Putting the Offense in Defense

Had I only known

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Geochronology Short Course at GSA 2014

As a graduate student in 2005 I was lucky enough to attend a Thermochronology Short Course sponsored by the Mineralogical Society of America. It was a 2 day event at Snowbird, a ski resort outside of Salt Lake City, just before the National GSA meeting that year. This was a pretty amazing experience for me: the course itself was great, but it was also a tremendous networking experience. The costs were kept low for students, and the talks ranged from methods-focused to applications more broadly, of all of the major thermochronology methods. The talks were also written up in a Reviews in Mineralogy and Geochemistry volume made available that same year, something I’ve used a reference ever since.

This positive experience is one of the reasons I am thrilled to be involved with a short course happening this October, just before the 2014 GSA in Vancouver. The course is sponsored by EarthScope, and will cover geochronology more broadly. Over the course of 2 days, specialists in all of the major geochronology methods will give introductory lectures on their techniques, designed for students and early career faculty who want to use geochronology in their work, but have little or no background. In addition, earth scientists who have integrated geochronology into their work will give methods seminars describing how they’ve used various methods to add temporal constraints to a variety of projects. The course will also kick off a graduate student geochronology award program, also sponsored by EarthScope, that will provide funds for graduate students to do their own geochronology. 

Best of all, the short course is free for students, and those who complete the course can even apply for funds to help reimburse travel costs.

For more information, make sure you visit the EarthScope website:

Short Course Information

Award Program Information

See you in Vancouver!


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World’s Leading Thermochronology Blog

After years of repeating that term on Apparent Dip, I am proud of the google results when you search for “world’s leading thermochronology blog”


Screen Shot 2014-07-22 at 3.07.19 PM

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This morning I was looking for a post I thought I’d written years ago to help explain the fundamentals of thermochronology. Although I have posts on 40Ar/39Ar and (U-Th)/He thermochronology, turns out I’ve never written a more basic post on the field itself. Genius I say!

So this post will try to take a step back from the methods and focus on the field more broadly. There will be plenty of overlap with older posts, but it’s my blog, so who cares?

We’ll start with geochronology. Geochronology is the name for any technique that can provide an absolute date of some geologic process. In geology, we are almost always talking about dating rocks, minerals, and other geologic materials using radioactive decay schemes, although the recent expansion of luminescence dating methods is an exception. In short, a radioactive parent atom decays to a stable daughter atom with some well-known probability. If you can measure the number of parents and daughters, and if you know that rate of decay, you can rather easily calculate a date. Geochronologists calculate these dates, and then use their skills as a geologist to interpret what exactly those dates mean. Perhaps it is the time a grain crystallized from a magma, or the time of peak metamorphic conditions, or the last time a layer of sand was exposed at the surface. Much of the work we do is that, attempts to put the dates into a geologic framework, and to use them to answer some outstanding geologic question. Calculating a date is rather easy, you just need a few pieces of information. To simplify things, the date you calculate is proportional to the ratio of stable daughter atoms to radioactive parent atoms. The more time has elapsed, the larger that ratio is. I have a separate write up of the age equation here if you are interested in the rather strait forward math.

Thermochronology is similar, however the systems we focus on are those where the loss or retention of the daughter products in the system is controlled by temperature. They are still being produced at the same rate, but what we care about is whether or not they stick around, or more specifically, what conditions favor their retention or loss? If you look at the age equation you can see the central control, an age you calculate is proportional to the ratio of the daughters to the parents in a given system,


Where t is time (the date you want to calculate), D is the number of daughter atoms in a crystal, and P is the number of parent atoms in a crystal. So if the daughters are being constantly lost from the system, the D is zero, and you will measure a zero-age. Only when the system starts to accumulate daughter atoms will the ratio become non-zero.

Thermochronology then refers to systems where the transition from open (daughters lost immediately) to closed (daughters retained) system behavior is controlled primarily by temperature. It is not the only control, but for a mineral and system to be a good thermochronometer, it needs to be the dominant control.

Imagine an apatite crystal with a few 10’s of ppm U and Th that is therefore constantly producing He atoms. If the crystal is hot, let’s say 200 °C or hotter, then the He atoms easily move through the crystal lattice and escape the system. In this case, D is always zero, so the crystal has an age of zero. If that crystal cools enough, all the way to 15°C for example, then the motion of the lattice has decreased enough that the He atoms are retained, and the daughter to parent ratio starts to increase. If the transition from open to closed behavior occurs over a relatively restricted temperature range, we call that the closure temperature of the system (blocking temperature is also used occasionally).

