Ringwood, Alfred Edward (Ted)

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RINGWOOD, ALFRED EDWARD (TED)

(b. Melbourne, Victoria, Australia, 19 April 1930; d. Canberra, Australian Capital Territory, Australia, 12 November 1993), geochemistry, mineralogy, geophysics, planetology.

Ringwood was one of the first scientists to investigate the importance of high-pressure phase transformations for the mineralogy of Earth’s mantle. He used experimental high-pressure, high-temperature techniques, and theory from crystal chemical models to make major advances in the study of Earth’s interior. He integrated his experimental results with geophysical observations of the deep Earth, and with geochemical information as well, to present influential models of the nature and evolution of Earth and also of the Moon and the solar system. On the return of lunar samples by the Apollo missions in the 1970s, Ringwood conducted experimental studies constraining the petrogenesis of lunar mare and lunar highland basalts, and he was the leading figure in the synthesis of the lunar sampling program into models of origin of the Earth-Moon system. He also applied his theoretical and experimental knowledge of mineral and melt equilibrium in devising suitable mineral hosts for high-level nuclear waste (the SYNROC [synthetic rock] concept).

Ringwood’s scientific career was almost entirely in Australia, and he used his physical separation from the scientific centers of Europe and the United States to foster independence and innovation, selecting short visits and attendance at key conferences to influence, while not being constrained by, the scientific mainstream. A very early recruit to the nascent earth sciences in 1960 at the Australian National University (ANU) in Canberra under Professor John Jaeger, he was a key figure in the remarkably rapid rise of the ANU in the 1970s to be one of the world’s leading research institutions in geophysics and geochemistry. Ringwood was committed to the ideal of the ANU as a distinctively Australian center of international leadership in research. He was director of the Research School of Earth Sciences at ANU from 1978 to 1983 and acknowledged the role played by the unique support of the ANU given by successive Australian governments from the 1950s to the late 1980s. This support permitted long-term investment in new initiatives of which Ringwood was a powerful supporter, including high-pressure research, the design and construction of the Sensitive High Resolution Ion Microprobe (SHRIMP), the establishment of geophysical fluid dynamics at ANU, and the development of mineral physics, seismology, and geodynamics.

Early Development Ted Ringwood was born in Kew, an inner Melbourne suburb. He was an only child in a family that strongly identified with Australia, including the tribal and suburban rivalries of Melbourne centered around the distinctive Australian Rules Football and the Victorian Football League. His father, also Alfred, enlisted as an eighteen-year-old in World War I, and his experiences of gas attack, trench feet, and other suffering in the trenches in France impacted heavily on his physical health in and on his outlook in later life. During the 1920s Ted’s father held a variety of unskilled jobs and was essentially unemployed from the beginning of the Great Depression. In later years he received a war service pension. Ted’s mother, Ena, and the wider family provided stability through difficult financial circumstances and placed a strong emphasis on the value of education.

Ringwood excelled academically through suburban primary school and won a scholarship to attend as a boarder the Geelong Grammar School, Victoria’s most prestigious private school. On completion of his secondary education, he won a Trinity College Resident Scholarship at University of Melbourne and began undergraduate studies in 1947. His academic interests were focused on geology and metallurgy and were balanced by a competitive participation in Australian Football in the Melbourne university team. On completion of his BSc degree with award of honors, he proceeded to the two-year MSc degree, based on a field mapping and igneous petrology project on Devonian Snowy River Volcanics in the sparsely populated and physically difficult terrain of eastern Victoria. He completed his MSc with honors in 1953 and immediately embarked on a PhD project at the University of Melbourne.

Influenced by reading the work of Victor M. Gold-schmidt on crystal chemical relationships, Ringwood chose a research topic that applied Goldschmidt’s ideas to understanding the behavior of elements during magmatic crystallization and that applied this crystal chemical approach from the rock scale to the scale of the structure of Earth. He was particularly interested in the use of crystal chemical concepts to predict the mineralogical constitution of the deep Earth and made a major contribution by using the magnesium germanate system as an analogue for the magnesium silicate system that dominates Earth’s interior.

