Put your hands together, people!

Somebody is one year old.

Paper Out

Stephan Klemme , Stefan Prowatke, Carsten Münker, Charles W. Magee, Yann Lahaye, Thomas Zack, Simone A. Kasemann, E. Joan A. Cabato and Benjamin Kaeser 2008. Synthesis and Preliminary Characterisation of New Silicate, Phosphate and Titanite Reference Glasses. Geostandards and geoanalytical research 32 32-54.

Eleven synthetic silicate and phosphate glasses were
prepared to serve as reference materials for in situ microanalysis of clinopyroxenes, apatite and titanite, and other phosphate and titanite phases. Analytical results using different micro-analytical techniques showed that the glass fragments were homogeneous in major and trace elements down to the micrometre scale. Trace element determinations using inductively coupled plasma-mass spectrometry (ICP-MS), multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS), laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) and secondary ionisation mass spectrometry (SIMS) showed good agreement for most elements (Li, Be, B, Cs, Rb, Ba, Sr, Ga, Pb, U, Th, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Er, Tm, Yb, Lu,
Zr, Hf, Ta, Nb) studied and provide provisional recommended values.

So here’s the story: Often the limiting factor in the accuracy of in situ geochemical analyses is the quality and applicability of the reference material or standard. Stephan wasn’t happy with the standards available to the geochemical community, so he synthesized his own, and the rest of us analysed them to determine the composition.
It isn’t much of a story, really. So in order to add some substance to this post, I’ll give the backstory as well. Stephan and I both did our PhD’s on the ex-pet group at ANU- he was a couple of years ahead of me. As it turns out, he was the student whith whom I perpetrated anecdote number three ten years ago (aside- Easter 1998 was ten years ago. Holy shit! Where did the decade go?)
So, fast forward 8 years, and in August 2006 he comes back to Australia for the Goldschmidt conference. Obviously, a boozy catch-up over dinner is required, and we shoot the shit over the usual subjects of kids, life, and inevitably, geology. My poster for that conference is on standard synthesis, so Stephan and Simone (I got to meet the entire German-Edinburgh contingent) tell me about these new ion probe standards they have been analyzing. I point out that we could get values out of those glasses, and he informs me that he’d already been invited to use the lab by his PhD advisor, and asks if I want to show them the ropes and get on the paper. So 5 days later, he and Simone rock up to lab, I set up the run, and away we go.
Stephan is very much a petrologist- I suspect his main interest was seeing how little silica he could put into the phosphate glass and still get a quench- but Simone is a ion probe guru, so she was naturally skeptical of the apparent simplicity of laser ICPMS work. So we spent most of the morning looking at various what ifs that could get spurious results, shooting standards, and looking for potential interferences. At the risk of sounding naff, doing science with one’s friends is a lot of fun.
I didn’t have much to do with the interpretation or statistics done on the data, but as the native English speaker I was supposed to fix any Germanisms in the manuscript. “Supposed to” being the key phrase. These guys write so well that I had maybe one prepositional change to suggest in the draft. In fact, I just noticed that the most glaring grammatical error in the final manuscript was in the paragraph that I wrote. Go figure.

Heard over the HF radio yesterday

..."yeah it is some sort of chloritized pyritic rock, but I don't really want to put a name to it... Some sort of vague igneous texture... drilling is shithouse, only three meters so far..."

It was all I could do to refrain from picking up the mike and saying, "Good luck boys. We're heading back to town today for a shower, a swim, and a cold beer. Should we have a round for you blokes, or are you on a dry site?"

The geochemical quantification of double beta decay

In 1933, Enrico Fermi proposed a theory of beta decay using the neutrino particle suggested by Wolfgang Pauli three years earlier. During this time period, the promising young physicist Maria Goeppert married an American guy named Mayer and started 15 years of two body-related unemployment in the States (In contrast, the gap between the publication of her book, “Elementary Theory of Nuclear Shell Structure” and the awarding of the Nobel prize for that work was only 13 years).

