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Biographical Memoirs: V.68 (1995)

Chapter: Harold Clayton Urey

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Suggested Citation:"Harold Clayton Urey." National Academy of Sciences. 1995. Biographical Memoirs: V.68. Washington, DC: The National Academies Press. doi: 10.17226/4990.
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HAROLD CLAYI ON UREY April 29, 1893-January 5, 1981 BY JAMES R. ARNOLD, JACOB BIGELEISEN, AND CLYDE A. HUTCHISON JR. HAROLD UREY WAS A SCIENTIST whose interests, accomplish- ments, and influence spanned the disciplines of chem- istry, astronomy, astrophysics, geology, geophysics, and biol- ogy. Although he was meticulous in his attention to cletail, his sights were always on broad questions at the forefront of knowlecige. His unusual powers of concentration and capacity for hard work accounted for much of his success in exploring en cl opening up major new fields of research, including his discovery of deuterium and work on isotope chemistry, isotope separation, isotope geology, en cl cosmo- chemistry. Urey's approach to a new area began with his becoming thoroughly familiar with what was known about the subject of his curiosity en c] then the formulation of a theory to explain a large amount of uncorrelated material, which was then followed by carefully planner! experiments. The latter frequently involves! the design of new experi- mental equipment beyond] the state of the art. As a graduate student in physical chemistry in the early A part of the section "Urey's Personal Life and His Political and Educational Activi- ties" in this memoir is taken with permission of the publisher from Memoir 43, by C. A. Hutchison fir., in Remembering the University of Chicago, Teachers, Scientists and Schol- ars, ed. E. Shils, copyright C)1991 by the University of Chicago. All rights reserved. 363

364 BIOGRAPHICAL MEMOIRS 1920s, Urey realized that future progress in that discipline would require a knowlecige of the quantum theory of atomic anct molecular systems, which was undergoing a revolution in Europe. He supplemented his command of mathematics en cl physics by formal coursework prior to going to the Bohr Institute in Copenhagen in 1923. His exposure there lecI to his formulation of the concept of the electron spin concurrent with but less complete than the Goucismit- Uhienbeck discovery. After completion of his text with Arthur Ruark, Atoms, Quanta and Molecules, one of the first English texts on quantum mechanics and its applications to atomic and molecular systems, Urey became interested in nuclear systematics. This led to his discovery of cleuterium. The conception of this search, the design of the experiment, the actual discovery, and its publication are a mocle! for the planning and execution of scientific research. His discov- ery of the differences in the chemical en c! physical proper- ties of cleuterium compounds lecI to his broacler interest in isotope chemistry and isotope separation. Here again he developer! the theory that lee! to the precliction of the mag- nitucle of isotope effects in the light elements. He followed this up with experiments to confirm the theory, en c! this lee! to his pilot plants that achieved the first concentration of AN, i3C, and 34S Urey's interest in (lemocratic government en c! world af- -fairs lee! to the sense of urgency that developed in the Man- hattan Project late in 1941. His major contributions and cleclication to the success of the program through his work on uranium isotope separation, heavy water production, anc! ~°B enrichment and his service on the various NRDC and OSRD committees relater! to the development of the atomic bomb have never been fully appreciatecl. With the war behind him Urey conceived the isotope thermometer anct its application to geochemistry. From there

HAROLD CLAYTON UREY 365 he became interested! in the moon, formation of the plan- ets, meteorites, the abundances of the elements, en c} fi- nally, the origin of life. He was a major supporter of the manned mission to the moon and was an active investigator in the program. Harold Urey was a warm en cl generous person. He was warm in all his personal relations and generous with his time, attention, en c] resources. To have known him and worked with him were unequaled experiences for each of the authors of this memoir. None of us conic! have pre- pared this memoir alone. UREY'S EARLY LIFE UP TO HIS ENTRANCE TO GRADUATE SCHOOL IN BERKELEY Harold Clayton Urey was born in Walkerton, a small town in Indiana, on April 29, IS93. His father, a school teacher and a minister in the Church of the Brethren, diecl at the time Haroicl was just starting his elementary schooling. Upon graduation from grade school at age fourteen, Urey barely managed to pass the entrance exams for high school. But in high school he became interested in all aspects of his work, clue, he saicI, to the excellent teachers he had there, en c] he immediately became the leacler of his class in all subjects, a position he maintained throughout his high school years en cl in college. When in All at age eighteen he gra(luated from high school, Urey became a teacher in a small country school in Indiana with some twenty-five children in various grades. After one year he went to Montana, where his mother, step- father, brother, and sisters had aIreacly gone, en c! taught in small elementary schools. It was while teaching in a mining camp that the son of the family with which he was living decided to attend col- lege, and this influenced Harold to do the same. He en- ~ - 1

366 BIOGRAPHICAL MEMOIRS terec! the University of Montana in Missoula in the autumn of 1914. By carrying a heavy scheclule of courses he was able to complete his college education in three years with a straight A record, except in athletics. He click this in spite of being required by his financial situation to wait on tables in the girls' dormitory and work one summer on the railroad being built there. Many years later in his Willard Gibbs Medal adclress he spoke warmly of the inspiration he re- ceivect from the professors at the University of Montana en c! of the beginning of his interest in science due to their counseling advice, in particular the influence of A. W. Bray, professor of biology. Under Bray's guidance Haroicl ma- jored in biology, and his first research effort was a study of the protozoa in a backwater of the Missoula River. His in- terest in the origins of life, a fielc! in which he was to make a major contribution much later at the University of Chi- cago, originated with that earliest research. Bray also en- couraged him to stucly chemistry, en c! he obtained a second major in that subject. WorIcT War T began as Urey entered the university, and at the time he completed his work there in 19:~7 the Uniter! States decIarect war. He was urged by his professors to work in a chemical plant, chemists being badly neecled at that time. During the rest of the war he worked at the Barrett Chemical Company in Philadelphia. In 1~919 after the end of the war he returned to the University of Montana as instructor in chemistry. After two years of teaching he realized that if he was to advance academically he wouIc] neec! to obtain a Ph.D. cle- gree. The head of the Chemistry Department at Montana sent a letter of recommendation to Professor Gilbert N. Lewis of the Chemistry Department of the University of California, Berkeley. A fellowship was offered to Harold,

HAROLD CLAYTON UREY 367 and so in 1921, at the age of twenty-eight, he entered the University of California as a graduate student. FROM CHEMICAL PHYSICS TO ISOTOPE GEOLOGY The educational facilities, opportunities, and philosophy of Berkeley's Chemistry Department matched Urey's inter- ests. The department stressed exploration of new ideas through original research and its weekly seminars. There were a minimum of formal requirements. Urey, neverthe- less, took the opportunity to enroll in courses in mathemat- ics and physics, which he deemed essential for his educa- tion as a chemist. In an unpublished autobiography (ca. 1969), Urey described his two years as a graduate student as "among the most inspiring of any of my entire life." His thesis was self-generated. The first part was an outgrowth of his unsuccessful attempt to measure the thermal ionization of cesium vapor. Bohr, Herzfeld, and Fowler had shown earlier that the ideal gas approximation leads to a dissocia- tion instability for an atom with an infinite number of states below the dissociation or ionization limit. its partition func- tion is infinite at all temperatures. Urey and later Fermi showed that the correction of the ideal gas approximation for the excluded volume of the dissociating species leads to a convergence of the partition function of the atom or mol- ecule. Urey's result was published in the Astrophysical four- nal. When he became interested in the moon and planets, Urey was wont to tell his younger astronomy colleagues that he published a paper in the Astrophysical journal before they ~ . . am. 1 ~ ~ , entered the field. l he second part of his thesis was of lesser long-term significance. He attempted to calculate the heat capacities and entropies of polyatomic gases before the cor- rect description of the rotational energy states of molecules had been established by quantum mechanics. When Urey received his doctorate in 1923, he realized

368 BIOGRAPHICAL MEMOIRS that there was much he needec! to learn about the struc- ture of atoms and molecules. He received a fellowship from the American Scandinavian Foundation and went to the Institute of Theoretical Physics, Bohr Institute, in Copenhagen. The institute under Bohr's leadership was a major center in theoretical physics, particularly the (level- opment of the new quantum mechanics and its application to atomic ant! molecular structure. There Urey became ac- quaintecI with Heisenberg, Kramers, PauTi, and Slater and the biochemist Hevesy. Before Urey returnee! to the Uniter! States in 1924, he atten(lecl a meeting of the German Physi- cal Society where he met Einstein and James Franck, who later became lifelong friends. On his return to the United States Urey took a position as associate in chemistry at Johns Hopkins University. There he continued his association with physicists, including Ames, Herzfelc3, and Wood of Hopkins; Brickwecicle, Foote, and Meggers of the Bureau of Stanciar(ls; and Tuve of the Carnegie Institution. His research at Hopkins ranged from sr~,l~- tions on the spin of the electron to cooperative exceri- _~ rip 1 ~ r-- ments with F. O. Rice on the disproof of the radiation hy- pothesis of unimolecular reactions. With Arthur Ruark, Urey wrote Atoms, Quanta and Molecules. He had established him- self as one of the new generation of chemists who applied the new quantum mechanics of Heisenberg en c! Schroclinger to chemistry. In the fall of 1929 Urey joinecl the Columbia faculty as associate professor of chemistry. He initiated both experi- mental ant! theoretical research. In the former area his work was mainly in spectroscopy- ultraviolet spectra of tri- atomic molecules and vibrational spectroscopy. He and his student Charles Bradley measured the Raman spectrum of silico-chIoroform, a tetrahedral molecule. They fount! that none of the molecular force fields in use at the time couict

HAROLD CLAYTON UREY 369 reproduce the spectra of tetrahedral molecules. They intro- duced a new force field, the Urey-Bradley field, which is an admixture of valence bond and central force fields. The Urey-Bradley field remains in use in the analysis of the vi- brational spectra of tetrahedral molecules. Urey's theoreti- cal work at that time was directed to nuclear stability and the classification of atomic nuclei. In 1931 Urey had on the wall of his office a chart of atomic nuclei. On the ordinate his chart was labeled "pro- tons"; on the abscissa he plotted "nuclear electrons." This was prior to the discovery of the neutron. The number of nuclear electrons is the number of neutrons in the nucleus. The atomic number or nuclear charge is the number of protons minus the number of nuclear electrons. For the light elements Urey's chart showed the stable nuclei OH, 2He, 6Li, 73Li, 9Be, JOB, and JOB. From nuclear systematics, Urey and others postulated the existence of 2H, 3H, and 2He. No isotopes of hydrogen or helium other than OH and 2He were known in 1931. From atomic weight consider- ations, to be discussed below, it was estimated that, if a stable isotope of hydrogen of mass 2 existed, its natural abundance would be less than 1:30,000 parts of OH. DISCOVERY OF DEUTERIUM As early as 1919 Otto Stern reported an unsuccessful search for isotopes of hydrogen and oxygen, other than the ones of masses ~ and 16, respectively. In 1929 two Berkeley chem- ists, W. F. Giauque (who had been a graduate student con- temporary of Urey) and H. L. Johnston, discovered the stable isotopes of oxygen, TO and i8O. Their natural abundances are 0.04 and 0.2 percent, respectively. The chemical atomic weight scale was based on the assumption that oxygen had only one isotope, mass 16. The atomic weight of hydrogen was based on the relative densities of hydrogen and oxygen .

