Let’s start with your childhood, where you’re from, your family at the time, if you have siblings, your early years, and when it was that you became interested in what has developed into your career as an astrophysicist or research scientist?
I was born in Richmond, Virginia in 1948, the youngest of four siblings – two brothers, a sister and myself. My father was a civil engineer for DuPont chemical company and designed HVAC systems for plants built in the late 30’s and early 40’s for the war effort. Our family moved around frequently back then, so my siblings and I were born in different states. When our father transferred to DuPont headquarters in Wilmington, Delaware, we moved to nearby Kennett Square, Pennsylvania, about 30 miles southwest of Philadelphia. During my childhood, my participation in outdoor activities with the Boy Scouts and my motivation by excellent high school chemistry and physics teachers stimulated my interest in the natural sciences.
I attended Purdue University in Indiana in part because Purdue had an excellent chemistry curriculum and because my second older brother, whom I had always admired, received his chemical engineering degree there. As an undergraduate, I was particularly fascinated by the periodic table of the elements and analytical chemistry. Experiences outside the classroom were also important. I noticed that another student in my dormitory had a little miner’s carbide headlamp on his desk. He explored caves as a member of the Purdue Outing Club and invited me to join. When we took caving and climbing trips in southern Indiana, I developed a fascination with geology, particularly about how caves form and about rocks generally. This kindled my interest in geochemistry, which ultimately guided my choices of graduate school and career. Three factors led to my decision in 1970 to attend Indiana University. One was IU’s strong geology and geochemistry programs. I also wanted to remain as near as possible to Shirley, my future spouse. The third reason was to continue exploring caves!
While at IU I indeed continued cave exploration. I joined the Cave Research Foundation (CRF), which maps caves and supports research in the national parks, particularly in Mammoth Cave, Kentucky, which is the longest cave in the world, with 250 miles of mapped passageways. My involvement with CRF deepened my interest in other aspects of geology and geochemistry.
(left) Cave in the Guadalupe Mountains, NM (D. Des Marais, 1980). (right) Climbing the 510 ft.-pit in Ellisons Cave, GA (D. Des Marais, 1972)
My NASA connection began when Dr. John Hayes became my graduate advisor in geochemistry. Hayes’ graduate dissertation had addressed organic compounds in meteorites. He was also involved with the Viking mission as a member of Klaus Bieman’s MIT research group, which created the mass spectrometer for the Mars Viking mission. I took Hayes’ class on mass spectrometry, and fortunately he liked my term paper! Soon after, I chose to do my dissertation with him on lunar sample analyses, focusing on carbon and other elements relevant to life. I first presented my work in 1972 at the third Lunar Science Conference, where I met Sherwood Chang, then chief of the Ames Exobiology branch. Sherwood was also investigating carbon and other elements in lunar samples. Sherwood, John, and others inspired me to continue in the space sciences.
That’s an Interesting path because many of our researchers had a postdoc with somebody or attended a conference and met someone through that network and found their way to Ames that way.
I then did a postdoctoral fellowship at UCLA with Dr. Isaac (Ian) Kaplan, whose biogeochemistry group also had analzed lunar samples. I continued developing methods for carbon isotopic analyses of very small samples. The carbon-13 to carbon-12 abundance ratios of molecules can offer clues about how they are formed. Isotopic measurements also help to identify contamination in meteorites and other extraterrestrial samples. Sherwood Chang wanted to create an isotope geochemistry laboratory in the Ames Exobiology Branch, and that led to my being hired at Ames in 1976.
You mentioned contamination of the meteorites. Was it geo-contamination or contamination from elsewhere that concerned you?
The basic analytical goal is to decipher the entire history of an extraterrestrial sample, starting with understanding the contents of an object when it was formed, which in most cases was billions of years ago. When an object was still in space, other events happened that altered its composition. But our major concern has been about what happens after a meteorite arrives here. Life has become so pervasive that its chemical ‘fingerprints’ are on virtually everything. It’s difficult to avoid these substances anywhere in the shallow Earth’s crust. Also, Earth is an inhospitable place for meteorites because its surface environments are relatively hot and moist compared to conditions in space. So our environment can alter the meteorites and add organic contamination.
What has been your most interesting work here at Ames?
I have had a near-unique opportunity to explore the biogeochemistry of carbon across a wide range of processes and environments that sustain our biosphere. I investigated the isotope geochemistry of carbon and nitrogen in lunar samples, meteorites, and oceanic basalts. Our molecular isotopic measurements of hydrocarbons in carbonaceous chondrites confirmed their extraterrestrial origins and provided clues about their synthesis. My measurements of mid-oceanic basalts and hydrocarbon gases in geothermal systems chracterized components from the mantle and from sedimentary organic carbon.
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