K-Ar and 40Ar/39Ar Thermochronology

In this post I'd like to outline some of the more important aspects of Ar/Ar thermochronology. I am going to start with a brief outline of the K-Ar technique, but spend most of the post on the more popular Ar/Ar variant. This post is a long time coming; as far as published reliable radiometric dates, I'd bet that Ar/Ar thermochronology is the most used chronometer in earth science (although I did recently hear Mark Harrison claim he had "age characterized" 100,000 zircons for U-Pb geochronology, so I could be way way off). There are a few primary reasons for the popularity of the method, some I'll discuss later. But first the basics.

Potassium (K) is the 7th most abundant element in the earth's crust, and is a major component of many common rock forming minerals. Very common minerals like biotite and muscovite mica and potassium feldspar contain weight percent levels of K. Naturally occurring K is made of 3 isotopes, ³⁹K (93.258%), ⁴⁰K (0.012%) and ⁴¹K (6.730%). ³⁹K and ⁴¹K are stable, ⁴⁰K is radioactive. Natural Ar is fairly abundant in the earth's atmosphere (~1% of the air we breathe) and is composed of three isotops, ⁴⁰Ar (99.600%), ³⁸Ar (0.063%), and ³⁶Ar (0.337%). ⁴⁰K decay is an interesting process, unlike the U and Th systems I've blogged about earlier which undergo a chain decay, ⁴⁰K has a branched or dual decay scheme. That means that 89.52% of the time, ⁴⁰K decays by beta emission to ⁴⁰Ca. 10.48% of time time, ⁴⁰K decays by extranuclear electron capture to ⁴⁰Ar. The ⁴⁰K to ⁴⁰Ar process is the one we will concern ourselves with in this post. ⁴⁰K - ⁴⁰Ca is rarely used as a geochronometer because Ca is so abundant in nature. It is hard to differentiate in minerals what Ca formed in the mineral from decay of K and what Ca was included in the original mineral structure. Argon, a noble gas, is rarely present in significant amounts within crystals, so we do not have to worry as much about the original ⁴⁰Ar component (although you will see later that the ⁴⁰Ar/³⁹Ar technique lets us deal even with "inherited" ⁴⁰Ar). ⁴⁰K has a half-life of 1.25 billion years (Ga), which makes it perfect for addressing a wide range of geologic problems. The graph below shows the evolution of ⁴⁰K, ⁴⁰Ca, and ⁴⁰Ar abundance versus time.

Like in all graphs that show parents and daughters, the curves intersect at the half-life. Focusing on the ⁴⁰Ar then, we can see that the daughter to parent ratio, or ⁴⁰Ar/⁴⁰K changes over time, like this
We can measure the ⁴⁰Ar and ⁴⁰K in a sample, and from that ratio, calculate an age. The age equation (shown below)

then relates the amount of parent (⁴⁰K), daughter (⁴⁰Ar) and time. Like with all geochronologic systems, actually calculating the age is fairly straightforward. The actual K-Ar age equation is a little more involved because of the branched decay I mentioned earlier, so the final form looks like thiswhere
is the ⁴⁰K decay constant (total)

and

are the decay constants for the two decay paths that produce ⁴⁰Ar, and

is the decay constant for ⁴⁰Ca production from ⁴⁰K. The term in the age equation just before the daughter to parent ratio therefore describes the fraction of ⁴⁰K decays that result in the formation of a ⁴⁰Ar atom.

The K-Ar geochronometer came into widespread use in the 1940's, once the basics of the decay scheme were worked out. There are two main issues with the technique, however, that are kind of a pain, and are the reasons that more often that not the ⁴⁰Ar/³⁹Ar technique is much more popular today. First, you cannot measure K and Ar on the same machine. Typically, samples would first be heated (often using an induction furnace) to very high temperatures (~1400°C). At these temperatures the Ar trapped in the sample is liberated and can then be measured. The ⁴⁰Ar from the sample would be spiked with ³⁸Ar, and then measured on a mass spectrometer. The degassed sample would then be retrieved from the furnace, and analyzed separately for ⁴⁰K. With the amount of ⁴⁰Ar and ⁴⁰K, you culd then calculated an age.
The second problem with the K/Ar technique is determining where the Ar came from. As I mentioned earlier, Ar is fairly abundant in the atmosphere, making up about 1% of what we breathe. It is also fairly common in groundwater and geo-fluids (fluids associated with igneous intrusions and metamorphism). Some of this Ar could become trapped in the crystals, therefore rendering the calculated age kind of meaningless. We know the atmospheric ⁴⁰Ar/³⁶Ar ratio very well, so by measuring the ³⁶Ar we can correct for this "trapped Ar", but we have to assume that the composition is atmospheric. In some cases this is a perfectly reasonable assumption, but with the advent of the ⁴⁰Ar/³⁹Ar technique, we are actually able to evaluate that assumption.

The basis of the ⁴⁰Ar/³⁹Ar technique is the fact that when K is bombarded with neutrons (in a nuclear reactor), some important reactions take place. Namely, ³⁹K is converted into ³⁹Ar. We know the natural ³⁹K/⁴⁰K ratio, so if we can measure the efficiency of this transformation in the reactor, we can use ³⁹Ar as a proxy for ⁴⁰K. This would allow us to measure an age by simply measuring the ⁴⁰Ar/³⁹Ar ratio of a sample. What is even better is that ³⁹Ar does not exist naturally, so we do not have to worry about any inheritance or atmospheric contamination.

³⁹Ar production can be described by this equation

where
is the neutron flux at energy Eis the neutron capture cross section at energy E for the reaction ³⁹K(n,p)³⁹Ar, and
is the duration of the irradiation. In practice, instead of measuring these values directly we figure them out using well defined age standards, producing this equation


where ⁴⁰Ar^* is the ⁴⁰Ar derived from radioactive decay, ³⁹Ar _K is the ³⁹Ar produced in the reactor from ³⁹K, and J is a term that incorporates all of the irradiation variables but can be calculated from standards of known age (determined with other methods), whereThe advent and refinement of the ⁴⁰Ar/³⁹Ar method solved some of the larger problems with the K/Ar technique. First, sample analysis became much more straightforward, measuring different isotopes of the same element is much easier that measuring different elements. Measuring a ratio of two isotopes is also easier that measuring abundances of two elements. The ⁴⁰Ar/³⁹Ar frees us from uncertainty in the spikes used during analysis.

