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HARMON CRAIG March 15, 1926–March 14, 2003 BY KARL K. TUREKIAN H (he never used his middle name) ARMON BUSHNELL CRAIG was born in the borough of Manhattan in New York City on March 15th, 1926. He died on March 14th, 2003, a day short of his seventy-seventh birthday. Craig was the prod- uct of two major forces in his life. His father, John Craig Jr., was from a family long in the theater as actors, direc- tors, and producers. Indeed, John Craig’s major activities, after his heroic involvement in World War I, were in run- ning theaters in the northeastern United States. Young Harmon was surrounded by a theatrical crowd during his early childhood. His mother came from a long line of activ- ist Quakers, who, starting before the Civil War, established schools for freed slaves. This activity moved the family from its initial homestead in Virginia westward, finally to Kansas. The influence of his mother’s ethos permeated young Harmon as his mother fed his inquisitive mind with books on a wide range of subjects, especially those heroic and exploratory in nature. It was the blending of the thespian and the Quaker ethos that shaped young Harmon in his early years and set the behavior pattern of his later life. Harmon’s youthful love of adventure, adventurers, and science blossomed into a career in the earth sciences when he discovered fossils in a rock on a family outing. He went 45

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46 BIOGRAPHICAL MEMOIRS off to the University of Chicago as a freshman with a clear idea of pursuing studies in geology. World War II inter- rupted his education. He went off to an officer’s training program in the navy and eventually joined the fleet in Nor- folk, Virginia. He returned to the University of Chicago after demobilization, and his future scientific life was shaped there. After World War II the faculty of the University of Chi- cago, weary of their part in the development of the atomic bomb, turned to research in areas of the most esoteric sorts. With mass spectrometers in place, Harold C. Urey and his students, postdocs, and research collaborators delved into the arcane worlds of determining the warmth of an ocean 100 million years ago, determining the ages of rocks and the Solar System, and exploring the chemistry of the Uni- verse. It was in this hotbed of national-defense-irrelevant research that Harmon Craig found himself. An undergraduate geology major at the University of Chicago, he was pro- pelled into this world of geochemistry and cosmochemistry without waiting to get his undergraduate degree. The measurement of ancient sea temperature depended on analyzing carbon dioxide released from calcium carbon- ate fossils and measuring the relative masses of carbon di- oxide composed of 18O and 16O. The constancy of the car- bon isotope loading on the carbon dioxide was tacitly assumed. Craig, for his thesis, measured the natural vari- ability of 13C/12C to establish the baseline for all future studies involving the carbon system. The independent discovery of natural radioactive 14C by W. F. Libby at the University of Chicago immediately led to the application of 14C to dating in archaeology and Pleis- tocene geology. The stable carbon isotope study from Craig’s thesis allowed for corrections due to mass fractionation and permitted the proper determination of radiocarbon ages

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47 HARMON CRAIG (later to be corrected to calendar years by accommodating the variations in the initial 14C/12C ). Craig’s thesis is still today the primary citation for all studies involving variations in 13C/12C in natural materials, Cited in studies ranging from the establishment of food chains to identifying sources of ancient marbles for statues, this remarkable thesis was the harbinger of the impact Craig would have in various areas of geochemistry and cosmo- chemistry. In the quest for the best measure, using meteorites, of the composition of the Solar System, the common assump- tion was that there was a uniform composition of the most likely nonvolatile raw material of the Solar System, chon- drites. There was a need for criteria by which bad analyses of chondrites could be systematically identified and sepa- rated from the worthy ones; that is, meteorites modified by weathering had to be rejected so that the true makeup of meteorites, in particular the chondrites, could be ascertained. With his mentor Harold Urey, Craig discovered that once the veil of quality certification had been rent, the chon- drites fell into at least two major groups. The Solar System was not so uniform after all. This discovery, later affirmed in several additional ways by others, gave us a totally new view of how and from what materials planets formed. In 1955 the eastern universities were not yet ready to accept the strange new world of geochemistry heralded pri- marily by Harold Urey and his friends, but California was not afraid to go where no man had gone before. Caltech, through the wisdom of Robert Sharp and Harrison Brown, hired a bevy of University of Chicago geochemists. The Scripps Institution of Oceanography—mainly through the foresight of Roger Revelle, its director—brought in Craig from Chi- cago.

