Unreliable Isotopic Clocks?

In More Fluctuations Found in Isotopic Clocks Brian Thomas thinks he has reasons why four different radiometric dating techniques are inaccurate. Well, three really – one of them isn’t even a clock, so far as I can tell, and is just thrown in there to cast a general doubt on the reliability and predictability of radioactive decay. This is standard fair for young Earth creationists – though taking a look at my archives it has been just over a year since I’ve reported on at DpSU of this exact type – and the narrative being put forth is that there are more inconsistencies and problems with specific techniques being found every day, and that the whole idea is suspect. This could not be further from the truth.

First, a word on radiometric dating. These techniques for providing absolute dates rely on measurements of relative amounts of certain isotopes specific to the particular variety of dating being preformed. The assumptions that are involved, and which creationists like to attack, are related to the starting levels of the parent and daughter isotopes along with the rate at which the spontaneous conversion happens, though these pieces of information tend to be fairly well worked out. Another important consideration is contamination, though as this tends to make things look younger than they really are you don’t see so much from creationists about them.

Radiometric dating does not happen in isolation. There are numerous different methods, each with their own, overlapping age ranges that they can work with. When very little or almost all of the parent isotope is present in the sample being tested you will get bad results, and you will look like a fool when you claim them to be legitimate – this is usually the problem when creationists come up with anomalous numbers for rocks from recent volcanic material and ancient fossils. That there are multiple, overlapping systems allows these ‘clocks’ to be compared with each other, and if you’re doing it right they almost always match. They are also consistent with other, relative age dating methods such as fossils – rabbit fossils appear after T. rex fossils, so we might get worried if the dates given for the rabbits are earlier than that for the T. rex. But again, this all works out as well as you could hope.

The consequence of all this is that, for all their hyping of various minor inconsistencies, creationists have little hope of truly toppling radiometric dating. They can talk all they like about how the flood could have caused an increase in decay rates – probably frying Noah in the process, as nuclear decay releases energy – but unless they can say how all the changes there caused could have moved every decay system all together, keeping everything consistent with both each other and with the fossils, then they really have no argument.

Now, specifics. First up is lead-lead dating:

One standard isotopic clock system uses decaying uranium isotopes. Uranium spontaneously and slowly decays to lead (Pb on the Periodic Table of Elements). Two different uranium isotopes, 235U and 238U, decay into lead at different rates. Geologists assume that the ratio between these is constant and known, giving a convenient shortcut to uranium dating, which only requires that the two uranium amounts be measured.

Of course, this shortcut age-dating method assumes that 238U and 235U have decayed at today’s rates throughout the past. It also assumes that the relative amounts of the two have been constant. Physics Today editor Johanna Miller recently wrote, “Standard Pb-Pb dating protocol uses a 238U/235U ratio of 137.88 with zero uncertainty. But several recent studies have cast doubt on that number.”

That Physics Today article is here, and it says:

Uranium–lead dating is an especially useful method because two U isotopes decay with different half-lives into two isotopes of Pb. That redundancy offers a convenient shortcut: If the 238U/235U ratio is already known—and researchers have long supposed that it should be the same everywhere on Earth—then dates can be derived from the 206Pb/207Pb ratio alone. But recent work has cast doubt on that “lead–lead” dating method, as researchers have found that the 238U/235U ratio varies more than they thought it did, or could. Now, in a systematic, high-precision study, Joe Hiess and colleagues of the British Geological Survey have found not only the highest 238U/235U anomalies yet seen (more than 5 parts per thousand) but also a mean 238U/235U ratio almost 0.5 ppt less than the established value. As a result, lead–lead dates could be wrong by a million years or more.

In translation, the starting levels of uranium vary slightly more than previously thought, adding an error to calculations that at the long ages being measured add up to millions of years. Thomas claims a second article also on this subject, but as it’s from 2008 it is presumably superseded by this.

He concedes that this change does not challenge the old Earth in the slightest:

Two to three million years are not a huge part of three billion. So, adjusting already-published dates to reflect these new and larger error margins will not displace billion-year-old age assignments. However, if today’s comparatively tame natural processes affect isotope ratios, then ancient and much more violent processes could have affected those ratios and rates much more, just as the helium in crystals and orphaned radiohalos imply.

Mentioned in the introduction of Thomas’ article were both helium diffusion and polonium haloes, which you can find more about at talk.origins.

Thomas here tries to claim that “much more violent processes,” i.e the Flood, could have influenced uranium ratios. However, from the abstract of the Hiess paper:

This data set exhibits a range in 238U/235U values of >5 per mil, with no clear relation to any petrogenetic, secular, or regional trends.