Screen Shot 2014-07-19 at 11.31.04 AM

In a cartoony way we can summarize that in the figure above, using the (U-Th)/He system as an example. Each decay system in each mineral has a different closure temperature. The figure below charts out a few of the more common systems, but there are many more.


It should also be noted that the “closure temperature” concept is an extreme simplification of very complicated behavior; thermodynamic shorthand for a wide range of kinetic properties. While useful, it depends on so many different factors and assumptions that it is incredibly important to spend time understanding its derivation and form before using scientifically. Think of the numbers in the above figure as being approximate.

Every geochronometer is in reality a thermochronometer, there is always a temperature dependance on the behavior of the daughter product. For some systems, like zircon U-Pb dating, this is irrelevant, because the closure temperature of Pb in zircon is exceedingly high, you essentially melt the host rock and likely the zircon before you start to get Pb to move. But in most cases, the difference between geochronology and thermochronology depends mainly on what question you are trying to answer, and what rocks you are working with.

Simplistically, thermochronology is best suited for dating the cooling of rocks. Because it generally gets hotter as you go deeper in Earth,  by integrating systems with a range of closure temperatures, it is possible to track the motion of rocks from the deep crust to the surface. Geologic processes that act to cool rocks off are therefore the easiest to date using thermochronology. Erosional exhumation and slip on normal faults are two of the most common processes that cool rocks off; indeed thermochronology as a field grew tremendously through application in environments dominated by extension and/or rapid erosion.


The cartoon above demonstrates how slip on domino-style normal faults can lead directly to the transport of rocks closer to the surface and their concomitant cooling. This style of faulting is common in the Basin and Range Province, and has helped understand the timing of extension throughout the region.

Other geologic processes are harder to date with thermochronology. Thrust faults, for example, are particularly tricky. Thrust faults don’t necessarily cool rocks off; they can create topography that can drive erosion that will cool rocks off, but that can post-date actual fault activity by tens of millions of years, as illustrated below. In fact, only in cases where erosion is very rapid (like in Taiwan), will thrust activity directly cool rocks off. The existence of thrust klippe, however, testifies to how often thrust faults empale material at a much faster rate than it is eroded away.

From Metcalf, J.R., Fitzgerald, P.G., Baldwin, S.L., and Muñoz, J.-A., 2009, Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone: Earth and Planetary Science Letters, v. 287, no. 3-4, p. 488–503.

From Metcalf, J.R., Fitzgerald, P.G., Baldwin, S.L., and Muñoz, J.-A., 2009, Thermochronology of a convergent orogen: Constraints on the timing of thrust faulting and subsequent exhumation of the Maladeta Pluton in the Central Pyrenean Axial Zone: Earth and Planetary Science Letters, v. 287, no. 3-4, p. 488–503.

Thermochronology is an incredibly powerful set of techniques, and their application to a wide range of geologic questions has helped add an invaluable temporal component to our understanding of earth processes. They must, however, be used with care and caution, especially in regions where geologic processes that don’t directly cool off rocks, or in fact can heat them up, are present.

The field of thermochronology is incredibly active. In the last few decades there have been huge advances in the number of systems we can use as thermochronometers, and our ability to understand and model thermochronology data. Want to know more? I highly recommend a 2005 Reviews in Mineralogy and Geochemistry volume dedicated to low-temperature thermochronology, or the classic “blue bible,” McDougall and Harrison’s Geochronology and Thermochronology by the 40Ar/39Ar method, which although focused on one system, has excellent background and review material. In addition, all national meetings commonly have thermochronology themed session, and of course this fall is the next International Conference on Thermochronology, this year in Chamonix, France. And of course, look for more content on the world’s leading thermochronology blog!

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Listen up apatite pickers!

He thermochronology involves a lot of time at a microscope and in a wet chemistry lab. These tasks require my attention, but once you get into the swing of things, can be a little dry. To help pass the time I usually listen to things, sometimes music, books on tape, or podcasts. I won’t go into a post on what music you should listen to – although my opinions on music are strong and unquestionably correct – and the most I’ll say about books on tape is that the Lord of the Rings on tape is fricking amazing. I would like to talk about podcasts though.

Podcasts aren’t really that old. When I first started listening to them it was more of a way to listen to NPR shows when I wanted to, instead of waiting around on Saturday mornings.  I then discovered the shows that only existed in Podcastlandia, shows about sports I like, current events, etc. For the past few years I’ve started listening to many podcasts in regular rotation, and a few have risen to the top. They aren’t necessarily sciencey, but interesting. For me to enjoy them consistently, they have to be well-edited and well-produced, few people can record themselves talking about something for an hour and have it turn out well. So what are thermochronic-approved, microscope-safe podcasts?