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48 BIOGRAPHICAL MEMOIRS Back then, instruments were not built in a day. As Craig was tooling up, he solved the fundamental problem of the fate of carbon dioxide in the atmosphere and the oceans. His theoretical solutions are valid to this day. Indeed, they anticipated the program for atmospheric CO2 measurements begun at Scripps by C. D. Keeling in 1957 at the instigation of Roger Revelle. Craig decided that somebody had better figure out all the controls on oxygen and deuterium isotopes in the hy- drologic cycle, especially if these isotopes were going to be used for paleoenvironmental reconstructions. In two elegant papers that resulted from his meticulous treatment of the problem for an appreciative Italian audience at Spoleto, he laid out the entire framework for discussing the role of kinetics and equilibrium in determining the isotopic com- position of the hydrosphere, including the oceans. (These papers are not generally available in the common litera- ture; neither are J. Willard Gibbs’s classic thermodynamics papers, which were published in an obscure Connecticut journal.) These Spoleto papers are the fundamental docu- ments that all atmospheric geochemists as well as hydrolo- gists and oceanographers turn to for guidance in many as- pects of light isotope geochemistry. He established the meteoric water line, which defines the unique linear relationship between hydrogen and oxy- gen isotope ratios in natural terrestrial waters. He also dis- covered the oxygen isotope shift in geothermal and volca- nic fluids, which showed (contrary to prevailing ideas) that the water in these fluids is overwhelmingly meteoric in ori- gin. This work provided the basis for studies of water-rock interactions in geothermal systems and in hydrothermal vents. Craig and his students subsequently studied the isotopic composition of atmospheric and dissolved oxygen and varia- tions in the composition of dissolved gases. This work led

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49 HARMON CRAIG to a method for determining biological oxygen production and consumption in the ocean mixed layer, as distinct from physical effects, and thus to a better quantification of bio- logical primary production rates in the oceans. In 1967 Henry Stommel suggested to a bunch of geo- chemists at a meeting at Woods Hole that it was about time that some scientists implemented a systematic study of the geochemistry and oceanography of all the oceans. With the new tracers and chronometers available to geochemists, this was the right moment to embark on this daunting enter- prise. George Veronis let the group of geochemists get to- gether with his theoreticians meeting at the Geophysical Fluid Dynamic Summer Institute to begin the planning. It became obvious to all who participated in the summer ses- sion that the leaders of what ultimately was to be called the Geochemical Ocean Sections Study (GEOSECS) should be Wallace Broecker of the Lamont-Doherty Earth Observa- tory, Harmon Craig of Scripps, and Derek Spencer of the Woods Hole Oceanographic Institution. With the help of many other geochemists the program did not self-destruct as some people thought (or hoped?), but rather accom- plished its main goals. GEOSECS spawned a number of important projects, many of which continue as follow-ups to this day. Craig was inter- ested in the rate of turnover of the oceans. Fritz Koczy had suggested that 226Ra with a 1,620-year half-life might be a good tracer of circulation, being introduced at the ocean bottom from sediments and making its way up with the water to the surface, decaying along the way. Edward Goldberg of Scripps had suggested that the daughter of 226Ra, 210Pb, could be measured as a surrogate. When Craig and his col- leagues pursued this path, they discovered that 210Pb was particle reactive and removed from the ocean by settling. Indeed, all the elements in the ocean that were particle

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50 BIOGRAPHICAL MEMOIRS reactive like 210Pb would have similar distributions and the removal from surface to depth and ultimately into the sedi- ments occurred. Another incorrect assumption was the expectation that 4He would be released from the ocean bottom. The expec- tation was to use atmospheric helium with its 3He dissolved in seawater in an isotope dilution experiment to measure the excess 4He putatively released from sediments. When Craig collected an ocean water profile and the talented Brian Clarke of McMaster University—who developed a tech- nique for measuring 3He/4He—measured this profile, the astounding result was that it was 3He that was in excess— not 4He. This discovery of primordial 3He in the oceans was made at the same time that I. N. Tolstikhin discovered pri- mordial 3He in hot springs in the Kuriles. The consequences of the oceanic discovery impacted not only the tracing of ocean circulation but also the understanding of the way the mantle expresses itself at ocean spreading centers and ocean island basalts. The discovery of excess 3He in the oceans from this productive collaboration was exploited in every way by Craig, his students, and his postdocs with many addi- tional remarkable discoveries resulting. Craig’s interests were not restricted to the oceans and the rocks at their boundaries; he also sought to understand the record of atmospheric changes recorded in cores from the Antarctic and Greenland ice sheets. He was one of the earliest workers to study gases trapped in glacier ice, and he showed that atmospheric methane has roughly doubled due to human activities over the past 300 years. He was also one of the first to study the geochemistry of atmospheric nitrous oxide and to work on the production, rate of in- crease, and isotopic budget of this natural and anthropo- genic modulator of Earth’s protective ozone layer. More