During the great depression, Goeppert-Mayer decided to up the intellectual profile of housewives by suggesting, in 1935, the possibility of double beta decay. Where an intervening unstable isotope prevented sequential single beta decay, double beta decay would allow transformation to a lower energy Z-2 nucleus by simultaneous double electron-antineutrino emission. Most of the double decay candidates are neutron-rich R-process elements such as ⁹⁶Zr, ¹⁰⁰Mo, or ¹³⁰Te. The predicted decay product of ¹³⁰Te is ¹³⁰Xe, a noble gas. In the late 40’s, an isotopic study of telluride minerals was performed, and a ¹³⁰Xe excess in Xenon from telluride ores was reported by Inghram & Reynolds (1950).

Subsequent noble gas results verified the existence of ¹²⁸Te – ¹²⁸Xe and ⁸²Se – ⁸²Kr systems, all before the first direct detection of a double beta decay was established in Elliott et al. (1987)- almost 40 years after the initial geochemical result, and 15 years after Goeppert-Mayer's death.

Unfortunately, the ability of Tellurium and Selenium minerals to quantitatively retain noble gasses is poor, as these minerals have low closure temperatures, and are easily deformed. They are also difficult to date directly. But as every hard-up geochemist knows, if you’re desperate for a date and you don’t know where to turn, it never hurts to look for a zircon.

The dating of zircon using the uranium-lead decay scheme is arguably the most popular and rigorous geochronological method currently available. And as it just so happens, ⁹⁶Zr is expected to decay into ⁹⁶Mo. Since zircon usually doesn’t have much initial Mo, It should be possibly to detect a ⁹⁶Mo excess, and use the U/Pb age from the same mineral to calculate a decay constant for ⁹⁶Zr (Technically, this method determines the ²³⁸U/⁹⁶Zr decay constant ratio).

This has been done a few times (e.g. here and here), but the process is complicated by the spontaneous fission of ²³⁸U. The fission products of this decay include most heavy isotopes of Mo, so the fissionogenic Mo excess and the double beta ⁹⁶Mo excess have to be deconvolved. The result is that the precision on ⁹⁶Zr double beta decay is fairly poor, with Wieser & De Laeter (2001) reporting a value of 9.4 ± 3.2 x 10¹⁸.

However, there is another promising double beta decay isotope. ¹⁰⁰Mo decays into ¹⁰⁰Ru. And molybdenite generally contains Re, so that the mineral can be dated using the Re/Os single beta decay scheme. And moly contains fuck-all uranium. It looks like the NSF thinks this is a promising technique as well, as they’ve awarded a $225,000 grant to a leading Re/Os lab for support for this and other experiments. And on the other side of the Pacific, Hidaka et al. 2004 have reported a result of 2.1 ± 0.3 x 10¹⁸.

In the meantime, the direct counting mob have continued to count decays. According to Barabash (2006), their current best determination of the ¹⁰⁰Mo halflife is 7.1 ± 0.4 x 10¹⁸. It will be interesting to see if the Denver Re/Os crowd can do better, and if either group can explain why the direct counting gang have halflives that are approximately a factor of 2 higher than the geochemists (counters have ⁹⁶Zr as 2.0±0.3x10¹⁹- also double the geochemical determination). Barabash 2006 does not address this discrepancy, or even reference the more recent geochemical results.

I’m also curious about the physicist’s budget. After all, I have a sneaking suspicion that the direct counting experiments cost a little bit more than a quarter million dollars.

