The Thermodynamic Sinks of this World
What would an elemental soup cook up to?
Always Off Equilibrium
I’ve set up the equilibrium world, the one thermodynamics seems to say we should have. As interesting as it is, we don’t have it, and no exoplanet will have it either. The building blocks are present in constrained amounts. Radioactive decay and large mass combine to build up temperatures and drive plate tectonics, processes that in turn lead to quite specific mineral forming events. For a given size planet, in time all the lighter noble gases will escape, as they by and large did here. If the size of the planet, volcanic activity, sources of energy are not right, water will disappear too or freeze, and dissolution of salts will not take place.
Then there is life. James Lovelock’s Gaia hypothesis, bolstered by Lynn Margulis’s insight, is that life creates disequilibrium. The abundant oxygen in our atmosphere (when there are so many ways to fix it, as we have seen) is direct testimony to the planet-forming power of life. There are theories of maximum entropy flow driving systems inevitably off equilibrium. Yet these theories are contested.
I think history—physical law + variety + happenstance, call it hazard, in the old, original sense of the word—creates and propagates a state off equilibrium, even without life. And there is no way to turn off history. We have a chanced, beautiful planet, its surface and atmosphere way off the thermodynamic state I’ve tried to explore. We had better be careful of what we have.
I am grateful to useful comments setting me straight by Mainak Mookherjee, Vaclav Smil, Don Rimstidt, Tyler Volk, David Schwartzman, Eugen Schwarz, Andreas Hermann and Michael O’Keeffe.
- Hazen, R. M., D. Papineau, W. Bleeker, R. T. Downs, J. M. Ferry, T. J. McCoy, D. A. Sverjensky and H. Yang. 2008. Mineral evolution. American Mineralogist 93:1693–1720.
- Johnson, D. A. 1982. Some Thermodynamic Aspects of Inorganic Chemistry. Cambridge: Cambridge University Press.
- Kleidon, A., and R. D. Lorenz, eds. 2005. Non-Equilibrium Thermodynamics and the Production of Entropy. Berlin: Springer.
- Lovelock, J. E., and L. Margulis. 1974. Atmospheric homeostasis by and for the biosphere: the Gaia hypothesis. Tellus 26:2–9.
- Schwartzman, D. W., and T. Volk. 2004. Does life drive disequilibrium in the biosphere? In Scientists Debate Gaia, ed. S. H. Schneider, J. R. Miller, E. Cris and P. J. Boston. Cambridge: MIT Press.
- Volk, T. 2007. The properties of organisms are not tunable parameters selected because they create maximum entropy production on the biosphere scale: A by-product framework in response to Kleidon. Climatic Change 85:251–258.