Thermodynamics of the Earth system: The Earth "Onion"

One of the main motivations of our research is to understand how the Earth functions as one system, and how it is affected by life.

This motivation relates closely to the work of the British scientist James Lovelock, who noted in the 1960ies that the Earth's atmosphere is unique among the terrestrial planets in that its composition reflects strong chemical disequilibrium and he attributed this uniqueness to the widespread presence of life. How could this be? Does this observation violate the very fundamental laws of thermodynamics? How is "disequilibrium" within the Earth system being generated and maintained? For this we need to understand how the laws of thermodynamics shape the functioning of the Earth system, its dynamics, interactions, and feedbacks.

In our work, we apply thermodynamics, specifically its extension to non-equilibrium thermodynamics, to Earth system processes to better understand what makes Earth system processes work. The term work is taken here in a strictly physical sense. The ability to perform work is needed to set things into motion, to lift mass, to transform matter, and to maintain chemical reactions. Ultimately, all work is derived from the planetary forcing, in terms of the received solar radiation, by depleting the heat of the interior, and through gravitational forces by other celestial bodies. To understand how these forcings translate to disequilibrium within the Earth system, we came up with a hierarchical view of Earth system processes that is depicted in the figure below. It qualitatively illustrates how the radiative forcing of the Sun (and the heat of the interior) is converted into the kinetic energy of atmospheric motion and mantle convection, and how these relate to the strength of hydrologic and geochemical cycling. It also shows how the resulting dynamics feed back to the drivers.

A more detailed description of this thermodynamic basis of Earth system functioning is found in the 'further reading' section below.

Figure Caption: Schematic diagram of the planetary hierarchy of free energy generation, transfer and dissipation (solid lines) and associated effects (dotted lines). The different layers are associated with different forms of free energy and gradients associated with disequilibrium. For instance, motion is associated with gradients in momentum and represent kinetic energy. Hydrologic cycling is associated with gradients in chemical potential and geopotential and is associated with potential and chemical free energy. From Kleidon(2010).

Thermodynamics of the Earth system: The Earth "Onion"

Further reading: