Are you looking for an undergrad research project, either for capstone credit (for UW Tacoma Environmental Science or Studies students) or for experience? We’re looking for new lab members! Here are a few ways you can get involved:
We’re finishing up some work using magnetic properties to look at sediment transport in mud from the Bengal Fan. We need someone who’s interested in doing some electron microscopy, and someone else who wants to hone their lab skills by separating sediment into size fractions (sand, silt, and clay) and analyzing magnetic properties. Both projects involve fun with big magnets, getting muddy in the lab, and going to the Geological Society of America conference in October. (The image from this post is a SEM element map from former student Aaron Burr’s capstone project; red is iron, blue is calcium, and green is silicon.)
Anybody interested in using magnetism to answer local environmental questions? Starting in late August, I’ll be looking for some students to determine magnetite content in some soil cores for a groundwater hydrology study.
We’re also hoping to start some experimental projects and fieldwork this year aimed at learning how transport through natural (river and dry grassland) and built environments might change the size distribution of magnetic particles in sediment. These projects are going to have some outreach and citizen-science components.
Contact me for further details: paselkin at uw dot edu.
Here is a tweet from a geologist halfway around the world about an art exhibit less than an hour from me. That’s a fun connection. But also: how often do you get to see a geology-themed art exhibit? I had to go.
I had the chance to go to that exhibit (The Contact: Quilts of the Sierra Nevada by Ann Johnston) today, the day before it closed. The Bellevue Arts Museum was mostly empty, and I went alone, so I got to take my time and look closely at the fabric art, which spanned the entire third floor of the museum. The exhibit benefited from close inspection: there’s even more geology in the works on display than I’d originally thought. Plus, downstairs was an exhibit of new works by emerging glass artists that had some interesting petrologic parallels.
What struck me was the degree to which an understanding of the geology informed the artwork. These quilts weren’t simply illustrations of geology: they were a way to deeply understand a landscape, both through analysis and creation. Apparently, Johnston’s family own the rights to a mining claim in the Eastern Sierra Nevada – it’s delineated with a thin thread on this quilted geologic map. I can imagine that , having grown up with this claim in the family, someone who is both an artist and a geographer (as Johnson is) would want to explore it from both perspectives.
A lot of my own work deals with fabric in the geologic sense: the arrangement of mineral crystals in a rock. In this sense, fabric is a three-dimensional thing: something that pervades a rock but may change from one part of an outcrop to another or even across one hand sample. Fabric is also something that, most of the time, you need to look closely at to be able to interpret. I was impressed by the detail and three-dimensionality of the (textile) fabric in this exhibit. In most of the pieces, the stitching added a layer of information beyond the fabric’s dye and reflectivity – in the same way as a rock’s fabric gives a geologist information beyond the rock’s composition.
For more images, click the gallery below.
The Contact: Eureka Chimney (2013): Stitches in this quilt of a collapsed mine tunnel add 3-dimensional detail to the piece. This patterning, while it doesn’t look exactly like a realistic rock fabric, has some of the same features. I especially like the detail on the tan and white blocks on the left edge of the quilt.
The Contact: 07.25.12 19:55 (2015) – I especially like how the stitches differentiate between the dark, fractured rock (gabbro?) in the foreground, the rock across the lake, and the sky.
The Contact: Cirque 1 and Cirque 2 (2016): The same cirque (glacially-carved amphitheater) at different times of day.
The Contact: Cirque 2 (2016): The detail here is amazing. Notice how the stitches take jogs to indicate slight changes in topography – stream valleys?
The Contact: Nevadan Orogeny (2011): Both the stitching and dyeing/printing here are incredibly detailed. The Nevadan Orogeny was a mountain-building event in the Jurassic and Cretaceous, during which the Sierra Nevada was probably a range of high mountains and active volcanoes, much like today’s Andes. The buckling and warping of the stitches, and the twisted, slashed fabric gave me a visceral impression of the forces at work down deep as a mountain chain rises.