370 BIOGRAPHICAL MEMOIRS gases and the atomic weight of natural oxygen equal to 16. Aston hacI cleterminec! the atomic weight of hydrogen based on ~6 0 = 16. The chemical value of the atomic weight of hydrogen was 1.00777 + 0.00002. Aston's mass spectrograph value, 1.00778 + 0.00015, recluced to the chemical scale using the 1931 values for the abundances of ]70 and ~80 was 1.00756. To reconcile the physical and chemical atomic weights of hydrogen, Birge and Menze} postulated the ex- istence of a stable isotope of hydrogen of mass 2 with a natural abundance of ~ :4500. Urey react Birge and Menzel's communication in Physical Review in August 1931. Within days he deciclec! to look for an isotope of hydrogen of mass 2 and outlined his plan of attack. He would need a method of detection, and it wouIc! be desirable to prepare samples enriched in this isotope. The design of the experiment was a moclel of how one shouIc! conduct a search for a small effect. It was the proto- type of the characteristics of Urey's work for the next two decades. As a method of ctetection, Urey en c! his assistant George Murphy chose the atomic spectrum of hyclrogen. An isotope of hydrogen of mass 2 should have reel shifted lines in the Baimer series. The shifts couIcl be calculated from the Ryclberg formula for the energy levels in the hy- cirogen atom after taking into account the relative masses of the electron and nucleus. They amountec! to I.] to I.S A in four lines in the visible part of the spectrum. These couIcl readily be resolvecl with the 21-foot grating spectrograph that hac! just been installer! at the Pupin Laboratory of Co- lumbia University. The latter had a (dispersion of I.2 A/ millimeter in the second order. To enrich the heavy iso- tope, Urey and Murphy chose the clistillation of liquid hy- cirogen. They estimated the fractionation factor for THIGH from THE in the range between the freezing and boiling points from a Debye mocle! for liquid hydrogen. Their esti-

HAROLD CLAYTON UREY 371 mated fractionation factor was 2.5. To achieve an overall enrichment of 100 to 200 above natural abundance would require evaporating 5 liters of liquid hydrogen to ~ ml. The heaw hydrogen should be in this I-ml residue. There were , , ~ . . . ~ · . ~ ~ ~ · ~ 1 ~ . . ~ 1 ~ ~ I ~ ~ ~ but two places in the United States capable ot procruc~ng ~ liters of liquid hydrogen in 1931. They were Giauque's labo- ratory at the University of California and the low-tempera- ture laboratory at the National Bureau of Standards in Wash- ington, D.C. The NBS cryogenic laboratory had been established by Hopkins physics graduate F. G. Brickwedde, , c' ~ . , _ who overlapped with Urey at Hopkins. It is not difficult to understand why Urey chose to collaborate with Brickwedde. During the period when Brickwedde was preparing the enriched sample, Urey and Murphy determined the opti- mum conditions for excitation of the atomic spectrum of hydrogen and suppression of the molecular spectrum. They did in fact find the lines to be expected for 2H in the atomic spectrum of natural hydrogen. They delayed publi- cation until these lines could be shown to increase in inten- sity in an enriched sample. In particular, it was necessary to rule out any possibility that the 2H lines were artifacts (e.g., ~~ ~ ~~ A. ~ · ~. ~1 _ 1 _~ I '~ghost77 lines trom periodic errors In tne ruling or one grar- ing or lines from the molecular spectrum). The first of _ r~c~wectcte s samples showed no increase in the intensities of the lines attributed to 2H. A less persistent person than Urey would have dropped the search. Brickwedde then pre- pared two more samples each by evaporation of a 4-liter batch of liquid hydrogen, this time close to the triple point, where the enrichment factor is somewhat larger than at the normal boiling point. Spectroscopic examination of these samples on Thanksgiving Day of 1931 confirmed the dis- covery of hydrogen isotope of mass 2, subsequently named deuterium. Urey reported his success to his wife, Frieda,

372 BIOGRAPHICAL MEMOIRS when he returned to his home in Leonia, New Jersey, hours late for Thanksgiving dinner. For the discovery of cleuterium, Harold Urey receiver! the Nobel Prize in chemistry in 1934. Urey was the thirc! American to receive a Nobel Prize in chemistry. He was young in comparison with most Nobel laureates in chemis- try prior to or since 1934. He was the first of the California school to receive a Nobel Prize. He valued the contribu- tions that his associates macle to the discovery for which he received the recognition ant! sharer! one-quarter of the prize money with F. G. Brickweclcle and G. M. Murphy. In Urey's Nobel lecture, cleliverec! on February 14, 1935, he called attention to the fact that Aston had just recleter- mined the physical atomic weight of hydrogen to be 1.0081. This value, if correct, wouIcl have brought the physical and chemical atomic weights of hydrogen into exact agreement and invaliciatec! the basis of Birge ant! Menzel's prediction. Urey would not have undertaken the search for cleuterium in 1931 and its discovery wouIc3 have been clelayect, perhaps for years. In 1932 Washburn anct Urey discoverer! the elec- trolytic separation of (leuterium from hydrogen. Dihy(lrogen gas generated by the electrolysis of water is depleted in cleuterium. This fractionation explains the failure of Urey and Murphy to finch any significant enrichment in cleute- rium in Brickwedde's first sample. Brickwecicle took special precautions before he undertook preparation of the en- richecT samples. He took all of his equipment apart and cleaned it thoroughly to eliminate artifacts from impuri- ties. Most significantly, the electrolyte in the cell used to generate the hydrogen to be liquef~ecl was replacecl by fresh alkaline solution. Brickwoclcle literally threw the baby out with the bath water. The dihycirogen procluced from fresh alkaline solution is clepletec! in deuterium. The Raleigh clis- tillation of this liquic! hydrogen brought the deuterium con-

HAROLD CLAYTON UREY 373 tent back to about natural abundance. As more and more water is added to the electrolytic cell to replace that elec- trolyzed, the deuterium abundances rise to the natural abun- dance level. THERMODYNAMIC PROPERTIES OF ISOTOPIC SUBSTANCES Urey's Nobel address was titled "Some Thermodynamic Properties of Hydrogen and Deuterium." The first part cov- ered the discovery of deuterium. Two-thirds of the address dealt with the differences in the thermodynamic properties of isotopes and the feasibility of isotope separation based on these differences. By the time Urey initiated his work on deuterium, calculation of the thermodynamic properties of ideal gases from spectroscopic data had been placed on a firm foundation. Such calculations are particularly simple when one compares the differences in behavior of isotopic substances. Under the assumption of the Born-Oppenheimer approximation, the large enthalpy changes from the differ- ence in the minima of the potential energies of products and reactants in a chemical reaction vanish for isotopic exchange reactions. Thus, Urey and Rittenberg calculated the differences in the degrees of dissociation of HCl~g) and DCl(g) and HI(g) and DI(g), respectively. They con- firmed their calculations with experiments on HI(g) and DI(g). Gould, Bleakney, and H. S. Taylor confirmed the Urey-Rittenberg calculations on the disproportionation of HD into H2 and D2. The success of statistical mechanics to predict differences in the chemical properties of hydrogen and deuterium led Urey and Greiff to extend the method to isotopomers of polyatomic molecules of carbon, nitro- gen, oxygen, and sulfur. For each of these elements, Urey and Greiff found exchange reactions with enrichment fac- tors in the range from ~ to 4 percent at room temperature. The predicted enrichment factors led Urey and Greiff to

374 BIOGRAPHICAL MEMOIRS suggest the chemical exchange methocl for the separation of isotopes of the light elements. The small elementary ef- fect was to be multiplied by countercurrent flow of two- phase systems. Each phase is to consist principally of one chemical species. When one phase is a liquid or liquid! solu- tion and the other is vapor, the process is entirely analo- gous to distillation. In fact, distillation technology can be reacliTy adapted to chemical isotope separation. To replace the boiler and condenser of a ctistilIation tower, one re- quires chemical reactors that convert one chemical species to the other quantitatively. The exchange reaction must be rapist and reversible. These principles led Urey and co-workers to develop the NH3(g)-NH+4(soltn.), HCN(g)-CN~(sol'n.), and SO2(g)-HSO3(soltn.) reactions for the enrichment of i5N, ]3C, and 34S, respectively, during the 1930s. Each of the reactions developed by the Urey school involvecl acicl-base exchange reactions in aqueous solution. These are the fast- est chemical reactions. Reflux was achieved by cheap re- agents acids and alkali. Compared with other isotope sepa- ration processes, centrifuges, and diffusion, the chemical exchange process and the relatect liquic3-vapor clistilIation have large throughput per unit volume of separating equip- ment. Urey and T. I. Taylor also achieved a small enrich- ment of the lithium isotopes on zeolites, the forerunner of the ion exchange version of chemical isotope separation. Most of the people who worked with Urey on isotope separation in the 1930s were postdoctoral fellows. This was rather unusual for the time in American universities. These were talented people interested in academic careers, for which there were few openings. In aciclition, there were professionals, a chemical engineer with expertise in distilIa- tion, and a recent Ph.D. in physics who built a Bleakney- type mass spectrometer for Urey's program. Urey had no clifficulty getting support from foundations after he discov-