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51 HARMON CRAIG recently his work focused on the physics and chemistry of gases in polar ice cores, including pioneering work on the gravitational separation of gases and isotopes within the permeable firn layer, and on the gravitational separation of rare gas isotopes as a measure of firn temperatures and thicknesses. This work is fundamental to the reconstruction of past atmospheric composition and isotopic variations based on measurements of gases in polar ice, and plays an impor- tant role in continuing efforts to understand past climatic change. In one of his last papers Craig made sense of the 32Si measurements made in the Geochemical Ocean Sections Study. Some scientists saw in the original measurements a hopelessly flawed set of data when tested with a simple model. Craig and his coauthors—including Somayajulu, who ini- tially made the measurements and was rightly indignant that the quality of his measurements was challenged—wrote a paper titled “Paradox Lost: 32Si and the Global Ocean Silica Cycle,” wherein the role of mixing of two sources of silica trapped by the collecting fibers explained the results and justified the measurements made by Somayajulu. So we see the man who’s eye for recognizing quality measurements first showed up in the paper on meteorites was active in deciphering a major marine geochemical problem. Craig influenced many areas as a result of his brilliance as a field observer, his skill and meticulousness as a mea- surer, and his genius as a profound theoretical thinker. These qualities, when found in one person, make that per- son able to improve our understanding of Earth in all its facets with the strength of a whole army. Yet this one-man army was not acting alone. In everything he did he was accompanied and encouraged by his wife, Valerie. Her pa- tience with Craig’s perennially searching mind, his friends

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52 BIOGRAPHICAL MEMOIRS with diverse qualities and interests, and the system in which she and her husband ultimately triumphed made the Craig enterprise one of inevitable success. Craig’s success was recognized and rewarded by a num- ber of prestigious awards, including the Balsan Prize, the Vetlesen Prize, the V. M. Goldschmidt Medal of the Geo- chemical Society, the Arthur L. Day Medal of the Geologi- cal Society of America, and the Arthur L. Day Prize and Lectureship of the National Academy of Sciences. He was elected to the American Academy of Arts and Sciences in 1976, and elected to the National Academy of Sciences in 1979. The University of Paris awarded him an honorary degree (an interesting follow-on to his father having re- ceived the Croix de Guerre from the French for his bravery in World War I). His alma mater, the University of Chicago, also awarded him an honorary doctorate while denying him an ex post facto bachelor’s degree. I thank John Craig III and Valerie Craig for insights into Harmon Craig’s career throughout his productive life. I have borrowed ex- tensively from an obituary that I wrote for Nature and one that Ray Weiss wrote for the Transactions of the American Geophysical Union (EOS).

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53 HARMON CRAIG SELECTED BIBLIOGRAPHY 1953 The geochemistry of the stable carbon isotopes. Geochim. Cosmochim. Acta 3:53-92. With H. C. Urey, The composition of the stone meteorites and the origin of the meteorites. Geochim. Cosmochim. Acta 4:36-82. 1954 Geochemical implications of the isotopic composition of carbon in ancient rocks. Geochim. Cosmochim. Acta 6:186-196. 1957 The natural distribution of radiocarbon and the exchange time of carbon dioxide between atmosphere and sea. Tellus 9:1-7. 1961 Isotopic variations in meteoric waters. Science 133:1702-1703. With D. Lal. The production rate of natural tritium. Tellus 13:85- 105. 1963 With L. I. Gordon. Nitrous oxide in the ocean and the marine atmosphere. Geochim. Cosmochim. Acta 27:949-955. 1965 With L. I. Gordon. Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleo-temperatures. Proceedings of the Third Spoleto Conference, Spoleto, Italy, ed. E. Tongiorgi, pp. 9-130. Pisa: V. Lischi & Figli. The measurement of oxygen isotope paleotemperatures. In Stable Isotopes in Oceanographic Studies and Paleotemperatures. Pro- ceedings of the Third Spoleto Conference, Spoleto, Italy, ed. E. Tongiorgi, pp. 161-182. Pisa: V. Lischi & Figli.

