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## Grad School 2: I want to go to grad school, so what should I do?

This post follows Grad School: A Primer, and is part of a series on graduate school aimed at my students. Other students are welcome to read it, but the focus is on UW Tacoma undergrads who are looking to do a thesis-based (a.k.a. research-based) MS or PhD in geoscience. Other grad school options – though maybe not all of the possibilities – are discussed in the first post of the series. Thanks to Bonnie Becker for her helpful comments on this post!

Suppose you’ve been mulling over graduate school, and you’ve decided that it’s for you. You have a good reason – maybe you like research, or maybe you want to teach, or maybe your plan to save the world (or maybe just a secure career with some hope of advancement) involves having an MS or a PhD – and you are OK with the commitment. Now: how do you actually do it?

Applying to a thesis-based MS or PhD program is much less standardized than applying to college. In some ways, it’s a bit more like looking for a job. Rather than taking SATs, writing a personal essay, and completing an application that’s more or less the same everywhere, the grad school application process involves making a personal connection with a potential advisor and submitting an application packet that includes recommendation letters, a resume, and a statement of purpose (a bit like a cover letter). Things like standardized tests (the GRE) and GPA matter, but much less so than the connections you make with faculty. However, different schools have different requirements, and the individuals involved can really make a difference.

Please understand that my knowledge of the grad application process comes mostly from my own experience, which was a long time ago, so take what I say here with a very hefty chunk of halite. I put together data from about 25 geoscience grad programs (not a random sample) as well as talking with with faculty and students in some of those programs. But there are probably some things I’m assuming based on my experience that might be different for you. Getting some different perspectives on grad school is necessary, and I’ll include some ways to do that at the end of this post.

### The Long Game

It used to be that, if you wanted to go to grad school in geology, you had to take certain courses as well as the Geology GRE. As the geosciences become more interdisciplinary and graduate schools try to recruit students with different academic backgrounds – physics, biology, chemistry, and, yes, environmental science – the “standard” set of courses has become less of a requirement. This is really good for our students. After looking at admissions requirements, I’m convinced that students who graduate our Bachelor of Science in Environmental Science program can meet the requirements for admission to a lot of geoscience programs, with maybe a little work. Keep in mind that, in many schools, course requirements aren’t set in stone, and missing classes can often be taken after you get in. You may also be able to take some of these courses after you graduate, as a post-baccalaureate or nonmatriculated student at UW Tacoma or UW Seattle.

Many geoscience grad schools still place a lot of importance on the following sets of “traditional” geology classes:

• Mineralogy, Igneous and Metamorphic Petrology (or Earth Materials), and possibly Geochemistry – identifying rocks and minerals and understanding how they form
• Sedimentology and/or Stratigraphy – how to reconstruct past environments through geologic time
• Structural Geology – folds, faults, and deformation
• Geomorphology – recognizing and interpreting surface features
• Field Camp – where you learn good practice in the field, how to interpret 3D relationships between rocks, and how to make maps

Of these, we teach Earth Materials, Sedimentology, and Geomorphology at UW Tacoma every other year, so be sure to look for them in the schedule. You may be able to get Environmental Chemistry to count as a geochemistry course  – it’s called “Aqueous Geochemistry” at many other schools.

Field camp is often a sticking point for students. It’s a big time commitment – usually 6 weeks in the summer, spent somewhere with lots of exposed rocks (I did mine in Montana and Wyoming). Although UW has a field camp, very few UW Tacoma students have taken it: the course (ESS 400) has stratigraphy and intro geomechanics/structural geology as prerequisites. You can do a field camp through another institution: look for one that accepts students from all institutions (many do), has prerequisites that you can fulfill, offers college credit, and is at a time that you can attend. Here is a list of field camps that you can check out. Southern Illinois University and University of Houston are good bets.

In addition, many grad schools require you to have a strong background in sciences other than geoscience. Many require a year of chemistry, a year of calculus-based physics, and a year of calculus. Chemistry isn’t a problem for our students – it’s required – but physics and calculus are beyond our degree requirements (although our pre-med students do take them). We’ve been trying to improve student support through the chem, physics, and calculus collaborative learning courses: those might be worth looking into to solidify your experience in these fundamental course series.

By the way, many grad programs have some sort of a GPA requirement, usually around 3.0 I didn’t note on my list of grad programs, but maybe I should have. This requirement is something to keep in mind, but don’t let it get you frustrated. Many programs consider only your major GPA, or only your GPA during your last two years of college. Honestly, GPA isn’t a great predictor of success in grad school, so I wouldn’t be surprised if it becomes less and less important in admissions. This isn’t a reason to slack off, just an acknowledgment that your GPA depends on a lot of factors, some of which you don’t have control over.

### Timing

Graduate school applications are typically due sometime between December and February. Every school is different. A few schools have a second deadline for students who want to start in the Spring. Some of the later admission deadlines come with the warning that students who apply late are not guaranteed financial support (whereas students who apply to the earlier deadline are).