H A R O L D C LAYT O N U R E Y 375 ered deuterium and received the Nobel Prize. In fact, he chose to share an award from the Carnegie Institution of Washington with a member of the Physics Department, T. I. Rabi. Rabi never forgot Urey's generosity and the impact it hacl on his program on molecular beam research. Urey was a good jucige of talent; his investment in Rabi paid off hanc3- somely for science, the Carnegie Institution, and Columbia University. Today, bureaucratic restrictions would make it impossible for someone like Urey to give part of a grant to another investigator, no matter how quaTif~ect or promising. During the 1930s, Urey and his co-workers measured the vapor pressures of compounds enriched in D, AN, and TOO. The values obtained for ~80 were utilized in the partial enrichment of i8O by the distillation of water. ISOTOPES AS TRACERS Enriched stable isotopes of H. C, N. O. and S have found wide application in agriculture, biology, chemistry, geology, and medicine. Urey used some of his enricher! isotopes, particularly i8O, to carry out tracer studies. He and Cohn measured the acid en cl base catalyzed exchange between water and acetaldehycle ant! acetone. They showed that ac- icis and alcohols do not exchange oxygen with water. They proviclec! the basis for Roberts en cl Urey to show unequivo- cally that it is the carbon-oxygen bond in the acic! that is broken in esterif~cation reactions. Their result has been of major importance in the elucidation of the mechanism of this important class of reactions. The use of ON as a tracer in biochemistry was initiated by Rittenberg en cl Schoenheimer with enriched samples supplied by Urey. PALEOTEMPERATURES When Urey moved from Columbia to the University of Chicago at the end of Woric! War IT, he deciclecl not to

376 BIOGRAPHICAL MEMOIRS continue his interest in isotope separation or to undertake any research with direct military application. His first prior- ity was to fill a prewar commitment to deliver the Liversicige lecture before the Chemical Society (Lonclon). For this pur- pose he decicled to update and expand the earlier calcula- tions of Urey and Greiff on isotope exchange equilibria using the advance method developed by Bigeleisen and Goeppert-Mayer at Columbia (SAM project) in lL943. The methoc! afforclec] the possibility of calculating the tempera- ture coefficient of an isotope exchange equilibrium con- stant in acictition to the logarithm of the constant with con- ficlence. In the course of these calculations Urey noticed that the fractionation factor for i~o/~6O exchange between CO3-2 ant! H~O(~) wouIc! decrease bv 1.004 between O° ant! 25°C. Urey recognized the potential of utilizing this temperature coefficient to measure paTeotemperatures. The method! clepenclect on the development of isotopic assay methods with a precision of better than 0.] percent in the ~8o/~6O ratio at the natural abundance level, which is 0.2 percent. Nier and Thode had each clevelopec! the clual collector methoc! of measuring isotope ratios with a preci- sion of 0.] percent of the ratio. There were aciclitional re- quirements to be met if the method! were to be useful. Isotope exchange equilibrium wouIc] have to be established in the precipitation of CaCO3 from H2O. The recorc! wouIcl have to be preserved over millions of years. It would be necessary to know the isotopic composition of the marine water in equilibrium with the CaCO3. Urey assembled a research group that included graduate students, postcloctoral fellows, a paTeogeologist, ant! an expert in electronics to attack these questions .. . . ,~ in a systematic way. They advanced the precision of measurements of isotope ratios by almost an order of magnitude en cl routinely obtained a precision of 0.02 percent in the ~8o/~6O ratio in CO2. In the applica-

HAROLD CLAYTON UREY 377 tion of their method, an unknown sample was intercomparec! with a stanciarct using a dual inlet system. The results were expressed in ~ o/oo = t(Rsamp~e/Rsran~ara) - i] x ]9000 The paTeotemperature scale was calibrates] by the isotopic analy- sis of CaCO3 samples precipitated from water at known tem- peratures. The latter yieldecl a thermometric scale in terms of ~ in goof! agreement with Urey's calculation and subse- quent refined calculations by McCrea, a Ph.D. student. The final proof of the paleotemperature-scale concept came with the ~ 95 ~ publication by Urey, Lowenstam, Epstein, en cl McKinney. They analyzer! the CaCO3 of a lOO-million-year- oIc! belemnite collected on the Isle of Skye by Cyril S. Smith. Samples of CaCO3 at various distances from the axis of the belemnite core were analyzed for ~8o/l60. They found the fossil had a life history of four winters ant! three summers. The winter temperatures were I5°C; the summer tempera- tures were 21°C. The winters grew progressively colder dur- ing the lifetime of the belemnite. Urey and his group founded a new branch of geology, which has flourished uncler the leaclership of his associates and students and their students. for this achievement he received the Arthur L. Day Mecial of the Geological Society of America and the Goldschmicit Mecial of the Geochemi- cal Society. . ~ · . ~ . TO . ~ · ~ - THE WAR YEARS, 1939-44: THE ATOMIC BOMB Inasmuch as HaroIc! Urey had stucliecI with Bohr cluring his year in Copenhagen it was natural for him to attend the Fifth Washington Conference on Theoretical Physics in ianu- ary 1939. It was at this conference that Bohr postulated that 235U was the fissionable isotope. The possible need for separating the uranium isotopes was obvious. As the recog- nized florid leacler in isotope separation, Urey's main po- tential contribution to fission research was clearly in that

378 BIOGRAPHICAL MEMOIRS fielcI. He thus became one of the members of the declicated group of scientists, centered at Columbia University, who investigates! nuclear fission before government contracts were available ant! who solicitec! and ultimately obtained govern- ment backing. Two papers written by Urey in lL938, "The Separation of Isotopes" ~ ~ 939, ~ ~ en cl "Separation of Isotopes" ~ ~ 939,5), throw light on the status of isotope separation at that time and on Urey's speculations about methods for separating isotopes of the heavy elements. He proposed a countercur- rent flow centrifuge, designee to attain a number of stages of separation in a single machine, thus reducing the num- ber of machines required in a cascade and the amount of material circulated between machines. Countercurrent flow in a machine was to be established by continuous ctistilIa- tion of a liquid (uranium hexafluoricle in the case of the uranium isotopes) from the bottom cap of the rotor and condensation on the top cap. The liquid wouIct then be thrown to the periphery en cl flow clown the walls, counter- current to the vapor flow. In a third paper, "Separation of Isotopes by Chemical Means" (1940,2), Urey concluded that separation of the uranium isotopes would lead to most interesting progress in the study of the fission process and discusser! the cen- trifugal fractionation column (countercurrent flow centri- fuge) as affording the separation method most likely to succeed. In early 1940 it was clefinitely established that 235U was the isotope fissionable by thermal neutrons. Urey, to- gether with a group of Columbia University faculty mem- bers, began work on uranium isotope separation in May 1940, ant! a contract with President Roosevelt's Committee for Uranium for this work was executed in August. At ap- proximately the same time, Urey was appointee! chairman of an Advisory Committee on Nuclear Research to give tech-

HAROLD CLAYTON UREY 379 nical advice to the Committee for Uranium. He coorcti- natec! experimental centrifuge studies at the University of Virginia; gaseous diffusion separation research at Harvard; and thermal diffusion, chemical separation, and centrifu- gal fractionation at Columbia. Urey undertook personal direction of research on chemi- cal separation of the uranium isotopes and on separation by the countercurrent centrifuge. The chemical separation involving uranium salts in immiscible solvents was not suc- cessful. The clistilling centrifuge mentioned above was aban- ctonecl in favor of an all-gas countercurrent centrifuge, the theory for which was developed by Karl P. Cohen and the design was developecl by Urey together with C. Skarstrom. Because some doubts tract been raised by opponents of the centrifuge project about the stability of countercurrent gas- eous flow, Cohen clevisec! the theory and C. Skarstrom and Urey developed the design for a single-stage flow-through centrifuge. In early 1941 Westinghouse undertook to built! a prototype of the flow-through design, a choice that hacl fatal) consequences for the centrifuge project. The Advisory Committee on Nuclear Research was soon reorganizer! uncler Vannevar Bush's National Defense Re- search Committee, and Urey and Dean George Pegram of Columbia University became members of a new parent Com- mittee on Uranium. Urey hac! broac! responsibilities for for- mulating the whole research program. In view of some uncertainty in 1940 with respect to the feasibility of a divergent chain reaction using natural ura- nium with graphite moderator, Urey became interested in the use of heavy water as an alternative moderator because of its greater efficiency and its practically zero neutron ab- sorption cross-section. Urey proposed using catalytic exchange between hydrogen and water to produce heavy water in

380 BIOGRAPHICAL MEMOIRS quantity. He invited professor H. S. Taylor of Princeton to study this process. Centrifuge work was undertaken in early ~ 941 by Westinghouse in Pittsburgh ant! also was continuing at the University of Virginia. Urey turned his attention to the gas- eous diffusion process. He reported in November 1940 an initial appraisal of separation by diffusion through porous barriers. K. P. Cohen measured the first actual separation by barriers using CO2/H2 mixtures. Estimates of plant size baser] on these observations shower! that a diffusion separa- tion plant would involve as large an undertaking as the centrifuge plant. The last half of 1941 fount! the uranium program in a stage of constant ferment. Plutonium hacT been shown to be fissionable. The English gaseous diffusion process seemed likely to succeecI, and the Columbia diffusion system was not far enough along to evaluate properly. Work in Britain indicated metallic uranium, and heavy water provided the best route to a chain reaction. The British were convinced that weapons couIcl be macle from reasonably small quanti- ties of 235U. The Uranium Committee was reorganized. A new Office of Scientific Research and Development was cre- atecl in the Executive Office of the President as the center for the application of science to national defense, and Urey was a member of its Section on Uranium. He was given responsibility for uranium isotope separation by exchange methods and for heavy water production. V. Bush and I. B. Conant tract overall responsibility for the uranium program. The chain reaction program was reoriented to plutonium production and weapons procluction. An electromagnetic separation project hac! been initiated. By the end of 1941 and early 1942 the program moved from the research to the engineering and construction phases. The attempt to arouse the government to the military po-