Second, it allows the geochronologist to evaluate the assumption that the "extraneous Ar" in the sample is atmospheric in composition. This is done by progressively degassing the sample at higher and higher temperatures (called step-heating experiments). The first temperature steps are at low temperatures, and tend only to liberate very loosely bound Ar from the crystal, perhaps Ar adsorbed to the surface of the crystal, or held near the surface. With increasing temperature we access and analyze gas that is more tightly bound up in the crystal structure. In the end we then have a series of steps, each with separate isotopic values. If the gas came only from the atmosphere, and was not related to any K, then ³⁹Ar/⁴⁰Ar would equal 0. If the gas was entirely radiogenic, and had no atmospheric input, then ³⁶Ar/⁴⁰Ar would equal 0. In truth, we typically have some mixture of inherited (or atmospheric) Ar and radiogenic Ar. If we plot up these values on an inverse isochron diagram we can determine what the composition of the extraneous Ar reservoir is, and therefore correct our values to determine the real age.

as shown above. If your sample is a mixture of inherited Ar from a single reservoir and radiogenic Ar of a single age, then your individual temperature steps will define a mixing line between those two compositions. We can use the inherited Ar composition to correct our ⁴⁰Ar values, and get the real age. It is also common to see the data displayed as an age spectra, shown below. Here, each box represents an indivual temperature step from a single sample. The y-axis is the age (here in Ma), corrected for extraneous Ar. The height of the box is proportional to the uncertainty of the measurements. The x-axis is the cumulative percent of Ar released. The steps are in order, so the first low temperature steps are on the left, and progressively higher temperatures towards the right. The width of the box is proportional to the amount of radiogenic Ar (⁴⁰Ar^*) released during that step. The large flat area in the middle of the graph is called a plateau and indicates that ages from different temperature steps agree. There is no real physical basis for the definitions of a plateau, and variations abound. Realistically, if our measurement precision was high enough, we would never see plateaus, because natural volume diffusion should round out the profile and make the early temperature steps slightly younger. But, age spectra are very common in literature, so it is important to know how to read them.

The inverse isochron diagram is much more powerful, and I am suspect of Ar papers that do not include inverse isochron diagrams. If the sample is very radiogenic, and there is little ³⁶Ar, then the corrections aren't significant, but still that information should be included. Plateaus and age spectra diagrams are interesting on their own, almost from a Psychology of Science perspective. Even though they are not the most powerful Ar/Ar tool, they are visually pleasing, and telling someone you got a nice plateau usually convinces them of your data quality faster than discussing inverse isochron diagrams. The definitions of a proper plateau usually involve some minimum number of consecutive steps representing some fraction of the total gas that are within error of each other for age and have no statistically discernible slope. You can imagine that if your measurements were kind of crappy, and the age uncertainty on each step high, then getting consecutive steps to agree isn't very difficult. As labs drive for higher and higher precision, and individual step ages have uncertainties less than 1% and official plateau get tougher and tougher to create, even when the age and sample are perfectly acceptable.

⁴⁰Ar/³⁹Ar thermochronology is a very common and useful tool for geologists, and is particulary interesting because it allows the direct examination of a number of the assumptions involved with radiogenic isotope geochronology. Later posts will examine the power of the technique in more detail.

Note - the inverse isochron diagram I used is one I made up just as a teaching tool, the age spectra is real data I collected a few years ago.

Foray into Politics marking an important anniversary

Disclaimer: I in no way pretend to be a historian or expert on war, politics, Haggar Slacks, or international relations. Geology posts will resume soon.

I was inspired today after reading ...Or Something and this post. I tend not to be too political on my blog, but seeing as today is a very important anniversary for my country, I wanted to get this out. First, some background.

Separating minerals for geochronologic analysis is a rather long and tedious process. There are many different steps, non of which are particularly difficult, but screwing them up can mean the complete loss of months of time and thousands of research dollars. Therefore, I can't juggle mineral separation with any activity that requires my eyes or hands, I have to keep those free for the task at hand. To keep myself entertained, I usually turn on my iPod and listen to music, a book on "tape", or, more recently, a podcast.

A few months ago I was "floating kspars" and listening to an American Radioworks Episode about the recently released audio tape collection of presidential phone calls and oval office conversations. I was struck by some of Lyndon Johnson's conversations, especially those that related to the Viet Nam War (although, for a true laugh I recommend his call to the Haggar clothing company requesting some custom made slacks, seriously, some of the funniest stuff I've ever heard). Back to Viet Nam. In particular I was struck by a conversation he had with Senator Eugene McCarthy (Democratic Representative from Minnesota) about the Viet Nam War. This conversation took place on February 1, 1966 (transcript and recording can be found here, more conversations from Johnson and other presidents are here or downloaded here including the aforementioned Haggar Slacks call).

President Johnson : What they [subscribers to the Walter Lippman - J. William Fulbright argument] really think is we oughtn't to be there [in Viet Nam] and we ought to get out. Well, I know we oughtn't to be there, but I can't get out. I just can't be the architect of surrender....I'm willing to do nearly anything a human can do, if I can do it with any honor at all.

As I said earlier, this conversation took place on February 1, 1966. This was the beginning of the escalation in Viet Nam, and just before the deadliest years of the war. According to the National Archives, as of 2/1/1966, there had been 2,670 American deaths in the Viet Nam War, less than 5% of the eventual total of 58,193. Hindsight is 20/20, but if Johnson could have looked ahead at the 55,523 more soldiers who would die before the U.S. got out of the war, you have to wonder if his definitions of honor and surrender would have changed. And why is the focus on honor anyways, shouldn't it be on doing the right thing and saving innocent lives? So when I hear talk of surrender now with Iraq, this is what I think of, I think of the 55,523 kids who could have been saved if someone would have had the guts and foresight not to think of their re-election, or even their short term legacy, but of the long term consequences of saving face. To realize that these are real lives, real people who will pay the price for their political ambitions.

I know that playing the "what if" game with history is dangerous and pretty fruitless. It is easy for me to look back and tell people what they should have done, years before I was even born. I just hope that in 41 years someone isn't writing the same blog entry about Iraq.

If you are interested, this conversation is on tape WH6602.01 9602, the part I highlighted starts at about the 1:28 mark (you can download the .mp3 from here).

