The second law of thermodynamics as a unifying theme of geosciences

Kim Kastens
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published May 21, 2010

Map of hurricane tracksHurricanes carry heat away from the tropics. <image info>
This post was triggered by an insight in Dave Mogk's Efficiency post: "A hurricane is an extremely efficient natural process that redistributes the thermal energy built up in tropical oceans by rapidly transferring this energy to colder, northerly latitudes."

It turns out that many Earth processes of global significance, in both solid and fluid earth, have this same effect of redistributing energy away from localities of high energy concentration towards localities of lower energy concentration. The net effect is a more dispersed spatial distribution of energy.

old map of GulfstreamOcean currents carry heat energy away from tropics.<image info>
Along with hurricanes and other mid-latitude storms, ocean currents such as the Gulf Stream also redistribute heat energy from the warmer tropics across higher latitudes. So does the global atmospheric circulation, most notably the Hadley cells.

polarward transfer of energy in atmospheric circulationAtmospheric circulation carries heat away from tropics.<image info>


Heat from earth\'s interiorVolcanoes, hot springs, and plate tectonic convection remove heat energy from earth's interior.<image info>
Another area of concentrated thermal energy within the Earth System is the earth's interior. Vulcanism has the net effect of transferring thermal energy from the hot interior of the planet to the cooler exterior. So do hydrothermal venting at mid-ocean ridges, and geysers and hot springs on land. And so does the upwelling limb of the mantle convection cells that drive plate tectonics.


Mountain with red arrow Erosion breaks up overconcentrations of gravitational potential energy.<image info>
It's not just thermal energy. Weathering and erosion have the net effect of breaking up over-concentrations of gravitational potential energy (aka mountains) and dispersing that energy in the form of kinetic energy of sediment particles down the mountainside and across the lowlands to the sea.


earthquake raypath diagram with red arrowSeismic waves transport energy away from the locus of elastic potential energy buildup.<image info>
Seismic waves originate from sites where excess strain energy has built up in the crust due to the motion of tectonic plates. This energy is transformed into surface and body waves which carry energy outwards to all parts of the solid Earth.


water wave diagram with red arrowWaves transport energy, but the water or rock involved just moves around more or less in place.<image info>
The essential nature of a wave is that waves move energy across long distances, while matter moves back and forth or around in a circle within a relatively small area or volume. Tsunami are another mechanism to disperse the energy that had been concentrated in the small area of a fault rupture and spread around the world's oceans The widely-viewed animations of the 2004 Indonesian tsunami make this point well.


Storm wave with red arrow Waves transport kinetic energy away from storm centers.<image info>
In a similar way, storm waves take energy that had been concentrated in a storm center and disperse it throughout the ocean basin, battering shorelines hundreds or thousands of miles away.


It seems to me that all of these instances of earth processes can be viewed under one umbrella explanation, as manifestations of the second law of thermodynamics, which states that in an isolated system, concentrated energy disperses over time. I haven't tried teaching this umbrella idea, but it seems to me to be a powerful conceptual framework that can integrate across otherwise disparate parts of the geosciences curriculum. In other words, an idea about increasing disorder in the physical realm can be used to decrease disorder in the mental realm.

earthquake raypath diagram with red arrow


Underpinnings of this idea:

Quite a few years ago, atmospheric scientist and educator par excellence Tony Del Genio told me in a casual hallway conversation that the purpose of mid-latitude storms was to transport thermal energy out of the tropics towards the poles so avoid an excess build-up of heat in the latitudes that receive the most insolation. I was dumbstruck by this notion that storms, which I had considered to be an annoyance and an anomaly, could be viewed as having a "purpose" in the grand scheme of things.

During a session of summer 2008 on-line journal club for the Synthesis of Thinking & Learning in the Geosciences project, we discussed work by Cindy Hmelo-Silver, in which she showed that students' understanding of complex biological systems could be supported if they were guided to conceive of the system in terms of its structures (e.g. lungs), behaviors (e.g. lungs inhale) and functions (e.g. lungs inhale in order to bring in oxygen to support the organism's respiration). We were easily able to transfer the "structure" part of this idea to physical Earth Systems (e.g. a volcano is a structure), and also the behavior part (e.g. a volcano erupts.) But we puzzled over what would be the Earth Science equivalent of the underlying functions. Tony's comment flashed into my mind, and I suggested that the "function" of a volcanic eruption could be to transport heat out of the earth's hot interior to be dissipated in the cooler atmosphere or ocean. Following this, other major Earth processes came to mind that could be viewed as serving the "function" of spreading energy out and away from regions of concentrated energy.

