geophysics, study of the structure, composition, and dynamic changes of the earth, its atmosphere, hydrosphere and magnetosphere, based on the principles of physics. The term was probably first used in Germany, where it appeared in scientific writings of the mid-19th cent. Geophysics, which embraces the concepts, data, and methods of various other sciences, is very broad in scope. For example, geology, meteorology, hydrology, oceanography, and seismology all enter into geophysical studies, with many of them overlapping (e.g., meteorology and oceanography in the study of possible global warming). Most techniques for locating subsurface petroleum, mineral deposits, and water supplies are reliant upon applied geophysics, including the use of seismic and electrical measurements at shallow depths and gravimetric, magnetic, and radiometric surveys at ground stations and in airplanes. Information is then correlated with visible surface features, subsurface conditions are inferred, and boreholes are drilled to determine the extent and richness of promising areas. Geophysics also is used to understand the interactions of the atmosphere and hydrosphere, including how certain anomalies in the ocean's circulation affect the atmosphere. Magnetosphere studies in geophysics concentrate on the magnetic field around the earth. Other geophysical studies are more specific, i.e. selenophysics, or the physics of the moon. Recent flyby spacecraft have accumulated extensive physical data, allowing geophysicists to theorize, by analogy to geophysical earth studies, about the underlying structures, atmospheres, and magnetospheres of other planets and satellites in the solar system.