Edward M. Stolper
California Institute of Technology
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Presented to Edward M. Stolper
Citation by David Walker
During the 1970s the moon, the planets parental to meteorites, and Mars joined the petrological agenda. Ed Stolper famously engaged this trifecta. As a Harvard undergrad in Jim Hays' lab Ed had the distinction of producing a thesis on the chemistry of lunar glasses which showed similarities to howardite meteorites. The light of the thesis was eclipsed by the heat generated by interaction with Ted Ringwood — without presenting the thesis. His master's effort was undertaken in Mike O'Hara's lab on the petrogenesis of the most important group of achondrites, eucrite meteorites. Ed showed that the prevailing notion that the eucrites were low pressure end-stage residues was less likely to be correct than that they were low pressure partial melts, a view that could also place howardites and diogenites into context. Having sorted out 4 Vesta (or from wherever else it is that the HED suite comes), Ed returned to Harvard to take on the rest of the solar system for a Ph.D. He produced an extraordinary synthesis of the SNC meteorites. The SNC source regions are Earth-like, although they are clearly not from the Earth. Ed showed that the proper sort of source region could be formed by charging a lunar or eucritic source region with an alkali-bearing component to stabilize clinopyroxene — an extraterrestrial mantle metasomatism if you like.
While Ed was writing up his thesis, I was busy trying to see if we had learned anything from the recent planetary explorations, which might be extrapolable. It looked to me as if planet size was a pretty good metric for fruitful comparisons. Several characteristics of igneous rocks correlate with the size of their body of origin, from bodies the size of 4 Vesta at the low end of the range sampled, up through the Moon, and on through the Earth at the high end of the size series. I ran a draft of this past Ed. It was returned with a fair amount of indignance. I mean didn't I know that the SNCs were asteroidally sourced? Because SNCs give a clear size reading somewhere between Earth and Moon, in terms of supposed size-related characteristics, size must be a bunch of nonsense. Thinking fast I replied, "Oh, you mean they have to come from Venus or Mars?" This bit of light entertainment on my part earned me a lecture on why I would better spend my time looking for the causes of things rather than looking at airhead correlations. True. But less than a day later Ed came back with the recent Viking Martian soil XRF analysis which he had stripped of sulfate and had shown was then indistinguishable from Shergotty. This was the start of "SNCs are from Mars" and although published early, it was not taken very seriously by anyone (truthfully, including us) for some time. Only later were lunar meteorites discovered in Antarctic ice leaving Jay Melosh uncharacteristically quiet about how it was impossible to get them here without destroying them. And also later N2 isotopes in gas bubbles in splash glass on an antarctic SNC proved to match the Martian atmosphere. Ed covered all this ground before he had his first real job!
This brings us to his 25 years at Cal Tech. I have time to do little more than illustrate this period with an example. H2O, CO2, Ar, etc. effervesce from volcanoes and can be made to dissolve into pressurized laboratory melts. How they do this and to what extent they do it and at what P,T, and X has been a matter of considerable interest since the early days of experimental petrology. Maybe we will never know if Barclay Kamb and George Rossman conspired to establish Ed's new presence at Cal Tech near George's IR lab or whether this was an accident. Either way the result is history. IR spectroscopy has proven admirably suited in Ed's hands to unraveling of the abundance and speciations of volatile substances in silicate liquid. Ed and his students have produced a stream of classic papers on topics including the solubility, internal speciation equilibria, and transport of these substances in glassy and liquid silicate. From this we have learned the solubility mechanisms and their dependence on composition. We also know more about degassing rates that impact styles of volcanism. Perhaps as important as the volatile budget itself is the associated material which is found to correlate with water in back arc basin basalts and subduction zone magmas. Ed and his colleagues have also explored the effects of volatiles on the physics and chemistry of the source melting part of the petrogenetic cycle with detailed thermodynamic models.
The first half of Ed's career has been considerably more productive and innovative than most full careers. He has gone from one spectacular accomplishment to another: eucrite melting, SNCs from Mars, "sandwich" MORB melting, H2O-OH-CO2-CO3 by IR; melt densification with pressure, continuous coordination change with pressure, density controls on eruption, fluid-related components in magma petrogenesis, magma degassing and volatile transport, activity models from limiting noble metal alloys, diamond traps for high-pressure melts, adiabatic melting analysis, Hawaiian stratigraphy, … the list is incredible. Please believe this list and join me in congratulating Ed Stolper with the Day Medal. We look forward to seeing what the second half of his career will bring.
