New staff member at Geophysical Lab

Organic Geochemistry Gordon Conference 1984; Marilyn 3rd row 2nd from left

         As a new staff member, it was exciting to move into my own dedicated laboratory space. The original Geophysical Laboratory on Upton Street in Washington, DC, was built in 1908, had 18-inch walls and big hallways. Director Yoder assigned me a laboratory to share with retiring staff scientist, Gordon Davis. Davis’ career focused on radiogenic dating of rocks. His laboratory was primarily a preparatory, “semi-clean” lab where he purified lead and other radiogenic isotopes for dating. For about a year, we “shared” the space with my culturing equipment on benches in the clean lab. It was an arrangement that would never really work, because I did not have full control over my lab space. Only many years later did I realize that this arrangement put the start of my career at a moderate disadvantage. Fortunately for me, after one year Gordon fully retired and I was able to renovate the laboratory, move in two isotope mass spectrometers, and build my first original vacuum line.

         After investigating hydrogen isotopes for several years, my interests turned to oxygen in organic matter with an experimental plan similar to what I had carried out for hydrogen isotopes. The analysis of organic oxygen was, at this time, limited to carbohydrates. The Caltech group was analyzing cellulose in plants and tree rings. John Hayes and his student Kim Wedeking at Indiana University were revising a method, originally described by Rittenberg and Ponticorvo (1956), for analyzing proteins and kerogens, compounds with N, S, and other elements. Tom Hoering and I followed their work closely. Their method, published only in Kim Wedeking’s dissertation, was based on a reaction with mercuric chloride (HgCl₂) to form a mixture of carbon monoxide (CO) and carbon dioxide (CO₂₎. Tom Hoering and I were working on a similar method. Organic matter was heated in an evacuated sealed tube with HgCl₂ at 500°C.  Products included both CO and CO₂, with HCl and other impurities that were separated by gas chromatography (Hoering and Estep, 1981). CO was converted to CO₂ by disproportionation in a high-voltage discharge apparatus where excess carbon is plated out on platinum electrodes. The method was never robust, and as a byproduct of the high-voltage discharge in the reaction chamber, NO₂ was formed from N₂ in organic matter. Multiple analyses of biological samples introduced NO₂  unwittingly into the flight tube of our homemade IRMS. NO₂ is notoriously sticky on metal surfaces. Eventually the IRMS would not pump down. A real disaster resulted in which Tom Hoering removed the flight tube, took it out on the lawn of the Geophysical Laboratory, and sandblasted it. In the environment of the Geophysical Lab, where everyone seemed to have research successes all the time, I felt deflated, maybe an “imposter”, but I immediately moved on to other projects.

         The analysis of oxygen isotopes in organic matter was my first failed project, but I learned a lot during the process. The most important lesson was learning to deal with failure. A scientist’s life is filled with a certain amount of rejection: manuscripts, proposals, ideas. Only rarely does one get affirmation and accolades. Learning to not give up, but to keep searching for the next promising idea, is key to a successful long-term career. For example, the vacuum line I designed was my first. Parts of it were constructed using Swagelock fittings for water-cooling lines. When the water was first turned on, the line dripped at every connection because I did not know how to assemble a Swagelock fitting properly. As Tom noted: “You have these in ass-backward.” In this system, I learned preparative gas chromatography, a skill needed for later work on oxygen isotopes in molecular O₂ and even later for continuous flow gas chromatography-combustion-IRMS (GC-C-IRMS).         

         Fortunately, I had the ability to shift my emphasis to two other major projects: the biogeochemistry of extremophiles living in hot springs and stable isotope biogeochemistry of nitrogen. On the way to attending a Plant Physiology conference in eastern Washington state in 1980, I made a trip through Yellowstone National Park armed with a newly purchased book authored by Thomas Brock entitled Thermophilic microorganisms and life at high temperatures (1978). The juxtaposition of my earlier work with microalgal cultures and isotope fractionation in comparison to naturally growing algal and bacterial mats struck me as the perfect analogous system with which to study Precambrian stromatolites. I devoured Brock’s book and was determined to set my sights on carrying out an ambitious field-based study in summer of 1981 in Yellowstone.