The contextual setting for this work was the advances in seismology revealing internal deep Earth structure—an upper mantle (30–400 km [18–250 mi] below Earth’s surface), transition zone (400–900 km [250–560 mi] below the surface), and lower mantle (900–2,900 km [560–1,800 mi] below the surface)—and debate on the cause of the rapid increase in seismic velocities through the transition zone. In “The Olivine-Spinel Transition in the Earth’s Mantle” in Nature (1956), he attributed the transition zone to polymorphic changes, in particular from monoclinic olivine to cubic spinel structure for (Mg,Fe)₂ SiO₄ composition. This work was the beginning of a lifetime of experimental and theoretical study of pressure-induced phase transformations in silicate and oxide minerals involving the major components of Earth’s interior (SiO₂, MgO, FeO, CaO, Al₂ O₃, Na₂ O, NiO). A particular feature of the work was the use of crystal chemical rules based on ionic radii and ionic charge in a systematic way to guide experimental studies of solid solutions in phases stable at low pressures, but at higher pressure capable of accepting greater proportions of magnesium silicate end-members. The use of germanate phases as low-pressure analogues of high-pressure silicate phases was followed by recognition and experimental study of potential roles for (Mg,Si) substitution for (2Al) in garnet structure and of perovskite (CaTiO₃) structure for CaSiO₃, ilmenite ([MgFe]TiO₃) structure for pyroxenes, and rutile (TiO₂) structure for SiO₂.

High-Pressure Studies Ringwood worked with a variety of solid media high-pressure apparatuses. From the mid-1980s he collaborated with several Japanese visitors and was very influential among Japanese scientists as he and they led rapid advances in ultra-high-pressure research. Recognition of his pioneering work included the naming of the dense spinel-form of (Mg,Fe)₂ SiO₄ composition “ringwoodite” and of the dense garnet-form of the (Mg,Fe) SiO₃ composition “majorite” (from Alan Major, Ringwood’s technical officer and colleague from 1963 to 1993).

In addition to the experimental studies and their application, Ringwood maintained a strong interest in the interplay between geodynamics, seismology, petrology, and petrophysics so that he applied the experimental constants to models of Earth’s behavior. A relatively late convert (in 1968–1969) from “fixist” to continental drift–plate tectonics, Ringwood addressed the interplay of chemical inhomogeneity and phase transformations in the penetration or arrest of subducted lithosphere at transition zone pressures. His 1975 book Composition and Petrology of the Earth’s Mantle synthesized the experimental work on phase transformations and its geodynamic implications and, equally important, brought together another main theme of Ringwood’s research, namely, the chemical composition and evolution of Earth.

Ringwood debated the issue of whole-mantle versus layered-mantle convection and argued that descending slabs (the “engine” of plate tectonics) would be deflected or aggregated within the transition zone due to the interplay between compositional differences and consequent differences in phase assemblages and densities of the downgoing slabs (oceanic crust and lithosphere) and surrounding peridotite mantle. He presented a substantial case that no major compositional difference exists between upper and lower mantle compositions and that the peridotite composition inferred for the upper mantle was consistent with the geophysical constraints on lower mantle properties.

In parallel with his work at very high pressure, he collaborated at ANU with David H. Green, Trevor H. Green, Ian A. Nicholls, and others on investigations using the piston cylinder apparatus (to pressure 4 GPa), complex natural rock compositions, and the newly developed electron microprobe to experimentally investigate petrological processes inferred for the uppermost mantle. Ringwood coined the name pyrolite for a model mantle composition of inferred peridotitic character, that is, one dominated by pyroxene and olivine. With his collaborators he experimentally determined the phase relations and the melting behavior of this model composition up to pressures of 4 GPa, that is, equivalent to mantle depths of approximately 130 kilometers (80 miles). Parallel studies of appropriately selected natural volcanic rocks (basalts, andesites) led to interpretations of depths of origin, degrees of melting, and melt-residue relationship for the different types of basaltic magmas occurring at mid-ocean ridges and hot spots, or sites of mantle upwelling. The reactions from low-pressure basaltic or gabbroic mineralogy (rich in plagioclase) to high-pressure eclogite mineralogy (rich in garnet) were studied experimentally, and a major role was ascribed to this transformation in providing a significant driving force for subduction of oceanic crust and lithosphere. For a period of thirty years from the 1960s, Ringwood was thus a leading contributor to the rapidly developing knowledge of Earth’s upper mantle, including its melting behavior and melt products, or volcanism, and high-pressure metamorphism. His work on Earth’s mantle and crust-mantle relationships was summarized in Composition and Petrology of the Earth’s Mantle.

