity of the K-Ar method? Why did Austin waste precious time and money analyzing samples that were known to contain mineral and glass impurities?

As a geologist, Austin should have known that minerals, especially zoned minerals, take more time to crystallize than quenched disorder glass.

How could he expect the relatively large and sometimes zoned minerals to be as young as the glass?!! The following additional comments by Swenson demonstrate that he does not understand the mineralogy and chemistry of the dacite: However, Dalrymple [] found that even volcanic glass can give wrong ages and rationalized that it can be contaminated by argon from older rock material.

In any debate, the debaters should provide the references or Internet links for their opponents so that the readers can evaluate both sides and really understand what's going on.

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Clearly, Swenson simply assumes that the volcanic glass contains 'excess argon. In his essay, Austin even admits that the glass still needs to be separated and analyzed for argon. Furthermore, many studies for example, the Haulalai basalt; Funkhouser and Naughton, demonstrate that Swenson and other YECs cannot automatically assume that modern volcanic glass contains excess argon. Although hypothesis 1 is plausible, until the argon isotope concentrations of the PURE glass are accurately measured for Austin's dacite if this is even possible we cannot properly evaluate this hypothesis.

Because Swenson does not provide a page number for his citation of Dalrymplethe identity of the volcanic glass with excess argon is uncertain. Perhaps, Swenson was referring to the following statement from Dalrymplep. Because the centers of the flows cool more slowly, any excess 40Ar and other gases can disperse out of the remaining melt before solidification.

While YECs explain geology by invoking talking snakes, magical fruit, and a mythical 'Flood', Dalrymple discusses legitimate chemistry and fluid physics, which is hardly relying on flimsy 'rationalizations' or implausible excuses.

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Furthermore, contrary to Swenson's claims, nothing in Dalrymple excuses Austin's sloppy approach to K-Ar dating. In particular, YECs have no justification for automatically assuming that the dacite glass contains excess argon. Even if the dacite glass does contain excess argon, Dalrymplep. Furthermore, if abundant excess argon is present in older rocks, Ar-Ar dating and K-Ar isochron dating can detect and eliminate its effects as examples, McDougall and Harrison,p.

Orthopyroxene retains the most argon, followed by hornblende, and finally, plagioclase. While Austin claims that orthopyroxenes should retain the most argon followed by hornblende an amphibole and finally plagioclase, he provides no references to support this claim. In reality, the crystalline structures of amphiboles, unlike feldspars and pyroxenes, contain open channels, which can hold argon gas and other fluids Klein and Hurlbut,p.

I'm skeptical that the defects and fractures in the orthopyroxenes and feldspars of Austin's dacites could hold more excess argon per mineral volume than the relatively large open structures within the hornblendes Dickin,p. Therefore, IF hypothesis 1 was the only factor influencing the dates of Austin's samples, I would expect the hornblende-rich 'fraction' to provide an older date than the pyroxene- and feldspar-rich 'fractions.

From the above discussions, we already know that hypothesis 2 is a likely explanation for Austin's old dates. To evaluate hypothesis 3, we should look at the crystallization order of the phenocrysts as suggested by Bowen's Reaction Series. The series states that certain minerals will crystallize in a melt at higher temperatures than other minerals. That is, different minerals have different freezing points. Mafic magnesium and iron-rich volcanic rocks, such as basalts, form from relatively hot melts C and hotter, Hall,p.

Felsic silica-rich rocks, such as granites, form at cooler temperatures perhaps as cool as CHall,p. The most common minerals in rocks of intermediate chemistry, such as dacites, are located towards the middle of the series.