Radiolab – I first heard this as a radio show. I remember it distinctly, I was driving to a David Francey concert at at the Earlville Opera House, it was a beautiful fall afternoon and I was on two-lane highways through a beautiful part of New York. On the radio came a Radiolab episode about sound, and how our brain processes sound. The episode is called Musical Language, and features a piece with Professor Diana Deutsch that made my BRAIN EXPLODE. This is still one of my favorite pieces of radio I’ve ever heard. Radiolab is now into 12 seasons, and going strong. In general the episodes are sciencey, usually about an hour long, very well produced, and entirely engaging. There is only one episode that I thought was poor (a tone deaf discussion about the relatives of Henrietta Lacks), but the rest are excellent. Radiolab is the best place to collect interesting things to say when discussions die down at dinner parties, bar none. Recent episodes have been turning a little too much towards mimicking This American Life (great stories but not the unique science pieces I got used to), however they are still great. The one general complaint I have is how rarely Earth Science pops up on their radar, even in their episode on time. Their live show though, Apocalyptical, was both one of their best shows AND geology-centric.

99% Invisible – 99pi, as those of us in the know call it, is now tied for my favorite podcast. It is nominally about design, but what I’ve discovered is that the reason design is interesting is because it touches on so many different aspects of life. Philosophy, culture, science, history, damn near everything. 99pi is exceptionally well produced, and is also one of the fist podcasts I listened to that wasn’t trying to fit into an NPR format. My first podcasts were all things that played on NPR, or hoped to be, and were therefore fit into pre-determined time frames. 99pi episodes can be 3 minutes long or 35 minutes long, the length is determined by how much time you need to effectively tell the story. No filler, just story. It’s like having a chef who knows exactly how much you want to eat, you never leave hungry or with leftovers. A great starting point that actually touches on geology is the recent episode Ten Thousand Years. 99pi is thoughtful and seems to match the tone of the story well, and recently finished a successful kickstarted campaign, which means more episodes!

Hang Up and Listen – I like sports. Except for golf, which is more of an activity than a sport (the test is always if you can drink beer the entire time and still do well then it is not a sport), I’ll watch and enjoy damn near anything. The problem though, is that much of the sports world is terrible. Really terrible: a bunch of self-important airbags who weasel public money to build stadiums, will happily screw over local fan bases for a dollar, promote bigotry, misogyny, and homophobia if it sells more season tickets, try to align themselves with the military in creepy and dishonest ways, actively destroy institutions of higher learning, and look the other way while their policies promote serious and irreversible injuries to their players. The ones I hate the most though, are the people who get paid to talk about sports. Not only are they usually wrong about things, but they are often the most self important of the bunch. Think about it, there are grown-ass adults who get paid good salaries to talk about 18 year olds playing a game…not saving lives, helping communities, or promoting anything beneficial to society, but literally 18 year olds trying to put a ball through a hoop. Entertaining, but still. So sports talk radio, or podcasts, are terrible. Almost all of them. There is a show on the radio where I live now that spends all year talking about high school football. Let that sink in, adult humans get paid to talk about high school football. OK, enough of that, enter Hang Up and Listen. It is a Slate podcast, and whereas Slate is touch and go (interesting articles punctuated with absolute crap), this podcast is actually great. The hosts are smart, they do their research, they talk about all kinds of sporting events, and are even rather good interviewers. They also don’t take sports too seriously, which is seriously important to me.

The Moth – The Moth is another show that pops up on NPR every once in a  while. It is a live storytelling event, where the participants can’t bring any notes and have to tell their stories from memory. Participants can be normal people or famous people, and the stories are generally engaging. Some break your heart (Lynn Ferguson’s recent story or Adam Wade’s story of his teenage years) and some are funny (like Erin Barker’s story of her dad dating again).

Sound Opinions – Another NPR show I rarely catch, but now listen to regularly as a podcast. Two nerdy music critics discuss all things pop/rock/modern music and revel in their nerdiness. The shows have your standard reviews and music news, but usually center around an interview or a retrospective on some artist or album. Check out, for example, their discussion of my favorite Neil Young album Rust Never Sleeps, or their retrospective on Dylan going electric. I don’t always agree with their reviews, but it is the best place I’ve found to hear new music.