Because grad school applications are due around the time of Winter break, it’s worth making a work-back plan for your application. As early as you can – up to a year before you apply – let your undergrad professors know what you’re doing and what your plans are. Starting in September (or even earlier), look into grad programs and start contacting faculty and students. Check the GRE schedule: you may have to register as early as September to take the GRE early enough to send your scores to the places you’re applying. Start writing your applications (and take the GRE) later in the fall, around November. Keep in mind that you may have one or two essays, in addition to a resume, transcripts, letters of recommendation, and maybe other materials, to send to the schools you apply to. If you’re applying to 4-5 grad programs, that may be a lot of work around finals and winter vacation.

### Where should I apply?

This is a tough and personal question. You are trying to find an advisor who is a good match for you, at a program that offers the degree you want, in a school that fits your needs. At the MS level, I’d put equal weight on the advisor and the grad program itself. If you’re looking to do a PhD, I’d focus a bit more on finding the right advisor. This is because MS degrees typically involve more coursework (determined by the grad program) than PhDs do. PhDs are more focused on developing your independence as a researcher, which most programs do (for better or worse) through individual mentoring. In both MS and PhD programs, you also have to consider factors like geography – do you want to (or need to) be in a particular area? – and financial support.

As a side note: I’d recommend looking at schools that allow you to switch between advisors, or that encourage you to do a “rotation” (like med schools do). I arranged to rotate when I got to grad school – it wasn’t officially sanctioned at Scripps – but it was helpful. After working in three different labs – programming computer models of sand dunes, studying clays in fault zones, and cooking up synthetic magnetite – I found a good fit. It helped that I had a department fellowship my first year, so I wasn’t beholden to any individual professor for funding. This can really help if you end up with an advisor with whom you don’t get along (fortunately not the case for any of the labs I worked in), or, even worse, an advisor or labmate who is engaged in harassment or other unethical behavior (also fortunately not the case for me!). For me, it was a question of which field of geoscience was most exciting and which advisor was the best match for my personality. I had a tough time narrowing it down at first.

### Making Contacts

Once you’ve found a school that interests you, you’ll need to make contact with faculty there to find a potential advisor. This is really the beginning of the application process itself, and is often the hardest part of applying to thesis-based grad programs. Jacquelyn Gill has some great suggestions in a blog post from 2013 called “So, you want to go to grad school? Nail the inquiry email”. Read her post and the comments! Brian Romans at Clastic Detritus also has a pretty good guide with some similar suggestions. What follows are a few of my suggestions that really just embellish on what Gill, Romans, and their commenters wrote.

Generally, in that first email, you don’t ask a potential advisor if you can work for them. Sometimes people use the phrase “opportunities in your lab” (Dr. Gill’s recommendation). I remember asking potential advisors whether they were “taking on new graduate students” (be sure to specify MS or PhD!). There are all kinds of reasons why a faculty member might not be interested in taking on more students. The faculty member might be close to retirement, they might be running low on grant funding, they might be getting ready to go on sabbatical or maternity leave, or they might have too many current students to pay adequate attention to one more. It’s often worth following up with faculty even if they aren’t taking on new students or don’t have opportunities in their lab, though: sometimes, faculty members can point you toward someone else at their university – or even elsewhere – who has opportunities in their lab.

### The GRE

Nearly all of the schools I looked at require you to take the general GRE. While the GRE doesn’t factor into graduate admissions as heavily as the SAT does into college admissions, it is still required. Many schools have a minimum score required for admission, but that’s not always a hard-and-fast rule. Do prepare for the GRE, though: our Writing Center, for example, offers workshops to prepare you for the written portion of the exam. There are also plenty of books available that give you an idea of what to expect from the rest of the exam. It’s not worth spending a lot of money for a prep course, but it is worth spending some time preparing so you’re not caught unaware.

I took the subject (geology) GRE when I applied to grad school, but that was in 1997. It was tough: there were a lot of questions about hydrogeology and economic geology, and I’d never taken those courses! Now, fewer grad schools require subject GRE scores. In fact, I don’t recall seeing any of the schools on my list with a geology GRE as a requirement. So I would not bother with the time, money, and stress of the subject GRE.

GRE scores are valid for five years after your testing date, so it’s best to take the test when you’re close to graduating, even if you’re planning to wait a year or two to go to grad school.

### Closing Thoughts

Graduate schools and the faculty in them want motivated students like you to apply. Most good advisors consider training grad students – like you – to be an investment in the future of their field, and many consider it a personal honor to have a grad student go on to become successful. So they want you to succeed. But they are also risk-averse, and many faculty at research institutions are hesitant to accept students from institutions they don’t know (read: from places other than big research schools). This means that as a student from UW Tacoma, you will probably have some extra work to do in order to convince potential advisors that you are motivated, and that you are likely to be successful. Building a network of people who know you, know your work, and can support you in the application process (and afterwards, in grad school) is therefore crucial.