The Contact: Vertical Joint (2013): I like the light and dark here, and the grain that the stitching makes. The fabric itself is spattered with dye or paint to illustrate crystals. The spattered fabric seems more plausible as rock here than in some of the other pieces – I can’t quite put my finger on why.
The Contact: Sierra Honeymoon (2015): I never thought of rocks in a particularly romantic way, but here two rock types (a darker one, presumably a gabbro, and a lighter, granitic rock) are held together by a few thin intrusions. The other side of this quilt is a sunset scene, with two figures silhouetted atop a ridge. Maybe one can take a metaphor too far, I don’t know. But to my unromantic mind, the two intrusions remind me that we geologists sometimes call magmatic bodies that cross two disparate regions of rock “stitching plutons,” making this a visual pun.
The Contact: Inside Granite (2015): This is a pretty faithful view of what you’d see in a microscope when looking in polarized light at a thin section of a granitic rock, like those from the Sierra Nevada. Much of the gray and white is supposed to be quartz or potassium feldspar (microcline; probably the gray at the bottom). There is a striped piece of plagioclase feldspar on the right, and what looks like biotite mica crystals in shades of orange, red, and green on the left. The black may be an oxide mineral – I’m not sure. I love how Johnson uses the stitching and color here to emphasize both the minerals’ microscopic structural features (cleavage planes of the mica, twin planes in the plagioclase) and the way the minerals’ shades change as you turn the microscope stage (called extinction; quartz and microcline fade in and out of black in a characteristic wave-like or patchy way – see the microcline crystal at the bottom).
The Contact: Inside Granite (2015): A detail.
The Contact: Cross Polarized Granite (left, 2015) and Cross Polarized Gabbro (right, 2014): Oh. My. Goodness. This is really what it’s like to look at these rocks in a polarizing (petrographic) microscope. But again, there’s more than that. The range of scales represented by pieces in this show is striking: these images represent crystals that are maybe a few millimeters long. In contrast, the areas that the geologic map and landscape quilts represent are several tens of kilometers wide. And yet the mineral grains here – the color fields and stitching patterns – are what produce the fractures and rock fabrics illustrated – also by color fields and stitching patterns – in pieces like Nevadan Orogeny and 07.25.12 19:55.
The Contact: Cross Polarized Gabbro (2014): Detail.
The Contact: Cross Polarized Granite (2015): My favorite detail of the whole show. This is a pleochroic halo (black) around a zircon crystal (blue). Zircon crystals often contain quite a bit of uranium. Particles produced from radioactive decay of the uranium damage the crystal structure of whatever is around the zircon crystal. This causes the optical properties of the damaged zone to change, often making a halo around the zircon crystal change colors as you turn it in polarized light. This play of colors is called pleochroism. It makes it easy to find zircon and other radioactive minerals, which can then be used to date the rocks they come from.
The Contact: 07.25.12 20:13 (2015): A sky like biotite…
Kim Brill – Plaza Blanca, New Mexico: Investigations (2016): From the Emerge 2016 exhibit. Glass art that looks geological. There’s a pretty huge overlap between glass art and experimental petrology.
Kiln-formed glass techniques, from the Emerge 2016 exhibit. More overlap between experimental petrology and glass art!
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?
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!
