GEOPHYSICAL EXPLORATIONS

GEOPHYSICAL EXPLORATIONS. Geophysics is a hybrid science (a combination of geology and physics) that achieved a distinctive identity only in the mid-twentieth century, which is understandable when it is recalled that neither geology nor physics emerged as distinctive disciplines until the mid-nineteenth century. The antecedents of geophysics reach back to Isaac Newton.

The geophysical exploration of the Americas began with the French expedition of 1735–1745 to the Peruvian Andes, which was led by Charles Marie de La Condamine and included Pierre Bouguer. Paired with a simultaneous venture to northern Scandinavia, the expedition attempted to verify the Newtonian prediction that the earth would be found to bulge at the equator and narrow at the poles, and the expeditions thus inaugurated the study of geodesy (measuring the earth's surface). About sixty years later, between 1799 and 1804, Alexander von Humboldt, accompanied by Aimé Bonpland, explored the American equatorial zone. In a romantic survey of natural history, Humboldt included such broadly geophysical measurements as terrestrial magnetism, which he linked to other physical phenomena—usually meteorological. These ventures set the style of geophysical exploration in America, establishing precedents for geophysics both as the direct object of an expedition—as in the pursuit of geodesy—and as a component of a larger reconnaissance including cartography, specimen collection, and geophysical measurements. For nineteenth-century America, the broader Humboldtean model was the more powerful: geophysics was rather an instrumental component of geographic surveys than a conceptual framework for geologic interpretation. After Darwin, this pattern was incorporated into an evolutionary model that supplied the theoretical context of earth science for more than a century.

Concern with applying physical theories and techniques gradually created an informal alliance between three scientific groups. Planetary astronomy, particularly as practiced by George H. Darwin, Osmond Fisher, and William Thomson (all British), addressed such problems as the formation, age, and structure of the earth. At the same time, "dynamical" geology, in contrast to historical or evolutionary geology, attempted to explain earth processes in terms of mechanics and physical laws. This group received some inspiration from such meteorologists as James Croll, who fashioned explanations for atmospheric dynamics based on physical processes; what physical chemistry and physical astronomy were to their respective disciplines, dynamical geology was to earth science. Finally, there was mining engineering, which provided technical training in metallurgy, mathematics, and physics at such schools as Columbia University and the University of California. Many of the instruments typical of geophysics, and many of the explorations that used them, stemmed from high-level prospecting, especially for oil.

In the exploration of the American West, geophysics is better understood in terms of certain themes and personalities than as a disciplinary science. Grove Karl Gilbert extended mechanics to problems in geomorphology and structural geology, framing quantitative geologic observations into rational systems of natural laws organized on the principle of dynamic equilibrium. Clarence E. Dutton, elaborating on speculations by John H. Pratt and George B. Airy, conceived the idea of isostasy, or the gravitational equilibrium of the earth's crust, and demonstrated how this pattern of vertical adjustment could become a compressive orogenic force (mountain formation, especially by the folding of the earth's crust). Dutton later made original contributions in volcanology and seismology. Samuel F. Emmons, Clarence King, and George F. Becker applied geochemical and geophysical analysis to the problems of orogeny and igneous ore formation. The latter two men were instrumental in establishing a chemistry laboratory in the U. S. Geological Survey and in applying its experimental results to geophysical phenomena. Becker explicitly attempted mathematical and mechanical models to describe ore genesis and the distribution of stress in the earth's crust. He was instrumental in the establishment of the Carnegie Institution's Geophysical Laboratory, served as the laboratory's first director, and bequeathed part of his estate to the Smithsonian Institution for geophysical research. Geophysics advanced in the context of a symbiosis (mutually beneficial relationship) of field exploration and laboratory investigation. In the case of the U. S. Geological Survey, Carl Barus staffed the laboratory and Robert S. Woodward furnished field geologists with information on mathematical physics. Woodward later directed the Carnegie Institution.

Following the work of the explorers, other geologists and geodesists—among them, Bailey Willis, Joseph Barrell, and J. F. Hayford—generated quantitative models for earth structure and tectonics. But explanations developed for glacial epochs best epitomized the status of geophysics: attempts to relate glacial movements to astrophysical cycles provided a common ground for geology, geophysics, astronomy, and meteorology, but the results were rarely integrated successfully. Significantly, the most celebrated attempt at global geophysical explanation remained an unassimilated hybrid. In developing the planetesimal hypothesis in 1904, Thomas C. Chamberlin preserved a naturalistic understanding of earth geology, while F. R. Moulton supplied the mathematical physics. The earth sciences continued to subordinate their data and techniques to a broad evolutionary framework.

By the early twentieth century, geophysics was a conglomerate of pursuits promoted through federal scientific bureaus (Coast and Geodetic Survey, Geological Survey), private or university research institutes (Carnegie Institution's Geophysical Laboratory, the Smithsonian Institution), companies engaged in mineral prospecting, and exceptional individuals. Geophysics, having neither a disciplinary organization nor a unifying theory, remained more an analytic tool than a synthetic science.

This condition persisted until after World War II. Thereafter, with new instruments and techniques developed for mining and military purposes, with additional subjects (especially oceanography), and with a theoretical topic to organize its research (continental drift), geophysics developed both an identity and a distinctive exploring tradition. This was well exemplified by the International Geophysical Year (IGY), planned for 1957 and 1958 but extended to 1959. In counterpoint to the space program, geophysicists proposed to drill into the interior of the earth. Although aborted in 1963, Project Mohole was superseded by other oceanic drill projects, especially the Joint Oceanographic Institute's Deep Earth Sampling Program (JOIDES) begun in 1964. The International Upper Mantle Project (1968–1972) formed a bridge between IGY and research under the multinational Geodynamics Project (1974–1979), which proposed to discover the force behind crustal movements.

In the late 1990s, geophysical exploration led to the Ocean Drilling Program. The program functioned from a ship called the JOIDES Resolution, named for the Joint Oceanographic Institutions for Deep Earth Sampling. Built to drill into the seabed for oil, the ship's high-technology laboratory was used by an international crew of scientists to conduct geophysical research. The program found evidence related to the impact of a meteorite at the end of the Cretaceous Era, evidence of ocean temperature changes in the Ice Ages, and documented changes in the earth's magnetic poles.

Geophysics is a revolution in physics, and its integrative concept, the theory of plate tectonics (formerly continental drift), rivals relativity and quantum mechanics in significance. Involving geophysical research in practically all fields of earth science, and paired with satellite surveys, plate tectonics constitutes a new inventory of natural resources and a scientific synthesis of the globe.

Geophysical exploration has, moreover, preserved its archetypal (original) forms, being international and corporate in composition, global in scale, and quantitative in data and being founded on the theoretical assumption of a steady state. It blends the styles of La Condamine and Humboldt, combining specific geophysical pursuits against a cosmic landscape. Yet the transformation is remarkable—the difference between Humboldt's surveying of sublime panoramas from the summit of the Andes, and the Earth Technology Resource Satellite (ETRS) radioing instrumental data to terrestrial computers.

BIBLIOGRAPHY

Botting, Douglas. Humboldt and the Cosmos. New York: Harper and Row; London: Joseph, 1973.

Fraser, Ronald. Once Round the Sun: The Story of the International Geophysical Year. New York: Macmillan, 1957.

Glen, William. The Road to Jaramillo: Critical Years of the Revolution in Earth Sciences. Stanford, Calif. : Stanford University Press, 1982.

Goetzmann, William H. Exploration and Empire: The Explorer and the Scientist in the Winning of the American West. New York: Knopf, 1966; New York: Norton, 1978.

Hallam, Anthony. A Revolution in the Earth Sciences: From Continental Drift to Plate Tectonics. Oxford: Clarendon Press, 1973.

Oreskes, Naomi. The Rejection of Continental Drift: Theory and Method in American Earth Science. New York: Oxford University Press, 1999.

Sullivan, Walter. Continents in Motion: The New Earth Debate. New York: McGraw-Hill, 1974; American Institute of Physics. 1991.

StevePyne/a. r.; f. b.

See alsoCarnegie Institution of Washington ; Climate ; Geological Survey, U. S .; Geological Surveys, State ; Mineralogy ; Wilkes Expedition ; andvol. 9:An Expedition to the Valley of the Great Salt Lake of Utah .