Hurricanes 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.
Ocean 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.
Atmospheric circulation carries heat away from tropics.<image info>
Volcanoes, 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.
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.
Seismic 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.
Waves 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 ( This site may be offline. ) make this point well.
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.
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.
