Archive | December 2014

Teaching Historical: The Big Ideas

OK, a lot of what has preceded this has been focused on the mechanics of the typical intro level historical geology class.  What are the big picture items that students should come away with?

At the broadest level, they are somewhere in the realm of knowing how we learn of the earth’s history from the rock record, knowing of the great changes in the earth over its history. Different instructors are apt to pick different aspects; one of our faculty didn’t include life history at all in their version of the class.  Courses often veer towards elements of geologic history evident in the vicinity of where the class is taught, so the Laramide is important in Colorado while the Acadian orogeny might merit more attention in New England. A less obvious element is to know how the different components of the earth system interact (solid earth changes affecting climate affecting life etc.).

A couple things strike GG as pretty essential for non-majors to understand.  One is the use (and potential abuse) of proxies.  There is no doubt that a full and rich understanding of proxy calibrations and errors is well beyond a typical intro class, but recognizing how geologists come to constrain elements of the geologic past–and how obtaining those constraints can be limited–is a piece of information that would better inform discussions of, for instance, how climates were different in the geologic past.

A second idea is the ability of the geologic record to inform us of long-term impacts of human activities independent of models [but usually not independent of proxies]. Right now, the Paleocene-Eocene Thermal Maximum (PETM) stands out as a shining example: pump carbon into the atmosphere and watch the ocean grow acidic and lead to marine extinctions, see it take more than 80,000 years for that carbon to get sequestered again and you gain some perspective on human carbon emissions.  Or take the increasingly strong evidence that the rate of climate change dictates extinctions more than the overall magnitude: the long increase in temperature through the Paleocene had less of an overall impact than the sudden rise with the PETM.

A third is the way that the different components of the earth system interact. Probably the classic one is the continued equable climate of Earth: even with a dim Sun the earth had liquid water on the surface.  Removal of carbon from the atmosphere by both organic and inorganic means has been essential.  Snowball Earth hypotheses illustrate this nicely (even if you don’t fully buy them). There is a good case to be made that the development of hard parts arose as the oceans grew richer in carbonate caused by massive erosion of continents prior to the Cambrian.

There are other ideas that might matter as much: the use of the historical record to anticipate disasters as diverse as landslides to supervolcanoes to meteorite impacts. Locating mineral resources is another valid topic. These are both pretty traditional. The concept of feedbacks, especially in the climate system, is a challenge for many students yet essential to understand how small changes in some climate elements can produce big changes in global climates.

What matters least?  Probably all the gory details in between.

Teaching Historical: The how-to manual

A really important part of historical geology is understanding how on earth this is done. After all, we don’t simply whisper to rocks, “what was it like when you were formed?”

In classes where we went through Steno’s Laws and radiometric dating and cladistics and all that first, students seemed to have difficulty in recognizing when these tools were employed within the “march through time.” Also, it meant that they focused on all the dates and things in the march through time, which frankly isn’t really what we care about the most.

So we’ve tried something different: we start right in on the march through time and when we encounter things we can’t figure out with the tools we have already, we need to learn about new tools.  Students see a motivation for the tool right off the bat. It doesn’t come out of thin air, there isn’t the “gee, what is this good for.” And we make the march through time less about exactly what happened and more about both the tools and themes that we really want to convey.

So, for instance, to determine the last few earthquakes on the San Andreas we find ourselves in a trench looking at fault traces. To interpret this we need two tools: an understanding of crosscutting relationships in sedimentary rocks and carbon-dating. So off we go to learn Steno’s Laws and try to apply them to our trench and then calibrate the relative dates using carbon dates.  As part of this, we also see that not everything is datable (an important concept) and thus that there is uncertainty in such interpretations (students loathe uncertainty). A small side benefit comes as we move farther back and cannot use carbon dating, because students often walk in the door thinking you can carbon date practically anything.

Of course once you’ve chopped up the course like this, the textbook is a mess: reading assignments are fractions of pages across multiple chapters.

Next up, perhaps, will be a discussion of some possible concepts that maybe should be the focus of a historical geology class…

Teaching Historical: Marching through time

OK, so texts are too detailed.  But surely to teach earth history you need to tell how the crust was made, how continents moved about, how archea led to prokaryotes [if you still like that term] led to eukaryotes, etc. So you have to start things at the beginning and move forward, right?

Well, GG disagrees.  Here is why: (1) This isn’t how we decipher a geologic history; instead we unravel the recent stuff and that gives us some clues about the older stuff. (2) We tell students that “the key to the past is the present” and then start them on stories of a planet with an unbreathable atmosphere with little or no life and no continents. Why should they believe any of this?  How does the present inform that past?