Before you apply, it pays to find out as much about grad school in general and about the specific schools you are applying to. I haven’t read it, but Bonnie recommends Getting What You Came For: The Smart Student’s Guide to Earning an M.A. or a Ph.D. by Robert Peters [Amazon, UW Library].

Whatever you do, don’t go to a grad school on the basis of the US News rankings!  I won’t even post them here because they aren’t worth reading. Grad school is an individual, subjective choice: one school or advisor may be good for one person, but terrible for another.

I plan to add a separate post with a resource list as I find more.

Accounts to follow on Twitter – These are just to get you started. There are LOTS more out there.

• Follow these accounts to get an idea of active research topics in academic geoscience (and help in finding potential advisors):
• Earthquakes and seismology: @DrLucyJones, @PNSN1, @seismoguy, @IRIS_EPO, @paleoseismicity, @MikaMcKinnon, @seismogenic
• Volcanism, igneous rocks, hard-rock geochemistry, and planetary science: @MeagenPollock, @AlisonGraetting, @StrangeIsotopes, @volcanojw, @davidmpyle, @volcanoclast, @eruptionsblog, @Tuff_Cookie, @sumnerd
• Paleomagnetism: @Orocline, @NanoPaleoMag, @ltauxe (my advisor!), @beckestrauss, @smtikoo
• Climate: @PdeMenocal, @ClimateofGavin, @coralsncaves, @ClumpedIsotopes
• Tectonics, deformation, metamorphism, geophysics: @seis_matters, @rapiduplift, @KeepItRheol, @TectonoAndy, @OpenTopography, @CPPGeophysics, @callanbentley, @allochthonous, @stressrelated, @metageologist
• Paleontology: @TomHoltzPaleo, @leafdoctor, @IceAgeEcologist
• Groundwater and surface water: @highlyanne
• Sedimentology: @clasticdetritus, @ZaneJobe, @climbing_ripple, @bedform, @zzsylvester
• Rotating-curator and variety accounts: @geoscitweeps, @RockHeadScience, @OnCirculation
• On academic survival: @youinthelab, @researchwhisperer, @raulpacheco, @smallpondscience, @hormiga
• Groups: @VanguardSTEM, @BLACKandSTEM, @UWTFellowships, @SACNAS, @UWsacnas

Here are a few articles in case you’re curious what am thinking about when I try to guide you through the grad school admissions process. Note that some of these are really in the weeds from your perspective as a student, but they’re what’s on my mind while writing this series… in case you want to know.

Articles

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I’ve had a few students discuss grad school with me lately, so I thought I’d offer my thoughts via the blog and open it up for comments. This is the first of a series of posts where I’m going to try to address some of the concerns that our students might have, specifically when applying to geoscience or oceanography programs. I’m going to start at the root of the problem: do you really want to (or need to) go to grad school? Please leave some comments if I’ve missed anything, or if I’ve got something wrong!

You need to decide whether grad school is right for you. So far none of my students have been lukewarm about grad school plans after graduating: either they want to go, or they don’t. Either is OK with me. I don’t want to see students deciding to go to grad school because it seems like “what you do” after college. If you have a plan, and go in with open eyes about what you want after your grad degree, you’ll be much happier. Unfortunately, many of my students want to go to grad school, but can’t do it right after college. Sometimes that means they never go. I’m going to address that in a separate post, because it’s kind of a big deal.

But figuring out whether grad school is right for you might be tough, particularly if you’re not familiar with what you can do with a geoscience degree. Are you interested in getting out into the field? An undergraduate degree, with field experience, might be OK for field technician jobs, such as those with the USGS. Experience does count, and it is possible to advance toward a career with a combination of a BS (or maybe a BA) and on-the-job experience. Developing some specific technical skills as an undergrad – in the context of your capstone project or in your classes – will help you get the foot in the door as a college graduate.

Are you interested in working as a consultant or at a state or federal agency? An MS, in those kinds of positions, shows that you are able to work independently and to take the lead on projects, making you more employable. You may additionally need a Professional Geologist’s (PG) certification – a subject for a later post. Are you interested in working in or managing a research lab? An MS or PhD is usually required for managerial-level and skilled lab positions (for example, operating an electron microscope or a paleomagnetic lab). MS-level positions are typically higher-paying than BS-level positions.

Do you want to teach? Elementary through high school education requires an education degree after your Bachelors. Several of my students have gone on to K-12 education, and it makes me incredibly happy to see UW Tacoma graduates teaching in the Tacoma Public Schools (particularly in science). Teaching science at the K-12 level requires a science degree and a teaching credential. If you want to teach in a 2-year college, you’ll need at least an MS; 4-year colleges typically require a PhD for tenure-track (more secure) positions, and may require it for non-tenure-track (often more precarious) positions. If you want to teach college, try getting teaching experience as a graduate student. Also be aware that any full-time college faculty job involves more than teaching.