HAROLD CLAYTON UREY 381 tential of uranium fission had finally succeeded. The chain reaction group at Columbia, headecl by Fermi en c! Szilarct, was moved to the University of Chicago. The scope of Urey's direct responsibilities in 1942 incluclec! the English ctiffu- sion separation method, the American diffusion method, and the centrifugation method. A decision hacI been made to transfer all uranium work to the United States, and Urey took special pains to see that the British diffusion ideas were seriously considered. In May 1942 the Section on Uranium's Executive Com- mittee, of which Urey was a member, was asker! by I. B. Conant to recommence a program to build atomic weapons. Their proposal to Conant showed strong input from Urey in that it placecl great emphasis on centrifuges en c! heavy water production. This program included construction of a centrifuge plant, a gaseous diffusion pilot and production plant, an electromagnetic plant, pile production of element 94, en c] a plant for heavy water production. It was estimates! that the proposed plans wouIc! result in the production of a few atomic bombs by July 1944. In the summer of 1942 the reported experimental results on flow-through centrifuges were disappointing, showing only 36 percent of theoretical efficiency. Urey's protesta- tions that countercurrent centrifuges wouicI be easier to build and were more efficient were to no avail. Centrifuge work remained at a low level. It is an irony of history that subsequent experiments in 1943 and 1944 proved that coun- tercurrent machines could operate close to theoretical effi- ciency. At least six nations have at the present time oper- ated countercurrent centrifuges with UFO, and it is the uranium isotope separation method of choice for five of them. In November and December of 1942 there was a commit- ment to a full-scale diffusion plant, a smaller electromag-

382 BIOGRAPHICAL MEMOIRS netic plant convertible later to full size, and heavy water plants. The research organization at Columbia University uncler Harold Urey's (lirect supervision had been growing rapiclly. In 1942 and 1943 Urey attracted many eminent scientists from academia and industry to assist in the development of components of the diffusion plant and in his other activi- ties. By the end of 1943 Urey hac3 more than 700 people working on gaseous diffusion alone and several huncirecI more, including those at other universities and industrial laboratories, working on various other researches. He had little taste for administration, en cl the burclen weighed heavily on him. This effort proclucec3 some notable successes. A new pro- cess was devised for producing heavy water, baser! on clual- temperature exchange between hydrogen sulficle anct wa- ter. A successful method for separating the boron isotopes was cleveloped for production of the crystalline i°B neecled at Los Alamos. Low-leakage seals for rotating equipment and mass spectrometers for process analysis, and leak (le- tectors, neecled for both laboratory research ant! plant con- struction, were clevisec3 en cl proclucecI. Progress was made on fundamental theory of separation by diffusion barriers. However, the barrier remained recalcitrant. Copper bar- riers were abanclonecI, ant! efforts were concentrated on nickel barriers. Both electrocleposited (Norris-Acller) and compressed powder barriers were tried. As 1943 wore on, it was realized that, despite heroic efforts, barriers with the properties, uniformity and ruggedness necessary for manu- facture were not available. Nevertheless, a pilot plant for manufacture of the electrocleposited barrier was being com- pletecl. Difficulties were also becoming apparent in the other production projects. The electromagnetic separators that

HAROLD CLAYTON UREY 383 hacl been installecl in Oak Ridge, Tennessee, were experi- encing severe operational problems. The laboratory in Chi- cago was openly critical of time schedules and of the graph- ite pile design that had been (levelope(1 by the DuPont Company. Urey saw his hopes for a contribution from the uranium , · · ~ A ~ ~ · · ~ ~ 1 ~ program to the Imminent 1Y]4 war crisis taue, even as nits fears of a German atom bomb remained lively. He renewed his efforts to realize a homogeneous heavy water uranium slurry reactor, proposed by Halban, for plutonium procluc- tion. This led to the research piles in Chicago ant! later in the 1950s to the Savannah River plutonium production re- actors. Urey championed P. Abelson's liquicl thermal diffu- sion process, which seemed a last hope to achieve timely weapons production. A plant was hastily authorizer! in Oak Ridge in the second half of 1944 and was used to enrich the feed to the electromagnetic plant. In the autumn of 1943 a new type of diffusion barrier, combining features of both the electro(leposited and com- pressed powcler barriers that had been previously devel- opecI, was proposed by the Kellex Corporation. In the spring of 1944 a plant began producing acceptable barrier mate- rial of the previously clevelopec3 electroclepositecl type, whose production had been urged by Urey. Ten thousand workers had been building a huge diffusion plant at Oak Ridge. Early in 1944 the Army (General L. R. Groves commancI- ing) made the decision to rely on the barrier clevelopecl at Kellex. Fortunately, both types of barrier eventually proved satisfactory. The first production from the gaseous cliffu- sion plant occurred in March 1945. The plant operates! with unprece(lentec3 reliability and economy (luring the post- war period, superseding all other methods, but most of the 235U for the Hiroshima bomb was produced by the electro- magnetic separation plant.

384 BIOGRAPHICAL MEMOIRS Early in 1944 when the decision was macle to rely on the new barrier being developed by Kellex, it was clear to Urey that the diffusion plant wouIcl have little relevance to the war effort. He relinquished barrier clevelopment to his as- sociate directors. Urey remained nominal head of the Co- lumbia laboratories until 1945, but his heart was not in it. From that time forward! his energies were directed to the control of atomic energy, not its application. COSMOCHEMISTRY Urey moved from Columbia to Chicago in 1945. Shortly thereafter he read a book by Ralph Baldwin, The Face of the Moon, which started him on a love affair with that object, which continued for the rest of his career. Colleagues at Chicago, or any available listeners, wouic! be treated to mono- logues, sprinkled with the names of craters and other tech- nical terms, which were impressive though bewiTclering. Urey came to regarc! study of the moon as a key to unclerstancI- ing the origin of the solar system. This lee! to a sustained, audacious attack on the broacler problem. His 1952 book, The Planets, is generally agreed to have begun the modern science of the solar system; it brought the term "cosmochemistry," as ctistinguishecl from geochem- istry, into the language. The work systematizer! the state of our knowleclge at that time and set forth a research agenda emphasizing physicochemical en cl chronological stucly of meteorites, the oIclest en cl least altered materials in our possession. Two papers out of many in the following years were espe- cially influential. Craig en cl Urey (1953,1) recIassifiecl the meteorites using chemical criteria anc! set the stage for cle- tailecI comparison between meteorite (chrondite) chemical abundances and those of nonvolatile elements in the sun and other stars. Suess and Urey (1956,2) user! meteoritic

HAROLD CLAYTON UREY 385 anct solar abundances to make an improved table of abun- dances of the elements, showing clearly the influence of nuclear shell closure and other specific nuclear effects on elemental and isotopic abundances. This paper was the ba- sis for the first successful account of the origin of the chemical elements in stars by Burbicige, Burbicige, Fowler, and Hoyle (1957~. The intimate interplay between chemical and astro- physical problems became widely understood for the first time. It is sobering to realize that when Urey wrote The Planets v even so basic a fact as the age of the earth was not yet settled. He began to look for experimental areas beyond the i~o/~60 system where his mass spectrometric skills coulcl be appliecl. A young graduate student named Jerry Wasserburg turned up at Chicago, and Urey put him to work on the 40K/40Ar isotopic (rating system. His thesis, which involved collaboration with R. I. Hayden of the Argonne National Laboratory and Professor Mark Inghram, was a first step on the path by which Wasserburg maple a number of fundamental contributions to geochronolov~y in subse- quent decades. v Urey took great interest in the existence of ctiamoncts in two classes of meteorites: stony objects callecl ureilites (not namecl for him) en c! big metallic meteorites like the one that macle Meteor Crater in Arizona. He hoped that the cliamonds were formed in thermodynamic equilibrium at high pressures. We know now that in the iron objects they were formed by shock; the situation in the ureilites is not so clear. It was a natural step for a chemist thinking about the origin of the planets to think about the origin of life on this particular one and perhaps on Mars or elsewhere. Starting from the abundance of hydrogen in the sun en cl other stars, and the abundance of methane in the outer planets, Urey

386 BIOGRAPHICAL MEMOIRS concluded that it was likely that the earth's atmosphere was originally reducing, rich in CH4 and NH3 rather than CO2 and N2. He suggested that thermodynamics favored the for- mation of organic compounds in such an atmosphere. Not long after this a graduate student named Stanley Miller presented himself to Urey ant! proposed to do an experimental thesis testing this hypothesis in the labora- tory. Urey tool him it was too difficult for a thesis problem, but Miller won a grudging permission to try. Within a month he was exhibiting organic muck in a flask containing meth- ane, ammonia, and water, excited by an electric discharge as a moclel for lightning discharges in such an atmosphere. Miller showecl that the solution products container! amino acicis and other possible precursor compounds for life. Some of us were present at a crowded seminar in which Miller presenter! his results, with Urey in the front row. By the end of the presentation it was obvious to all that this was an important milestone. In the question period Enrico Fermi turned to Urey and said, "I understand that you and Miller have clemonstrated that this is one path by which life might have originated. Harolcl, do you think it was the way?" Urey replied, "Let me put it this way, Enrico. If God didn't do it this way, he overlooked a goocl bet!" Today the as- sumed early reducing atmosphere is no longer widely ac- ceptecI, but the impetus given by Urey still remains. THE LA JOLLA YEARS In 1958 Urey passed a milestone his sixty-fifth birthday. When it became clear that he would then become emeritus at the University of Chicago, his friends at the newly form- ing University of California, San Diego, led by Roger Revelle, offered him an appointment there, and he accepted. That was the year after the Soviet launch of Sputnik I, ant! na- tional attention was focused on space. The National Aero-