All lights burning bright: Apparent Dip Music Club Concert Review #1

This post has nothing to do with earth science, geology, thermochronology, or Brian Urlacher. It does have to do with an excellent singer/song writer, so if that floats your boat, read on.

Today I attended my first concert since moving out east, David Francey playing at the Earlville Opera House in nearby Earlville, NY. Here goes the review.

The background - I stumbled upon David Francey about a year ago, when I was in the middle of trying to write my thesis, and before I had heard any positive responses to job applications. Needless to say I had a few million things in my brain that would start swirling around the moment I woke up and would reach hurricane force by noon. I found David Francey's album The Waking Hour on iTunes, downloaded it, and didn't stop listening to it for at least a few months. It seemed to fit my situation perfectly, Francey's songs are incredibly well written and heartfelt, his voice suits the songs perfectly, and The Waking Hour, as an album, just does not have a weak point. The Waking Hour got me through the first draft and re-writes of all of my thesis chapters, drives and flights between Seattle, Sacramento, and BWRU, and many a anxiety filled late night bout of insomnia. The Waking Hour has since joined Trace, No Code, Between the Breaks Live, and El Corazon as albums I credit with getting me through various challenges in my life. As much as I loved the album I then hit a wall; although Francey released his first album in 1999, only one was available in the U.S., and my budget at the time did not include extra for import discs. Fortunately, over the past decade I have formed an extensive and international network of like minded music aficionados, some of whom I turned on to David Francey, and are now living in Canada (Professor Van Halen). By the fall I had Francey's complete catalog, which of course did not disappoint. As I told the guy sitting behind me today, I recommend them all.

The artist - Francey is a singer/songwriter (and occasional guitar player) who was born in Scotland and moved to Toronto when he was twelve. This means he has an excellent accent, primarily Scottish but with distinctive Canadian features. His songs are drawn primarily from his personal experiences, which is the flavor of folk music I like the most. I compared him in an earlier post to Stan Rogers, not so much in sound or voice or even style, but in the feeling of his songs. Very influenced by place, experience, and probably most importantly, people. This is of course very different from crappy coffehouse poetry "folk music", a lilting and opaque brand of "music" that poor undergrads at tiny liberal arts colleges are subjected to on a regular basis. Sorry, flashback; I've seen a ton of folk singers in concert, and the degree to which newage (which as THM reminds us rhymes with "sewage") and whiny reject poets have infiltrated folk music is alarming. I believe I can ward off these evil spirits by loud regular doses of Francey, Stan Rogers, Townes Van Zandt, Jerree Small, Greg Brown, Gillian Welch, Todd Snider, and The Be Good Tanyas........anti-newage voodoo (see my music links sidebar for suggestions).

The venue - The Earlville Opera House is a nice small venue in a tiny town just south of Colgate University in New York. It was built in 1892, fell into ruin, and is now being restored. Getting there meant an excellent drive through New York on a perfect sunny day. Very nice. Their upcoming folk lineup at the Opera House is pretty solid, if you live in the area check it out.

The concert - David was accompanied by guitarist Craig Werth. He played two sets with a good mix of older songs and some from his newest album, Right of Passage. Even though he apologized for his voice (he had a cold or flu), he sounded excellent, as did Werth, even when singing the a capella "Torn Screen Door". Concerts have a way of changing how you feel about the artist and/or specific songs, depending on the performance; folk singers in small venues especially. Francey introduced each one of his songs with a story about how or why he wrote it, or maybe something about his life that was relevant to the song. I tend to like a song more when I know what it is about, well, as long as the story isn't lame. This is a common folk singer technique, and is one of the main reasons I enjoy small concerts so much. Today I came away really liking "All lights burning bright", "The Waking Hour", "Kansas", and "Under the Portland weather." I liked all 4 of these already, but now that I know the story behind them I put them up with some of my Francey favorites. I don't want to spoil the stories. He has a live album (the one I don't have, and today I was broke and therefore couldn't augment my collection, it'll have to wait), but if you like his studio work (you can preview two of his albums on iTunes), you will like his concerts. In addition, he seemed genuinely nice and appreciative of the folks who came out to see him. This is crucial for me, there isn't much more annoying than discovering a musician you like is actually an immature stuck up retread (we can call this Ryan Adams Syndrome).

The verdict - Excellent, well worth everything. My live music batteries were entirely drained this morning, but are now nice and full. Francey makes excellent albums and puts on excellent shows.

Follow Up to the Last Post - Cheap Food

To follow up on the last post with something related, I offer this article. It describes how the governer of Oregon has decided to try to live on food stamps for a week. I know nothing about the governor of Oregon but I am a big fan of experiments like this. A week isn't a terribly long amount of time, but so many people in charge have absolutely no idea what life is like for the average American (let alone the average citizen of the world, that is of course a completely different story). The total budget for a weeks worth of food (if you are on food stamps) is $21.00, which makes my occasional trips to the Wegmans olive bar seem completely extravagant.
This is kind of interesting, after the shootings at Virginia Tech last week I had thought about blogging about my experience working in the mental health field, specifically my frustrations. I decided not to, but now thinking about the price of food my experience at this job comes up again. During the year after college and before graduate school, I worked as a counselor at a residential treatment facility (read: group home) for severely emotionally disturbed teenagers. It was a definite change of pace for me. An odd job, the average work day could be spent restraining 200lb violent 17 year olds for a few hours and watching against suicide attempts, or I could spend all day playing football and bar-b-qing. Anyways, where does food come in? Well, seeing as we were contracted by the State, we had to provide a set diet for the kids. Every two weeks we got menus, and then had to do the grocery shopping and cooking for the group. We would get in trouble if we strayed too far form the set diets. Technically the kids were supposed to help with the cooking but with the frequency of problems they were usually kept off limits from any kind of cooking implement. It turned out that of the counselors working during my shift, I was the only one who was much of a cook at all. As such, I got very familiar with the official state recommended diet for 11-7 year old boys. The food we had to provide was amazingly unhealthy, very meat, cheese, and starch heavy dishes, very few fresh vegetables (save for iceberg lettuce "salads"), and almost no fruit. A typical weekend breakfast would include either pancakes or french toast, scrambled eggs, sausage or bacon, regular toast, and occasionally a banana. Follow this with a grilled "cheese" and french fry lunch, and cheese burgers, tater tots, canned corn, chip and salsa dinner. What made this worse was that the budget we were give to shop with was just appalling, so that even when a decent cook like myself was around, there was no way to afford anything of any quality at all. Mushy apples (the kind you buy in the 10lb bags), fake cheese, kleenex style bread, etc. And they wondered why the kids always gained weight; add the food to the fact that many of their medications sapped their energy, easy path to obesity. On the upside, I did learn to cook a mean pot roast (quite an accomplishment for a vegetarian), and my french toast was pretty solid. But still, with all of the money spent trying to address the kid's many mental issues, I was always amazed at how little attention was paid to their physical health. And, since we were their legal guardians, what kind of life lessons were we really teaching? OK, this has turned into a ramble, good night.