Backstory – This show features 3 historians (each specializing in a different period of American history) who put a historical perspective on current events. They’ll bring in experts, interview people, and add their own views, and are particularly good at contextualizing current situations. I find this show to be entirely entertaining and accessible, but they also retain enough of their academic historian chops to also make it educational and self reflexive. For a geoscience swing, check out their recent history of oil in America.

This American Life – Of course I have this. TAL defines modern NPR for me, it was the first show I heard that I thought spoke more to my generation than to my retired neighbors. TAL has over 500 episodes and can easily soak up a few days. Not all of the episodes are great of course, but some are stunningly good, my favorites being Conventions (especially act 3), and the hilarious Fiasco! As TAL has grown as a show, they’ve used their resources well to produce longer multi-episode pieces on tough subjects including time on an aircraft carrier.

There are a dozen or so others that I check in with not so regularly, but these are the shows I don’t miss. What I’d now love is for suggestions, I have a lot of microscope time coming up! Please leave ideas in the comments.

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John Perry, Lord Kelvin, and radioactive decay

I’ll admit I am behind on Cosmos. I’ve watched some of the originals on Netflix, and plan on binge watching the Neil deGrasse Tyson version soon. Tyson is one of the best ambassadors of science we’ve heard from in a long time, and the clips I’ve seen are promising. It is big enough and good enough to make the anti-sciece crowd grumbly, which is a good sign. What I want to talk about today though isn’t directly from the show, but was instead inspired by a discussion I heard on the radio about a recent episode. My local NPR station has a regular feature about Cosmos, basically wrapping up the most recent episode with a physicist and a local radio host. Tonight they were talking about the age of the earth, a topic near and dear to my heart. The conversation came around to early attempts to date the earth, especially the attempts to use the cooling of the earth to determine its age. The most famous scientist to have tried this was of course Lord Kelvin, and the story of his “too-young” dates, the discovery of radioactivity, and the disapproval and ultimate validation of the geologic community is something that is repeated in most introductory courses. This was a story I’d heard, one that I’d repeated, and one that I now know is fricking wrong.

The story we often learn is that Kelvin calculated his age based on a continuously cooling body, and that his big mistake was in assuming that the earth was only losing heat. At the time we knew next to nothing of radioactivity, so it made sense that he didn’t include the heat generated from radioactive decay in his equations. We are told then, that Kelvin was incorrect primarily because he didn’t include this source of heat. This is a nice story, geologists roundly thought his dates were way too young, and serves as both a nice victory story for the geologists, and as a cautionary tale about how important it is to know the right input variables into your calculations.

I learned this, I taught this, I used it as a point of pride for geology (take that physicists!) Then in 2007, I read this paper, and I learned that I was wrongedy wrong wrong.


England, P., Molnar, P., and Richter, F., 2007, John Perry“s neglected critique of Kelvin”s age for the Earth: A missed opportunity in geodynamics: GSA Today, v. 17, no. 1, p. 4–9.

In 2007, Phil England and his super famous co-authors published a short paper in GSA Today that kind of blew my mind. They present two main points: first, a simple illustration of why the heat generated from radioactive decay is simply not sufficient to explain why Kelvin was wrong, and second, a discussion of work done by John Perry, a contemporary of Kelvin’s, that should be the awesome story we tell when we teach. I’ll let you read the paper, but in short, John Perry (Kelvin’s one-time assistant) correctly pointed out in an 1895 paper that Kelvin’s assumption of a purely conductive earth could invalidate his conclusion. It turns out that if you ignore radioactive decay and model the cooling age of the earth assuming a layered planet with a convective layer, you actually can get very close to the true age of the earth. Kelvin’s big omission wasn’t radioactivity, but convection. As England et al (2007) summarize:

The story of Kelvin and the age of the Earth is often told as a David-and-Goliath struggle, with the geologists in the role of the underdog armed only with the slender sword of geological reasoning, while Lord Kelvin bludgeoned them with the full force and prestige of mathematical physics. Kelvin’s come- uppance is often taken as evidence that simple physics ought not to be applied to geological problems, but there have been numerous occasions when simple physical models have had great explanatory power in geology. Perry’s critique of Kelvin’s calculation reminds us that even well-posed physical models can sometimes be misleading, but recognition of their flaws may lead to major advances.

I love papers like this, simple illustrations of simple concepts. Since 2007, when I teach the age of the earth, I now always teach about John Perry.

