In my drive to get everything in the lab automated, I’ve set up a checkout system for the lab books. To check books in or out, use this form, or scan with your phone. Note that on the mobile app, you will have to type in your UW NETID, whereas on the browser form you will need to log in.
If you are a UW Tacoma student who uses Zotero as a reference manager (as I suggest my students do), you can now output a bibliography in the modified CSE format that we use in our science courses at UW Tacoma. The hallmarks of the modified CSE format are:
So, for example, here is a bibliographic entry in the standard CSE format:
Hodges KV. 2000. Tectonics of the Himalaya and southern Tibet from two perspectives. Geological Society of America Bulletin 112:324–350. [accessed 2015 Apr 14] http://gsabulletin.gsapubs.org/content/112/3/324.full
Note that the link won’t work unless you have access to Geological Socienty of America publications, which most students don’t at home. The link gets even more convoluted when you are trying to find an article through EBSCOHost or another repository that stores the articles behind a paywall. I see this all the time in student papers. So instead, using this format, you can reference the article as if you had it in print:
Hodges KV. 2000. Tectonics of the Himalaya and southern Tibet from two perspectives. Geological Society of America Bulletin 112:324–350.
Easier, huh?
Here is how to download the file to the Zotero Standalone application:
modified-council-of-science-editors-name-year-author-date.csl) and select it.Here’s the second in a series that explains the basic ideas in paleo-, geo-, and rock magnetism. I’m hoping to separate the real-life mysteries and wonder from the jargon that sometimes makes magnets seem like magic tricks. Have a question about any of these posts? Or about any aspect of paleomagnetism? I’d love to hear it. Please comment!
If you’ve taken an intro-level geology class, or if you’ve read much about magnetism, you have probably heard that Earth acts like a giant magnet because of something in its core. Earth’s core is a giant lump of metal at our planet’s center. We’ve never been there and have no samples of it, even though, as the crow flies, it’s just a little further from here than Chicago. We do know three important things about the core:
More on all of those later. We also think that Earth’s core the giant magnet responsible for Earth’s magnetic field. But here’s the weird thing about Earth’s core. When I say that the core is a “giant magnet,” I don’t mean it in the sense of the things that stick to your fridge. Although iron-nickel alloys like the core would probably stick to your fridge if they were suitably magnetized, they would lose their magnetic stickiness at the high temperatures deep in the Earth (more on that later, too). So how could the core be at such a high temperature and still be a magnet, producing Earth’s magnetic field?
The answer has to do with those giant electromagnets you might have seen at auto wrecking yards. These have an enormous coil of wire through which runs an electrical current. The electric current produces a strong magnetic field, allowing the coil to hold up big iron things like cars. In the Earth, though, the electric current isn’t passing through wires – it’s caused by the swirling around of molten iron in the outer core.
Earth’s core is more complicated than a coil of wire. In the wrecking yard, the coil of wire becomes a magnet when it’s hooked up to an electrical generator – forcing a current through it. In the Earth, the outer core is both generator and electromagnet [1]. Electrical generators work by moving conductive wires through magnetic fields. In Earth’s core, the flow of molten iron and nickel in the outer core moves the conductive material through Earth’s magnetic field instead. That is the same magnetic field produced by the electrical currents in the molten metal. This confusing process is an example of a feedback loop.
Physicists love feedback loops (as do other scientists and mathematicians). Physical systems with feedback behave in interesting ways. You could imagine starting the molten outer core flowing in a certain way under a very weak magnetic field, maybe from the Sun or something else. Suppose this situation is not strong enough to cause a big electric current in the core. Earth’s core, then, might not be able to sustain its electric generating activity for very long. Alternatively, you might be able to imagine a pattern in which the outer core fluid flows in a way that causes big electrical currents. such a pattern could make Earth’s magnetic field stronger as time goes on.
The flow of molten metal in Earth’s outer core is controlled by a bunch of other factors besides the magnetic field. For example, the outer core loses more heat where the mantle above it is cold [2]. The formation of the inner core, heat due to radioactive elements, and the rotation of the Earth, all make the behavior of the outer core very difficult to predict. The unpredictable behavior of the core can make Earth’s magnetic field strengthen, decay, wander, and even reverse itself. Nonetheless, over the past ten or so years, observations of Earth’s magnetic field through geological time have become numerous enough [3], and models of core behavior [4] have become precise enough, that we can draw some conclusions about some features of our planet’s core, which will be a topic for later. [5]
[1] Dynamo is another term for electrical generator. Earth’s outer core is sometimes referred to as the geodynamo. For more information on this topic, see Glatzmaier, G.A., and Olson, P., 2005, Probing the Geodynamo: Scientific American, v. 292, no. 4, p. 50–57, doi: 10.1038/scientificamerican0405-50.
