Furthermore, paleomagnetic data had shown that the magnetic pole had also shifted during time. Plate tectonics theory explains why: Earth’s geography has changed through time and continues to change today. These collision areas, called convergent boundaries, create mountain ranges. (1956). One type of motion is produced by seafloor spreading. The discovery of magnetic striping called for an explanation. mountain ranges are located where they are. While the mechanism of such an impressive thermal event remains a debated issue in Venusian geosciences, some scientists are advocates of processes involving plate motion to some extent. He further argued that if continents could move up and down in the mantle as a result of buoyancy changes produced by erosion or deposition, they should be able to move horizontally as well. certain regions may have deadly, mild, or no volcanic eruptions. The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like (visco-elastic solid) asthenosphere. Bringing together a large mass of geologic and paleontological data, Wegener postulated that throughout most of geologic time there was only one continent, which he called Pangea, and the breakup of this continent heralded Earth’s current continental configuration as the continent-sized parts began to move away from one another. In effect, the ocean basins are perpetually being “recycled,” with the creation of new crust and the destruction of old oceanic lithosphere occurring simultaneously. What Do Astronomers Use to Study Quasars? Seafloor and continents move around on Earth’s surface, but what is actually moving? In the late 19th and early 20th centuries, geologists assumed that the Earth's major features were fixed, and that most geologic features such as basin development and mountain ranges could be explained by vertical crustal movement, described in what is called the geosynclinal theory. This finding, though unexpected, was not entirely surprising because it was known that basalt—the iron-rich, volcanic rock making up the ocean floor—contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times. Picture two convection cells side-by-side in the mantle, similar to the illustration in figure 3. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea, and in 1928 that convection currents within the mantle might be the driving force. During the late 20th and early 21st centuries, it became apparent that plate-tectonic processes profoundly influence the composition of Earth’s atmosphere and oceans, serve as a prime cause of long-term climate change, and make significant contributions to the chemical and physical environment in which life evolves. New magma from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. Lateral density variations in the mantle result in convection; that is, the slow creeping motion of Earth's solid mantle. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. No matter what, smashing two enormous slabs of lithosphere together results in magma generation and earthquakes. Distinguished scientists, such as Harold Jeffreys and Charles Schuchert, were outspoken critics of continental drift. Most geologic activities, including volcanoes, earthquakes, and mountain building, take place at plate boundaries. What portion of the Earth makes up the “plates” in plate tectonics? The stripes alternate between those with magnetic material orientated toward magnetic north, and those oriented in the opposite direction.  This view however has been contradicted by a recent study which found that the actual motions of the Pacific Plate and other plates associated with the East Pacific Rise do not correlate mainly with either slab pull or slab push, but rather with a mantle convection upwelling whose horizontal spreading along the bases of the various plates drives them along via viscosity-related traction forces. These explanations remained popular until the 1950s and stimulated belief in the ancient submerged continent of Atlantis. Only four years after the maps with the "zebra pattern" of magnetic stripes were published, the link between sea floor spreading and these patterns was correctly placed, independently by Lawrence Morley, and by Fred Vine and Drummond Matthews, in 1963, now called the Vine–Matthews–Morley hypothesis. Two- and three-dimensional imaging of Earth's interior (seismic tomography) shows a varying lateral density distribution throughout the mantle.
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