Posted in earth science, geochronology, Great Contributions, teaching, Things I Wish I'd Thought of, Uncategorized | Leave a comment

The Root of the Problem

Like many nerds I have liked my favorite societies and funding agencies on Facebook. Two of them posted this press release from the NSF today summarizing a study that suggests that students in classes that have activities and interaction do better than those who are in classes that are purely lecture based. Not surprising of course, and not restricted to STEM fields. Plenty of students do well with lectures, but interaction in some form is important. In short:

“A significantly greater number of students fail science, engineering and math courses that are taught lecture-style than fail in classes incorporating so-called active learning that expects them to participate in discussions and problem-solving beyond what they’ve memorized.

What this press release doesn’t discuss though, are two key problems that exist that will make solving this problem exceedingly difficult; absurdly large classes and temporary adjunct labor.

Doing interactive classes is simple when you have 20 students. You can bring in materials, hold discussions, do lab exercises, etc. 100 students gets tough, and 150 or more and you are really fuchsited. I know, I know look at these great iClickers we can use where we can have all 600 students in a lecture hall participate. Besides being total crap, that type of interaction isn’t really what is being talked about in this study. This study was focusing on activities that helped students learn to “think like a scientist,” I’ve been a scientist now for years and I have yet to meet a problem that I’ve solved via multiple choice. iClickers and all other edu-hoaxes are not the same as actual interaction.

In addition, designing and implementing in-class activities takes time. You might want to prep materials before hand, and you will undoubtably refine the exercise over time. Great it you are full time, but with a large majority of classes being taught by adjuncts, this is unrealistic. Adjuncts are not paid for prep time, often have exceedingly limited resources, and have no guarantee, or even reasonable expectation, that they will ever teach at that school again.

So if you are full time and have a class of 25, awesome. I was lucky enough to go to a school like this, lots of small classes and an environment that both attracted and helped foster innovative teaching methods. This isn’t the case for most students though, most students in science classes at the college level are not going to be in small classes with full time faculty. These ideas on how to improve education are well and good, but we cannot pretend like there aren’t systemic and structural failings in the modern university that make the implementation of these recommendations on a large scale unrealistic. I suppose my point is that fixing American science education (or any education, this isn’t limited to STEM field, those are just the ones I know the best) will take much more than telling people to be more interactive. We also need to rebuild the environment where interaction can happen for all students, not just for the students lucky enough to be in a class of 20 with a full time instructor.

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For the Love of Field Trips

Years ago I was asked to fill out a survey that dealt with the recruitment and retention of geology majors. Specifically, many schools have introduced environmental science majors which have siphoned off potential geologists**, generally draining students from the more “traditional” geology departments. Some departments combine the fields, but many geologists are still interested in how they can boost enrollment. There are boatloads of ideas, of course, from rebranding, reforming the course tracks and requirements, emphasizing non-academic career paths, and putting more emphasis on the introductory courses where you might sway the undecided. For me though, the best way to think about this questions is to simply ask those of us who decided to become geologists what exactly drew us to the science. I knew that I wanted to be a scientist, but like many I knew damn near nothing about geology until I was sitting in my first introductory course, a field requirement, my first year in college.

A picture from my first long-form field trip, Capitol Reef NP.

A picture from my first long-form field trip, Capitol Reef NP.

So if I ask myself that question, “why did I want to become a geologist?”, there is really one answer that stands above the rest…..field trips. Now the actual work of being a geologist isn’t that similar to what an 18-year old does on a field trip, but what these trips did for me was open up an entire world of scientific questions, bizarre landscapes, methods of inquiry, and unique personalities that I wanted to be a part of. I lucked into a college and a program that did a lot of the normal field trips; we had weekend trips around the upper midwest, and fall- and spring-break trips to the Boundary Waters and North Shore of Lake Superior. The big one though, was that every May, the morning after graduation, we’d pack up our 16 passenger vans and head out for a 2-week trip to somewhere totally different than the rolling hills of glacial debris and Ordovician limestone quarries that surrounded our campus. My first trip, and the one that made me decide to pursue geology, was to the Four Corners region of the Colorado Plateau. Other trips included the New England Coast, Rio Grande Rift, and Death Valley and the Eastern Sierra.

Delicate Arch. I saw this for the first time and started reading Desert Solitaire on a field trip

Delicate Arch. I saw this for the first time and started reading Desert Solitaire on a field trip

My school wasn’t big or rich, but the department managed to do these trips and keep the costs very low for the students. We cooked our own food, and usually ended up needing less than $200 to cover the entire trip, $100 to help offset gas, and the rest for food. I figured this was a normal thing for a geology department to do, and that when I went to schools with larger endowments, more resources, and more majors, that these trips would be ubiquitous. So when I realized how rare these types of trips are, cheap, long, and open to anyone who has passed an introductory course, my immediate thought was that if you want to increase the number of majors, then pack up the vans!

