2 years of solar

Note the decreased sampling rate in year two due to decreasing novelty and increased travel. Here they are stacked:

After 2 years: 6700 kwh produced, 5230 kwh used.

Twenty years...

Twenty years ago, in the early afternoon, I stomped up a small mountain in the cool Georgia autumn, and stopped walking.  It had been a long walk, a bit over five months, and the trail I was walking on ended there.  As I was twenty years old at the time, this was almost half a lifetime ago.  When I started the Appalachian Trail, the main question in my mind was, “Can I get to the other end.”  When I got there, my main concerns, judging from the notes in my Journal, seemed involve food.  I guess I’m not really the philosophical sort. 

I started walking because it was the only thing I really wanted to do.  I didn’t like college, the alternatives weren’t very appealing, and ever since my uncle pointed out that the trail in the Virginia mountains was the same trail as the one my folks took me to in New Jersey, I wanted t osee for myself if these familiar paths in the disconnected lands of home and summer holiday land could really be connected ,simply by walking a lot.

 I stopped walking because my feet hurt.  The end of the trail helped too, of course, but there are people who simply turn around and walk back the way they came.  There are people who walk because they have nothing else left in life.  I called them trail zombies, and they terrified be because I could see myself becoming one of them. It would be so easy, to lose touch with everyone, sell anything that didn’t fit in my pack, and walk until the end of my days. Instead, I stopped walking.  I went home, looked up people who I’d lost touch with in college, went back to school in ’94.  It wasn’t easy, as I’ve always been a bit of an introvert and a misfit, but somehow, 20 years later, here I am with a house, a wife, a job and a couple of kids. I still love bushwalking, and get out whenever my commitments to the above listed allow, but these days, every walk has an end, and a return to civilization. Hopefully the next 20 years will go as nicely.

Carbonado, the diamond that looks like pizza.

I like to horrify current and recent students by telling them that I spent a month of my PhD figuring out what sort of film to use for best capturing the colors produced by the cathodoluminescence centres in carbonado diamond.  Of course, by the time it came to submit my thesis, I then had to spend days scanning all those slides.  Although, I still have a poster somewhere that is made from big glossy 8x10 prints, all glued to cardboard backing.

Now if you'll excuse me, I need to chase some kids off my psilphytopsid lawn...

Argon-Argon Dating: The Simple Version

  Sciency Thoughts has a post up on recent high-precision ³⁹Ar/⁴⁰Ar dating of the Toba supervolcano in Indonesia.  Unfortunately he seems a bit confused about the technique.

Argon has three naturally occurring isotopes: ³⁶Ar, ³⁸Ar, and ⁴⁰Ar. Potassium also has three isotopes, ³⁹K, ⁴⁰K, and ⁴¹K.  One of these isotopes, ⁴⁰K, is radioactive, with a half life of about 1248 million years, and one of its stable decay products is ⁴⁰Ar.

 In the universe, and in Jupiter and the Sun locally, ³⁶Ar is the most abundant argon isotope, followed by ³⁸Ar.  In the cosmic scheme of things, ⁴⁰Ar is so rare that we don’t even know what its overall abundance is.

However, Earth is a rocky planet.  It was not able to hold onto much gas during its formation, so there is very little ³⁶Ar and ³⁸Ar here.  Earth has lots of potassium though, so almost all the Ar in the atmosphere is ⁴⁰Ar, which is the decay product of ⁴⁰K.

In a potassium-bearing mineral, the ⁴⁰K decays into ⁴⁰Ar, so you can measure the ratio of these two isotopes to figure out how old the mineral is.

The problem is that it is technically very difficult to measure a potassium argon ration accurately, because one is a reactive solid, and the other is an inert gas.  They require different sorts of ion sources, different mass spectrometers, and there are all sorts of chemical effects that complicate the measurement.

If you want an accurate ratio, it is much easier to measure isotopes of the same element.

So for ³⁹Ar-⁴⁰Ar dating, what happens is that the mineral of interest is put into a nuclear reactor and bombarded by neutrons.  Some of the ³⁹K (the most abundant stable potassium isotope) absorbs a neutron, ejects a proton, and transmutes into radioactive ³⁹Ar.  ³⁹Ar has a half-life of a few hundred years, and is virtually non-existent in nature.   So as long as you know your nuclear ³⁹K to ³⁹Ar conversion ration well, this method allows you to use the ³⁹Ar as a proxy for ³⁹K.  The handy thing is that because it is argon, not potassium, it behaves chemically just like the other naturally occurring argon isotopes, so you can measure it in a gas source mass spectrometer much more accurately than you can measure the chemically different ³⁹K and ⁴⁰Ar.