Land Use, Veggies, Food, and Farm Subsidies

THM pointed out this article in the New York Times Magazine by Michael Pollan. Pollan is the author of The Omnivore's Dilemma (in addition to lots of other things), and this article is on a similar topic. The article is primarily about the economy of nutrition and the effects that the farm bill has on the price and production of food. At it's heart this is also a land use issue, and therefore appropriate for posting on an earth science blog. I'll do a proper review of The Omnivore's Dilemma at some point in the future, but as for now you'll have to settle for the links.

Apparent Dip Music Club Update - David Francey Concert

I took advantage today of a repetitive lab procedure to reserve a ticket for my first concert in a long time, and the first since I made it to the northeast. This Sunday David Francey is playing in a nearby town (not much of a drive at all), and Thermochronic has a ticket! I blogged about David Francey when I first started Apparent Dip, I even embedded some YouTube videos of him performing. Unfortunately the videos are no longer available on YouTube, but for just $15.00 I'll be able to see him live. This will of course lead to the first Apparent Dip concert review, but that's it for now. I post this mainly because I am excited, but also to point out that David Francey has a pretty extensive tour he is in the middle of, so if he is coming to a little opera house a short drive from you, my bet is that it will be well worth the travel.

The Age Equation

This post is inspired by some emails I've received as well as a good group of google searches that have pointed folks to Apparent Dip. The Age Equation is central to geochronology, and forms the basis for age calculations. It is actually fairly simple to derive, so here we go

In the following derivation, N is the number of radioactive parent atoms at time t, N₀ is the original number of radioactive parent atoms, D is the number of stable daughter atoms, λ is the decay constant, and t_½ is the half life of a radioactive atom. The situation I use as an example is one parent and one stable daughter. Slight modifications are needed for multiple parents (the (U-Th)/He system), multiple daughters (⁴⁰K decay), or the use of unstable daughters in a decay chain (U-series dating).

The activity, or rate of decay of a radioactive isotope is proportional to the number of radioactive atoms present


By introducing a proportionality constant λ (which we will call the decay constant), we can turn the above equation into



Because the λ is in units time^-1, and the number of atoms decreases with time, we also throw in a negative sign. Rearrange this equation


and integrate from N₀ (original number of radioactive parent atoms) and t=0 (time zero)

and we get


since t0 = 0, this leads to

which can be rearranged to


The above equation describes the number of radioactive atoms left after time t. The decay constants, along with their uncertainties, are readily available (I'll list some of the geologically important ones at the end of this post). Decay constants are inherent properties of the nucleus that describe the probability that an atom will decay. I blogged about demonstrating this phenomenon with M&M's here

OK, so the above equation is handy, but when we work with geologic samples, we don't know N₀, the original number of parent atoms in the crystal, so can we put this equation into terms of things we can measure today?

In a system with one parent and one daughter, N₀ is the sum of N, the number of parents left, and D, the number of daughters produced.


So if we put the last two equations together, we get this


Which is entirely in terms of things we can measure in the lab. The next steps are simple mathematical rearrangements






Until we get an equation that solves for time and whose variables are all things that we can measure.


I've been using the decay constant up until now, which as I said earlier describes the probability that an atom will decay. The half-life of an isotope is a more intuitive measure, the half-life is a unit of time over which half of the radioactive atoms in a given population will decay. You can easily see the relationship between the decay constant (λ) and half-life (t_½) with this simple exercise. At t_½, half of the parents have decayed and turned into daughters, so N=D, and D/N = 1. So let's plug that into our age equations



and we get the relationship between λ and t½



So the equations are pretty straightforward. As I said, they get a bit more complicated for more complicated decay schemes, but the basics are all the same.

Here are some of the more important radioactive isotopes, decay constants, and half lives. I got this information from table 1.1 of Alan Dickin's Radiogenic Isotope Geology (2ed), he has the references for the appropriate scientific papers listed as well.

Isotope	Decay Constant (yr-1)	Half-Life
40K (40Ar)	5.81 X 10-11	11.93 Ga
40K (40Ca)	4.962 X 10-10	1.397 Ga
40K (total)	5.543 X 10-10	1.25 Ga
235U	9.8485 X 10-10	703.8 Ma
238U	1.55125 X 10-10	4.468 Ga
232Th	4.9475 X 10-11	14.01 Ga
87Rb	1.402 X 10-11	49.44 Ga
147Sm	6.54 X 10-12	106 Ga
176Lu	1.86 X 10-11	37.3 Ga

And, as usual Ga means billion years, and Ma is million years. Now you too can enjoy hittin' the geochronic.

NCSE Web Resources

The National Center for Science Education is now offering free access to a variety of digital resources dealing with recent evolution related trials and general evolution and science promotion. I haven't checked out the files myself [yet] but the NCSE has a good track record, so I thought that shouldn't stop me from advertising.

To see the archives click here.

Springtime at ESRU

Mild, sunshiny days, chirping birds, bright flowers...Spring is such a magical time of year, even here at ESRU. I thought I'd share some pictures I took yesterday morning.


Odd weather abounds in my first year in the northeast, we had more snow on easter than we did on christmas, and now weeks past opening day I am wishing I hadn't taken off my snow tires.

Wunderground and free public data

The following post may seem like I am meandering but there is a point, I promise, stay with me.