I intended this post to lay out the foundation for a series on grad school. Keep an eye on this space for posts focused on the courses you need to take as an undergrad, how to apply to grad schools (including timelines!), how grad school classes are different from undergraduate classes, and a list of helpful resources. In the meantime, you can answer these questions in the comments below:

• If you’ve been to grad school, what do you wish you knew beforehand?
• If not, what are you most concerned or curious about regarding grad school?

Image: Lock and key, from Arthur Mee and Holland Thompson, eds. The Book of Knowledge (New York, NY: The Grolier Society, 1912). https://etc.usf.edu/clipart/4500/4514/lock_1.htm Honestly, I can’t find a good grad school image, so this metaphor will have to do.

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## Undergrad Research Symposium Abstracts: Coming Up!

Presenting at the Undergraduate Research Symposium in Seattle (the “URS”) is a great opportunity to show off your work, and to get useful feedback from a broader range of perspectives than you’d get in the UW Tacoma program alone. It’s a good chance to network, too, if you are interested in a job or grad school in Seattle. The first step in participating in the URS is to write and submit an abstract.

By the time you are ready to present at the URS, you’ll have had to write an abstract in TESC 310, and maybe even in 410 and some other courses, so the idea of an abstract is probably not a new one. But the specifics of URS abstracts need a little bit of explaining. Fortunately, the Undergraduate Research Program has a good website about abstracts, and runs workshops on abstract writing (including one that has been recorded in case they don’t have one at UW Tacoma). Here are a couple of things to keep in mind:

• Abstracts have to be 300 words or less. That’s SHORT!
• Abstracts should be written for a general audience. Don’t assume the audience knows the context you’re talking about: try to focus on the big picture. Also avoid jargon (if you have to use a technical term, such as “magnetic anisotropy”, use it when you describe your methods).
• One nice way to indicate the sentence where you’re reporting results is to use a phrase like “Here we show that…” (you don’t need to use those words exactly).
• We usually talk about an “hourglass” structure to an abstract. If you’re really ambitious, consider your abstract as a story. Science communicator Randy Olson boils it down to the “And/But/Therefore” framework. Could you describe your work in this format?
• The sooner you have your abstract done, the better. The URS staff send back abstracts that are poorly written or not for a general audience. You’d have to rewrite it if you do. I will read your abstract before it’s accepted, too, and if the facts aren’t right or the interpretation isn’t justified, I’ll make you rewrite it. So: better to get that done in the draft stage!

Good luck! And let me know if you have any problems.

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## Lab Fun

Lest you think all we do in my lab is mess around with magnets, I’m posting a few tweets with photos of today’s lab barbecue! Bonnie and I have an annual summer party for students, alums, and associates in our labs. Unfortunately, my camera is broken, so I have to rely on photos taken by Bonnie and her student Megan, at the links below. Geoduck! Grilled oysters with bacon! Chocolate Olympia oysters, ammonites, and trilobites! A good time was had by all.

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## Magnetic Susceptibility

My students and I are preparing to go up to Bellingham on Thursday to do some work in the paleomagnetic lab up there, so we spent today’s lab meeting getting everyone acquainted with the data they are going to collect. I started explaining something in the lab meeting that I thought could use a demonstration. So here it is.

Rocks might have lots of different magnetic particles in them. They might contain magnetite, an iron oxide that forms in igneous and metamorphic rocks as well as in soils; they might contain titanomagnetite, a common  consitituent of oceanic basalt; they might contain maghemite that formed as magnetite was oxidized — rusted — by weathering, or they might contain maghemite that formed in soils; they might contain hematite or goethite, indicating soil formation in dryer or wetter environments… there are even rock-forming minerals like pyroxenes and micas that are magnetic to a certain extent. In addition to forming in different environmental conditions, all of these minerals have particular quirks in their record of Earth’s magnetic field. So we need to be able to tell the kinds of magnetic minerals apart.

One way we differentiate between magnetic minerals is by their response to weak magnetic fields. So I tried a little experiment. I put a bunch of different materials inside a wire coil. I could send a current through the coil, producing a (weak) magnetic field at the coil’s center. I also set up a magnetometer to measure the magnetic field just outside the coil.

