geophysics, major branch of theEarth sciences that applies the principles and methods ofphysics to the study of theEarth.

A brief treatment of geophysics follows. For full treatment,seegeology: Geophysics.

Geophysics deals with a wide array of geologic phenomena, including the temperature distribution of the Earth’s interior; the source, configuration, and variations of the geomagnetic field; and the large-scale features of the terrestrial crust, such as rifts, continental sutures, and mid-oceanic ridges. Modern geophysical research extends to phenomena of the outer parts of the Earth’satmosphere (e.g., the ionospheric dynamo, auroral electrojets, and magnetopause current system) and even to the physical properties of other planets and their satellites.

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Everything Earth

Many of the problems of geophysics areanalogous to those ofastronomy because the subject studied is rarely under direct observation, and conclusions must be drawn largely on the basis of mathematical interpretation of physical measurements. These include measurements of the Earth’s gravitationalfield with gravimeters on land and sea and artificial satellites in space; magnetometric measurements of the planet’s magnetic field; and seismological surveys of subsurface geologic structures using reflected and refracted elastic waves produced by earthquakes or by artificial means (seeseismic survey).

Research conducted with geophysical techniques has proved extremely useful in providing evidence in support of the theory ofplate tectonics. Seismographic data, for instance, have demonstrated that the world’s earthquake belts mark the boundaries of the enormous rigid plates thatconstitute the Earth’s outer shell, while the findings of paleomagnetic studies have made it possible to trace the drift of the continents overgeologic time.