So why do I love field trips so much? Let’s begin…

There are of course different types of field experiences, and I’ll categorize them broadly into field work, field camp, and field trips. There is overlap, but there are some aspects of each category that I feel makes them distinct.

White Sands NM

White Sands NM

Field Work is hard. It is often awesome, but it I can also be very, very, hard. You are often in a small group (2-6) or alone (avoid if possible), and are in the field for a few days to a few months. Your job can vary, but often includes some combination of taking measurements, collecting samples, mapping, and making more generalized observations. You are often on a strict schedule, and try to go out and work even if the weather is terrible. You can spend a lot of time in relatively unknown areas, and spend a lot of time searching for interesting things. You need a ton of prep work before you head into the field, both scientifically and logistically. Field work is done by people who are geologists, and who are working on a research project.

Tufa Towers in Mono Lake

Tufa Towers in Mono Lake

Field Camp is a class. It can also be both hard and awesome. In the U.S., this is typically some off-campus experience, up to 2 months long, where you learn how to do field work. You are often working in areas where the professors know a lot, and where they have designed the exercises to progressively introduce the students to the skills and concepts they’ll need to do field work. It is useful even for those who don’t end up as field geologists, because it also teaches you how to read maps, and how to understand the level of extrapolation and interpretation required to make a map. Field camp is most often taken by people who want to become geologists.

The west end of Monarch Canyon, Death Valley NP

The west end of Monarch Canyon, Death Valley NP

Field Trips are just awesome. They are a bear to lead and plan, but if you are a participant, they are just awesome. They are designed to show off the most interesting, important, and unique aspects of a region, and are usually designed by people with extensive knowledge and experience of a particular region. Field trips are for anyone.


I contend that field trips are a superb recruiting tool, and I make that assertion based on my own experience.

Lake Tahoe at sunset

Lake Tahoe at sunset

My first year in college I was an 18 year old who wanted to do some sort of outdoorsy sciencey thing with his life. My first idea was biology, largely because I was raised by biologists, and my high school had awesome biologists (including an amazing class full of field trips called The Plants and Animals of California, ahhhh, the pre- standardized test obsessed world of the early 1990’s public high school where faculty had the latitude necessary to inspire students) but effectively no geologists. There was an earth science class, but it wasn’t required, and was mainly pushed to people who had a hard time in science. If you were serious you took anatomy or physics.

Field trip members at the end of a day along the Scottish Coast

Field trip members at the end of a day along the Scottish Coast


In my second semester that first-year I took a historical geology class as a requirement. It was a pretty awesome lab class, introductory geology with a focus on fossils, evolution, and paleogeography. We had a variety of field labs, which I liked, but more importantly I had my eyes opened to an entire branch of science that studied the outdoor world but didn’t smell like formaldehyde. As I’ve explained, the geology department at my alma mater ran a long form field trip every year, with the small group of faculty trading off leadership responsibilities. It was open to anyone who’d passed a class, and only cost $100 (plus food, but that was done cheaply). I had an unpaid internship lined up for that summer, but I had 2 weeks to spare, so I figured what the hell.

An Alaskan Fall day looking at huge piles of conglomerate

An Alaskan Fall day looking at huge piles of conglomerate

As a kid, I grew up in California, and spent a lot of my time in the summers in northern Wisconsin. I was familiar with those places, and I love them. But, they did not prepare me for the Seussian landscapes of southern Utah. Sometime between the goosenecks of the San Juan, Delicate Arch, and Sunset over Grand Canyon, I knew that I wanted to spend more time learning about these places, and I knew that geology was a field that would let me do that.

Field trips also give young students a chance to interact less formally with older students and faculty, and usually include days with local geologists. So they can help build community and expose the larger world of earth science. We visited with geologists at active mines, state geologists in the field, graduate students just starting their projects, and faculty from other schools who showed off the local hotspots.

The Racetrack, Death Valley NP.

The Racetrack, Death Valley NP.

The field trips I’ve been able to go on as a graduate student, post-doc, and research scientist continue to reinvigorate my love of earth science. They still do their job, and the people who lead them, organize them, lobby to fund them, and write field trip guides, should be given enormous credit. I’ve even been able to go on some field trips associated with meetings lately, which have also been stupendous. In my experience, field trips are some of the main forces for recruiting geologists, generating collaboration, and developing scientific communities.