However, there was serious disagreement among our group about the legitimacy of thinking of energy dissipation as a "function" being served by the various Earth processes. The critique was that this view was too "teleological," which was bad bad bad in a scientific discussion. I had to look up this word, and learned that a "teleological argument" is an "argument for the existence of God or a creator based on perceived evidence of order, purpose, design, or direction — or some combination of these — in nature." I certainly never intended to be making such an argument, which is why, in this blog post, I present this idea as a "unifying theme" rather than as an Earth function in the structure/behavior/function framework.

For the Cutting Edge workshop on "Developing Student Understanding of Complex Systems in the Geosciences," Barb Dutrow submitted an essay entitled "Minerals as recorders of complex systems with coupled processes," in which she wrote: "When magma intrudes cooler host rocks, the energy is dissipated to the surrounding rocks through a series of thermal, chemical and mechanical processes." This leads me to think that contact metamorphism may be yet another example of a major Earth process that has the net effect of transferring energy away from areas of high concentration and spreading it out across areas of lower concentration. But my knowledge of metamorphic processes is too feeble to make this case. Readers, please help.





The second law of thermodynamics as a unifying theme of geosciences --Discussion  

Hi Kim,
Once again you've written a very thought-provoking post. I am in the process of re-designing my Environmental Geology and Natural Hazards class for the fall, and I might just take up this idea as some kind of unifying theme. (Inspired by Tom Hickson's example of teaching a course with no lectures, I am aspiring to that goal.) In the same way that natural hazards are processes stemming from the dispersion of energy, management of environmental hazards can be seen as attempts to concentrate (or scatter) various substances where they do the least harm... I am trying to think of ways to communicate to my students that there is no such thing as "throwing something away." Thanks for your thoughts!

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Thanks, Christa,

I would be fascinated to hear about what happens if try to intertwine this idea into your Environmental Geology and Natural Hazards class. Dave Mogk gave me a pointer to a fascinating (but heavy-duty) book called "Order out of Chaos: Man's New Dialog with Nature," by Ilya Prigogine, which also features entropy as one of the organizing principles of nature.

Kim

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Hi Christa: I've tried to teach my Environmental Geology class using an Earth System approach since ca. 1992. Half the course is focused on hazards (all our favorites), and half the course is focused on resources. Transfer of mass and energy are central themes in all of the topics I cover, and I ask these questions in each unit: What are the Earth materials? What processes are at work? What is the source of energy? What are the energy and mass pathways and reservoirs? Temporal questions are focused on rates, fluxes, residence time, recurrence intervals. And finally, what happens when humanity gets in the way of these natural processes? (And then, how can we live safely and sustainably on Earth)

At the Complex Systems workshop, in my introductory essay I described my emphasis on work done by or on the Earth system. This can be mechanical work (e.g. earthquakes), chemical work (driven by thermodynamics, chemical reactions), biological work, and increasingly, anthropocentric work (humans are definitely harnessing energy and altering the system). Work requires consumption or liberation of energy (e.g. PV work done in a piston cylinder).

I would just note that nature hates gradients, and there is always the tendency to drive towards the lowest energy state. Any time there is a concentration of energy (e.g. heat) in one part of the system, there is necessarily flow to normalize the distribution of that energy. Another way to say this for students: Things fall downhill. This is true for kinetic energy (boulders rolling downhill), transfer of heat on a global scale (i.e. weather systems; high pressure flowing towards low pressure), and of course there are many more examples in Nature. This also opens the question of stable, metastable, and unstable states (e.g. diamonds are thermodynamically not forever, but the kinetic rate of back reaction is excruciatingly slow, thus diamond is metastable at the surface of the earth). And it also begs the question of how you define the system (open, closed, isolated), and with what boundary conditions.

This all gets back to the question of entropy (which might be considered to be the energy in the system that is not available to do work). Even though local "order" is established in one part of the system (e.g. minerals crystallizing in a magma chamber) and higher order structures emerge (life itself), the universe on the whole loses its ability to do work. Read Prigogine (but set aside about a month to work through this text....very dense, but worth the effort).