So there are some different options once you pitch out the need to explain every last detail and the need to tell the story from the start.  First, pick out elements of the past that illustrate the grand themes you are interested in.  These can be fairly concrete things like proxies and extinction and more diffuse concepts like feedbacks between geosphere, biosphere and atmosphere. Start with the stuff that is pretty familiar.  So, for instance, the course GG teaches starts with figuring out when the next earthquake on the San Andreas fault is likely to occur, which requires knowing when the past few earthquakes were.  This builds off of the death and destruction theme common in physical geology and is of more than passing interest to many students. And, since we are dealing with calendar years and a modern landscape, we can see how the present informs the past because this is hardly a distant past that operates under strange rules.

Adopting this approach means that as you look farther back, you start to see things that simply aren’t part of the world today: mastodons, dinosaurs, an absence of glaciers, Pangea, an absence of animals on land, detrital pyrite, banded iron formations. As you encounter these, you try to see how to explain them, and this leads you to the eventual conclusion that that hopelessly strange Precambrian world is really based off of what we see today.

OK, now some of you noted that GG starts with the next earthquake….but when do we talk about how to do historical geology?  That will be up next….

Teaching Historical: Texts

In teaching historical geology at the intro/nonmajor level for many years, GG has run up against a number of problems that he has tried to work around.  Felt like a good time to review some of these and see if there are better solutions. For starters, let’s talk texts.

Amazingly in many ways, many (most?) students prefer to have a textbook. And of course there are a number of them out there. They all tend to have the same basic structure: introductory chapters on how to do historical geology followed by a series of chapters starting in the Precambrian and moving forward to the present. You’d think that this was ideal given how common that structure is.

However, in teaching the class, several of us noted that students often failed to connect the intro chapter material to the applications seen in the “march through time”: ask students how some event in the Precambrian was dated and you might hear about carbon dating. Many times GG collected the page of notes students were allowed for exams and found them filled with trivia.  The reason? The text had the names of nearly every orogeny and numerous detailed descriptions of minor evolutionary milestones.  Which might be important? The student couldn’t tell and so tried to write it all down.

Look, no non-major (and a fair number of majors) are not going to need to separate the Alleghenian orogeny from the Appalachian later in life. Why the strong focus on all the details? Is this really what matters?  Frankly, most historical texts are like bad history texts, a litany of names and dates with no real rhyme or reason. It seems this is motivated by a desire to have all the pieces that any instructor might need with the added history of how these courses have been taught over the years.

So textbooks often are an anchor around an instructor’s neck. GG actually has dropped a required text but still provides readings in an optional text simply because many students are so dependent on them. And, interestingly, assigning readings on a website has the curious result that reading isn’t done.

Next up: What might be the best march through time?

Classroom tension

No, this is not about angst in taking exams.  It is about teaching intro science classes.

The New York Times just ran a piece about how teaching science in intro lectures is becoming more dynamic in an attempt to be more successful.  This is old news at the University of Colorado, where we had the Science Education Initiative start systematically adjusting science education for more than 7 years. Much of the emphasis is on small group activities within lecture classes. And yet the news story made the Grumpy Geophysicist scramble over the Times webpage looking for a place to comment.  Well, no such luck, so the complaints have to be here.

First one point GG agrees with was this quote: ‘“Higher education has this assumption that if you know your subject, you can teach it, and it’s not true,” Dr. Uvarov said. “I see so much that I was missing before, and that was missing in my own education.”’ In general, faculty are the ones who succeeded at getting material from books and classic lectures and so may be the very least prepared to help those for whom classic lectures and texts really don’t work. The recognition that faculty need help before teaching a class is a helpful one.

Before going further, a disclaimer:  GG is not a great teacher.  Probably not even good and maybe seriously subpar. So caveat emptor.

The sentence that set GG off: “There are many explanations [for why more dynamic modes of teaching are not employed], educators say, including the low value placed on teaching, tradition, pride and the belief that science should be the province of a select few.” [One should wonder who the “educators” are that inform this quote, as they are clearly not the educators teaching the classes in question].

“Belief that science should be the province of a select few”!?! Really? That is way off base.  Does anybody really hold that opinion? While it is undoubtably true that some are better at doing science than others, that doesn’t mean that only a few should understand science.

First, some general comments.  Yes, there are faculty who will not change how they teach an intro class (or a grad class, for that matter).  It usually takes 2-3 times teaching an intro class to develop material fully enough for the class to be taught without working nearly full-time on it; asking a faculty member to go through that process again (when they are senior enough to have all the committee work and research responsibilities filling their days) will meet resistance. Is this “tradition” or “pride”? Not so much: it is prioritizing work (so the “low value placed on teaching” can indeed play a role here). And some classes, once developed, need little tuning (does basic physics change year to year? No) while others do  (does paleoclimate change? Ur, more than we might like, so each iteration of a historical geology or paleoclimate course is likely to require updating).