As a graduate student, I helped plan a few field trips, and I understand why many programs stopped running as many. They take tons of time to plan, especially the first time. They also take time to lead, which for faculty trying to manage research projects, service, publications, and their own private lives, can be tough. But I contend that they are one of the most effective recruiting tools available.

Fingal's Cave, Isle of Staffa, Scotland.

Fingal’s Cave, Isle of Staffa, Scotland.


** As an aside, I consider environmental science to be a subset of geology, not something separate. I was told once by a committee member that naming a department of geology and environmental science is the same as naming a department math and calculus. Geologists just need to own it.

*** Also, all of the pictures in this post are ones I took on various field trips.

Posted in earth science, pictures, teaching, Uncategorized | Leave a comment

The Great M&M Experiment

Teaching about radioactive decay and geochronology has its challenges. I think it is important to include in introductory courses, and I’ve tried a variety of exercises and techniques to try to convey some of the more important aspects. My goals are simple really, I want the students to understand the basics of how the systems work and why they are reliable. My favorite exercise to help me teach about decay, is without a doubt, the Great M&M Experiment.

Let’s start by discussing some of the things that can confuse students, particularly the odd fact that on the scale of an individual atom, radioactive decay is unpredictable, but on the scale of billions of atoms, it behaves literally, like a finely tuned clock. This is actually a very familiar concept to them, they just might not realize it. It is the same concept, for example, that explains why Las Vegas exists, and why the house always wins. We typically bombard them with concepts like “half-life,” which are often intended to simplify things, but in my experience rarely do. Many students think that the concept of a half-life is goofy, and is something that has been imposed upon a decay system.

I’ve started taking a different approach, one that tries to explain the basic concept using something they all understand and then transitions to the complex systems geoscientists deal with.

I call it the Great M&M experiment, but you can also do it flipping coins or anything else. M&M’s are delicious, and only have an “M” printed on one side. So it you take a Dixie cup full of them and turn it over on a lab bench, about half of them will land with the “M” up, and about half will land with the “M” down. This isn’t news, but it turns out that if you have enough M&M’s, you can easily create a decay curve. Here’s how I do it.

1. Give everyone some number of M&M’s. With small classes I’ll do 30, with large classes maybe 10. With really large classes I use a variation that uses pennies, I’ll explain that later**.

2. Have them turn the cup over onto a desk or bench, making sure not to dump candy on the floor. I usually have them put down paper to they can eat things when they are done.

3. If an M&M lands with the “M” side up, we say it has decayed, and we remove it to a second Dixie cup.

4. Count the number of candies that didn’t decay and record that number.

5. Place the candies that didn’t decay back into the tossing cup, and repeat steps 2-4 until all of the candies have decayed.

6. Compile the numbers up front, counting the number, or percent, of the total candies left undecayed after each step. What you’ll end up with is something like this.



Results from a 2003 M&M experiment

Results from a 2003 M&M experiment

These are the results from the largest experiment I ever ran, where 40 students each had 100 M&M’s. I show both the results for each step (average and standard deviation), and the “theoretical” relationship. When I used this many candies, I wasn’t surprised at how well it worked, however since this run I’ve started using fewer and fewer total candies. A total of 40 even works well, kind of amazing.

OK, so that is great. But what is important I think is to demonstrate where the exponential decay curve comes from. It isn’t magical or made up, but is the natural result in a system that is governed by probability. You can then discuss what these curves would look like if instead of a 50% chance of decay, you used dice, or something with 10 sides. Compare the M&M curve to these

Screen Shot 2014-05-03 at 12.43.36 PM

Please forgive the terrible color scheme, I made this before I became the Excel ninja that I am today.

These are still exponential decay curves, they just take longer to “flatten out.” A six-sided die (yellow), where we say it decays when we roll 1 for example, takes a bit longer. Nerd dice with 12 or 20 sides would take even longer.

Half-life, and the decay constant, are really just ways of describing the shape of the curve, how quickly the number of parents declines. You can show how the amount of time (or flips) required to cut the number of M&M’s in half is constant, for example. A curve for 238U would look about the same, just instead of the number of rolls, we’d be looking at time, and it would take 4.5 billion years to lose half of them. In fact, you can think of 238U as a die with bajillions of sides. Something like this

Screen Shot 2014-05-03 at 12.49.25 PM

So the terms we use are really just ways to describe the curves, and the curves are just the natural result of any process governed by probability. From this, transitioning to a decay and accumulation curve, and then to the parent to daughter ratio of a system (what we actually measure), isn’t that dramatic of a leap.