Why might the field inside the coil be different from what I measure with the magnetometer? This is a secret that is not addresed in the physics textbook we use in Physics II: there are two different ways of describing magnetic fields. We call the magnetic field that the magnetometer $\vec{B}$, and we measure it in Tesla. But there are two kinds of things that produce that magnetic field. One is the current through the coil, and the other is whatever is inside the coil (or outside it but close by). So we say that there is an applied magnetic field (applied by the coil to whatever is inside it) as well as a little bit of extra magnetic field due to whatever we put inside the coil. In physics terms, we call the applied magnetic field $\mu_0\vec{H}$, and the bit of extra field from whatever is in the coil $\mu_0\vec{M}$. Both of these are measured in A/m. We say that:

$\vec{B} = \mu_0(\vec{H}+\vec{M})$

There are two ways you can get a little bit of extra field from putting stuff inside the coil. A large number of Earth materials become magnetic when you put them in a magnetic field, but then revert to what most people would call “non-magnetic” when the magnetic field is turned off. For example, if you put an iron-bearing garnet crystal inside an area with zero magnetic field, it wouldn’t attract a compass needle. But as soon as you turn the magnetic field on, the compass needle begins to deflect – ever so slightly – toward the garnet. We call that garnet paramagnetic. Other minerals, like quartz, are diamagnetic: put them in a magnetic field, and the compass needle deflects away from the mineral. For both paramagnetic and diamagnetic materials, the effect on the compass disappears when you shut off the magnetic field you’ve applied. We call this an induced magnetization.

Some materials also have a remanent magnetization – a magnetization that remains after the $\mu_0\vec{H}$ field is switched off. Magnetite is a good example of this. Besides behaving like an induced magnet, magnetite also has induced magnetic behavior.

So: I took pieces of a bunch of different materials – steel, teflon, hematite, and various other minerals – and put them in the middle of the coil to see what would happen to the magnetic field as I increased and decreased the current. I tried the mica in two different directions (with the edge pointed toward the magnetometer, and with the flat face 45° from the magnetometer) to see if there was an effect.

Here is a plot illustrating the response of these materials to the magnetic fields produced in the coil:

The first thing you might notice is that all materials, more or less, make a linear trend on this plot. So the total magnetic field is proportional to the applied field. The biggest effect is in the bar magnets: they are ferromagnetic (the line of points does not intersect the origin, meaning that there is some magnetic field that remains when you turn off the $\mu_0\vec{H}$ field). The rest of the materials have a different slope, varying between low (Teflon) and high-ish (empty sample holder, keys, nail).

The ratio between applied magnetic field and a material’s (induced) magnetization is called magnetic susceptibility. It is given the symbols k, κ, or χ. If you were to measure magnetic susceptibility carefully, you could identify differences between these minerals – perhaps even between the different orientations of the mica. To do that, you need to have a good idea about what the response of your magnetometer would be if your coil were empty. That’s your model for how your measurement device works. It’s just a linear equation here: $y = m x$ (using the variables we have here, $B = \chi_0\mu_0H$). You can then subtract your prediction based on the empty coil model from all of your $\vec{B}$ magnetic field measurements to see whether the stuff you put in the coil is adding to $\vec{B}$ (ferromagnetic, paramagnetic) or decreasing it.

Here is what you get when you subtract out the empty sample holder’s response:

On these graphs, a positive slope indicates a material that behaves as a paramagnet; a negative slope indicates a diamagnet. Most of these materials behave like a combination of the two – not a particularly steep positive slope (except for the bar magnets) and a variety of negative slopes. The Teflon rods have the steepest negative slope because they contain the most diamagnetic material. Because ferromagnetic materials retain a $\vec{M}$ when the applied magnetic field is reduced to zero, their behavior shows up as a vertical offset of the whole graph, as seen in the bar magnets and in the hematite, below:

Here is the R code for the graphs:

…and the data file.

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## How Old is Earth’s Inner Core?

This post summarizes a publication in the journal Nature (note paywall):

Biggin, A.J., Piispa, E.J., Pesonen, L.J., Holme, R., Paterson, G.A., Veikkolainen, T., and Tauxe, L., 2015, Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation: Nature, v. 526, no. 7572, p. 245–248, doi: 10.1038/nature15523.

Earlier this month, an article about the age of Earth’s inner core made a big splash on both traditional and social media. The early history of Earth’s core – and particularly the inner core – aren’t things that scientists understand particularly well. Nonetheless, the question of when the inner core formed is a part of bigger questions about how Earth got here and what makes it unique.  We think that the inner core began to form once Earth had cooled a certain amount after its fiery infancy [1]. The inner core, then, is a sort of a thermometer for the early Earth: knowing exactly when the inner core started to form gives us some insight into just how hot Earth was shortly after its formation [2]. And I’m talking really hot here – magma oceans, not global warming. Other aspects of Earth that we consider more or less unique would have developed once Earth became cool enough. Plate tectonics and life are two examples.

Geochemists have fairly strong evidence from isotopes of the elements Hafnium and Tungsten that Earth’s metallic core must have formed in the first 50 million years of our planet’s history [3]. Earth has an unusually large core for a planet of its size. We think this is at least partially due to a Mars-size rock that plowed into the Earth early in the Solar System’s history. Computer simulations of this planetary collision indicate – and geochemistry confirms – that the event would have spun off some rocky material, becoming the Moon. The denser, metal-rich stuff left behind in the crash would have migrated toward the center of the developing Earth, forming our oversized core.