The initial ³⁹K-⁴⁰K ratio doesn’t very much in nature, and is taken as constant (I think- I’ve never actually done Ar-Ar). But the take-home point is that ³⁹Ar-⁴⁰Ar dating is not its own decay system.  It is the ⁴⁰K-⁴⁰Ar decay system, but using a nuclear reactor to change some of the potassium into an unstable argon isotope to make the nuts and bolts of measuring it easier. 

A few brief words on sexual harassment in academia

 It appears to be sexual harassment revelations week here in the science blogosphere, so I figured I’d share a brief story.

In the year 2000, when I was a PhD student, I talked to the student counseling unit about making a formal complaint about sexual harassment by a senior member of staff.

They made it clear to me that taking this course of action would result in revocation of my student visa and deportation from Australia.

I chickened out and kept my mouth shut.

I was fortunate enough to be in a position where I was able to put my head down, write up, and finish my degree by making this choice.  Since that time, I have learned of other international students at other universities who did the right thing, and were deported for reporting. 

I tell myself that had I gone through with reporting, I would have been disappeared long before having the opportunity to make an official statement (way back before blogs, shipping someone halfway around the world was an effective way of shutting them up). And I thought that the incidents which I wished to report were not severe or well documented enough to bring to the police.  But while this is true, here I am, 13 years later, still awake at one in the morning second-guessing myself.

The recent round of revelations has focused heavily on the perpetrators of sexual harassment. Which is good.  But reporting wrongdoing is much more difficult than it should be, due to  the institutional coercion that universities use to protect their reputations at the expense of their students.

Not much going on here

I realize that for the last few years, this blog has been sputtering along with a low level of volume and quality. I can offer neither explanation nor remediation at this stage.  But I have listed a few of my old favorites below, for anyone looking for straightforward explanations of how geology explains, among other things, sex, drugs, and Rock and Roll.

Phase Equilibria of Pie Crust
Thermodynamics of Hot Chicks
Cetacean Liposuction
Relativistic Obesity
Geologic Lifespan of Jon Bon Jovi
Stars get Lonely Too
Testing the Earthquake-Modesty Connection
Dear Hypothesis

Harry Connolly new series Kickstarter

In "The best book you've never read", I mentioned that Author Harry Connolly, fantastic Urban fantasy "Circle of Enemies", which was an amazing novel that hardly anyone has managed to get a hold of.  It turns out that the Author is launching his next series on Kickstarter.  The appeal finishes tomorrow, but anyone interested in getting in on this can still do so, if you read this blog post in the next 12 hours.

Jailbait zircons

As the company SHRIMP driver, I do a fair bit of demonstration analyses for potential customers.  One thing that has become increasingly common over the past two years is demonstration of the ability to successfully date jailbait zircons.  For those of you unfamiliar with the term, a jailbait zircon is a zircon so young that dating it while making all the usual assumptions will get you into all sorts of trouble. 

The chief problem is that for deep geologic time, we assume that the ²³⁸U to ²⁰⁶Pb decay is a simple process. In actuality, there are eight alpha decays and more beta decays than I can remember in this process, but most of the intermediate daughter products are short-lived relative to the age of the analyst, much less the Earth.

However, if you are dating a phase that is much, much younger than the Earth, then these intermediate decay products can become important.  Corrections need to be made relating to whether or not now-extinct intermediate species were incorporated into the target mineral more or less efficiently than uranium. 

For minerals which are a few hundred thousand years old, or younger, you can abandon the uranium-lead system entirely, and use uranium-thorium dating instead.  This simply looks at how close to secular equilibrium ²³⁰Th and ²³⁴U have grown after their initial incorporation into the target mineral in a unequilibrated ratio.  The linked wikipedia explanation is good (at least qualitatively).  Check it out.

Of course, even for targets old enough for uranium-lead dating, in addition to the theoretical problems above, there is the practical problem of measuring a statistically significant amount of very low levels of radiogenic lead, while somehow keeping common Pb contamination to an absurdly low level.  Because one of the nasty things about the disequilibrium species is that they disrupt many of the assumptions that are needed to accurately and precisely correct for common lead.  Which means that if you can’t keep the blank down, you’re screwed.