It is unclear, therefore, what you can do to influence these ratios, and what could be pinned on the Flood. What’s more, if the Flood could influence the ratio then why, when measured in the now, should it be even this constant across the globe. Once again, creationists need their changes to decay rates to be unreasonably consistent across the board.

Some samariumNext up is samarium-neodymium dating, also mentioned in Miller’s article:

Another isotope system used for dating, though more rarely that uranium, is that which occurs when a radioactive samarium isotope decays to the element neodymium. A 2012 Science report re-measured samarium’s decay rate, finding that it occurs only about 66 percent as fast as “the currently used value” for age dating. This is a huge discrepancy! It means that all published samarium-dated rock ages need to be re-evaluated.

Brian’s wording implies that the decay is slower than previously thought, meaning that ages need to be revised upward, but in fact it’s the half-life that is 66% less, making the old ages overestimates. The paper – A Shorter 146Sm Half-Life Measured and Implications for 146Sm-142Nd Chronology in the Solar System – can be found in the form of a pdf on arXiv. In there we find the reason why this “huge discrepancy” – which it truly is, numbers wise – is not such a big deal. Firstly, the paper claims that its findings are consistant with some other measurements, though not with what is currently used:

Our value is shorter by ~30% than the values (102.6 ± 4.8 Ma) and (103.1 ± 4.5) Ma from (22, 23), respectively, and consistent (within larger uncertainties) with the two earlier works of Dunlavey and Seaborg (20) and Nurmia et al. (21), ~50 Ma and 74 ± 15 Ma, respectively.

Secondly, but more importantly, it seems that using the longer half life measurements was leading to results – or at least one result – that were inconsistent with those derived from other decay methods, with the paper concluding:

A recent study by Borg et al. (32) dated a Lunar sample, ferroan anorthosite (FAN) 60025, by three methods, Pb-Pb, 147Sm-143Nd and 146Sm-142Nd. The Pb-Pb and 147Sm-143Nd systems gave consistent ages of 208.8 ± 2.4 and 201 ± 11 Ma, respectively, but the 146Sm-142Nd age, 250+38-30 Ma, showed a discrepancy. Our value of 146Sm half-life revises the latter to 175 +25-20 Ma (Table 1) and removes most of this discrepancy, bringing the 146Sm-142Nd age into agreement with the 147Sm-143Nd age. This is an important point considering that FAN 60025 is now the only rock dated precisely enough with the different systems to trace their decay. The new 146Sm age of FAN60025 remains in accord with the revised younger age of the Lunar array isochron.

There’s the importance of using multiple systems. Thomas would have had a better argument when the dates disagreed with each other, not now that they match. Dates will need to be revised, but the Earth remains old.

In addition, Purdue University just applied for a patent on a solar flare warning system that relies on ways in which the earth-sun relationship somehow alters nuclear decay rates. Purdue News reports that “Advance warning could allow satellite and power grid operators to take steps to minimize impact and astronauts to shield themselves from potentially lethal radiation emitted during solar storms.” Their invention would rely on detecting changes in the rate of manganese 54 decaying to chromium 54. Researchers observed the decay rate changes occurring about a day prior to solar flares.

Getting a patent doesn’t mean that it will work, I have to point out. More relevantly, however, the half-life of manganese 54 is only 312.12 days, so I don’t think it’s being used for dating purposes. We know that some decay systems are less reliable than others, which is part of the reason why they aren’t all used. Pointing out fluctuations in an isotope not used for dating is irrelevant, and unless Thomas knows how precisely how the sun does it, and more importantly how the Flood could have managed to do it to a much greater degree with different isotopes and without killing Noah, then he is grasping at straws.

Last but not least, we have radiocarbon dating:

Even carbon dating is in hot water. Scientists typically use this method to age-date carbon-containing objects thought to be only tens of thousands of years old. The relevant radioactive carbon isotope (14C) decays so fast that it should no longer exist in earth materials that are a million or more years old.

This again. Repeat after me: carbon-14 decays to a background level caused by other low-level processes contaminating the sample, not to zero. But Thomas has more:

Recently, researchers measured elevated levels of 14C in correlated tree rings and attributed the spike to an unidentified “massive cosmic event.” If natural processes did alter carbon isotope ratios, then why trust dates that assume the ratios were never altered?

Well the dates do not assume that the ratios were never altered, so there is no problem, right? Tree rings and the like are used to calibrate the starting levels of carbon-14. In this case we have a temporary increase in carbon-14 levels of 1.2% – which would by its nature lead to underestimates of carbon dates – caused by an event of as yet unknown provenance dated to 774 or 775 AD. What Thomas really needs is a Flood-related decrease in carbon-14 levels, and that’s harder to do. This study does not put the accuracy of carbon dating into doubt.