The origin of the inner core presents a bigger problem. Right now, we know about the inner core from the patterns of seismic waves that travel from one side of the Earth to the other, crossing different parts of the core. But seismic waves are ephemeral, dissipating soon after we record them. There are no seismic records from Earth’s past.

Earth’s magnetic field, generated in the fluid outer core (the geodynamo), might give us some clues about when the solid inner core formed. It takes some energy to generate Earth’s magnetic field. In the modern Earth, we think that the growing inner core powers the geodynamo: as the iron-nickel inner core crystallizes, light elements are spit out into the fluid outer core. The density difference between the sinking iron and nickel and the rising light elements, along with the temperature difference between the hot core and relatively cold mantle, cause the outer core to churn like a boiling pot of soup on the stove. This vigorous churning – thermal and compositional convection – produces a strong magnetic field relative to those of most other terrestrial planets. Without the inner core to drive the compositional part of the convection, the core would need to be very much hotter if we wanted it to produce a magnetic field like the one we have today.

Unlike seismic waves, we do have a record of magnetic fields from very old rocks. Since about the 1980s, geophysicists have been trying to identify patterns in the waxing and waning of Earth’s magnetic field over the billion-year timescales that we would need to look at planetary evolution. If we can identify a time when Earth’s strong and relatively stable magnetic field switched on, the reasoning goes, we might be able to tell when the inner core began powering the geodynamo.

I hedge my bets here about the magnetic field-inner core connection because of two main problems: first, it’s hard to measure the strength of Earth’s magnetic field in the past, and second, Earth’s magnetic field has varied through time due to a number of factors besides the inner core.

As far as the first problem goes, we have to make a lot of assumptions when using old rocks to look at Earth’s magnetic field. We assume that the rocks recorded Earth’s magnetic field reliably in the first place, through processes that we understand well. We assume that rocks are able to hold onto their magnetization for billions of years. We assume that the same rocks have not been remagnetized or demagnetized throughout their long histories. Although we have ways to test some of these assumption, our ability to do the tests depends on geological circumstance – whether the rocks contain certain dateable minerals, whether they have been folded or broken up and re-cemented together, or whether they are crosscut by more recent rocks, for instance. Even for young rocks, reading the strength of Earth’s magnetic field is much harder than looking at the direction of the ancient magnetic field (more on the specifics in a later post). Add to that the fact that rocks that have been around longer are generally more likely to have been re-magnetized, and you have a lot of reasons to doubt the paleomagnetic record of multi-billion-year-old rocks. For this reason, Andy Biggin and his co-authors on the recent Nature paper are choosy about which published data they use for their analysis [4]. Unfortunately, because of the problems mentioned here, and because there just aren’t many old rocks to choose from, reliable data on Earth’s magnetic field from the first four billion years of Earth’s history are few and far between. This is not the fault of the paper’s authors: reliable as the data may be, there are a lot of gaps. There are almost no useful data from the time interval between 300 million and one billion years ago. If you consider only the most reliable ancient field data from very old rocks – as Biggin et al. do – it is still difficult to draw a convincing long-term trend, since the estimates of Earth’s magnetic field strength vary widely for any particular range of ages. Nonetheless, in the set of data discussed in October’s Nature article, the average magnetic field estimate for the time period between  1.4 and 2.4 billion years ago is lower than that of the chunk of time between 0.5 and and 1.3 billion years ago. So perhaps we should be looking at rocks between 0.5 and 2.4 billion years old for other indications that the inner core formed. We also need to work at sorting out long-term trends from short-term variations for these very old rocks.

The second problem with the magnetic field-inner core connection is that Earth’s magnetic field is sensitive to things besides the growth of the inner core. For example, we think that the geographic pattern of hot and cold spots at the boundary between the mantle and the core might influence geodynamo activity [5]. We see this effect in both the intensity and in the reversals of Earth’s magnetic field. The hot and cold spots are related to convective motion in the mantle and perhaps to old, cold chunks of tectonic plates that have sunk over hundreds of millions of years. This would mean that the strength of Earth’s magnetic field may change on the few-hundred-million-year time scales associated with plate tectonics. Biggin et al. average data over long time periods to get rid of these fluctuations – akin to averaging weather variations to look at climate – but they acknowledge that especially long-lived patterns of heating and cooling may influence their averages. The further we look back in time, the fewer assumptions we can make about plate tectonic activity and its consequences. A electrically conductive molten layer of rock that may have blanketed the core early in Earth history (a “deep magma ocean”) could also have affected the early geodynamo [6]. More importantly, although geophysicists have made incredible strides over the past decade simulating core behavior, it’s not entirely clear how the average intensity of the magnetic field is related to the power driving the geodynamo. My impression (as a non-modeler) is that modelers agree that if the power available to move stuff around in the outer core drops below a certain lower limit, the geodynamo would shut off. But does more power necessarily mean a stronger field? The intensity of Earth’s field is not the only indicator of geodynamo activity. We might seek clues from other aspects of Earth’s magnetic field, such as how often the North and South magnetic poles switch, the rate at which the poles move, or the degree to which Earth’s field is similar to that of a bar magnet (Biggin et al. do explore the latter issue to a certain extent).