We in the American northeast have been enjoying a pretty late winter this year, meaning, it's a hell of a lot colder than April is supposed to be. The place I used to live was, in general, much warmer, and I got to thinking of the temperature difference between where I used to live. This got me hitting Wunderground, a weather site I started checking thanks to my Mom (an amateur weather guru who often knows more about my weather from 3000 miles away than I do). One of the cool things about Wunderground is that they make it easy to download historical weather data. For example, after about 10 minutes of clicking and Excelling I made this
Which shows the temperature difference between where I lived in grad school and where I live now. The y-axis is the difference in average daily temperature (°F) between old home and new home; values above 0 mean it is warmer at BWRU, and values below 0 mean it is warmer here at ESRU. The line is a five day running average. Why 5 days? I have no idea, but I'd appreciate a good reason if anyone can think of one. There are a couple things I noticed after putting this together. First, we had a really warm winter here at ESRU, until well into January it really wasn't much warmer back at BWRU. Second, there is an odd apparent periodicity in the running average, with a fortnightly recurrence. You can sum up my statistical analysis of this feature with the words "Jack Squat," but it is still potentially interesting. The maximum difference was just a month ago, March 6th when it was 59° colder here than there.

OK, great, it is colder in the northeast than a western school at a lower latitude, big shocker. Doing this though reminded me of an exercise I came up with when teaching an earth hazards course in 2004, again using Wunderground. In February of 2004 there was flash flooding in the southern part of San Francisco. Pretty exciting, there was water rushing down stairwells and elevator shafts at San Francisco State University. At this time I was teaching this earth hazards course at an area school, so I used Wunderground to come up with this homework. I had the students get the rainfall data for two days from the same station, the flash flood day (2/25/2004) and another day, a few months earlier that had some serious rainfall but resulted in no flash flooding (12/29/2003). This is the graph they were supposed to come up with

The y-axis is rainfall rate (in inches per hour), and the x-axis is time. The total rainfall for both days was actually remarkably similar, actually 12/29 had more cumulative rainfall, but the flash flood day had all that rain packed into less than an hour, instead of spread out over the day. Basically I was driving home the point that flash floods, unlike regional floods, come from large amounts of rain in small amounts of time.
What both of these exercises got me thinking about is free public data sets. Wunderground does not provide the kind of really rigorous data I'd use if I was working on an actual publishable study, but as a teaching tool or means of illustrating basic earth science concepts, it is fantastic. So Wunderground is great for relatively recent weather data. What about other public earth science related data repositories?

And So It Goes, R.I.P Kurt Vonnegut

Author Kurt Vonnegut died last night at the age of 84. In memorium and related to my last post, the following quote can easily be adapted to our discussion of reviews of scientific papers

Any reviewer who expresses rage and loathing for a novel is preposterous. He or she is like a person who has put on full armor and attacked a hot fudge sundae.

Kurt Vonnegut (1922-2007)

More on Reviews

Recently Lab Lemming started a good discussion on some of the issues involved with scientific reviews, specifically reviewer anonymity. This, and related posts throughout the geoblogosphere were especially timely for me. In the past two weeks I have reached two milestones in my scientific career. First, I wrote and submitted my first official review of a paper submitted to an honest to god reputable scientific journal. I was pretty excited about this to begin with. I have heard many of my bosses and older sciencey folk talk in exasperated tones about all of the papers they have to review and what a pain it was. I suppose after I've done this a hundred times I'll be sick of it, but for now it made me feel like a real professional geologist person. Anyways, I spent a lot of time on this review, wrote and re-wrote my comments, slept on it, read the paper a fourth time, and finally sent in the final comments. In general I was positive in my review, although I did raise some excellent points, which I hope to be thanked for generously in the acknowledgements paragraph of the final paper. How will I be thanked? Well, as an anonymous reviewer of course. This was a tough call for me. Theoretically I do not like anonymous reviews. I stand behind my comments and evaulation, so why don't I attach my name to them? I wasn't overly harsh or negative, and I even pointed out lots of good things. But why do I still fear retribution because I recommended acceptance only with revisions? Truth is, I think as a post-doc who will in the not too distant future be on the job market, I am not sure how much I want to risk souring potential search committee member's opinions of me. I do not yet have the position or name recognition to feel insulated at all from negative vibes. Even though I know I gave a fair and honest assessment, I left my name off the final review. Maybe Thermochronic is just a big old chicken?

And, let's add smarmy hypocrite to big old chicken, because I have also spent the past week grumbling about the second milestone of the past two weeks that I have achieved, namely getting an off-the-mark and anonymous negative review of a paper. This is not a paper I am first author on, but that has not stopped me from cursing anonymous reviewer #n under my breath. I don't know if anonymity played much of a role in making this review crappy, but I would at least like the name of a geologist to google and curse at while I take breaks from revisions. What kills me about this review is that (1) all of the other reviews were very positive, and (2) the comments actually didn't raise any significant issues, just the reviewer's unfamiliarity with some of our standard laboratory techniques.

I like the suggestion of Lab Lemming to include signed copies of reviews with tenure packages. I actually think we could take this a little farther and make reviewer anonymity temporary. If a paper gets published, and a year later the names of the reviewers are made available, then as long as the reviews were honest I think many of the fears of pay-back would be gone. Right now I am all hopped up, stomping around when I think of anonymous reviewer #n and his/her goofy comments, but when the paper is published, a year from now, the emotion of the rejection would be largely gone, and I'd be able to see the review in a much clearer light. Come to think of it, as I sit at the "Scientific Paper of the Year" awards banquet with my co-authors we will probably laugh about the whole incident. So, how's that, a statute of limitations on reviewer anonymity.

EOS and Wikipedia #2

For a follow up to my previous post, I'd just like to redirect you all to Ron Schott's Geology Home Companion Blog and this post. Ron has obviously thought a lot more about using the web as a geoscience resource than I have, and he brings up a lot of very good points on the matter. He also talks about the GeoWiki project he is spearheading, which is something we geoblogospherons (my new name for members of the geoblogosphere, which also sounds like a sub atomic particle) should become involved with.