Screen Shot 2014-05-03 at 12.49.46 PM


Screen Shot 2014-05-03 at 12.53.15 PM

I’m not saying this is magic, and that everyone will get it immediately. I’ve just found that terms like “half-life” and “decay constant” are big stumbling blocks for students. Showing them the origin and meaning of those terms really isn’t difficult, and can be easily tied to ideas they already understand.

** In really large classes, I’ll hand out 1 penny to each student, and have them all stand up. They flip the coin, and if they flip heads they sit down. Sure I have to count the whole class, but that gets easier each flip, and with even 100 students, generates a great decay curve like clockwork.

Posted in Academia, geochronology, Primers, teaching, Uncategorized | 1 Comment

Developing a sense of place

I’ve noticed a few common threads in the books, movies, and songs that I like the most. For whatever reason, I tend to respond to media that describes place well. It wasn’t something that I did on purpose, but something I notice in retrospect. These can be book-long meditations on stark landscapes like Desert Solitaire, The Worst Journey in the World, or Wind, Sand, and Stars, or simple phrases in songs and poems that get stuck in my head. I wouldn’t be surprised if this is one of the reasons I was drawn to the earth sciences, not only do you get to experience a variety of landscapes, but you actually study the things that specifically make landscapes unique.

I’ve been lucky to be able to travel as much as I have. I’ve lived in all four time zones in the continental U.S., spent lots of time in some of the more remote and barren parts of America, and visited China, Europe, British Columbia, and Alaska. Most of the traveling has been for work, which means that large chunks of this time have been in places not often frequented by tourists, but of course full of rocks.

So, let’s combine these two things: I pay a lot of attention to places and landscapes, and I’ve been fortunate enough to experience a nice amount of them. This is all as a prelude for a rant: Turns out that what drives me nuts more than most any other absolutely trivial thing is this: when T.V. shows and movies are “set” in a place that is obviously not where they are filmed. Let me explain:

I first noticed this with the classic mystery series Murder She Wrote. I remember watching this show with my mom as a kid, and it turns out now that my wife absolutely adores it (You can stream it on Netflix, and she loves having shows on in the background while she works, but she’ll wonder why I need to explain this because it is the GREATEST SHOW EVER). Now, Murder She Wrote was set in Maine, but the outside shots were all filmed in Northern California. When I was a kid, I didn’t know that Maine looked different than Northern California, but then I started traveling a bit. So now, every time you see the sun setting over the ocean, or a big honkin’ redwood tree in the background of the scene where people are being run down by a remote controlled car, I can feel my blood pressure rise a little. Murder, She Wrote is of course not alone, most shows are not shot on location. One of my current favorites, Justified, uses the Southern California coast ranges to fill in for rural Kentucky, something I am compelled to point out every episode (trust me, people love this). The “coal mine” in Zoolander was actually filmed in a hard-rock mine in New Jersey that is famous for its fluorescent minerals, Toronto often doubles for New York City in cop dramas, and of course any trip to the Alabama Hills includes a discussion of how many times it turned up in westerns as some not-California place.


Generic western setting, Alabama Hills, California. Picture by Thermochronic using Kodachrome 64, something I miss.

I am not a stickler for accuracy in most other respects. I can even enjoy how weird labs look on TV, or how terribly academia is usually portrayed. I typically watch things because I like the story and the social/ethical/moral/human questions that they explore, and I don’t care that much if things aren’t portrayed exactly “right,” it all depends on the purpose of the story. For some reason this thing bugs me, but it also interests me. What makes a place “close enough” to pass? I am sure it depends on the budget and the story, but how do you go about choosing a location? That is why I was so interested when I came across this map, published by Paramount Pictures in 1927.

The map was intended to convince financial backers that the industry could film damn near anything within a short drive of the studios. And check it out, 57 years before J.B. Fletcher started solving murders the studio executives already knew the coast could pass for New England. I grew up in a place that could pass for the Mississippi River, just a few hours drive from the French Alps and Siberia! I wonder though how much this matters now, with the inexpensive ubiquity of CGI technology, perhaps all of these places can now be mapped inside some green screen studio in Burbank. For me, when you go CGI your attention to accuracy should improve, you no longer have the excuse of location. If you need help with the details, perhaps you should just hire a rant-prone geologist? We are very affordable.

Posted in earth science, Rants, science and society, The Woods, Uncategorized | 1 Comment