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Hi Dave,
I wish I could have taken your Environmental Geology course in my misspent youth; it sounds awesome. I don't think that energy and entropy are up front and center in most people's Earth Systems approaches, especially in courses for non-specialists. If we were to succeed in establishing the idea in our students' minds that energy underlies everything, it would be easier for them to comprehend and anticipate the significance of peak oil and energy descent.
Kim

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This post was editted by Tom Parsons on Jul, 2010
IMO the second law of thermodynamics makes a fine unifying principle for the driving force behind geophysical activity, but even something that general can't be thought of in isolation.

When energy goes from one place or form to another, always trying to become more diffuse or less well organized, it can't do this by magic. Students need to know the menu of available physical mechanisms, or they won't be able to visualize the processes and know why certain ones might predominate in certain situations. Without a viable mechanism to do something or go somewhere, energy is trapped, or at least forced to act on very different timescales depending on the routes it can and can't follow. Good thing, too, or we couldn't find any live batteries to put into our portable electronics.

With respect to the teleology problem -

Back before email, in 1984, I wrote James Lovelock to call his attention to Don L. Anderson's paper in Science "The Earth as a Planet: Paradigms and Paradoxes"(27 Jan, 1984, v223, No 4634, p 347). The sentence (on p 348) "Thus there is the interesting possibility that plate tectonics may exist on the earth because limestone-generating life evolved here" seemed like something Lovelock would enjoy, even though the term "Gaia" was scrupulously avoided. He had in fact missed seeing the paper, and we exchanged a few letters, of which one paragraph of his seems relevant here:

"So you also find it helpful to imagine yourself reduced to the existence of an electron and to wonder then what it might do. Doing just this 25 years ago gave me a very happy time inventing the so called electron capture detector. A cheerful disregard of the [scorn heaped on the] teleological fallacy and its offspring anthropomorphism does seem to give one a mean advantage. Perhaps this is why it is condemned."

In the same spirit, I feel sure that it is helpful to think about "what energy wants". Anthropomorphizing lets us use some very well developed neural circuitry that we have evolved to model the likely behavior of others.

If this be the teleological fallacy, make the most of it!



As an old chem/physics/math teacher and lifelong fan of science and education, I love the way you guys think and I'm really glad that I happened to find your blog! Sadly though, I fear that things will get worse before they get better in science education.

I have a couple of ideas on the questions you raise about motivating students and presenting material, and a couple of geoscience questions of my own that I hope you can help me with.

THE SHORT VERSION:

Young humans emulate people they admire, envy, and want to be like. Unless they feel this way about scientists, science teaching will always be an uphill battle and most of the best students will go where they see payoffs they can understand: money, power and glamor.

To make them into good students destined to become scientists: show them real examples of scientists who are visibly having fun doing science, and who get at least enough money and respect to enjoy *some* of what society offers as rewards to the favored. Tell them stories with scientists as fun-loving heroes. People are evolved to learn from stories and to imitate storied behavior.

Consider the last time that a lot of money and talent went into such an effort, post-Sputnik. Enjoy Hume and Ivey's classic films, "Random Events" and "Frames of Reference" (dated in style, but both quite enlightening on issues still poorly understood by undergrads). Show geoscience students Munk's classic "Waves Across the Pacific", which is still not too badly dated despite its now primitive-looking technology.

Too long already - Longer version and questions - maybe later.

Best regards,
Tom
(PS - Utterly coincidental that when googling myself just now, after fighting my way past a couple of more prominent 'Tom Parsons' I came upon this total-surprise reference, relevant to storytelling and learning http://globalmitch.com/post/607599368/we-are-the-stories-we-tell-ourselves. Which reminded me of the principal who accused me of not being a teacher, but an entertainer. Maybe not a bad thing to be.

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Hi Tom, Welcome to Earth & Mind; thanks for your comments and please visit again.

With respect to the idea that it would be "helpful to imagine yourself reduced to the existence of an electron and to wonder then what it might do," there is some research that makes the case that scientists at the frontiers of knowledge do exactly this, imagine themselves as actors inside their data sets. Ochs et al (1994, 1996) observed six months of discussion among a lab group in physics, and the scientists describe themselves as moving around in their data, for example in a phase transition diagram. The authors consider this as a "liminal state" with one foot in the world of the lab group and one foot in the world of the atoms.

Ochs, E., S. Jacoby, P. Gonzales, 1994, Interpretive journeys: How physicists talk and travel through graphic space, Configurations, v. , p. 151-171.

Ochs, E., P. Gonzales, S. Jacoby, 1996, "When I come down I'm in the domain state": Grammar and graphic representation in the interpretative activity of physicists, p. 328-369, in Interaction and Grammar, Cambridge University Press,

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