EOS and Wikipedia

In a [relatively] recent issue of EOS (v.88, n.11, p.134-135), Mark Moldwin et al. discuss the popularity of Wikipedia as a source for undergraduate research in science classes. According to their informal survey, for most of the 300 surveyed students, Wikipedia was the first stop for them during their research process. The authors then briefly discuss the quality of information available on Wikipedia for their areas of interest, and end with a call for other specialists to do the same. I have never been a fan of internet "research", it seems to always end up with crappy papers rich with downloaded figures and light on critical thinking. But, I am also aware of the present reality, that when you start a research project outside of your area of specialization, the internet is the first place you go. Seriously, if I want to figure out who all of the people Stan Rogers sings about in "Northwest Passage" are, I am going to google it, or check out Wikipedia's page on the topic. If I want to go in depth, sure, then I head to the library and/or bookstore, but the internet, or more specifically Wikipedia, does perform an important role as a starting point. Seeing as how this is the present state of affairs, it is important that the information is at least correct. I spent some time last night looking at the wiki pages for my areas of specialty, and I must say I am unimpressed. They aren't really wrong, just incomplete, outdated, and rather uninspiring. So, I have decided that over the next few months I'll be adding to and updating the pages that I know the most about. I think this would be a worthwhile endeavor for the geoblogosphere. Many of us have written posts that deal with basic earth science concepts (see my sidebar), and between us all we could probably square away significant wiki real estate. So, take a look at a few pages and let me know what you think. This is in no way an endorsement of internet based papers. Students who turn them in should get low grades and reprimands, end of story. Peer review is too important of a concept in science to be replaced by anything, even google, and students need to know that. We should use wikipedia as a way to point people in the right direction, that's it.

Incidentally, this fits well with my current situation, I've been working on a post about K-Ar and Ar/Ar thermochronology for a while, but have yet to be happy with it. Perhaps it can serve double duty.

Disclaimer : Apparent Dip is not responsible if you have a debilitating attack of wikipeditis, the common affliction so perfectly illustrated by xkcd.

Mike Slackenerny, Ph.D.?

If you've ever taken the tour down my sidebar, you've seen the link I have to the Ph.D. Comics strip. This has been one of my favorites for years, it appeared regularly in the student paper at my graduate institution, and the online archives got me through one overnight mercenary shift on an ion probe blasting zircons. Today's comic shows regular character Mike Slackenerny turning in his thesis to the university registrar. Now, if you follow the strip, you know this is significant because Slackenerny has been in grad school for some untold and absurdly long period of time. What I loved about this strip though was that it is actually true. When I took a "final" copy of my thesis to the university registrar (same registrar, by the way, that is alluded to in this strip), I was told I needed to adjust the margins, I had to add 1/10th of an inch to the right (non binded) side. I luckily had not printed this version on the insanely expensive all cotton thesis paper I later had to use (which, of course doesn't count as a qualified tuition expense on my 1098-t). What got me was that the official measuring stick was an old wooden ruler that was worn down on the corner, you actually couldn't see the markings on the last 1/4 inch, which made me confused about the need for such precision. Allegedly, even though the margins in my thesis LaTeX file were set right, paper has enough lateral movement in printers that you need to add extra width. Anyways, not that anyone cares about the trials of printing final thesis copies, but I thought it a good way to advertise Ph.D., the comic strip. Check out my sidebar for the most recent comics, or click through to the site for the complete (free) archives. Here are a few of my favorites...

Thermochronic Book Club #1 - T.Rex and the Crater of Doom by Walter Alvarez

A while ago I blogged about how I would be challenging myself to read and blog about 5 popular science books over the course of the next year. I solicited suggestions, set a start date, and then, dropped the ball. There are two primary reasons that my geology blogging has been slack lately; first, I finally submitted a manuscript I've been working on, and second, it's NCAA March Madness time, the greatest American sporting event (by a long shot), and so have been a little distracted.

The paper took longer than I had hoped to submit, perhaps because to be honest I am not all that thrilled with it. The science is good, the data important, and the results make sense and need to be published, but for a number of reasons the results are not sexy nor earth-shattering. I know not all science is supposed to be ground-breaking, but still. At least it is out the door, we'll see what the reviewers say.

As far as the NCAA goes, those of you who don't follow or care about the Men's Basketball Championship tournament, during the first four days of the tournament, 48 single elimination games were played all over the country, resulting in some stunning upsets and nail biting finishes. I now live on the east coast of America, which means the games start late here, and finish late, so if I want to watch any I have to stay up past my bed time; this has cut into my other recreational activities (read: blogging).

But, I did finish my first book of the challenge, T. Rex and the Crater of Doom by Walter Alvarez.
I have been meaning to read this book since the 2002 Geological Society of America national meeting in Seattle where I saw Walter Alvarez receive the Penrose Medal. I had actually gone to the awards ceremony because at the same time, John McPhee was also receiving a medal (The GSA Public Service Award) and wanted to hear his acceptance speech. For me, though, Alvarez's acceptance speech really stole the show. I've been looking all over the internet for a transcript with no luck, but regardless, I remember it as being one of the more poetic and heartfelt speeches I had ever heard (especially at GSA). In his talk he briefly discussed the work he is most famous for (and the topic of this book), but more importantly spent time talking about the aesthetics of field work, and the importance of the friendships he had built over the years working on this project. I remember him ending with an image of the end of a field day, sipping wine in some perfect valley in Italy surrounded by friends and the excitement of the story they were all unraveling. Anyways, that was 5 years ago, and the fact that I am only now getting around to reading the book is a little silly, but here we go.

T. Rex and the Crater of Doom chronicles the events that lead to the discovery of evidence for a major extraterrestrial impact at the Cretaceous - Tertiary (or K-T) boundary, the time when all of the dinosaurs (and many other animals) suddenly went extinct, roughly 65 Million years ago. Alvarez began working on a series of limestones in the Appenine Mountains of Italy in an attempt to use paleomagnetics to chart microplate rotations in the Mediterranian. The section he was analyzing stretched over the K-T boundary, preserving an exceptional marine record of that time period. They never found evidence for microplate rotation, but they had stumbled upon something much more significant. What they eventually found was a huge spike in the amount if Iridium present in the clay layer at the K-T boundary. They published this finding in Science in 1990 (Alvarez et al., 1990, Iridium Profile for 10 Million Years of the Cretaceous-Tertiary Boundary at Gubbio [Italy]; Science v. 250, n. 4988, pp. 1700-1702). The Iridium concentrations were such a find because Iridium is not very common in the crust of the earth, most of the Iridium the planet contains is locked up in the core. Meteorites have similar bulk compositions to the earth, but can be completely destroyed upon impact, vaporizing themselves and leaving a fine layer of meteor dust spread around the world. Meteor dust is enriched in Ir compared to the highly differentiated earth crustal rocks, so it shows up as distinct spikes in abundance.

From Alvarez et al., 1990

This is a figure from the Alvarez paper showing the Ir concentration (in parts per trillion) versus stratigraphic position in the limestone. Background Ir levels are barely above the minimum sensitivity of the instrument, but at the K-T boundary there is an enormous peak. This "Iridium Anomaly" has since been found all over the world at the K-T boundary.

