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a hypothesis, credited largely to Alfred Wegener, that suggested all present continents once existed as a single supercontinent
continental volcanic arc
mountains formed in part by igneous activity associated with the subduction of oceanic lithosphere beneath a continent
convergent plate boundary
a boundary in which two plates move together, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle
divergent plate boundary
a boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor
linear zone of irregular topography on the deep-ocean floor; follows transform faults and their inactive extensions
a proposed concentration of heat in the mantle capable of introducing magma that in turn extrudes onto Earth's surface
a coherent unit of Earth's rigid outer layer that includes the crust and upper mantle
a sensitive instrument used to measure the intensity of Earth's magnetic field at various points
magnetic time scale
the detailed history of Earth's magnetic reversals developed by establishing the magnetic polarity of lava flows of known age
a mass of hotter-than-normal mantle material that ascends toward the surface, where it may lead to igneous activity
the proposed supercontinent that 200 million years ago began to break apart and form the present landmasses
the theory that proposes Earth's outer shell consists of individual plates, which interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself
a mechanism that may contribute to plate motion; involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity
the hypothesis first proposed in the 1960s by Harry Hess, suggesting that new oceanic crust is produced at the crests of mid-ocean ridges, which are the sites of divergence
a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and "pulls" the trailing lithosphere along
a huge landmass that consists of all, or nearly all, of the existing continents combined into one
transform fault boundary
a boundary in which two plates slide past one another without creating or destroying lithosphere
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