All of this is to say that, while the Nature article represents the best of our knowledge right now, there’s still a log way to go before we can conclusively say when the inner core formed. We are much closer than we were when I was a graduate student (when I graduated in 2003, only about 36% of the studies used in this paper had been published [7]). This is an exciting time to be a paleomagnetist!

[1] Rubie, D.C., Nimmo, F., and Melosh, H.J., 2007, Formation of Earth’s Core, in Treatise on Geophysics, Elsevier, p. 51–90.

[2] The Earth may have got rid of some of its initial thermal energy before the core formed.

Stevenson, D.J., 2007, Earth Formation and Evolution, in Treatise on Geophysics, Elsevier, p. 1–11.

[3] Basically, radioactive Hafnium-182 preferentially goes into molten metals, whereas its decay product, Tungsten-182, stays in rocks. Comparison between Tungsten-182 concentrations in meteorites and the Earth indicates that the radioactive Hafnium-182 must have separated from the mantle about 50 million years after Earth initially formed.

Lee, D.-C., and Halliday, A.N., 1995, Hafnium–tungsten chronometry and the timing of terrestrial core formation: Nature, v. 378, no. 6559, p. 771–774, doi: 10.1038/378771a0.

Rubie, D.C., Nimmo, F., and Melosh, H.J., 2007, Formation of Earth’s Core, in Treatise on Geophysics, Elsevier, p. 51–90.

[4] The Nature paper that I’m discussing here is a meta-anlaysis, meaning that it analyzes data collected in many studies to draw a broad conclusion. The authors rate estimates of magnetic field strength from 53 studies on a scale (QPI) according to how many assumptions have been verified in the experiment and field work of the original study. Most studies published these days get about a 3 out of 6 on the QPI scale. More about the types of experiments – called paleointensity experiments – in a future post.

[5] Although there has been more recent work on this topic, here’s the original reference:

Glatzmaier, G.A., Coe, R.S., Hongre, L., and Roberts, P.H., 1999, The role of the Earth’s mantle in controlling the frequency of geomagnetic reversals: Nature, v. 401, no. 6756, p. 885–890, doi: 10.1038/44776.
[6] Ziegler, L.B., and Stegman, D.R., 2013, Implications of a long-lived basal magma ocean in generating Earth’s ancient magnetic field: Geochemistry, Geophysics, Geosystems, v. 14, no. 11, p. 4735–4742, doi: 10.1002/2013GC005001.
[7] Just for my own interest, I plotted up the number of studies and the number of magnetic field intensity estimates from the dataset that Biggin and co-authors use. The graph shows how many of these studies (and field estimates) of different quality indices have been published each year. There’s a definite shift from publishing papers with few assumptions justified (QPI 1 or 2) to those with more checks (QPI 3 or above)! I do wonder how many more rock units are available for study – sounds like a useful GIS project!

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## Updating Site

I’m in the middle of updating this site with a new theme and more photos. Please bear with me as I re-attach photos to blog posts.

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## Getting Involved in Undergraduate Research

Almost 20 years ago, I was lucky enough to be a student participant in two undergraduate research programs – the Keck geology consortium and Caltech’s SURF program (full disclosure: I didn’t participate in all aspects of the SURF program). The Keck program in particular involved a summer spent mapping and studying gabbro [1] on the island of Cyprus – a fragment of old ocean crust. That project introduced me to independent fieldwork, paleomagnetism, study design in geology, and a large network of friends and mentors. Some members of that network would later become collaborators and my Ph.D. advisors. Many of my friends became geoscientists.

If you are an undergraduate science student and have the chance to do a research project, I can’t stress how important it is to take that opportunity. Whether or not you end up in science, you develop experience, skills, and personal connections that will help you later in life. If nothing else, you get to find out if a particular area of science is right for you. While this experience is associated with a bit of a sacrifice – particularly for many of my students who have family and/or work obligations during the summer – there are some programs that will work with you to make it easier. Some offer a stipend, and others might be located near where you live or work and have flexible hours.

How do you find a good program? Here are some national programs in geoscience and environmental science that I recommend. If you’re going with a different one, I recommend talking to the faculty members involved to get a feel for how they mentor their students, how many students are involved, and what they think you’d get from the program. Also talk to former students if you can.