I don't want to give away the whole story, because the book is certainly worth reading. Alvarez does an excellent job capturing the process of science and presenting it for the readers in a way that is very interesting to read. It shows that what we find is rarely what we set out to prove, and that some of the most interesting and exciting scientific discoveries are born from the ashes of failed studies.

I've heard versions of this story many times during my geologic career, but the book still kept me interested. Alvarez adds enough background that the story is easy to follow (even for those with no real background in geology), without sounding too basic or redundant. These are qualities I think public science books need to have, especially when done in a genuinely readable style.

There are aspects of this book I found particulary interesting, but they didn't really center around the impact story. The first was his discussion of the tension in the geologic community over uniformitarianism. This idea is often summed up using a quote from Charles Lyell, "The present is the key to the past." Basically, if we want to know how something happened in the past, then we should observe today's processes. There is no need to involve "catastrophic" phenomena to understand geologic features, and that rare and catastrophic events (like impacts) have little role in the history of the earth. I had of course learned about this idea (which is still largely true, but I'll get to that in a minute), but the tension and disagreement over the importance of catastrophic events was something I never really had a feel for. This debate was happening during my lifetime, really during the beginning of my geologic education. The problem, as I see it, was that embedded in the concept of uniformitarianism is a time scale. Things that seem rare and catastrophic on the human time scale (large volcanic eruptions like Yellowstone, extra-terrestrial impacts, some of the floods that occurred when the dams of glacial lakes broke, etc...) are, from perspective of geologic time, fairly common. So it's not really that we have to call upon events that no longer happen, only that we have to expand the idea of everyday geologic phenomena.

The other aspect of the book I really enjoyed was his discussion of how geology, as a science, changed in nature from when he was doing his Ph.D.

Geologic mapping was satisfying and useful, but in retrospect most of it seems to me to have been intellectually pretty routine. While early twentieth century physicists were reading "the thoughts of God," in Einstein's phrase - exploring the majestic curvature of spacetime on the scale of the universe and disovering the weird quantum behavior of the infinitesimarlly small-geologists labored to reconstruct the paths of ancient rivers and the pattern of lands and seas at various times in the past.....Geology simply asked its apprentices to learn the techniques of geologic mapping and to memorize a lot of complicated terminology and then it sent them out to add to the growing knowledge of the rock record of the Earth.
And yet, with hindsight, we can see that the mapping was an investment which is now paying great dividends. Physics could make great discoveries quickly by reducing complicated problems to simpler components because physics investigates the fundamental laws of Nature, which do not change and do not become more complex through time. Geology seeks to understand the earth, which has evolved over 4,600 million years, accumulating more and more historical complexity in its rock record. That century and a half of mapping the Earth produced the detailed knowledge of the rock record which is now allowing geology to emerge as a mature science, skilled at interpreting historical complexity, and therefore perhaps the discipline best prepared to lead science into the holistic world of the twenty-first century. [emphasis added]

First, I'd like to point out that "that century and a half of mapping" is not really over. There are many regions of the world (even the continental US) that still need to be mapped (or remapped). It is a necessary step in understanding the geology of a region, and it introduces and refines most of the skills geologists need (primarly, it hones observational skills). Second, all geologists need to be able to create and read geologic maps, and any attempt to remove this from a curriculum is detrimental to the science. But, geology has changed. This is obvious to anyone who has checked out older theses from their university library; expectations are now very different. This is no surprise, I am sure all disciplines are similar, but I like to keep it in mind. I am tuned to lectures from people older than me about how easy younger generations have it, but that just isn't true. Expectations, abilities, and realities are all different. I suppose as I transition into a grumpy old man I should also keep it in mind.

The final aspect of the book I'd like to touch on is how well it describes what I think all geologists (perhaps all scientists) dream of happening to their research. You stumble upon something that ends up being enormous, and changes the face of science forever. There is no doubt that Walter Alvarez is an exceptional scientist who worked very hard for many years to accomplish what he did, but he also freely admits the role of chance in his discoveries. Things worked out well for him, and I think it instills hope that crazy and unforseen exciting discoveries are out there waiting to be made. Not in the project I finally submitted for publication, but I am sure they must be somewhere.

T. Rex and the Crater of Doom is worth the read, even if you already know the punchline. It is also rather short (which, Mrs. Apparent-dip-but-with-a-different-last-name can tell you is a key factor in my book-choosing process: I turned in 4 papers in 4 different classes on The Red Badge of Courage during my high school and college life).

I am not sure which book I'll be taking on next, but this is off to a good start. Any other thoughts on this book, or if anyone wants to comment on a recent paper by Gerta Keller et al. Chicxulub impact predates K–T boundary: New evidence from Brazos, Texas that appeared in Earth and Planetary Science Letters (Earth and Sanitary Appliance Letters?) Volume 255, Issues 3-4, 30 March 2007, Pages 339-356, I'd appreciate it.

Global Climate Energy Project, Big Oil, and Big Benefactors

I read this article today about a recent decision by a major benefactor of Stanford University to withdraw a $2.5 million dollar gift to the university because Stanford recently accepted a $100 million dollar gift from ExxonMobil. The ExxonMobil gift was part of a combined $250 million dollar grant from a variety of of donors to create a new research institute at Stanford called the Global Climate and Energy Project. This institute will bring together scientists from a wide variety of disciplines to look for ways to "meet future energy needs without worsening global warming." Included in the article is this quote.

“Exxon Mobil is trying to greenwash itself, and it’s using Stanford as its brush,” Yusef Robb, who has worked with Bing on climate issues, told The Mercury News. “We think that people who give to Stanford do so because they want to help the future leaders of this nation, not because they want to advance the agenda of ExxonMobil.”

I am by no means a fan of ExxonMobil in the political or environmental sense, I am sure they, like most any other company in the world, make decisions based on short term profits and not on some sun-shiney moralistic ideal. But I think Bing's logic is twisted for a few big reasons.

1. I don't see the problem with a company trying to "greenwash" it's image. I don't believe companies can be moral or immoral, they can just do good things or bad things. ExxonMobil has plenty of bad company points, as I have already blogged about (and then some for sure), but why should that stop them from doing something good? Giving money to research aimed at developing energy alternatives seems like a good thing (as long as there are no strings attached, see point #3.)
   
