by Academician Viktor KHAIN, Institute of the Lithosphere of Fringing and Inland Seas, Russian Academy of Sciences REVOLUTION IN GEOLOGY: PLATE TECTONICS Late in the 1960s and early 1970s the solid earth sciences ceased to be descriptive and got down to explaining geological processes by means of physical and mathematical laws. The new trend in research - geodynamics - united efforts of geologists, geophysicists and geochemists who focused on the nature of forces and processes occurring on our planet. In particular, those responsible for changes in its outer shells, including the lithosphere and the crust. There came a theory describing the development of the lithosphere as interaction of an ensemble of relatively monolithic plates, or the plate tectonics theory which wrought a virtual revolution in the earth sciences. The new theory relied on novel methods of research: geophysical (seismic, paleomagnetic, geothermal), isotope-geochemical, geological (experimental mineralogy, petrology). Upgraded, these and other innovative techniques (such as deep-water drilling, exploration of the earth from outer space) confirmed the basic principles of plate tectonics, for one, the vast importance of major lateral displacements (shifts) of earth rock. In keeping with the plate tectonics theory, the lithosphere of the earth falls into a small number of plates, of large and medium size, always in motion with respect to one another. These shifts are of triple nature-the plates may diverge move apart to form gaps that come to be filled with basaltic magma (the process of sea-floor spreading along mid-ocean ridges) or converge move toward one another, with one of them, an oceanic plate, underthrusting another (the process of subduction, "pushing under", on the periphery of continents or along island arcs); or else the plates may slide relative to one another along vertical rifts. Plate shifts obey the theorem of Leonard Euler, a great savant of the 18th century: a relative motion ... Read more