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54 BIOGRAPHICAL MEMOIRS 1967 With A. Longinelli. Oxygen-18 variations in sulfate ions in sea water and saline lakes. Science 156:56-59. 1969 With W. B. Clarke and M. A. Beg. Excess 3He in the sea: Evidence for terrestrial primordial helium. Earth Planet. Sci. Lett. 6:213- 220. Abyssal carbon and radiocarbon in the Pacific. J. Geophys. Res. 74:5491-5506. 1970 With W. B. Clarke and M. A. Beg. Excess helium 3 at the North Pacific Geosecs station. J. Geophys. Res. 75:7676-7685. 1971 With R. F. Weiss, Dissolved gas saturation anomalies and excess helium in the ocean. Earth Planet. Sci. Lett. 10:289-296. 1972 With V. Craig. Greek marbles: Determination of provenance by iso- topic analysis. Science 176:401-403. With Y. Chung and M. Fiadeiro. A benthic front in the South Pa- cific. Earth Planet. Sci. Lett. 16:50-65. 1973 With S. Krishnaswami and B. L. K. Somayajulu. 210Pb - 226Ra: Radio- active disequilibrium in the deep sea. Earth Planet. Sci. Lett. 17:295-305. 1974 A scavenging model for trace elements in the deep sea. Earth Planet. Sci. Lett. 23:149-159. 1975 With W. B. Clarke and M. A. Beg. Excess 3He in deep water on the East Pacific Rise. Earth Planet. Sci. Lett. 26:125-132. With J. E. Lupton. Excess 3He in oceanic basalts: Evidence for ter- restrial primordial helium. Earth Planet. Sci. Lett. 26:133-139.

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55 HARMON CRAIG 1977 With R. F. Weiss, P. Lonsdale, J. E. Lupton, and A. E. Bainbridge. Hydrothermal plumes in the Galapagos Rift. Nature 267:600-603. 1979 With R. F. Weiss and H. G. Ostlund. Geochemical studies of the Weddell Sea. Deep Sea Res. 26:1093-1120. 1981 With J. E. Lupton. A major helium-3 source at 15°S on the East Pacific Rise. Science 214:13-18. 1982 With C. C. Chou. Methane: The record in polar ice cores. Geophys. Res. Lett. 99:1221-1224. 1983 With W. A. Rison. Helium isotopes and mantle volatiles in Loihi Seamount and Hawaiian Island basalts and xenoliths. Earth Planet. Sci. Lett. 66:407-426. 1986 With R. J. Poreda. Cosmogenic 3He in terrestrial rocks: The summit lavas of Maui. Proc. Natl. Acad. Sci. U. S. A. 83:1970-1974. 1987 With T. L. Hayward. Oxygen supersaturation in the ocean: Biologi- cal vs. physical contributions. Science 235:199-220. 1989 With R. Poreda. Helium isotope ratios in Circum-Pacific volcanic arcs. Nature 338:473-477.

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56 BIOGRAPHICAL MEMOIRS 1992 With K. A. Farley and J. Natland. Binary mixing of enriched and undegassed (primitive?) mantle components (He, Sr, Nd, Pb) in Samoan lavas. Earth Planet. Sci. Lett. 111:183-199. 1993 With K.-R. Kim. N-15 and 0-18 characteristics of nitrous oxide: A global perspective. Science 262:1855-1857. With J. M. Edmond, R. F. Stallard, V. Craig, R. F. Weiss, and G. W. Coulter. The nutrient chemistry of the water column of Lake Tanganyika. Limnol. Oceanogr. 38:725-738. 1994 With K. A. Farley. Atmospheric argon contamination of ocean is- land basalt olivine phenocrysts. Geochim. Cosmochim. Acta 58:2509- 2517. With T. E. Cerling. Geomorphology and in-situ cosmogenic isotopes. Annu. Rev. Earth Planet. Sci. 22:273-317. 1995 With Y. Horibe. D/H fractionation in the system methane-hydro- gen-water. Geochim. Cosmochim. Acta 59:5209-5217. 1996 With R. C. Wiens. Gravitational enrichment of 84Kr/ 36Ar ratios in polar icecaps: A measure of firn thickness and accumulation tem- perature. Science 271:1708-1710. 2000 With B. L. K. Somayajulu and K. K. Turekian. Paradox Lost: Silicon 32 and the global-ocean silica cycle. Earth Planet. Sci. Lett. 175:297- 308.

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57 HARMON CRAIG