Read More…

A late AGU response: Making the Laramide

One of GG’s colleagues reported that there was discussion of his talk well after he had left the room (having to leave to collect a spouse from the airport). On the very off chance anybody who cares finds this, here is something of a response to what GG was told was being discussed. A lot of this should be in a 2011 paper by GG and others in Geosphere.

First a note on the talk, which was to argue that the presence of foreland basement-cored mountain ranges (like the southern Rockies) need not require a “flat slab,” which is a slab that travels horizontally along the base of the continental lithosphere. “Foreland basement cored mountain ranges” is shorthand for mountains created well inboard of the more typical mountains formed by shortening of the continental crust near a subduction zone; these mountains typically arise in places where the thickness of sedimentary rocks is thin and so when the thrust faults develop, they are relatively steep and bring the crystalline crust below up, where it is exposed by erosion.  The main mechanical explanation for such mountains was that the oceanic slab was scraping along against the bottom of the continent.  A simple balance of stresses requires that the horizontal stresses increase the farther inland the slab goes, so the stresses are highest where the slab finally turns downward. However, this mechanism will shear the continental lithosphere; one numerical model of this process in 1988 removed all the continental lithosphere in the western U.S., a prediction not supported by observation. In the talk, GG pointed out an alternative, outlined in that 2011 paper, and noted that the physical mens of generating mountains like the southern Rockies is not well established, so the presence of such mountains need not reflect the presence of a flat slab.

The main point was, to use the observation of the mountains to infer what the slab was doing requires an understanding of how the mountains were made; a simple reliance on a single modern example is inadequate. (Not mentioned in the talk is that there are several profound differences between the Laramide and the modern Sierras Pampeanas, the three most relevant being the less deformed Colorado Plateau, which lacks an analog in South America, the Pierre Shale basin in northern Colorado and SE Wyoming, while the pre-uplift Sierras Pampeanas had very little sediment accumulation, and the obliquity of the subduction in North American vs. near normal subduction in South America.  That the South American margin today seems to erode the upper plate while that in North American seemed to accumulate material could also be relevant).

<Phew>

Read More…

One eye, two eyes, red-ite, blue-ite

Wandering the poster halls at AGU one could be excused for thinking that poster printers had a discount for use of red and blue ink, so common were the two colors on seismological posters. Just like political maps now use red for Republicans and blue for Democrats to the point where we talk of red and blue states, in seismic tomography red is stuff that is seismically slower and blue seismically faster; this wasn’t always the case and it is mildly amusing to look back to see where this arose.

Of course part of this is the development of color in scientific publications. While color was present in presentations long ago, it wasn’t common because figures were handdrawn. Making the same figure twice—once in color and once in black and white—was not a good use of funds or time.

When seismic tomography was first developing in the late 1970s and 1980s, most publications were still black and white or had hefty charges for inserting color figures. So, for instance, Kei Aki’s foray into making a tomographic map of California (Kei wrote one of the base papers behind seismic tomography) used black and white contours as did Sue Raikes’s results for southern California, though Raikes added patterns to the highs and lows. When Gene Humphreys made his early tomographic maps while working with Rob Clayton, they used black and white patterns with whiter areas having lower velocities and blacker areas were higher velocities.

Because much of the tomography being done was imaging the mantle, where the presumption was that most of the seismic velocity variations were from temperature, putting red at the slow end and blue at the fast end of a color bar made a lot of sense as red converted warmth and blue cold. GG can’t say when this started, but it may well be back in oral presentations in the 1970s (poster presentations were rare back then). The convention was strong enough that Gene Humphreys and Ken Dueker, in discussing their work on imaging the mantle in the western U.S. in the early 1990s, often posed the question of “what was the green mantle”? (Green in their maps was intermediate from red to blue).

Anyways, move forward to today and that use of colors is deeply entrenched, but the implications suggested might be too simple.  Slow material (“red-ite”) might be wet, it might have a different orientation of seismic anisotropy, it might be more fertile mantle, in addition to possibly being warmer. “Blue-ite” could be the opposite of those things. The problem in some sense is that with the colors so deeply entrenched and the interpretation so well known that many non-seismologists (and, to be fair, a lot of seismologists) take these colors as direct proxies of temperature, which they are not (we should discuss another day the issues with the lateral variations in velocity we usually show and how challenging those can be to interpret in a cross section).

Anyways, just a thought.  If you see red and blue seismic anomalies, “red-ite” and “blue-ite” might be better terms than warm and cool…