ytsme Schreef:
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> Zelfs de jonge-aarde creationist Brown moet in een
> boekbespreking toegeven, dat er tegen de
> radiometrische datering weinig is in te brengen en
> dat de “jonge aarde” niet langer te verdedigen
> is.If a date does not agree with the expected age of its geologic period, and no plausible explanation can be found, then the date is called anomalous. But if we really understand what is going on, then we should be able to detect discrepant dates as they are being measured, and not just due to their divergence from other dates.
Geologists often say that the percentage of anomalies is low. But there are quite a number of rather outstanding anomalies in radiometric dating that creationists have collected. These anomalies are reported in the scientific literature. For example, one isochron yielded a date of 10 billion years. A Rb-Sr isochron yielded a date of 34 billion years. K-Ar dates of 7 to 15 billion years have been recorded. It's also not uncommon for two methods to agree and for the date to be discarded anyway. Samples with flat plateaus (which should mean no added argon) can give wrong dates. Samples giving no evidence of being disturbed can give wrong dates. Samples that give evidence of being disturbed can give correct dates. The number of dates that disagree with the expected ages is not insignificant. I don't know what the exact percentage is.
Many dates give values near the accepted ones. But even these often differ from one another by 10 or 20 percent. And quite a few other dates are often much, much farther off. Whatever is making some of these dates inaccurate could be making all of them inaccurate.
It's interesting to note that in a few cases, old radiometric dates are above young ones.
The fact that different methods often give different dates is noted by geologists. Here are some quotes from http://hubcap.clemson.edu/spurgeon/books/apology/Chapter7.html:
“It is obvious that radiometric techniques may not be the absolute dating methods that they claimed to be. Age estimates on a given geological stratum by different radiometric methods are often quite different (sometimes by hundreds of millions of years). There is not absolutely reliable long-term radiological ”clock". The uncertainties inherent in radiometric dating are disturbing to geologists and evolutionists…
As proof of the unreliability of the radiometric methods consider the fact that in nearly every case dates from recent lava flows have come back excessively large. One example is the rocks from the Kaupelehu Flow, Hualalai Volcano in Hawaii which was known to have erupted in 1800-1801. These rocks were dated by a variety of different methods. Of 12 dates reported the youngest was 140 million years and the oldest was 2.96 billion years. The dates average 1.41 billion years. "
Another source said that about 5 or 6 of the historic lava flows give ages in the hundreds of thousands of years. Geologists explain the Kaupelehu date by the lava being cooled rapidly in deep ocean water and not being able to get rid of its enclosed argon.
Here are some quotes from John Woodmorappe's paper, “Radiometric Geochronology Reappraised,” Creation Research Society Quarterly 16(2)102-29, p. 147, September 1979, that indicate that radiometric dates are scattered, and that anomalies are often not reported:
“Improved laboratory techniques and improved constants have not reduced the scatter in recent years. Instead, the uncertainty grows as more and more data is accumulated … ” (Waterhouse).
“In general, dates in the `correct ball park' are assumed to be correct and are published, but those in disagreement with other data are seldom published nor are discrepancies fully explained.” (Mauger)
“ … the thing to do is get a sequence of dates and throw out those that are vastly anomalous.” (Curtis et al)
“ … it is usual to obtain a spectrum of discordant dates and to select the concentration of highest values as the correct age.” (Armstrong and Besancon).
“In general, strong discordances can be expected among ages deduced by different methods.” (Brown and Miller)
Woodmorappe also mentions that very self-contradictory age spreads in the Precambrian era are common.
In addition, Woodmorappe gives over 300 sets of dates “that are in gross conflict with one another and with expected values for their indicated paleontological positions.” This table is limited to dates that approach 20% discrepancy, too old or too young. This does not include dates from minerals that are thought to yield bad dates, or from igneous bodies with wide biostrategraphic ranges, where many dates are acceptable. He states that the number of dates within range are less than the number of anomalies, except for the Cenozoic and Cretaceous. When one adds in the fact that many anomalies are unreported, which he gives evidence for, the true distribution is anyone's guess. He also combines evidence from the literature to conclude that “somewhat less than half of all dates agree with 10% of accepted values for their respective biostratigaphic positions.” I believe this estimate even includes igneous bodies with very wide biostrategraphic limits, and does not include unpublished anomalies.