Solar System and Lunar Studies Following completion of his PhD research, Ringwood spent fifteen months as a postdoctoral fellow with Francis Birch at Harvard University. This visit, his longest sojourn outside Australia, introduced Ringwood to experimental high-pressure work, but he also used the opportunity to begin a study of meteorites and to view meteorites in the context of a growing body of knowledge of solar elemental Abūndances and of the variations in density, moment of inertia, and so on among the planets. In the late 1950s and early 1960s he addressed the chondritic Earth model and discussed the nature and origin of the solar system. He argued that several meteorite classes had formed by auto-reduction processes from parental type I carbonaceous chondrite and emphasized the role of melting and differentiation in precursor bodies in relating suites of meteorite samples. He stressed the importance of differing oxidation states as explanations for different densities among Venus, Earth, and Mars.

In 1960 Ringwood advocated a modified version of Charles Darwin’s fission hypothesis, in which Earth’s Moon is drawn off from Earth’s mantle after core separation (in contrast to models of lunar capture, for example). The lunar samples returned in 1969 provided a field of fertile study in themselves, but their chemical compositions also provided a basis for comparisons with Earth materials and thus prompted vigorous debate on Earth-Moon relationships. Ringwood used the high-pressure laboratory and his experience in studying terrestrial basaltic rocks to test models of petrogenesis of lunar mare basalts and models advocating mare or highland basalt compositions as representative of the lunar interior. Primitive or parental mare basalt compositions were identified and constraints were placed on temperatures and depths of origin as partial melts from a differentiated lunar interior. As the fission hypothesis gathered support with a giant impact as the preferred cause of the detachment of the Earth material, Ringwood remained skeptical on the grounds that a giant impact would have caused catastrophic melting of the core and mantle. He advocated ejection of protolunar material by multiple smaller impacts after separation of Earth’s core. The subject remains a debatable one. Ringwood’s views on the origin and differentiation of the solar system and of the Earth-Moon system in particular were summarized in his book, Origin of the Earth and Moon (1979).

Nuclear Waste and SYNROC Mineral exploration in Australia through the 1960s and 1970s identified major deposits of uranium mineralization. Growth of the international nuclear power industry, alongside the Nuclear Non-Proliferation Treaty (1968), which attempted to limit the number of states developing nuclear weapons, made the mining and export of uranium a political issue in Australia. Australia, with major coal and natural gas reserves, does not generate power by nuclear means, but environmentalists were strongly opposed to uranium mining and enrichment, and to the use of uranium in thermonuclear reactors whether in Australia or overseas. A principal concern was and remains the disposal of high-level nuclear wastes with high levels of radioactivity, including long-lived radioisotopes. These wastes present a radiological hazard that requires management for timescales of thousands of years, and no nation has yet proceeded to implement permanent disposal of its high-level wastes, whether from military or industrial processes.

In the mid-1970s public debate in Australia about the export of uranium was intensive and divisive. At the same time, most nations with nuclear power programs (which were the potential purchasers of Australia’s uranium resources) planned to consolidate and solidify their high-level wastes in glass matrix as the first barrier to mobility of radioactive isotopes. With his experience in geochemistry and background geological knowledge of the behaviors of glass and minerals over geological time scales, along with his knowledge of subsurface conditions of temperature and fluid mobility, Ringwood recognized that the glass matrix strategy was less than ideal. In geological terms, glass is not stable and is readily hydrated or leached by circulating groundwater. Using crystal chemical arguments and knowledge of the behavior of minerals containing radioactive elements over geological time scales, Ringwood developed the concept of crystalline ceramics as hosts to the radio nuclides of nuclear wastes and patented his concept as SYNROC (from synthetic rock). SYNROC is a titania-based ceramic, the constituent minerals of which have the capacity to immobilize, in their crystal lattices, most of the radio nuclides of high-level nuclear wastes. In its further development, the SYNROC concept has developed particular compositions tailored to specific waste forms, and SYNROC remains a significant factor in the planning for military and industrial nuclear waste disposal. It is noteworthy that the launch of the SYNROC concept by Ringwood in 1979 was attacked both by the environmentalist lobby and by the nuclear industry. The latter, in part already committed to the glass waste form, did not welcome the criticism implicit in Ringwood’s advocacy of “an improved wasteform.” The environmentalist lobby did not welcome any weakening of their case for the total intractability of nuclear waste management.

The development and advocacy of SYNROC was consistent with Ringwood’s contributions to science. It was independent; unconstrained by the dominant paradigm, or “establishment” view; insightful; based firmly on basic science principles; and imaginative, “big-picture” science in its applications.