Science shows that isotopic clocks are not all trustworthy. The isotope ratios and rates upon which they depend are variable, even on today’s comparatively calm earth surface. During the tumultuous Flood, when immeasurable quantities of mantle material were ejected onto earth’s surface and water potentially contaminated everything, isotopic clocks ticked much, much faster.

It all ends with a footnote:

When heated to plasma, bare nuclei of rhenium radioisotopes decay a billion times faster than normal. See Bosch, F. et al. 1996. Observation of Bound-State β- Decay of Fully Ionized 187Re: 187Re- 187Os Cosmochronometry. Physical Review Letters. 77 (26): 5190-5193.

Yes, you can influence decay rates in the lab. But turning the Earth into plasma without killing Noah but while ensuring that everything gets evenly baked? Not likely.

21 thoughts on “Unreliable Isotopic Clocks?

  1. The carbon cosmic event thing is actually a sterling testament to the reliability of the method. Despite the fact it messes with the calculations C14 dating uses, science was still able to detect and date the event. An amateur historian was even able to find a reference to a cosmic event consistent with what was predicted in a contemporary book.

    What’s the phrase I’m looking for? Ah yes.

    Science works bitches.

  2. But turning the Earth into plasma without killing Noah but while ensuring that everything gets evenly baked? Not likely.

    Is this an example of Kiwi understatement?

  3. I sent this email to the ICR (ahead of reading Peter x’s blog post):

    http://www.icr.org/article/6957/
    “Even today, researchers are finding small but significant changes in isotope decay rates…”.
    NO THEY AREN’T.
    The links provided point to greater variations in U238/U235 ratios than thought and a shorter half-life for Sm146.
    “Adjusting already-published dates to reflect these new and larger error margins will not displace billion-year-old age assignments.” Correct.
    “However, if today’s comparatively tame natural processes affect isotope ratios…”. The ratios in question ONLY affect the two uanium-lead dating methods.
    http://www.purdue.edu/newsroom/releases/2012/Q3/new-system-could-predict-solar-flares,-give-advance-warning.html
    “The system works by measuring differences in gamma radiation emitted when atoms in radioactive elements “decay,” or lose energy. This rate of decay is widely believed to be constant, but recent findings challenge that long-accepted rule”.
    Please correct me if I am wrong, but radiometric dating methods used to date the Earth don’t rely on decay processes that produce gamma rays. And the isotope in question here is chlorine36 (though your article suggests manganese54).
    “”Either neutrinos are affecting decay rate or perhaps an unknown particle is.””
    “If natural processes did alter carbon isotope ratios, then why trust dates that assume the ratios were never altered?” As far as I know scientists are aware that carbon14 ratios (not decay rates) have varied, by a small amount, over time within history and pre-history.

    An example of successful radiocarbon dating: http://www.guardian.co.uk/uk/2012/aug/05/medieval-volcano-disaster-london-graves

    Your article is typical YEC ‘science is in a crisis’ rhetoric.

    • I think it is actually manganese – from that article:

      The Purdue experimental setup consists of a radioactive source – manganese 54 – and a gamma-radiation detector. As the manganese 54 decays, it turns into chromium 54, emitting a gamma ray, which is recorded by the detector to measure the decay rate.

      But it’s a little confusing. The chlorine one is actually used for dating, but we also have the question of how great the effect is beyond simply whether it is there or not.

    • You are right. I must have skipped a paragraph (it was dusk and I hadn’t yet turned the light on). I only spotted: “Findings showed a clear annual variation in the decay rate of a radioactive isotope called chlorine 36, with the highest rate in January and February and the lowest rate in July and August, over a period from July 2005 to June 2011” (and may have missed: “The findings agree with data previously collected at the Brookhaven National Laboratory regarding the decay rate of chlorine 36”).

  4. Brian Thomas again shows his total ignorance of the subject in question. Remember, Creationists have set themselves on a pedestal above every ‘evolutionist’ [insert appropriate field of expertise here – say, geo-chronologist]. Brian Thomas lets his ignorance show when he says:

    ‘Two different uranium isotopes, 235U and 238U, decay into lead at different rates. Geologists assume that the ratio between these is constant and known, giving a convenient shortcut to uranium dating, which only requires that the two uranium amounts be measured.’

    What he wad trying to paraphrase from the Physics Today article was:

    ‘Uranium–lead dating is an especially useful method because two U isotopes decay with different half-lives into two isotopes of Pb. That redundancy offers a convenient shortcut: If the 238U/235U ratio is already known—and researchers have long supposed that it should be the same everywhere on Earth—then dates can be derived from the 206Pb/207Pb ratio alone.’