HAROLD CLAYTON UREY 387 nautics and Space Administration also was new, and the first U.S. satellites were reaching orbit after some embar- rassing failures. At UCSD Urey joined a small number of younger faculty members who were planning a major university with a strong science ant! engineering sicle. He immediately started up a vigorous research program, involving both carbon en cl oxy- gen isotopic measurements (for paleotemperatures and other purposes) and comparable data for heavier solic! and gas- eous elements for ciating. At the same time, his presence on campus gave a mark of quality to the place that other new foundations couicl not match. While professing himself unsuitable for any administrative functions, Urey was flying to Washington frequently to press advice on the new space agency. According to Robert {astrow, it was Urey who per- suadec3 NASA to make unmanned! missions to the moon an early focus of its space efforts. In 1960 UCSD formed its Department of Chemistry, with Urey as one of its foundling members. Others were old friends and clisciples~ Joe Mayer, Jim Arnold, Hans Suess, en c! Stanley Miller. Urey was particularly emphatic about the importance of biochemistry, which became a major component of the developing department. In the following years he influenced the department and university mainly by example. Urey was very active at the time of Apollo 11, when the first lunar samples were returned and the first ciata were appearing. Though he (unfortunately) almost never talked about the past, he told his colleagues one story that time. He told us that it was only in 1910, when he was seventeen years oIcI, that he saw his first automobile in rural Montana. Less than sixty years later his friends showed him the first rock returned from the moon, an achievement in which he had playecl a significant role. His powers of concentration, even into his eighties, were

; 388 BIOGRAPHICAL MEMOIRS remarkable. He couIcl think intensively about one problem for long periods; his well-known absentmindeciness was the inverse of his sharp focus on one important problem at a time. He love c! science. One scene may give the flavor of the man at the end of his career. On any given morning he might burst into the Office of a colleague eager to talk. Seeing the colleague perhaps discussing current research with students, he would apologize and begin to back out. Of course, he was invited in. He would then rush to the blackboarct and begin "I've finally figured out...." He would soon be pouring out words faster than even close associates could assimilate them. "Does that seem right?" he would say at the end. Maybe one question or comment would emerge. He'cl thank the group warmly, again apologize, and rush out. The effect of this display on young graduate students was remarkable. Urey's last two scientific papers were written and pub- lishec! in 1977, when he was eighty-four years oict. Years earlier the largest research buil(ling on campus, housing chemists ant! engineers, hac! been christened! the Harold and Frieda Urey Hall, to recognize the role they both played in the founding and early development of UCSD. UREY'S PERSONAL LIFE AND HIS POLITICAL AND EDUCATIONAL ACTIVITIES Thus far we have been concerned! with the scientific achievements of HaroIcT Urey. He is also well remembered by all who knew him as a person intensely interested in the well-being of his fellow man. This concern was displayer! not only for his students, research associates, and faculty colleagues but also with respect to social and political prob- lems of national and international importance. He hac! a great interest in such problems, some of them closely re- lated to the wartime work with which he had been involvecI.

HARO LD C LAYT O N U REY 389 He devoted the same concentrated effort and careful thought to their possible solutions as he clid to the solving of the problems of his scientific researches. Having concluciecl that certain actions were required, he then, with the same vigor and determination that were characteristic of his scientific work, wouIcI bent! every effort toward furthering these ac- tions. While at Columbia University he hacl been chairman of the University Federation for Democracy and Intellectual Freedom and a champion of loyalist Spain. As early as 1932 he espoused Clarence Streit's Atian tic Union plan for a world governmental federation. He became greatly ctisturbec! by the rise of Hitler and the progress of Nazism. He was active in securing posts for refugee scientists and in extencI- ing his hospitality to them when they arriver! in this coun- try. In her book Atoms in the Family, Laura Fermi recounts how Harold and his wife Frieda helpect her and her hus- band Enrico become their neighbors in Leonia, New Jersey, when the Fermis arrived at Columbia University from Italy. As WorIcl War IT enclecI, Urey, then at the University of Chicago, became concerned and worrier! about the poten- tial of atomic bombs, in whose creation he had played such an important role. His interest in world government, be- gun at Columbia University, returned with renewal vigor. He worked diligently on the public speaker's platform anal, through his writings presented in the press, toward the cre- ation of a florid free of the changers and dreac! of war. During this period of lecturing and writing on the prob- lems created by nuclear energy developments, Urey actively opposed congressional passage of the May-Johnson bill, which he feared would permit military control of peacetime ac- tivities in the field! of nuclear energy. He strongly supported the eventual McMahon bill in its final form and was a leacler in the fight for its passage. His doubts concerning the jus-

390 B I O G RAP H I C A L M E M O I R S tice of the executions of Ethel en cl Julius Rosenberg for atomic energy secrecy violations receiver! national attention. His views on this matter were not ones that were popular with large sections of the American public. He was caller! before the House Un-American Activities Committee. He wrote, "l doubted seriously if justice hacI been clone. T was only interested in one question. Had they indeed violated the laws of the Uniter! States and tract justice been done? It is my firm conviction that justice was not clone in that case." HaroIcl Urey was an educator, in the unclergracluate and graduate classroom, in the research laboratory, ant! on the public platform. At the enc! of WorIcl War IT, he returned to teaching at a time when many, including himself, felt that this country had, in the course of intensive war research, temporarily abanclonecI both basic research and the train- ing of a new generation of scientists. At this time, when many were worried about how to keep the "secret" of the atomic bomb and how to prevent dominance by the Soviet Union, he wrote, "The real problem that faces this country is a long-term one. It is a problem of the proper education and inspiration of our youth." He approached with great zest the teaching not only of graduate students but also of first-year unclergracluate chemistry courses. His interest in the "inspiration of our youth" even extended to public grade schools. His wife Friecia wrote, "He enjoyed nothing so much as taking his moon-gIobe to the fifth gracle class in the La JolIa schools and telling the students about the moon and the planets." Harold was fond of en cl proud of his family. While at Johns Hopkins University, he visited his mother, then living in Seattle. While on that visit he renewecl his acquaintance with a friend from his University of Montana clays, and she introclucec! him to her younger sister Frieda Daum, who was working as a bacteriologist. As Roger Revelle of La Jolla

HAROLD CLAYTON UREY 391 clescribed it, "Harold Urey was never thought of as an out- cloor man but he spent the next two weeks hiking in the Cascade Mountains with Friecia. Within a year they were marries! and their careers as mountaineers were ended. Af- ter that Haroicl's outdoor activity was confined to his gar- den." Friecia and Harolicl hacl three slaughters (Elizabeth, Frieda, anct Mary Alice) and one son John). At the time Heroin was notified of the award of the Nobel Prize, Frieda was expecting their thirc! chiTci. In order to be with Friecia he diet not attend the December 10 ceremonies in Stockholm. Mary Alice was born on December 2, and Friecia en cl HaroIc! sailer! for Stockholm the following February and attencled a special award ceremony. The friendliness and hospitality of HaroIcl and Frieda and their family brought people together socially in a way that creates! a most pleasant academic atmosphere and acIded greatly to the enjoyment of life on the part of the families of Harold's fellow faculty members en c! of the research as- sociates ant} students in the universities of which he was a member. HaroIc! was greatly concerned with the welfare of his sci- entific colleagues, students, and postdoctoral research asso- ciates. He was always interested in his students' develop- ment of their own inclepenclent scientific careers. He was concerned that they be established in suitable posts upon completion of their researches in his laboratory and was active in locating suitable academic and other positions for them. He was cliligent in seeing that they received appro- priate credit for their work uncler his supervision. The first paper on the establishment of the Urey paleotemperature scale was published uncler the sole authorship of his stu- dent John McCrea. Likewise at Urey's insistence, the sole author of the first article on the Urey-Miller theory en cl

392 BIOGRAPHICAL MEMOIRS experiment on the origin of terrestrial life was his student Stanley Miller. Abolition of the boundaries between scientific clisciplines was a basic tenet of Urey's philosophy. His own academic career, describer! above, was exemplary in this respect. Con- cerning his stay at Bohr's Institute for Theoretical Physics he said, "Bohr dicin't know T was a chemist. He thought T was a physicist." He claimed he hacI learner! most of his physics in Copenhagen restaurants while (lining with Pro- fessor H. A. Kramers. In 1933 Harold founded the interdis- ciplinary fournal of Chemical Physics, which provided an ap- propriate medium for publication of the aIreacly-large body of work that bridged the traditional fielcis of chemistry and physics. He became the first editor of that journal, a posi- tion he held until 1940, by which time it had become a leacling scientific journal. Urey may be considered to have establishecI at least four fielcis of scientific research: stable isotope chemistry, including isotope geochemistry, geochronology, and isotope separa- tion; paleotemperature measurement; cosmochemistry; and the origin of terrestrial life. The scope of his interests ant! influence are reflected in the thirty-two chapters of the monograph Isotopic anal Cosmic Chemistry contributed by former students, postcloctoral associates, ant! colleagues on the oc- casion of his seventieth birthday. Karl Cohen, in an obitu- ary in the Bulletin of the Atomic Scientists, said, "Urey's pio- neering work underlies every method of isotope separation successfully employed on a large scale, for every element from hydrogen to uranium." Craig, Miller, and Wasserburg, in their introduction to Isotopic anal Cosmic Chemistry, wrote, "The measurement of the paleotemperatures of the ancient oceans stands as one of the great clevelopments of the earth sciences; a truly remarkable scientific and intellectual achieve- ment." Cohen, Runcorn, Suess, and Thocle in the Biographi-

FI A R O L D C LAYT O N U R E Y 393 cat Memoirs of the Royal Society of London, speaking of Harold as "the founder of the field of cosmochemistry" wrote, "Urey, uncloubtedly, was the first who rigorously defined this field by its problems and by asking precise questions." His ideas concerning the primordial atmosphere and the beginning of life on earth opened up a completely new approach to the study of the origin of life on this planet. Urey's vigorous ant] concentrated pursuit of these re- searches and his enthusiastic interactions with those around him concerning his latest ideas continued to the end of his life. After his retirement at age sixty-five from the Univer- sity of Chicago and his arrival at the University of CaTifor- nia, his work continued with unabated intensity, and he publishecl 105 scientific papers, 47 of them concerned with his study of the moon, in the remaining twenty-three years of his life. Some ten years after his retirement from Chi- cago he was asked by Professor James Arnold in La Volta, "Harold, why (lo you put in so many hours at work?" Urey replied, "Well, you know I'm not on tenure anymore." WE ACKNOWLEDGE THE ASSISTANCE of Elizabeth Urey Baranger, Karl P. Cohen, and Stanley L. Miller in the preparation of this memoir.

