In which I was instructed into the secret ways of the Minervals, High Priestesses of the Illuminati.
The Minervals are a clan of badass ladygeos (and ladyphysicist) who do luminescence research (Illuminati, luminescence… get it? hehehe). They hosted a shortcourse this year and my only complaint is that I wish I had taken this course years ago.
If you’re a graduate student like myself, one of the things your committee might ding you for is using blackbox science. Basically, you should understand how and why a particular technique works rather than just relying on a machine or a lab to spit out an answer. I have basic, working knowledge of how OSL works, but decided a crash course in the technique would help keep my committee happy (which may or may not be a huge part of your ‘job’ as a PhD student). Plus, I love knowing things. That sounds silly, but I genuinely love knowing how things work and why things work, and thinking about how things connect or how we can use some knowledge to generate other knowledge. I’m just a deeply nosey human being.
Rather than give away all the Illuminati secrets, I’ll give you a little taster of the things I learned. And let me just say that the course instructors are High Priestesses of these dark arts for a reason. Their explanations of the technique and the science behind it were thorough but so accessible. I struggle with physics and chemistry, but never felt lost.
Things I already knew:
- You use pipes to collect samples, that way the sediment is not exposed to light. Basically, OSL measures the amount of time since a grain of quartz or potassium feldspar last saw the Sun. So if your sample gets exposed to sunlight or other light while you’re collecting it, you’ve just reset the clock, so to speak. Rather than your sample being buried 2,000 years ago, you’ll find out that it definitely saw the Sun last Tuesday.
- OSL is tricky and high error compared to other techniques like radiocarbon dating, but is really useful for dating things without any organic matter. In my case, there’s not much charcoal in Central Plains sediment, so radiocarbon dating can be problematic.
Things I Didn’t Know or Hadn’t Thought About
- This science actually uses real cloaks of darkness.
If your sediment or sample isn’t a pipe-able sample (e.g., it’s a big slab of rock or is just a little handful of sediment stuck between roof fall in a cave), you can go out under cover of darkness and collect the sample that way.
If you are not yet powerful enough to summon natural darkness at your will, you can manufacture some darkness via black plastic tarps, blankets, quilts, and blackout curtains sewn into an *actual cloak*. You may also need to just about bury yourself to collect certain samples. I’ve done some silly looking things for science, but cover of darkness sampling has me easily beat.
- Back at the lab, the darkness continues.
I knew samples had to be kept in the dark else they would reset, but I didn’t think about the fact that the lab would have to be dark while they were being processed. This means samples are being sorted, chemically etched with HCl and other acids, etc. in labs that look like photography dark rooms. I’ve spent years joking about how dark the labs on tv shows (e.g., Bones, CSI, NCIS) are, but I stand corrected. Maybe they had some OSL samples in there.
- OSL is accurate but not super precise.
I knew the error bars for OSL samples were typically pretty big, but I didn’t know why. You get one shot at reading the signal stored in a grain, but you then have to do tons of measurements to understand what that signal means. That takes time. Additionally, there are tons of factors that influence how you translate the signal to an age. The moisture content of the sediment, including changes in moisture content over time, the sediment in a 30 cm sphere around the grain, the grains immediately around the grain you’re analyzing, how the grain was transported to its burial spot, where in the water column or mass movement that particular grain traveled… essentially, there are so many variables that it is virtually impossible to get below 5% error. Really crazy!
- It’s not all just OSL.
I probably should have known this, but OSL (optically stimulated luminescence) is for quartz, and IRSL (infrared stimulated luminescence) for feldspar. Also, apparently optically stimulated luminescence isn’t the best term for the technique, it’s just the term that ended up in the literature. Funny how often that happens.
Moving away from the science itself, the course and the Minervals were the best way for me personally to start GSA. This cadre of scientists were–in addition to being incredibly knowledgeable–funny, friendly, supportive of one another, and they clearly enjoy working together. Those are the types of geoscientists I grew up around, but not something I see all that often in my now-daily life. It was refreshing to be around these scientists, and even more exciting that they were all women. High Priestesses indeed.
Here are a few of my favorite moments:
- Shannon Mahan explains a particular plot. “I didn’t do anything fancy in R, I just found the option that adds color to your data points. So I added color to the data points”.
- Shannon explains that OSL, like so much else in science, isn’t always straight forward. And discovers why she gets so many tough samples.
“About a third of samples are easy, they make sense right away. Another third take real work to understand, and the last third are really confusing and I don’t figure them out for a long time. I have samples I figured out twenty years later while working on something else”. “Do you all find that, too?”, Shannon asks the other Minervals. “Oh, we just send that third to you. ‘Send them to Shannon, she loves tough samples'”, Tammy laughs.
- Ginni explaining the origins of luminescence science. “Some one gave him [Sir Robert Boyle] a diamond, and he discovered that it would glow after being held up to a candle. He then [reading from slide] took it to bed with him and ‘held it against the warmest part of his naked body’… I’d love to see the reviewers faces if I proposed this sort of experiment”.
- Ginni on the problems of working in a dark lab. “But then I leave the lab, where I have been in the dark all morning, and have to walk across the very bright courtyard to my office, and invariably someone stops me and wants to talk, but they have their back to the Sun so I’m staring right into the light, tears streaming down my face and then they think I’m crazy”.
Things for which I have no quotes, but that make me deeply happy:
- The Minervals not only joked with one another and referred to one another at certain points of expertise, they also redirected focus to one another when necessary. They took pains to not take over from one another, and to push people’s questions back to the person in charge of that particular section of the course. The Minervals also made sure to mention their fourth member who couldn’t attend the short course. They pointed out which parts their fourth member had worked on, the things their students had done, and noted that not every OSL lab did things the exact same way but that it didn’t change the quality of the work. I don’t often deal with scientists who are so supportive of one another and of the people in their field more generally. It was refreshing and really heartening.
- We talked about Climate Strike Day and the issues we’ll all be facing (but that will disproportionately affect people of color and in the ‘global south’).
- The short course included a coffee break at the lovely Royal Coffee Bar and cookies to keep us awake in the dark of the classroom, and ended with a lightly raucous happy hour at the utterly charming Bar Bianco. If you know me–and by now you probably do–, you know I love a cackle-fest. Especially if it involves science talk, story telling, and some drinks. Such a fab way to end the day!
Learning the secrets of the Illuminati was a full day in and of itself. So when happy hour wound down, I headed for the Airbnb where one of my grad colleagues awaited. We went to dinner, took a quick evening swim (omg, the Airbnb has a pool… it’s so nice), and went to bed by 10 pm. The next day was field trip day and I needed to be rested!
Yours in LadyGeoscience,
PS. Don’t forget to follow #blogoftheladygeos on Instagram! I’m trying to post photos in (vaguely) real time, just in case I get swamped and can’t keep up with blog posts (it’s already happening… ugh.). And if you’re a LadyGeo at GSA or some other conference (or just doing cool stuff), use the hashtag!
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