|Action & Reaction - June 2000|
|by Do-While Jones|
In my line of work (which involves a lot of hardware troubleshooting and software debugging), the key to success is recognizing the difference between what we know to be true and what we assume to be true. Whenever we run into an electronic circuit that doesn’t work the way we expect it to, or a computer algorithm that doesn’t do what we think it should, the problem is always that we have made an incorrect assumption. Once we figure out the incorrect assumption, we generally can find the answer to the problem.
Creationists seem to have a better handle on what they assume to be true by faith, and what they have experimental proof of, than evolutionists do. Evolutionists appear to accept many things by faith without realizing it.
Last month we printed Tim Thompson’s response to one of our essays. In it, he makes several assumptions, apparently without realizing it. If he were the only one who makes these assumptions, we would not bother to mention it. But since these assumptions are so commonly made, it is worth investigating them.
However, I do happen to know how to tell one Lead from the other, as would any physicist of sufficient erudition. Naturally occurring Lead comes with a particular distribution of stable isotope ratios (which means that none of those listed here are radioactive). Isotope Relative Abundance ------- ------------------ 208 52.4% 207 22.1% 206 24.1% 204 1.4% The final product of the Uranium 238 decay chain is Lead 206, which as you can see from the table, makes up about 24% of any natural Lead sample. If I find a sample that is 50% isotope 206 instead, then it's a good bet that there used to be some U-238 laying around that has since turned into Pb-206. Furthermore, the excess above 24% tells me how much U-238 there was.
Is that an assumption, or a verified fact? How can one know what the “natural” distribution is? There are three ways for determining distributions. Let’s illustrate these ways using a simple example.
The second way to determine how much thiamin is in each vitamin tablet is to go to the plant and observe the manufacturing process. We could see how much thiamin is put into the recipe, count the number of pills made from the recipe, and determine the amount of thiamin per pill. The second method, therefore, requires knowledge of the process that created the product.
The third way is to buy a bottle of vitamins, remove one of the pills, and do some chemical tests that measure thiamin. If we just analyze one pill, we will get just one answer. Suppose that answer is 1.49997846 mg. If we analyze a second pill, it may turn out to have 1.49926755 mg. What is the right answer? We have to analyze lots of pills, preferably from several different batches of vitamins. Then we can use statistical analysis to find the average amount, and the amount of variation from pill to pill. So, the third method involves measurement and analysis.
Now, let’s get back to lead (whose chemical symbol is Pb). A book might tell us that 24.1% of lead is Pb-206. We can assume that to be true, if we have faith in the author of the book. But how does the author of the book know the percentage?
We know that the author of the book could not have used the second method. Regardless of whether the lead was produced by an exploding star or a spoken word, the author wasn’t there to observe the process. He could not possibly have observed the lead being put into the rock.
That means he either read it in another book and accepted the value by faith, made up the number out of thin air, or measured it himself. If he read it in another book, the author of that other book either read it in yet another book, made it up, or measured it. Hopefully, the cycle finally ends with someone who actually measured it, rather than making it up. And, hopefully, it was measured accurately.
All measurements, “as any engineer of sufficient erudition knows” , have tolerances associated with them. The amount of Pb-206 in naturally occurring lead is 24.1% ± X%. We need to know, ”What is the value of X?”
Suppose, as Tim proposed, you take a sample of lead and find that it is 50% Pb-206. What does that mean? It depends entirely upon your assumptions. If you assume that the Earth is only a few thousand years old, you conclude that, in some cases, the percentage of Pb-206 naturally occurring in lead can be as high as 50%. If you assume that the earth is billions of years old, you conclude that some of the Pb-206 came from radioactive disintegration of uranium, and you “correct” your measurement of naturally occurring lead by calculating how much U-238 decayed into Pb-206 and subtract that from the measured amount to determine the portion that is “naturally occurring”. Please follow this carefully. We know that there must be some samples of lead that have more than 24.1% Pb-206. If there weren’t, then all rocks would date to 0 years old because there wouldn’t be any Pb-206 that supposedly came from uranium. What is the justification for saying that the “excess” Pb-206 (that is, the amount greater than 24.1%) didn’t occur naturally? The justification depends upon the assumption that there was uranium there that decayed into Pb-206 over a long period of time.