2004 Arthur L. Day Medal - Response by Edward M. Stolper
Thanks, Dave, for that generous introduction. I first met Dave at Harvard in the fall of 1970, when I was a 17-year-old freshman and he was a graduate student. He has been a close colleague, friend, and mentor ever since, so I am very pleased that he was able to introduce me today.
When I listen to the list of accomplishments that Dave ascribes to me, several things strike me.
First, although most of the problems I have worked on involve igneous processes, there is otherwise no simple theme to them, and it has sometimes appeared to me to be a random walk. Some studies have been experimental and some theoretical; some such as drilling in Hawaii involved field work and others were computational; some of the experiments were at atmospheric pressure but others were at pressures to hundreds of kilobars; some studies have dealt with terrestrial processes but others had to do with extraterrestrial processes. To be honest, this has always bothered me a bit, because I greatly admire scientists who identify an important problem, develop a coherent, long-term plan, and then proceed to make systematic and deep contributions to that problem. My approach has been more opportunistic, often by chance learning of something new that intrigued me; or stumbling across an idea (like the notion mentioned by Dave that certain meteorites might come from Mars); or having a colleague suggest that there is an important problem that I might consider thinking about; or reading a paper with a group of students and deciding that we could resolve an issue raised in the paper; or hearing a seminar on something and deciding that I had a better idea; and so on. Although the opportunistic approach has its rewards, I confess to sometimes wondering from where the next interesting idea might come, if at all.
Second, in pursuing this eclectic approach to being a scientist, I was molded by my time with Dave and Jim Hays as an undergraduate and graduate student at Harvard and by Mike O'Hara as a graduate student at Edinburgh, but even more so by my long association with Caltech. University departments have cultures that make them distinctive, and these represent and symbolize a value structure on which the department prides itself and that is passed on to the students and young faculty members who join the community. I have come to believe that the definition of departmental culture and its imprinting on future generations are among the most important aspects of academic leadership. In my own case, interactions with senior colleagues at Caltech, among them Tom Ahrens, Sam Epstein, Barclay Kamb, Bob Sharp, Lee Silver, and Jerry Wasserburg, played especially significant roles in helping me to form my own value structure as a scientist.
Third, when you try to cover so much ground, you surely cannot do it all by yourself, because you are constantly venturing into new areas where you cannot know or understand all the background or subtleties, so you need colleagues willing to work with and guide you. For me, these have included many gifted students, postdocs, staff members, and faculty colleagues at Caltech and elsewhere. How in the world could I have worked on hydrogen and carbon isotope fractionation between magmas and vapor without Sam Epstein? How could I have studied the shock wave compression of silicate melts without Tom Ahrens? Where would my work on martian meteorites have gone without Hap McSween? How could I have known how to quantify H2O- and CO2-bearing species in glasses and melts without George Rossman? I would never have pursued drilling in Hawaii without Don DePaolo and Don Thomas. Who would ever have expected me to study oxygen isotopes in ocean island lavas on my own, without John Eiler and Ken Farley? And any insights I have had into isentropic mantle melting and the validation of them using state-of-the-art thermodynamic modeling would have been for naught without Paul Asimow and Marc Hirschmann. The list goes on and on, and needless to say, I thank you all, including those I have not mentioned.
And finally, for many of the topics Dave mentions, I could assemble a group that would swear up and down that I got it all wrong! To them, I would only say that a diversity of viewpoints on complex problems — and nearly every problem in earth science is complex and typically underconstrained — is a sign of a healthy community. But there is another angle to this I would like to emphasize. I will always recall overhearing a meeting between our Penrose medalist, Gary Ernst, and a much younger scientist. Gary was still at UCLA at the time, and we had wonderful monthly lunchtime seminars in which we brought together the petrologists and geochemists at Caltech, UCLA, and USC. We were meeting in the Buwalda Room at Caltech that month, and as we were assembling before lunch began, the younger scientist was lying in wait for Gary, and accosted him with some new results on amphibole stability that disagreed with work Gary had done decades before. The younger scientist took up an aggressive posture, expecting a blast from the great man. But Gary put his arm around the younger man's shoulders and disarmed him with the simple statement, "Oh, I'm so glad someone finally got that right." The point is that sometimes scientists contribute by posing important problems, thereby stimulating significant work by others. And I certainly hope that if faced with a similar situation, I will have the grace to follow Gary's example.
Thank you Dave, members of the audience, and the GSA for this great honor. Several of my friends, colleagues, mentors, and heroes are previous Day medalists, and I am pleased and humbled to have my name appear on the same list.