394 BIOGRAPHICAL MEMOIRS HAROLD CLAYTON UREY Born: Walkerton, Indiana / April 29, 1893 Married: tune 12, 1926 to Frieda Daum Children: Gertrude Elizabeth Baranger Frieda Rebecca Brown Mary Alice Lorey John Clayton Urey Hobbies: Gardening and raising orchids (cattleya, cymbidium, and others) EDUCATION University of Montana, Missoula, 1914-17, B.S. in biology with a . . . minor In c. 1emlstry University of California, Berkeley, 1921-23, Ph.D. in chemistry with a minor in physics American-Scandinavian Foundation Fellow, Niels Bohr Institute for Theoretical Physics, Copenhagen, 1923-24 PROFESSIONAL EMPLOYMENT 1911-14 Teacher in rural schools in Indiana, 1911-12; Montana, 1912-14 1918-19 Barrett Chemical Co., Baltimore, research chemist 1919-21 University of Montana, instructor in chemistry 1924-29 Johns Hopkins University, associate in chemistry 1929-36 Columbia University, associate professor of chemistry, 1929-34; Ernest Kempton Adams Fellow, 1933-36; professor of chemistry, 1934-45; executive officer, Department of Chemistry, 1939-42; director of war research, SAM Laboratories, 1940-45 1933-40 Journal of Chemical Physics, editor 1945-58 University of Chicago, Institute for Nuclear Studies: Distinguished Service Professor of Chemistry, 1945-52; Martin A. Ryerson Distinguished Service Professor of Chemistry, 1952-58 1956-57 Oxford University, George Eastman Visiting Professor 1958-70 University of California, San Diego, professor of chemistry-at-large

HAROLD CLAYTON UREY HONORS, PRIZES, AND AWARDS 1934 Nobel Prize, Chemistry Willard Gibbs Medal, American Chemical Society 1935 Silver Medal, Research Institute of America 1940 Davy Medal, Royal Society, London 1943 Franklin Medal, Franklin Institute 1945 Manhattan Project Certificate of Award for Service, U.S. War Department 1946 Medal of Merit, President Harry S. Truman 1950 Distinguished Service Award, Phi Beta Kappa Centennial Award, Northwestern University 1957 Jesuit Centennial Citation, Chicago 1960 Silver Medal, Research Institute of America Cordoza Award, Tau Epsilon Rho Law Fraternity 1961 Alexander Hamilton Award, Columbia University 1962 l. Lawrence Smith Medal, National Academy of Sciences 1963 Remsen Memorial Award, American Chemical Society, Baltimore Section 1964 University of Paris Medal National Medal of Science 1966 Gold Medal, Royal Astronomy Society, London American Academy of Achievement Award, Golden Plate Award 395 1967 Man of Distinction Award, Women's Guild of Temple Emanu-El, San Diego 1969 Chemical Pioneer Award, American Institute of Chemists Arthur L. Day Medal, Geological Society of America Leonard Medal, Meteoritic Society 1970 Linus Pauling Award, Oregon State University 1971 400th Anniversary of Johann Kepler Medal and Citation, American Academy of Arts and Sciences 1972 Gold Medal Award, American Institute of Chemists 1973 Honorary Council and Medal, Higher Council of Scientific Research, Barcelona Silver Medal, 50th Anniversary of International Fair of Barcelona Knights of Malta Award Priestley Medal, American Chemical Society

396 BIOGRAPHICAL MEMOIRS NASA Medal for Exceptional Scientific Achievement 1974 Headliner Award, San Diego Press Club Medallion, Honorary Member of Indiana Academy, Indianapolis Dedication of the Harold C. Urey Laboratory for Isotopic Paleotemperature Research, University of Miami, Coral Gables, Florida. 1975 V. M. Goldschmidt Medal, Geochemical Society 1976 NASA Group Achievement Award, U.S. Members of Joint Editorial Board for Foundations of Space Biology and Medicine, for joint US/USSR treatise 1978 Honorary member UCSD chapter of Phi Beta Kappa HONORARY DEGREES 1935 Princeton University, D.Sc. University of Montana, D.Sc. 1939 Rutgers University, D.Sc. 1946 Columbia University, D.Sc. Oxford University, D.Sc. 1948 Washington & Lee University, D.Sc. 1951 Yale University, D.Sc. University of Athens McMaster University, D.Sc. 1953 Indiana University, D.Sc. 1955 University of California, LL.D. 1957 University of Birmingham, D.Sc. University of Durham, D.Sc. 1958 Wayne State University, LL.D. 1959 Hebrew Union College, Jewish Institute of Religion, D.H.L. 1960 University of Saskatchewan, D.Sc. 1962 Israel Institute of Technology, D.Sc. 1963 Gustavus Adolphus College, D.Sc. University of Pittsburgh, D.Sc. University of Chicago, D.Sc. University of Notre Dame, LL.D. University of Manchester, D.Sc. 1965 1966 1967 University of Michigan, D.Sc. 1969 Franklin and Marshall College, D.Sc. 1970 McGill University, D.Sc.

HAROLD CLAYTON UREY PROFESSIONAL ASSOCIATIONS Academia Scientiarum Olisiponensis, Lisbon (Lisbon Academy of Sciences) Academic Royale des Sciences, des Lettres et des Beaux Arts de Belgique (Honorary) American Academy of Arts and Sciences American Association for the Advancement of Science American Association of University Professors American Astronomical Society American Astronautical Society (fellow) American Chemical Society American Geophysical Union (honorary fellow) American Institute of Chemists (honorary) American Philosophical Society American Physical Society . Associacion Venezolana pare el Avance de la Ciencia (honorary) Chemical Society, London (honorary fellow) Federation of American Scientists (life member) Franklin Institute (honorary) French Chemical Society (honorary) German Society of Aeronautics and Astronautics (honorary) Geological Society of America Illinois State Academy of Science International Association of Geochimica and Cosmochimica International Astronautical Academy International Platform Association Mellon Institute (honorary) Meteoritical Society (fellow) National Academy of Sciences National Institute of Sciences of India (honorary) Phi Sigma Biological Society (honorary) Royal Astronomical Society, London (associate) Royal Institution, London (honorary) Royal Irish Academy (honorary) Royal Society, London (foreign member) Royal Society of Arts and Sciences, Goteborg Royal Swedish Academy (honorary) Smithsonian National Association Societe Royale des Science de Liege (foreign member) 397

398 BIOGRAPHICAL MEMOIRS Weizmann Institute of Science (honorary fellow) World Academy of Arts and Sciences, American Division (corresponding member) CLUBS Chemists' Club, New York (honorary) Cosmos Quadrangle and Tavery (Chicago)

HAROLD CLAYTON UREY SELECTED BIBLIOGRAPHY 1923 399 The heat capacities and entropies of diatomic and polyatomic gases. I. Am. Chem. Soc. 45:1445-55. 1924 The distribution of electrons in the various orbits of the hydrogen atom. Astrophys. J. 59:1-10. On the effect of perturbing electric fields on the Zeeman effect of the hydrogen spectrum. Klg. Danske Videnskabernes Selskab, Math.- fys. Medd. 6:11-19. 1925 The structure of the hydrogen molecule ion. Proc. Natl. Acad. Scat. U.S.A. 11:618-21. 1926 With Y. Sugiura. The quantum theory explanation of the anomalies in the 6th and 7th periods of the periodic table. Klg. Danske Videnskabernes Selskab, Math.-fys. Medd. 7:3-18. With F. R. Bichowsky. A possible explanation of the relativity dou- blets and anomalous Zeeman effects by means of a magnetic electron. Proc. Natl. Acad. Sci. U.S.A. 12:80-85. 1927 With A. E. Ruark. Impulse moment of the light quantum. Proc. Natl. Acad. Sci. U.S.A. 13:763-71. 1928 With F. O. Rice and R. N. Washburne. The mechanism of homoge- neous gas reactions. I. The effect of black-body radiation on a molecular beam of nitrogen pentoxide. [. Am. Chem. Soc. 50:2402- 12. 1929 With L. H. Dawsey and F. O. Rice. The absorption spectrum and

400 BIOGRAPHICAL MEMOIRS decomposition of hydrogen peroxide by light. ]. Am. Chem. So c. 51 :1371-83. With L. H. Dawsey and F. O. Rice. The mechanism of homogeneous gas reactions. II. The absorption spectrum of nitrogen pentoxide and its method of decomposition. {. Am. Chem. Soc. 51 :3190-94. With G. I. Lavin. Some reactions of atomic hydrogen. [. Am. Chem. Soc. 51:3286-90. 1930 With H. Johnston. Regularities in radioactive nuclei. Phys. Rev. 35:869- 70. With A. E. Ruark. Atoms, Molecules and Quanta. New York: McGraw- Hill. 1931 With C. A. Bradley, {r. Raman spectrum of silicochloroform. Phys. Rev. 37:843. The masses of Oi7. Phys. Rev. 37:923-29. With G. M. Murphy. The relative abundance of Ni4 and Ni5. Phys. Rev. 38:575-76. The alternating intensities of sodium bands. Phys. Rev. 38:1074-75. With C. A. Bradley, in The vibrations of pentatomic tetrahedral molecules. Phys. Rev. 38: 1969-78. With H. Johnston. The absorption spectrum of chlorine dioxide. Phys. Rev. 38:2131-52. The natural system of atomic nuclei..~. Am. Chem. So c. 53:2872-80. 1932 Nuclear structure. Nature 130:403. With F. G. Brickwedde and G. M. Murphy. A hydrogen isotope of mass 2. Phys. Rev. 39:164-65. With F. G. Brickwedde and G. M. Murphy. A hydrogen isotope of mass 2 and its concentration. Phys. Rev. 40:1-15. With F. G. Brickwedde and G. M. Murphy. Relative abundance of Hi and H2 in natural hydrogen. Phys. Rev. 40:464-65. With C. A. Bradley,.lr. The relative abundance of hydrogen isotopes in natural hydrogen. Phys. Rev. 40:889-90. With E. W. Washburn. Concentration of the FI2 isotope of hydrogen