If one finds a sample with 25% Pb-206, it might just be that, under some conditions, the amount of Pb-206 naturally occurring lead can be as high as 25%. Since you have a sample that contains 25% Pb-206, isn’t it reasonable to conclude that the amount of Pb-206 might naturally be 25% in some cases?
The only way to explain away the obvious conclusion is to assume a long time and radioactive decay. In Tim’s words,
From the explanation above, you can see that a radiogenic history will skew the relative abundance of isotope 206 relative to the other isotopes, which are not decay products. On an atom-by-atom basis, we cannot tell which ones were there to begin with, and which came from the decay of U-238. However, we do know that the excess above about 24% indicates how much was added (in bulk) by U-238 decay. That will tell us how much U-238 has decayed, and that related to how much is present, and the known half life, will in principle reveal the age of the sample.
One cannot know for a fact that the excess above 24% came from U-238 decay. That is a consequence of the old-earth assumption.
There is a second assumption, too--specifically that the Pb-206 came from U-238 decay rather than U-235 fission (or another undiscovered nuclear reaction).
We will concede one point to Tim. He correctly states:
I hate to disappoint you (well, so maybe I don't all that much!). But, the examples you give of reactors and bombs do not in fact represent any variation in decay rate, and are therefore irrelevant. In both cases, the energy comes from a chain reaction of neutron- induced spontaneous fission in U-235. In the case of the bomb, the reaction is allowed to run away; in the case of the reactor, the reaction is controlled (we hope). However, radiometric dating involves the alpha decay of U-238, which is quite a different process. The fission reaction leaves lots of junk behind in the form of intermediate nuclei resulting from the symmetric (or asymmetric) splitting of the U-235 nucleus. It is very easy to tell one from the other, and so very easy to tell whether or not this process has been effective in nature (which in fact it has, in the natural reactors at Oklo in Gabon). … Heavy etching by high-energy particles from the blast would reveal the true nature of events quickly [distinguishing decay from fission], as would the effect of exposure to high gamma ray and neutron fluxes (which would once again upset the isotope ratios).
If an atomic scientist examined all the various isotopes, he could distinguish natural rock from atomic waste or debris from a nuclear blast. I was thinking strictly in terms of the parent and daughter elements. Heavy etching would be evident, assuming the fission occurred after the rocks had cooled. If the fission occurred while the rocks were forming, who knows?
Assumption (1) is false; neither the initial abundance, nor any knowledge of same is necessary for most radiometric dating. Specifically, the "isochron" method was designed for just that purpose. Multi-isotope methods will also eliminate the need for such knowledge.
The isochron method does, in fact, make assumptions about the initial abundance of the daughter material. The explanation of exactly how it works is long enough that it will be a major portion of the feature article next month.
Assumptions (2) & (3) are only partially true. Leeching and contamination are like anything else in nature: They don't just "happen", they are caused to happen by some agency or process. In many cases, perhaps most cases, one can tell by a simple examination of the sample, whether or not it has been exposed to a source of contamination, or a leeching agent. Both leeching and contamination change the chemistry and/or the isotope ratios in the sample. That evidence in turn can tell you what happened, and maybe even how to compensate for the effect.
In view of the very high cost of radioactive dating, if “one can tell by a simple examination of the sample, whether or not it has been exposed to a source of contamination, or a leeching agent,” why would anyone ever send a leeched or contaminated sample to the lab? Why is the leeching or contamination not noticed until after the lab gives the “wrong” date?
Assumption (4) [that enough time has passed for radioactive decay to occur] is nonexistent. No such assumption is made. Rather, the time period is derived from the radiometric method, which will also reveal that not enough time has in fact passed, if that is indeed the case.
We hope we have already shown that one has to assume an old age, or one won’t try this technique. Of course, there is one other reason why one might try to date a young rock-to see if the method really will “reveal that not enough time has in fact passed.” That’s why creationists have tried to date recent volcanic eruptions which occurred on known dates. These experiments have shown that radiometric methods often fail to reveal that the rocks are too young to date.
Perhaps you could point to a specific place, where radiometric dating does not support the geologic column? You know, something like "at this spot these people did radiometric dating and it didn't work". It would be, I think, more efficacious.
Ok. We promise to do that next month when we discuss isochron age dating, the “excess argon” problem, and why it is necessary to “calibrate” carbon 14 dating.
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