These plates move relative to one another above a hotter, deeper, more mobile zone at average rates as great as a few inches per year.
Evidence for Continental Drift
Most of the world's active volcanoes are located along or near the boundaries between shifting plates and are called plate-boundary volcanoes. The peripheral areas of the Pacific Ocean Basin, containing the boundaries of several plates, are dotted with many active volcanoes that form the so-called Ring of Fire. The Ring provides excellent examples of plate-boundary volcanoes, including Mount St. However, some active volcanoes are not associated with plate boundaries, and many of these so-called intra-plate volcanoes form roughly linear chains in the interior of some oceanic plates.
This figure shows the boundaries of lithosphere plates that are active at present.
Continental Drift: Theory & Definition
The double lines indicate zones of spreading from which plates are moving apart. The lines with barbs show zones of underthrusting subduction , where one plate is sliding beneath another. The barbs on the lines indicate the overriding plate. The single line defines a strike-slip fault along which plates are sliding horizontally past one another. The stippled areas indicate a part of a continent, exclusive of that along a plate boundary, which is undergoing active extensional, compressional, or strike-slip faulting.
The ocean floor is thus pushed at right angles and in opposite directions away from the crests. By the late s, several American investigators, among them Jack E. Oliver and Bryan L. Isacks, had integrated this notion of seafloor spreading with that of drifting continents and formulated the basis of plate tectonic theory. Oceanic ridges occur along some of the plate margins.
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Where this is the case, the lithospheric plates separate, and the upwelling mantle material forms new ocean floor along the trailing edges. As the plates move away from the flanks of the ridges, they carry the continents with them.
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- Fossils as Indicators of Continental Drift* | Nature.
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On the basis of all these factors, it may be assumed that the Americas were joined with Europe and Africa until approximately million years ago, when a rift split them apart along what is now the crest of the Mid-Atlantic Ridge. Subsequent plate movements averaging about 2 cm 0. It seems likely, though it is still unproven, that this breakup of a single landmass and the drifting of its fragments is merely the latest in a series of similar occurrences throughout geologic time.
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See Article History. Read More on This Topic. In German meteorologist Alfred Wegener, impressed by the similarity of the geography of the Atlantic coastlines, explicitly presented….
When Continental Drift Was Considered Pseudoscience
Facts Matter. Start Your Free Trial Today. Learn More in these related Britannica articles:. In German meteorologist Alfred Wegener, impressed by the similarity of the geography of the Atlantic coastlines, explicitly presented the concept of continental drift. Though plate tectonics is by no means synonymous with continental drift, the term encompasses this idea and derives much….
Continental Drift Theory: Understanding Our Changing Earth
The geologic evolution of Antarctica has followed a course similar to that of the other southern continents. Similarity in patterns of…. The continents are distributed at different latitudes, and latitudinal position affects the temperature of oceanic waters along continental margins the combined area of the continental shelf and continental slope ; in short, sedimentary deposition is climatically sensitive.
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