More On Deep Carbon

These days we worry quite a bit about the global Carbon cycle, which we clever primates have been blithely monkeying with for a couple of centuries—with impressive results.

But, of course, we mostly worry about the tiny fraction of the planet that we can see because we live here.  Human activities are mostly confined to the surface of land and sea, and the atmosphere.  As we are learning, it is quite within our power to alter the distribution of Carbon and other materials, and thereby significantly change the global climate and life.  Climate and life at the surface

In recent decades, it has become clear that there is a lot more to our planet than the part where puny Carbon-based primates can live.  There appears to be life deep down in the rocks, and also vast amounts of Carbon (living or not) in the Earth’s mantle.  This matters, because all of the human disturbance at the surface are potentially dwarfed by changes rising up from (or sinking down into) the depths.  A slight increase in the transport of Carbon could totally change the surface, overwhelming anything we’ve done recently, or ever could do.

Some of this “deep carbon” is in soils, some of it is ocean sediments, and some of it is in the rocky mantle.  The latter is under intense heat and pressure, but that’s about as much as we really know.

How does chemistry work down there?  This is a hard problem because we cannot visit or sample with instruments.  In fact, we can’t even simulate the conditions with current technology.

This winter researchers at the University of Chicago report new computational simulations of how ions and other molecules work in water at these high pressures [2].  This heroic work is based on “first principles”, i.e., quantum theory.  We can’t actually experiment with these molecules, but we do have solid theory.

The basic idea of the initial work is to characterize the spectroscopy of these molecules in solution, which can be used to interpret and extrapolate measurements we can make.  I.e., we can measure spectra from nature, but interpreting them requires understanding of the physics of the source.

[Caveat: I do not understand the theory or methods discussed in this paper.  I’m taking it all as read.]

The study finds that there probably is more Carbon than earlier geophysical models computed. I.e., there is even more Carbon underground that estimated, which presumably can move out to the surface and in from the surface.

“The results obtained here for the γ ratio imply a higher concentration of bicarbonate ions than previously considered”  ([2], p.5)


I love these first principle computations, because they use technology I helped develop in small ways.

I don’t understand the physics, but I do understand the computation. This computation used a cluster of linux systems (640 processors, 1TB memory), which runs open source science code in parallel.  Between Moore’s law and the parallel software we developed in the 80’s and 90’s, it is now possible to actually compute the theoretical behavior of several dozen atoms.  Wow!

“There are 62 water molecules and one Na2CO3 or NaDCO3 molecule in the cubic simulation box with periodic boundary conditions. “ ([2], p. 5)


  1. Emily Ayshford, Simulations identify missing link to determine carbon in deep Earth reservoirs in Pritzker School of Molecular Engineering – News, February 10, 2020. https://pme.uchicago.edu/news/simulations-identify-carbon-earths-mantle
  2. Ding Pan and Giulia Galli, A first principles method to determine speciation of carbonates in supercritical water. Nature Communications, 11 (1):421, 2020/01/21 2020. https://doi.org/10.1038/s41467-019-14248-1

 

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