HAROLD CLAYTON UREY 401 by the fractional electrolysis of water. Pro c. Natl. Acad. Sci. U.S.A. 18:496-98. With G. M. Murphy. The relative abundance of the nitrogen and oxygen isotopes. Phys. Rev. 41:141-48. 1933 Editorial. i. Chem. Phys. 1 :1-2. With D. Rittenberg. Some thermodynamic properties of the H~H2 and H2H2 molecules and compounds containing the H2 atom. [. Chem. Phys. 1:137-43. With J. Joffe. The spin of the sodium nucleus. Phys. Rev. 43:761. Separation and properties of the isotopes of hydrogen. Science 78:566- 71. With R. H. Crist and G. M. Murphy. Isotopic analysis of water. i. Am. Chem. Soc. 55:5060-61. 1934 With D. Rittenberg and W. Bleakney. The equilibrium between the three hydrogens. [. Chem. Phys. 2:48-49. With R. H. Crist and G. M. Murphy. The use of the interferometer in the isotopic analysis of water. [. Chem. Phys. 2:112-15. With D. Price. The synthesis of tetradeuteromethane. [. Chem. Phys. 2:300. With V. K. LaMer and W. C. Eichelberger. Freezing points of mix- tures of H2O and H22O. J. Am. Chem. So c. 56:248-49. With F. G. Brickwedde, R. B. Scott, and M. H. Wahl. The vapor pressure of deuterium. Phys. Rev. 45:566. With M. H. Wahl. A cascade electrolytic process for separating the hydrogen isotopes. Phys. Rev. 45:566. Significance of the hydrogen isotopes. Ind. Eng. Chem. 26:803-6. Deuterium and its compounds in relation to biology. Cold Spring Harbor Symp. 2:47-56. With R. B. Scott, F. G. Brickwedde, and M. H. Wahl. The vapor pressure and derived thermal properties of hydrogen and deute- rium. J. Chem. Phys. 2:454-64. With D. Rittenberg. Thermal decomposition of deuterium iodide. /. Am. Chem. Soc. 56: 1885-89. With S. H. Manian and W. Bleakney. The relative abundance of the

402 BIOGRAPHICAL MEMOIRS oxygen isotopes oi6 Old in stone meteorites. [. Am. Chem. Soc. 56:2601-9. 1935 With L. A. Weber and M. H. Wahl. Fractionation of the oxygen isotopes in an exchange reaction. [. Chem. Phys. 3:129. With M. H. Wahl. Vapor pressures of the isotopic forms of water. [. Chem. Phys. 3:411-14. Some thermodynamic properties of hydrogen and deuterium. In Le Prix Nobel en 1934, pp. 1-10. Stockholm: Kungl. Baklryckenet. Also published in Angew. Chem. 48:315-20. With L. l. Greiff. Isotopic exchange equilibria. [. Am. Chem. Soc. 57:321-27. With G. K. Teal. The hydrogen isotope of atomic weight two. Rev. Mod. Phys. 7:34-94. 1936 With A. H. W. Aten, in On the chemical differences between nitro- gen isotopes. Phys. Rev. 50:575. With G. E. MacWood. Raman spectra of the deuteriomethanes. i. Chem. Phys. 4:402-6. With A. H. W. Aten, fir., and A. S. Keston. A concentration of the carbon isotope. i. Chem. Phys. 4:622-23. With G. B. Pegram and I. R. Huffman. The concentration of the oxygen isotopes. i. Chem. Phys. 4:623. 1937 With T. I. Taylor. The electrolytic and chemical-exchange methods for the separation of the lithium isotopes. J. Chem. Phys. 5:597-98. With l. R. Huffman, H. G. Thode, and M. Fox. Concentration of NO by chemical methods. J. Chem. Phys. 5:856-68. 1938 Chemistry and the future. Science 88:133-39. With M. Cohn. Oxygen exchange reactions of organic compounds and water. /. Am. Chem. Soc. 60: 679-87. With I. Roberts. The exchange of oxygen between benzil and water and the benzilic acid rearrangement. J. Am. Chem. Soc. 60:880-82.

HAROLD CLAYTON UREY 403 With I. Roberts. Esterification of benzoic acid with methyl alcohol by use of isotopic oxygen. {. Am. Chem. Soc. 60:2391-93. With H. G. Thode and I. E. Gorham. The concentration of Ni5 and S34. /. Chem. Phys. 6:296. With T. I. Taylor. Fractionation of the lithium and potassium iso- topes by chemical exchange with zeolites. [. Chem. Phys. 6:429-38. 1939 The separation of isotopes. In Recent Advances in Surface Chemistry and Chemical Physics, pp. 73-87. Washington, D.C.: American Asso- ciation for the Advancement of Science. With K. Cohen. Van der Waals' forces and the vapor pressures of ortho- and parahydrogen and ortho- and paradeuterium. [. Chem. Phys. 7:157-63. With I. Roberts. Kinetics of the exchange of oxygen between ben- zoic acid and water. {. Am. Chem. So c. 61:2580. With I. Roberts. Mechanisms of acid catalyzed ester hydrolysis, es- terification, and oxygen exchange of carboxylic acids. [. Am. Chem. Soc. 61:2584. Separation of isotopes. In Reports on Progress in Physics, vol. 6, pp. 48- 77. London: The Physical Society. 1940 With C. A. Hutchison, Jr., and D. W. Stewart. The concentration of Ci3. f. Chem. Phys. 8:532-37. Separation of isotopes by chemical means. [. Wash. Acad. Sci. 30:277- 94. With G. A. Mills. The kinetics of isotopic exchange between carbon dioxide, bicarbonate ion, carbonate ion and water. i. Am. Chem. Soc. 62:1019-26. 1942 With E. Leifer. Kinetics of gaseous reactions by means of the mass spectrometer. The thermal decomposition of dimethyl ether and acetaldehyde. J. Am. Chem. Soc. 64:994-1001. With I. Kirshenbaum. The differences in the vapor pressures, heats of vaporization, and triple points of nitrogen (14) and nitrogen ~ 15 ~ and of ammonia and trideuteroammonia. I. J. Chem. Phys. 10:706-17.

404 BIOGRAPHICAL MEMOIRS 1943 With A. F. Reid. The use of the exchange between CO2, H2CO3, HCO3 ion and H2O for isotopic concentration. [. Chem. Phys. 11 :403-12. 1945 With l. D. Brandner. Kinetics of the isotopic exchange reaction between carbon monoxide and carbon dioxide. [. Chem. Phys. 13:351-62. The atom and humanity. Science 102:435. 1946 Methods and objectives of the separation of isotopes. Pro c. Am. Philos. Soc. 90:30-35. Atomic energy in international politics. Foreign Policy Rep. 22:82-91. 1947 The thermodynamic properties of isotopic substances. /. Chem. So c. (London) 1947:562-81. 1948 Oxygen isotopes in nature and in the laboratory. Science 108:489-96. 1950 With C. R. McKinney, l. M. McCrea, S. Epstein, and H. A. Allen. Improvements in mass spectrometers for the measurement of small differences in isotope abundance ratios. Rev. Sci. Instr. 21:724- 30. The structure and chemical composition of Mars. Phys. Rev. 80:295. - 1951 With H. A. Lowenstam, S. Epstein, and C. R. McKinney. Measure- ments of paleotemperatures and temperatures of the upper cre- taceous of England, Denmark, and the southeastern United States. Bull. Geol. Soc. Am. 62:399-416. With S. Epstein, R. Buchsbaum, and H. A. Lowenstam. Carbonate- water isotopic temperature scale. Bull. Geol. Soc. Am. 62:417-26. Cosmic abundances of the elements and the chemical composition of the solar system. Am. Sci. 39:590-609.

HAROLD CLAYTON UREY 405 The origin and development of the earth and other terrestrial plan- ets. Geochim. Cosmochim. Acta 1:209-77. The social implications of the atomic bomb. Sci. Educ. 30:189-196. 1952 The Planets. New Haven, Conn.: Yale University Press. On the early chemical history of the earth and the origin of life. Proc. Natl. Acad. Sci. U. S.A. 38:351-63. The origin and development of the earth and other terrestrial plan- ets: a correction. Geochim. Cosmochim. Acta 2:263-68. Chemical fractionation in the meteorites and the abundance of the elements. Geochim. Cosmochim. Acta 2:269-82. The abundances of the elements. Phys. Rev. 88:248-52. 1953 With H. Craig. The composition of the stone meteorites and the origin of the meteorites. Geochim. Cosmocham. Acta 4:36-82. Chemical evidence regarding the earth's origin. In XIIth Congress for Pure and Applied Chemistry: Plenary Lectures, pp. 188-214. The deficiencies of elements in meteorites. Mem. So c. R. Sci. Liege 14:481-94. 1955 On the origin of tektites. Proc. Natl. Acad. Sci. U.S.A. 41:27-31. The cosmic abundances of potassium, uranium and thorium and the heat balances of the earth, the moon and Mars. Proc. Natl. Acad. Sci. U.S.A. 41:127-44. Distribution of elements in the meteorites and the earth and the origin of heat in the earth's core. Ann. Geophys. 11:65-74. Origin and age of meteorites. Nature 175:321. 1956 Diamonds, meteorites and the origin of the solar system. Astrophys. J. 124:623-37. With H. E. Suess. Abundances of the elements. Rev. Mod. Phys. 28:53- 74. Regarding the early history of the earth's atmosphere. Bull. Geol. So c. Am. 67:1125-28.