There have been criticisms of John Woodmorappe's study, but no one has given any figures from the literature for the true percentage of anomalies, with a definition of an anomaly, or the degree of correlation between methods. Steven Schimmrich's review of this study often concerns itself with John W's presentation of geologists explanation for anomalies, and not with the percentage of anomalies; the later is my main concern.
Here are a couple of more quotes about anomalies:
“Situations for which we have both the carbon-14 and potassium-argon ages for the same event usually indicate that the potassium-argon `clock' did not get set back to zero. Trees buried in an eruption of Mount Rangotito in the Auckland Bay area of New Zealand provide a prime example. The carbon-14 age of the buried trees is only 225 years, but some of the overlying volcanic material has a 465,000-year potassium-argon age.”
A similar situation is reported in the December 1997 issue of Creation ex nihilo in which lava with a K-Ar age of about 45 million years overlays wood that was carbon dated by 3 laboratories using AMS dating to about 35,000 years.
Still another evidence for problems with radiometric dating was given in a recent talk I attended by a man who had been an evolutionist and taken a course in radiometric dating. The teacher gave 14 assumptions of radiometric dating and said something like “If creationists got a hold of these, they could cut radiometric dating to pieces.”
Another evidence that all is not well with radiometric dating is given in the following quote from Coffin p. 302:
“We find that most primary radioactive ores that have not been exposed to weathering exist in secular equilibrium. Many sedimentary uranium ores are not.”
Since equilibrium should be reached in 1 million years, this is a problem for sediments that are assumed to be older than 1 million years.
On another point, if we can detect minerals that were not molten with the lava, as has been claimed, then this is one more reason why there should be no anomalies, and radiometric dating should be a completely solved problem. But that does not appear to be the case, at least (especially) on the geologic column.
I'm not claiming that anomalous results are being hidden, just that the agreement of a mass of results, none of which has much claim to reliability, does not necessarily mean much.
Picking out a few cases where radiometric dates appear to be well-behaved reminds me of evolutionary biologists focusing on a few cases where there may be transitional sequences. It does not answer the overall question. And as I said above, I'm also interested to know how much of the fossil-bearing geologic column can be dated by isochrons, and how the dates so obtained compare to others.
Concerning K-Ar anomalies, here is a quote from Woodmorappe's paper cited above, p. 122:
“K-Ar ages much greater than inferred earth age are also common. Gerling et al called attention to some chlorites yielding K-Ar dates of 7 to 15 b.y. It had been noted that some minerals which yield such dates (as beryl, cordierite, etc.) can be claimed to have trapped excess argon in their channel structures or to have fractioned the Ar isotopes, but none of this can apply to the simple mica-like structures of chlorite. They also pointed out that for the anomalies to be accounted for by excess argon, unreasonably high partial pressures of Ar during crystallization would have to be required. They concluded by suggesting some unknown nuclear process which no longer operates to have generated the Ar.”
This implies that excess argon is coming from somewhere. Here is another quote from Woodmorappe about isochrons, since some people think that mixing scenarios or other age-altering scenarios are unlikely:
“Shafiqullah and Damon said: ”The Ar40/Ar36 vs. K40/Ar36 isochrons are valid only when all samples of the system under consideration have the same non-radiogenic argon composition. If this condition does not hold, invalid ages and intercepts are obtained. Models 2-9 yield isochron ages that are too high, too low, or in the future, sometimes by orders of magnitude."
from Woodmorappe, “An Anthology of Matters Significant to Creationism and Diluviology, Report 1,” Creation Research Society Quarterly 16(4)209-19, March 1980, p. 218.
The fact that the only “valid” K-Ar isochrons are those for which the concentration of non-radiogenic argon (Ar36) is constant, seems very unusual. This suggests that what is occuring is some kind of a mixing phenomenon, and not an isochron reflecting a true age.
The following quote is from http://www.pathlights.com/ce_encyclopedia/Index.htm:
“Processes of rock alteration may render a volcanic rock useless for potassium-argon dating . . We have analyzed several devitrified glasses of known age, and all have yielded ages that are too young. Some gave virtually zero ages, although the geologic evidence suggested that devitrification took place shortly after the formation of a deposit.” *J.F. Evernden, et. al., “K / A Dates and Cenozoic Mannalian Chronology of North America,” in American Journal of Science, February 1964, p. 154.
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