    He not only has no understanding of lead-lead dating but he totally confuses isotope ratios and isotope decay rates. For a very clear summary from the British Geological Survey, seach for ‘238U/235U Systematics in Terrestrial Uranium Bearing Minerals’ in http://www.bgs.ac.uk/nigl/News.htm

    The new research makes a minor correction to the previously unverified ratio and adds an appropriate error range. This is called progress. Nothing to see here – lets move on.

    Next we have samarium-neodymium dating. I am as ignorant as Brian Thomas here but I have located the original paper: arxiv.org/pdf/1109.4805

    I am sure that it is quite beyond his understanding but I don’t think that it means what he thinks it means. We are talking about an isotope that has already completely decayed!

    He also adds a lot of padding in the form of standard, long debunked, creationist pseudo-science with the usual list of creationist citations – again nothing here.

  5. If carbon-14 changes itself which each decay, but K-40 doesn’t, what is the proof that you are finding Lambda with Nuclear Magnetic Resonance. It is wishful to say Ur-235 automaticly changes to lead, and it is total wishful thinking to say Ur-238 which is stable is a good parent isotope for lead.

  6. It is obvious that Ur-235 gives off NMR regardless of isotopic change; and since Ur-238 is stable, it would seem not to be isotope, and give off NMR.

  7. a)Using coolness of the earth to compute its age with the presumption that the earth would be in molten state:
    Using coolness to compute the age of the earth might not be reliable for the fact that its computation has presumed this earth could be in molten state or in other words, it could be in liquid form.
    However, the initial stage of earth could be either in solid state that would be fully or partially covered with or without water. The water might be either warm or cold and that I do not like. If the earth would be in solid state that would cover with or without water, it would not take much time for the earth to cool down. Thus, the computation of the age of the earth by means of its coolness would not be feasible since the earth might be in solid state cover with water.
    b)Benoit de Maillet (1656-1738), a French anthropologist and diplomat, measured declining sea level and arrived the conclusion that the earth would be 2 billion years.
    His computation would not be feasible since sea level could rise as shown in the website address:
    http://www.reuters.com/article/2012/07/01/us-climate-sealevel-idUSBRE8600EG20120701
    The rise of sea level has caused his computation of the age of the earth to be unreliable.
    c)Radioactive dating method has been used to test the same stratum of rock and yet the same results (within the margin of error) would produce. The reason to explain this is simple. Using the same isotope to test on the same stratum of rock would produce almost the same result due to the same rock would produce the same unstable atomic nucleus of ionizing particles and electromagnetic radiation in spite of its spontaneous emission.
    The following is the list of some isotopes that are used for dating:
    Parent daughter half-life
    Samarium-147 Neodymium-143 106 billion years
    Rubidium-87 Strontium-87 50 billion years
    Uranium-238 Lead-206 4.47 billion years
    Potassium-40 Argon-40 1.3 billion years
    Uranium-235 Lead-207 704 million years
    Uranium-234 Thorium-230 80,000 years
    Carbon-14 Nitrogen-14 5,730 years
    Question has to be raised. If all the materials as mentioned above would have been created ever since the beginning of this earth, how could the scientists compute the half life of decay rate for Lead-206 from Uranium-238 to be 4.47 billion years? The reason is simply that the half life of decay rate for, let’s say, Lead-206 from Uranium-238, should be 0 if they would have been created at the same time in the very beginning. As the decay could be 0 if these materials would have been created in the very beginning, how could the Scientists be sure of its reliability and to use it to compute the age of the earth to be billion years?
    Besides, even if one material could be the transformation from another, how do the Scientists compute the figure of half life decay rate? For instance, how could the Scientist get 4.47 billion years or not 4 thousand years or others for Uranium-238 to decay to Lead-206? This half year decay rate that has been established by Scientists has pushed the age of the earth and even fossils, i.e. dinosaurs, to billion years. Whenever they use this isotope to test a rock to guess its age, it would give them billion of years since the decay rate has already set by them in the first place to push up to billion years.
    Thus, radioactive dating method is rather subjective and not accurate since the half year decay rate is indeed questionable.

  8. Thank you, Zuma. I guess Ur-238 is too unstable for nuclear reactions, and Ur-235 is preferred. Sorry about the mistake.

    • I think he meant if the earth is 4.5 billions old, why do we still have Uranium-235 and Uranium-234 given their short “half-lives”. The lack of suggestion of a full-life also shows more evidence of wishful thinking.

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