406 BIOGRAPHICAL MEMOIRS The origin and significance of the moon's surface. Vistas Astron. 2:1667-80. 1957 Boundary conditions for theories of the origin of the solar system. Prog. Phys. Chem. Earth 2:46-76. 1958 With H. E. Suess. Abundance of the elements in planets and mete- orites. Handb. Phys. 51:296-323. The atmospheres of the planets. Handb. Phys. 52. Composition of the moon's surface. Z. Phys. Chem. (N.F.) 16:346-57. Some observations on educational problems in the United States with particular reference to mathematics and science. School Sci. Math. March: 168-72. 1959 With S. L. Miller. Organic compound synthesis on the primitive earth. Science 130:245-51. With S. L. Miller. Origin of life (reply to letter by S. W. Fox). Science 130:1622-24. 1960 The origin and nature of the moon. Endeavor 19:87-99. The moon. In Science in Space, a report by the Space Science Board, National Academy of Sciences, pp.185-97. Washington, D.C.: National Academy of Sciences. The planets. In Science in Space, a report by the Space Science Board, National Academy of Sciences, pp. 199-217. Washington, D.C.: National Academy of Sciences. 1961 With N. Kokuku and T. Mayeda. Deuterium content of minerals, rocks and liquid inclusions from rocks. Geochim. Cosmochim. Acta 21 :247-56. On possible parent substances for the C2 molecules observed in the Alphonsus crater. Astrophys. f. 134: 268-69. Criticism of Dr. B. Mason's paper on The Origin of Meteorites. J. Geophys. Res. 66:1988-91.

HAROLD CLAYTON UREY 407 The dynamic nature of the atmosphere. In The Air We Breathe A Study of Man and His Environment, ed. S. M. Farber and R. H. L. Wilson, pp. 9-20. Springfield, Ill.: Charles C. Thomas. 1962 With V. R. Murthy. The time of the formation of the solar system relative to nucleosynthesis. Astrophys. f. 135:626-31. Evidence regarding the origin of the earth. Geochim. Cosmochim. Acta 26: 1-13. Origin of the lifelike forms in carbonaceous chondrites. Nature 193:1119- 33. Lifelike forms in meteorites. Science 137:623-28. Origin of tektites. Science 137:746-48. The origin of the moon and its relationship to the origin of the solar system. In The Moon, ed. Z. Kopal and Z. K. Mikhailov, pp. 133-48. New York: Academic Press. 1963 With V. R. Murthy. Isotopic abundance variations in meteorites. Science 140:385-86. The origin and evolution of the solar system. In Space Science, ed. D. P. LeGalley, pp. 123-68. New York: John Wiley & Sons. The origin of organic molecules. In Nature of Biological Diversity, ed. i- M. Allen, pp. 1-13. New York: McGraw-Hill. 1964 A review of atomic abundances in chondrites and the origin of meteorites. Rev. Geophys. 2:1-34. With E. C. Anderson and M. W. Rowe. Potassium and aluminum-26 contents of three bronzite chondrites. [. Geophys. Res. 69:564-65. The role of man in space. In Bioastronautics Fundamental and Prac- tical Problems, vol. 17, ed. W. C. Kaufman, pp. 61-64. North Holly- wood, Calif.: Western Periodicals. With S. L. Miller. Extraterrestrial sources of organic compounds and the origin of life (in Russian). In Problems of Evolutionary and Technical Biochemistry, pp. 357-69. Moscow: Science Press. 1965 With R. L. Heacock, G. P. Kuiper, E. M. Shoemaker, and E. A.

408 BIOGRAPHICAL MEMOIRS Whitaker. Ranger VII (Part II). Experimenters' Analyses and In- terpretations, pp. 1-154, Technical Report No. 32-700, {et Pro- pulsion Lab-NASA. 1966 Chemical evidence relative to the origin of the solar system. Mon. Not. R. Astron. Soc. 131: 199-223. The capture hypothesis of the origin of the moon. In The Earth- Moon System, ed. B. G. Marsden and A. G. W. Cameron, pp. 210- 12. New York: Plenum Press. With R. L. Heacock, G. P. Kuiper, E. M. Shoemaker, and E. A. Whitaker. Rangers 8 and 9 (Part II). Experimenters' Analyses and Interpretations. Technical Report No. 32-800, let Propulsion Lab-NASA. Observations on the Ranger VIII and IX Pictures, pp. 339-61. Tech- nical Report No. 32-800. let Propulsion Lab-NASA. Observations on the Ranger VII Pictures. Technical Report No. 32- 700. Jet Propulsion Lab-NASA. With I. R. Arnold. Biological materials in carbonaceous chondrites. In Biology and the Exploration of Mars, ed. C. S. Pittendrich, W. Vishniac, and J. Pearman, pp. 114-24. Washington, D.C.: National Academy of Sciences. 1967 Study of the Ranger pictures of the moon. Proc. R. Soc. London, Ser. A 296:418-31. The abundance of the elements with special reference to the iron abundance. (Harold Jeffreys Lecture). J. R. Astron. Soc. 8:23-47. Parent bodies of the meteorites and the origin of chondrules. Icarus 7:350-59. The origin of the moon. In Mantles of the Earth and Terrestrial Plan- ets, ed. S. K. Runcorn, pp. 251-60. London: John Wiley & Sons. 1968 With K. Marti. Surveyor results and the composition of the moon. Science 161:1030-32. The origin of some meteorites from the moon. Naturwissenschaften 55:49-57. The problem of elemental abundances. In Origin and Distribution of

HAROLD CLAYTON UREY 409 the Elements, ed. L. H. Ahrens, pp. 207-53. Oxford: Pergamon Press. Dalton's influence in chemistry. In John Dalton and the Progress of Science, ed. D. S. L. Cardwell, pp. 329-44. Manchester: Manches- ter University Press. 1969 Early temperature history of the moon. Science 165:1275. With G. I. F. MacDonald. Geophysics of the moon. Science 5: (5) :60- 66. With B. Nagy. Organic geochemical investigations in relation to the analyses of returned lunar rock samples. In Life Sciences and Space Research VII, pp.31-45. Amsterdam: North-Holland. Birth and growth of the oceans. In Oceanography, The Last Frontier, ed. R. C. Vetter, pp.31-44. Forum Series, Voice of America, U.S. Information Agency, Washington, D.C., broadcast for October 1969. 1970 With K. Marti and G. W. Lugmair. Solar wind gases, cosmic-ray spallation products and the irradiation history. Science 167:548- 50. With B. Nagy, C. M. Drew, P. B. Hamilton, V. E. Modzeleski, M. E. Murphy, W. M. Scott, and M. Young. Organic compounds in lu- nar samples: pyrolysis products, hydrocarbons, amino acids. Sci- ence 167:770-73. With B. Nagy, M. Scott, V. E. Modzeleski, L. A. Nagy, M. Drew, W. S. McEwan, J. E. Thomas, and P. B. Hamilton. Carbon compounds in Apollo 11 lunar samples. Nature 225:1028-32. With M. E. Murphy, V. E. Modzeleski, B. Nagy, W. M. Scott, M. Young, C. M. Drew, and P. B. Hamilton. Analysis of Apollo 11 lunar samples by chromatography and mass spectrometry. Pyroly- sis products, hydrocarbons, sulfur and amino acids. Proceedings of the Apollo 11 Lunar Science Conference, vol. 2, pp. 1879-90. 1971 With B. Nagy, I. E. Modzeleski, V. E. Modzeleski, M. A. Jabbar Mohammed, L. A. Nagy, W. M. Scott, C. M. Drew, I. E. Thomas, .

410 BIOGRAPHICAL MEMOIRS R. Ward, and P. B. Hamilton. Carbon compounds in Apollo 12 lunar samples. Nature 232:94-98. Was the moon originally cold? Science 172:403-5. A review of the structure of the moon. Proc. Am. Philos. Soc. 155:67- 73. 1972 . With K. Marti. Lunar basalts. Science 176:117-19. With D. M. Anderson, K. Biemann, L. E. Orgel, {. Oro, T. Owen, G. P. Shulman, and P. Toulmin III. Mass spectrometric analysis of organic compounds, water and volatile constituents in the atmo- sphere and surface of mars: the Viking Mars Lander. Icarus 16:111- 38. Abundance of the elements. Ann. N.Y. Acad. Sci. 194:35-44. The origin of the moon and solar system. In The Moon, ed. S. K. Runcorn and H. C. Urey, pp. 429-40. Dordrecht, Holland: Reidel. Maria Goeppert Mayer (1906-1972~. Year Book Am. Philos. Soc. pp. 234-36. Evidence for objects of lunar mass in the early solar system and for capture as a general process for the origin of satellites. Astrophys. Space Sci. 16:311-23. 1973 Cometary collisions and geological periods. Nature 242:32-33. With V. E. Modzeleski, I. E. Modzeleski, M. A. Tabbar Mohammed, L. A. Nagy, B. Nagy, W. S. McEwan, and P. B. Hamilton. Carbon compounds in pyrolysates and amino acids in extracts of Apollo 14 lunar samples. Nat. Phys. Sci. 242:50-52. With S. K. Runcorn. A new theory of lunar magnetism. Science 180:636- 38. 1974 Evidence for lunar type objects in the early solar system. In High- lights of Astronomy, ed. G. Contopoulos, vol 3, pp. 475-81. Comment on winning the Nobel Prize. New Sci. 64:10-17. 1975 With S. L. Miller and J. Oro. Origin of organic compounds or~ the primitive earth and in meteorites. [. Mol. Evol. 9:59-72.

FI A R O L D C LAYT O N U R E Y 411 With H. Alfven. Testimony on the California nuclear initiative. En- ergy 1:105-8. 1977 With J. A. O'Keefe. The deficiency of siderophile elements in the moon. Philos. Trans. R. Soc. London Ser. A 285:569-75. With I. Oro and S. L. Miller. In Energy Conversion in the Context of the Origin of Life, ed. R. Buvet et al., pp. 7-19. Amsterdam: North- Holland. r

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Biographic Memoirs Volume 68 contains the biographies of deceased members of the National Academy of Sciences and bibliographies of their published works. Each biographical essay was written by a member of the Academy familiar with the professional career of the deceased. For historical and bibliographical purposes, these volumes are worth returning to time and again.

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