References:
Barabash (2006) (How is one supposed to reference arXiv entries?)
Elliott S R Hahn A A and Moe M K 1987 Phys. Rev. Lett. 59 2020
Goeppert-Mayer M 1935 Phys. Rev. 48 512
Hidaka H Ly C V Siziki K 2004. Physical Review C, 70, id. 025501
Inghram M G and Reynold J H 1950 Phys. Rev. 78 822
Wieser M E De Laeter J R 2001 Phys. Rev. C 64, 024308

The preferred paleontologist replies

At the beginning of this month, I ran a poll asking folks which paleontologist they would prefer working with: Josh Smith, the alleged sexual predator, Spencer Lucas, the alleged plagiarist, or Marcus Ross, the self-avowed young Earth paleontologist. Dr. Ross won the poll handily, and as it turns out, he is a reader of the Lounge. He sent me the following email, followed permission to post:

Dear Dr. Lemming,
Thanks for including me in your recent paleo poll, I thought the idea was hilarious. I’ve enjoyed checking your blog in the year or so since the NYT article came out. I have to say, I really enjoyed your blog post on the topic, as you took a far (far!) more measured and thoughtful approach to the issue.
Though we will disagree on issues of Earth history, thanks for being civil, and for finding ways to have fun with the news of the day. And I’m very pleased that the readers of your blog would pick me as a preferred co-worker. Dubious award or not, I now know that there exist entities in the Great Chain of Being below “trained parrot” young-Earthers (a la PZ Meyer’s description of me).
Cheers,
Marcus

Anyway, I’d like to thank Dr. Ross for having the grace and character to react so well to my sometimes callous sense of humor. I am still waiting for concession speeches from Drs. Smith and Lucas, but I suspect that they are respectively busy ogling perspective students or forming judicial committees which will impartially decree that 7 is larger than 32.

Comments are currently open, but please stay civil. I don’t want to come back from the field to find that the organic slime of the internet has spontaneously evolved into a fauna known colloquially as the troll.

Economic geology from first principles

I have to say that I kinda fell into the resources industry by accident. I was offered a job unexpectedly, it sounded like and interesting opportunity, so I said yes. Most of my formal geologic training is in big picture academic geology and associated analytical science, in which concepts and techniques are derived from first principles.

Industrial geology isn’t really like that, but that doesn’t mean that I can’t try. So I will. The law of supply and demand suggests that the price of a mineral should be related to the demand for it, and its abundance. Demand is beyond the prevue of geology, so we will ignore this half of the law for now. Doing this suggests that the price of a mineral should be related to the abundance of that element.


Above is a figure that plots the market price for various elements (US$ per mole) vs their crustal abundance (atomic ppm). If demand was irrelevant and the Earth’s crust was homogeneous, then these elements ought to fall on some sort of negatively sloped trend. As seen from the graph, maybe a third or so of the elements do, but the bulk fall somewhere to the left of the trend.

There are two ways to interpret this. The first is that there is reduced demand for these elements. The second is that the Earth’s crust is not homogeneous. Geology allows us to address this second option.

If the crust was homogeneous, we exploration geologists would be out of work. Mines aren’t just stuck in any old place, they are put where it is most economical to extract a particular resource. In general, this corresponds to am area where geologic processes have concentrated one or more elements of interest. So it is possible that the elements to the left of the trend are elements that are concentrated by geologic processes more easily than other elements.

Have another look at the figure. The elements labeled in yellow are chalcophiles. These are elements that will preferentially form sulphides instead of silicates in the presence of sulphur. This provides an enrichment mechanism not available to elements that only occur as oxides, so that the local concentration of these elements can be orders of magnitude higher than their average crustal abundance.

So if you were curious about why it is that economic geologists are always nattering on about sulphur, this is the reason. Even if the average crustal abundance of Pb is a few ppm, sulphide precipitation can concentrate it to 10% or more, which would place it to the right of Al on this figure.

The outback tours Osaka

In the better late than never category of blog announcements, I wanted to point out for my Japanese readers that a exhibition of the paintings of Utopia artist Emily Kame Kngwarreye is currently on tour at the National Museum of Art in Osaka. Utopia is in the same general non-specific part of the NT as some of our ground, so it's the least I can do to plug the local talent.

p.s. in completely unrelated news, there is still no winner for Where on (Google) Earth? #117.

Convection

Dry.


Wet.


How do you like to remove heat from boundary layers?