• GeoCorps: Paid internship opportunities to do geoscience in the National Parks and other federal sites. Requirements and application dates vary.
• The Summer of Applied Geophysics Experience through Los Alamos National Labs in New Mexico. A fantastic hands-on experience in environmental geophysics in the field. Requires a year of physics and calculus. Application date unknown.
• The Keck Consortium is still around! Although it’s run by faculty from liberal arts colleges, students from elsewhere have applied. However, outside applications are not an option for the upcoming cycle due to budget cuts. Requirements depend on the project. Application date unknown.
• The UNAVCO Research Experiences in Solid Earth Sciences for Students: learn about GPS, LIDAR, and other geodetic (earth-measurement) techniques in the field. Requirements include “some” physics, math, and geoscience, but are not very strict, as far as I can tell. Application opens November 16, 2015.
• Undergraduate Studies in Earthquake Information Technology through the Southern California Earthquake Center and the University of Southern California. This program is unique because it focuses not just on seismology, but on earthquake hazard communication, and on forming interdisciplinary teams to build ways (often online) to communicate earthquake hazard effectively. Application dates and requirements unknown.

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## Writing for this blog

I wrote an assignment for my students yesterday. I ask them to write a blog post (watch for those soon), and give them some guidelines for doing so. I thought it was worth putting up here both for public comment and because I think it’s a nice statement about what I’m trying to do here.

I highly recommend that everyone who goes through my lab learn how to explain their project to the public. This is partially because you’ll have to do it when you get to Senior Seminar (TESC 410). Evan more importantly, it’s because we scientists need to be better about engaging the public with our science. If we don’t, we run the risk of becoming the kind of caricature of a scientist you see in the movies: academics with no connection to the real world.

So, to make that connection with the public, we have a blog. Or rather, I do, since I’m the one who usually writes for it. I try to explain what’s exciting about my science in a way that college students taking an intro class (or any interested people at about that level) might understand. The audience I write for isn’t stupid, but they might not be familiar with the jargon we use as scientists and the kinds of graphs we show each other. They might not care about the details of my work, but they do care about what’s new, exciting, or potentially relevant. Why I do things is much more relevant than how I do them. My audience also cares about stories (I think), including stories about how science works for me.

There are no strict rules about writing a blog post. This is an assignment with no strict page limit or style guidelines. Really, it’s the ideas and how you convey them that matters. I’ve seen a lot of good material on how to run a blog in general. I’m collecting it below. Some of it might be helpful if you’re writing a single post. In the broader sense of communicating your science, I’ve found some useful guidelines in Nancy Baron‘s book Escaping the Ivory Tower. Baron directs an influential program called COMPASS that focuses on preparing scientists to better communicate with the public. Her book has a lot of useful information about how to make sure your science is relevant to different audiences (politicians, journalists, filmmakers, etc.).

One of COMPASS’s signature tools is the Message Box, a scheme for organizing your scientific ideas so you can pitch them to non-scientist readers. Working your ideas into a message box is hard. But it’s good preparation for writing a blog post. Plus it forces you to think about how your science s relevant… which is the whole purpose of doing it! If you want to give the message box a try, there is a template here.

Guidelines:

Aim for about a page of text, with an image. If you don’t have an image, I can help.
You can use informal language, but don’t be sloppy. People will read this.
Have you taken pictures? Drawn comics? Found places on Google Maps? Great! I’m a visual person, and I like having good images on the blog.
Aim to engage people rather than to explain. Stories are good.
Avoid jargon, but don’t dumb it down. Explain it when you have to. I think of my posts as initiating readers into the club of people who understand what I’m talking about.
Look at other blog posts for inspiration.

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## A Visit to the Gulf Core Repository

While at Texas A&M University for our postcruise editorial meeting [1] with some old friends from the Bengal Fan expedition, I took the opportunity to visit IODP’s Gulf Core Repository.

Fortunately, Curatorial Specialist Hannah Kastor, who sailed with us in the Bay of Bengal, was there to show us around the repository. Along with Michael Weber, my bunkmate from the ship, Hannah and I checked out the cold-storage facility that stores ocean drilling cores from the Eastern Pacific and Southern Oceans as well as the Caribbean Sea and Gulf of Mexico. There are also some surprises mixed in there.

[1] Although we spent many hours writing and editing our reports on the ship, we were under a lot of time pressure on the cruise. Fast writing isn’t necessarily good writing. So, typically, a subset of the scientists from a drilling expedition gets together after the expedition to edit the reports. We had the benefit of shorter shifts (not 12 hours! Yay!), good communication with the outside world, fast internet access, and an publications staff including editors and illustrators. Soon after we’re done, we should have a document that looks like this example from a previous expedition. It won’t be published for a year due to the post-cruise moratorium – we get a year’s head start on publications from our work – but you can read a summary here.

The editing session is also a bit of a reunion. It was great seeing friends from the ship again!