His Methodology and Significance Ringwood’s modus operandi used sound theory to devise an experimental approach, robust experimental data to constrain an hypothesis or hypotheses, and imaginative extension into implications or consequences of favored hypotheses— leading to further testing toward confirmation or rejection. He was not afraid to change his views but preferred to be proved in error by his own efforts rather than by others. In accepting the Feltrinelli International Prize by the National Academy of Italy in 1991, Ringwood said, “Our understanding of the Earth in all her aspects has developed dramatically during the last 25 years. This has been an exhilarating period to have been an Earth Scientist. I feel very fortunate and fulfilled to have been able to participate in some of these developments.”

Ted Ringwood was a leader of international stature and distinctively Australian in his independence and selective association. The composition, origin, structure, and dynamics of Earth and the origin and evolution of the solar system were debated and successfully explored in the latter half of the twentieth century, with Ringwood as a major contributor and an influential, articulate, and leading intellect.

Honors and Awards Ringwood’s work was widely honored by medals, distinguished lectures, and election to fellowships of scientific societies. Among others, he received the Bowie Medal of the American Geophysical Union in 1974 and the Goldschmidt Medal Award of the Geo-chemical Society in 1991; perhaps his most prestigious award was the Feltrinelli International Prize in 1991, granted by the National Academy of Italy. His research contributions remain influential through his more than three hundred scientific articles, and two books, Composition and Petrology of the Earth’s Mantle and Origin of the Earth and Moon, which synthesized many of his investigations and ideas. Ringwood’s research was prematurely terminated by his death from lymphoma in 1993.

BIBLIOGRAPHY

WORKS BY RINGWOOD

“The Principles Governing Trace Element Distribution during

Magmatic Crystallization. Part I. The Influence of Electro-negativity.” Geochemica et Cosmochimica Acta 7 (1955): 189–202. Application of Goldschmidt’s rules on crystal chemical relationships to trace element behaviors in the crystallization of igneous rocks. “The Principles Governing Trace Element Behaviour during

Magmatic Crystallisation. Part II. The Role of Complex Formation.” Geochemica et Cosmochimica Acta 7 (1955): 242–254. Explores the roles of complex formation in trace element behavior in crystallization of silicate melts. “The Olivine-Spinel Transition in the Earth’s Mantle.” Nature

178 (1956): 1303–1304. Application of germanate as analogues of silicate crystallization to predict the role of high-pressure phase transformation in Earth’s interior. “The System Mg₂ SiO₄-Mg₂ GeO₄.” American Journal of Science

254 (1956): 707–711. Initial study of germanate and silicate melts and crystalline solid solutions. “On the Chemical Evolution and Densities of the Planets.”

Geochemica et Cosmochimica Acta 15 (1959): 257–283. “Chemical and Genetic Relationships among Meteorites.”

Geochemica et Cosmochimica Acta 24 (1961): 159–197. “Present Status of the Chondritic Earth Model.” In Researches on

Meteorites, edited by Carleton B. Moore. New York: Wiley, 1962. “Chemical Evolution of the Terrestrial Planets.” Geochemica et

Cosmochimica Acta 30 (1966): 41–104. “Genesis of Chondritic Meteorites.” Reviews of Geophysics 4

(1966): 113–175. “Some Comparative Aspects of Lunar Origin.” Physics of the

Earth and Planetary Interiors 6 (1972): 366–376. Exploration of models of lunar origin, based on results from Apollo landings and lunar sampling.

Composition and Petrology of the Earth’s Mantle. New York:

McGraw-Hill, 1975.

Origin of the Earth and Moon. New York: Springer-Verlag, 1979. “Immobilization of Radioactive Wastes in SYNROC.” American

Scientist 70 (1982): 201–207. A synthesis of research into the identification of crystalline host minerals for immobilization of high-level nuclear waste. “Flaws in the Giant Impact Hypothesis of Lunar Origin.” Earth and Planetary Science Letters 95 (1989): 208–214. A critical look at proposals of lunar origin by a single large impact on Earth. “Phase Transformations and Their Bearing on the Constitution and Dynamics of the Mantle.” Geochemica et Cosmochimica Acta 55 (1991): 2083–2110. A review of the applications of high-pressure study of phase transformations to infer the dynamical behaviors and chemical composition of Earth’s interior.

With William O. Hibberson. “Solubility of Mantle Oxides in

Molten Iron at High Pressures and Temperatures: Implications for Core-Mantle Reaction and the Nature of the D” Layer in the Lower Mantle.” Earth and Planetary Science Letters 102 (1991): 235–251. “Volatile and Siderophile Element Geochemistry of the Moon: A

Reappraisal.” Earth and Planetary Science Letters 111 (1992): 537–555.