2. I am sure the Bing family has in the past had plenty of money invested with oil companies (perhaps without them even knowing about it.) Most banks and mutual funds and things of that sort do. So why would it be OK to have investments that use companies like ExxonMobil to make money, but not want anyone else to benefit. Bing could of course only have "socially responsible" investments. I don't know all that much about him, other than what I can find on imdb.com and related entertainment sites, so if Mr. Bing does only have socially responsible investments, flies commercial airlines (so as not to waste energy with private planes), takes public transportation as often as possible and drives a hybrid when he can't, lives in a modest home complete with native fauna in the garden and of course, no swimming pool (I am guessing he lives in Southern California since he is a Hollywood dude), a nice compost pile where he can put the scraps from his locally grown vegetarian cooking, then I will perhaps agree with his decision.
3. This institute could be very important. It makes sense that energy companies want to invest in the future of energy, but isn't this something we all have a vested interest in. It states explicitly that Stanford University will own any and all patents produced by the institute, so they won't directly make money from this.
4. The gift he is rescinding was a general gift to the university; the gift he is complaining about is building a new institute. So, the general student population will be hurt, but those involved in the institute won't.
5. I think oil companies are easy targets to complain about. Truth is, like almost all large companies, they do some pretty bad stuff. I have no problem passing laws that regulate oil companies or the use and/or acquisition of energy, but I also think that the first place we need to look is at our energy use. If there wasn't such an absurd demand for oil, then oil companies would just be another podunk company, it is our use that gives them the power they have. Another example, I think, is Ted Turner. I again agree with him on most things, but he flies around the world in a private jet, perhaps the most energy inefficient mode of transportation known to man (well, except for perhaps spotted owl powered space shuttles or other monstrosities). Fly first class if you must, mingle with the dregs of society and enjoy the average in-flight movie; a small price to pay for your planet. Hell, they could even afford those super sweet Bose noise cancelling headphones, those would make even coach seats bearable. This kind of reminds me of people who drive SUV's to Whole Foods so they can buy organic arugula.
   
6. Stanford, I am sure, has had investments in ExxonMobil for a long time, as does anyone, or anything, with a diversified investment portfolio (see point #1). Why is it an issue now? Why doesn't Bing work with Stanford to create a socially responsible investment portfolio, or encourage Stanford to use it's shareholder clout to help redirect wayward corporations?
7. Let's pretend that every major oil company in the world except ExxonMobil had contributed to the institute, my bet is that people would then complain about how ExxonMobil isn't doing enough to help find energy alternatives.
8. Does his action help solve a problem, or is it simply a publicity stunt? If the end goal is to reduce our dependence on fossil fuels and reduce the production of greenhouse gases, does this help, hinder, or do nothing? Would he rather take away $100 million dollars from the institute, would that solve the problem?
   

I have no problem with Mr. Bing's positions or politics, I just think this is an odd reaction. Perhaps he could direct the gift into something that directly counteracts what he dislikes about ExxonMobil. Maybe create his own institute, one that develops oil company free investment plans. This isn't the first time a major benefactor has broken a promise of support to Stanford, and I don't think in either case the decision made much sense.

I am, however, excited to see that Steve Bing is producing a film version of Beowulf, which ranks as my #1 all time solo--road- trip book-on-tape. It got me to and from Seattle many times.

Peak Oil and Biophysical Economics

I recently had the chance to see Charlie Hall (from SUNY-ESF) give a lecture on Peak Oil. I think like many geologists I've either seen and/or read quite a bit about the concept of peak oil recently, so the material itself wasn't entirely new, but Dr. Hall also introduced an idea I was not familiar with, but have had in my head since the talk. I'll get to that in a second, first, for the uninitiated:

The figures I am using are all from the wikipedia Peak Oil page, just a disclaimer

Peak Oil is an idea first developed by one of this century's great geologists, M. King Hubbert. He introduced his theory in the late 1950's as a way of predicting future oil supplies. The idea is fairly simple, and is based on the fact that oil is a non-renewable resource, and there is consequently a finite supply of oil in the world. Oil production will follow a bell shaped curve. As the demand for oil increases, oil companies increase their supply as much as they can; pumping fields at full capacity and discovering new reserves. Demand continues to increase, but fields begin to dry up, and new fields just don't exist, so production declines. Whatever the exact shape of the curve, the logic is pretty plain, the integrated area under the curve is equal to the total amount of recoverable petroleum reserves in the world. This is Peak Oil, the idea that there will (or has been) a peak in oil production, and that at some point production will decrease, about as rapidly as it initially increased. This model works very well for individual oil fields, or even national reserves

The red curve shows US oil production versus time, with a peak in 1970, and a slight secondary bump thanks to the north slope of Alaska. World oil is in blue.
This is the theoretical production curve (red) and actual data for Norwegian production. I don't want to argue the specifics of the model; whether or not the curves are symmetric, how much technology can help (answer jack squat), when the peak is, etc.. There are some truths that you just can't get around, namely that the amount of oil in the world is finite. and that at some point we will be using more than we can extract, and production rates will decline.

Arguments against peak oil seem to follow the lines of "the market solves everything." As supply decreases, price increases, and demand decreases, thank god for the market, it will save us all. Oil will get expensive, and some budding entrepreneur will devise some amazing technology that will save the world! At some level I suppose that is true; if there are humans around in 500 years, they will undoubtedly not be using oil as their primary energy source (they will of course be using flux capacitors). Whether or not it happens isn't the problem, but instead what happens during the transition. Dismissing peak oil with some dreamy ode to market forces ignores how nasty things can get in the face of scarce resources. Technology will find alternatives, but when? Do we decide now to solve the problem before it gets too hairy, or do we wait until something resembling this happens? Hell, remember when stores would run out of Beanie Babies and all hell would break lose? I think oil might be worse.

This brings me to biophysical economics. The term, as used by Charlie Hall, refers to an economic theory that does not violate the laws of nature, especially trivial little ideas like thermodynamics. This is of course a major problem with simple supply and demand, it assumes that supply is only limited by something like factory output. For example, no matter how much the price of oil increases, the supply cannot, and any reasonable replacement would take much longer to develop than the oil would last. Economic theory rooted in physical realities, I like it.

I am less an economist than I am a petroleum geologist (not much), so this post is really not in my wheelhouse. This has sparked my interest though. Are there any more econ-minded folks out there who know about biophysical economics, or any economic theory that explicity takes into account the laws of nature? Any notable economists who consider the natural world, or economics programs that require some line of study like this?