"Deep Carbon Through Deep Time" short course, GSA 2014

On Saturday, October 18, during the 2014 Geological Society of America annual meeting in Vancouver, I attended the short course “Deep Carbon Through Deep Time” sponsored by the Deep Carbon Observatory (DCO, ten-year interdisciplinary international project originally administered out of the Geophysical Laboratory, Carnegie Institution of Washington [CIW], now [2022] at Institut de Physique du globe de Paris) and the Mineralogical Society of America. Having experience, either long-term or in passing, with a temperature range of carbon-bearing or organic rocks from mushy ocean floor muds through the anchizone to graphitic schists, I was interested in boldly going deeper than I carbonaceously had gone before.

What is the purpose of the Deep Carbon Observatory initiative? To quote from the short course description, “Yet in spite of carbon’s importance to geology, many aspects of the physical, chemical, and biological behavior of Earth’s subsurface carbon-bearing systems remain unresolved. . . How do deep reservoirs form and evolve? How does carbon move from one deep repository to another?”

Since most of us, when we think of the carbon cycle, usually consider the relatively-shallow upper crust, and Phanerozoic oceans and atmosphere, this short course could have been called “Deeper Carbon Through Deeper Time” because that is where it took me. As Robert Hazen, DCO Executive Director, and Craig Schiffries, DCO Director and former GSA Director for Geoscience Policy, wrote in the first chapter, "Why Deep Carbon?" in Carbon in Earth (2013, Reviews in Mineralogy and Geochemistry, Volume 75; http://www.minsocam.org/MSA/RIM/RiMG075/RiMG075_Ch01.pdf), possibly 90% of the earth's carbon may be in the Earth's deep interior: if carbonaceous chondrite meteorites, used as a compositional model for early planets, have 10-100 times the concentration of carbon as the earth's known carbon reservoirs, where is our missing carbon? Hazen and Schiffries write that identifying and quantifying carbon fluxes to and from the mantle are key in answering this question.

Seven speakers in the short course covered a range of topics within the four DCO communities (extreme physics and chemistry; reservoirs and fluxes; deep life; deep energy) including deep (mantle/core) carbon cycle, diamonds, volcano outgassing, carbon fluids, deep extremophiles. These talks averaged 45-minutes to an hour each, which for soporific me in a small windowless conference room, could have meant a constant battle to stay awake, but I found the talks so gripping that only a couple times all day did I have to pinch myself.

A common theme among the talks was the history of the carbon itself: where it is now, where it had been, how long it was there: transport, reservoirs, residence time (=cycle time). Radiometric age dating, trace element geochemistry, and staple isotopes are among the techniques used on natural samples obtained through deep drilling or that have been brought within our relatively shallow sampling reach by geologic processes (i.e. diamonds). The magnitude of transit in time and depth for Earth carbon was apparent in Steve Shirey's (CIW) diamond talk in which inclusions captured within those crystals record ancient and profound journeys. While I have familiarity with crustal scale advective heat flow in basin thermal modeling, and some of that research has been associated with deep extremophile studies (how hot was the microbes’ environment), it was fascinating to hear Barbara Sherwood Lollar talk about adjacent (meter-scale), but separate, water sources in deep South African gold mines where one source had relatively young meteoric water and the other, unmixed, was millions of years old, both bearing microbes. Sherwood Lollar has also identified 1.5 billion-year-old fluid (non-microbial-bearing) in fractures in a deep mine in Ontario.

While there was a lot of new information presented, relative to my own background, the major take-away for me was a new or expanded scope of thinking about Earth carbon history and distribution. Perhaps the best example was the first talk by Bob Hazen on Mineral Evolution. From our earliest education as geologists, we are aware that plate tectonics, lithospheric differentiation, oxygen atmosphere, life were not present at planet formation, but evolved over the first few billion years of Earth history. However, I never knew or considered that the number of and variety within minerals has changed also, even though now this seems blatantly logical. Hazen’s talk went beyond the Earth and its infancy to mention where the first mineral formed: diamond condensed from supernova vapor in the early universe. The big stunner for some of us was that there are organic minerals, taking the definition of mineral as anything that creates a diffraction pattern, not the general inorganic vs. organic classifier we are initially taught.

Although the DCO initiative focuses on carbon, this endeavor encompasses essentially all disciplines of the earth sciences. I started to list the involved disciplines that came to mind, but realized I was listing everything under the geoscience umbrella. While participating researchers focus on what their own specialties can add to carbon knowledge, the conversation fostered by the DCO will produce a comprehensive and connected understanding of the Earth carbon system, and expand our individual scientific experience from local to “cosmos”-politan in terms of time, space, and process.

I highly recommend Carbon in Earth, Reviews in Mineralogy and Geochemistry, Volume 75 (2013, 680 pages), the medial publication of the 10-year DCO project. Many of the speakers at the short course are authors of chapters in this volume. It (and its spectacular graphics) is available as an Open Access publication at http://www.minsocam.org/MSA/RIM/Rim75.html.