First of all, what is grad school? When I say “grad school”, it might mean a bunch of academic things you can do after you get your BS or BA. Usually, professors mean masters (MS) or doctoral (PhD) work – the standard “academic route.” Often, people get a MS and then, if they decide to go on, a PhD (I wish I’d done that). Sometimes students enroll in a PhD program directly after graduating college (I did), maybe getting an MS as part of it (I didn’t). An MS usually focuses on applying existing knowledge to a more or less well-defined problem. MS projects are in some ways like more complex, in-depth, super-sized capstone research projects. A PhD focuses on developing an independent research focus and expanding your field of science significantly beyond what’s already known. Besides the standard academic route, however, you might consider other graduate programs: there are graduate degrees in education (a teaching credential or an MEd), law (JD), medicine (MD, DDS, PharmD, DVM, MN, etc.), engineering (MEng), and technical degrees or certificates (GIS Certificate, Certificate in Wetland Identification and Delineation, Masters in Geospatial Technologies…), all of which can help get you into different careers – even ones with a geoscience focus. For the most part, though, I’ll be talking here about the MS/PhD route because that’s what I’m familiar with. I think students also need the most help with that pathway.
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.
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).
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.
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.
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 , 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 , and the bit of extra field from whatever is in the coil . Both of these are measured in A/m. We say that:
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 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 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: (using the variables we have here, ). You can then subtract your prediction based on the empty coil model from all of your magnetic field measurements to see whether the stuff you put in the coil is adding to (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 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:
materials<-c("Bar Magnets","Keys","Nail","Teflon Rods")
AP<-ggplot(data=DT,aes(x=Current..A.,y=Magnetic.Field..mT.))+geom_point(aes(color=Item))+facet_wrap(~ItemType)+scale_color_brewer(palette='RdBu')+xlab("Current (A)")+ylab("Total Magnetic Field (mT)")
MP<-ggplot(data=DT[ItemType=="Mineral"],aes(x=Current..A.,y=Magnetic.Field..mT.))+geom_point(aes(color=Item))+scale_color_brewer(palette='RdBu')+xlab("Current (A)")+ylab("Total Magnetic Field (mT)")
DP<-ggplot(data=DT[ItemType=="Empty"],aes(x=Current..A.,y=Magnetic.Field..mT.))+geom_point(aes(color=Item))+scale_color_brewer(palette='RdBu')+xlab("Current (A)")+ylab("Total Magnetic Field (mT)")+stat_smooth(method='lm',aes(color=Item,fill=Item))
models<-DT[,list(model=list(lm(Magnetic.Field..mT. ~ Current..A.))),by=list(Item)]
plotly_POST(AP, "All Materials, Magnetic Susceptibility")
plotly_POST(MP, "Minerals, Magnetic Susceptibility")
plotly_POST(MP+stat_smooth(method='lm',aes(color=Item,fill=Item))+scale_color_brewer(palette='RdBu'),"Minerals, Magnetic Susceptibility (With Trendlines)")
plotly_POST(DP, "Empty Holder")
AP2<-ggplot(data=DT,aes(x=Current..A.,y=Bcorr))+geom_point(aes(color=Item))+facet_wrap(~ItemType)+scale_color_brewer(palette='RdBu')+xlab("Current (A)")+ylab("Extra Magnetic Field* (mT)")
MP2<-ggplot(data=DT[ItemType=="Mineral"],aes(x=Current..A.,y=Bcorr))+geom_point(aes(color=Item))+scale_color_brewer(palette='RdBu')+xlab("Current (A)")+ylab("Extra Magnetic Field* (mT)")
plotly_POST(AP2, "All Materials, Corrected Magnetic Susceptibility")
plotly_POST(MP2, "Minerals, Corrected Magnetic Susceptibility")
plotly_POST(MP2+stat_smooth(method='lm',aes(color=Item,fill=Item))+scale_color_brewer(palette='RdBu'),"Minerals, Corrected Magnetic Susceptibility (With Trendlines)")
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 . 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 . 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 . 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 . 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 . 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 . 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 ). This is an exciting time to be a paleomagnetist!
 Rubie, D.C., Nimmo, F., and Melosh, H.J., 2007, Formation of Earth’s Core, in Treatise on Geophysics, Elsevier, p. 51–90.
 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.
 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.
 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.
 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.
 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.
 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!
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  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.
Please let me know about other opportunities in the comments. I’ll try to keep this list up to date when I find out more information about the programs above!