[2] For example, we think that the lowermost mantle is cold where old slabs of subducted lithosphere have piled up. We can actually image this through a technique called seismic tomography (a topic for another day).
[3] The state of the art in crunching together high-resolution records of past magnetic fields is described in Korte, M., Constable, C., Donadini, F., and Holme, R., 2011, Reconstructing the Holocene geomagnetic field: Earth and Planetary Science Letters, v. 312, no. 3-4, p. 497–505, doi: 10.1016/j.epsl.2011.10.031. Definitely not beginner material.
[4] For information about a geodynamo simulation that includes reversals, see Gary Glatzmaier’s website.
[5] Want additional information? See David Stern’s The Great Magnet, The Earth.
When I tell people that I study the history of Earth’s magnetic field, I get a bit self-conscious – as if I just told someone I specialize in Santa Claus. Geologists call us “paleomagicians” for a reason. You can’t see magnetic fields. You can’t touch them. Unlike most geological stuff, nothing obvious happens if you hit a magnetic field with a hammer. Once you understand a few things about Earth’s magnetic field, though, it becomes a bit less mystical. In the next few articles, I’ll try to bring Earth’s magnetic field … um … down to Earth.
Number 1: Compasses line up with magnetic fields. Although you can’t see a magnetic field, you can see its effects. In the pre-GPS days, when we still used maps and compasses, we used those effects all the time. Compass needles (which are themselves magnets) line up with magnetic fields. One end of the compass needle is the “north seeking” end, which points toward Earth’s North Magnetic Pole [1]. But wait: Earth’s North Magnetic Pole is not its North Pole! And the North Magnetic Pole moves from year to year. Here is a movie showing the angle your compass would point (relative to True North… as in North Star North) at different places on Earth, over the past 400 years more or less. Scientists made this animation in part by looking through old navigation logs, matching ships’ compass readings with the same ships’ positions based on speed estimates (dead reckoning) and star sightings [2]. Keep an eye on the North Magnetic Pole – where the lines converge in the Northern Hemisphere – as it drifts aimlessly around the Arctic. How random is this drift?
We want to how Magnetic North changes through time because it helps us navigate. But that’s really not the main issue now that we have GPS. We want to know how Magnetic North wanders because it’s a puzzle, and because it brings up some even more fundamental puzzles about the Earth. Why does Magnetic North wander? Where has it wandered in the past? If we were to watch a compass for, say, a million years, would it point at the true North Pole on average? And what, if anything, does that wandering tell us about the Earth?
[1] Physicists (and geophysicists) represent magnetic field lines in a few different ways: as arrows that line up the way compasses would (field vectors), as lines that connect those arrows (field lines), or, confusingly, as lines that illustrate the strength of the magnetic field (contour lines). You can play around with some of these representations here.
[2] If you want to see the original work, it’s by Finlay and Jackson (2003) and Jackson et al. (2000). These are not meant to be entry-level papers.
Starting late next month, I’ll be at sea in the middle of the Bay of Bengal as part of IODP Expedition 354. Going to sea for months at a time is something new and exciting for me. I’m going to be blogging here about my experience, starting with preparations for the cruise. I hope that you, the reader, will find something here that excites you as much as it does me. I’m a paleomagnetist, which means that part of what excites me about this cruise is the chance to track Earth’s magnetic field through geologic time. So if I want you to follow me, I’ll have to explain why I think geological magnets are freaking awesome.
I’m also secretly hoping that you, reader, will hear me out when I make a fool of myself in front of my colleagues or get seasick (wait – do I get seasick?), because, frankly, I’m also a little terrified. The cruise is TWO MONTHS long. I’ve never been away from my wife and kids for this long before. I’ve never been to this part of the world. Research-wise, working with magnetism of sedimentary rocks is relatively new to me. I may be a scientist, but I’m a human being, too, and I may at times just need to connect with you people in the outside world.
