In 1912 the meteorologist Alfred Wegener described what he called continental drift, an idea that culminated fifty years later in the modern theory of plate tectonics. Wegener expanded his theory in his 1915 book The Origin of Continents and Oceans.
Armed with the knowledge of a new heat source, scientists realized that the Earth would be much older, and that its core was still sufficiently hot to be liquid. By 1915, after having published a first article in 1912, Alfred Wegener was making serious arguments for the idea of continental drift in the first edition of The Origin of Continents and Oceans.
In 1912 the meteorologist Alfred Wegener described what he called continental drift, an idea that culminated fifty years later in the modern theory of plate tectonics. Wegener expanded his theory in his 1915 book The Origin of Continents and Oceans.
Armed with the knowledge of a new heat source, scientists realized that the Earth would be much older, and that its core was still sufficiently hot to be liquid. By 1915, after having published a first article in 1912, Alfred Wegener was making serious arguments for the idea of continental drift in the first edition of The Origin of Continents and Oceans.
During the 1920s, 1930s and 1940s, the former reached important milestones proposing that convection currents might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust.
By the late 1920s, seismologists were beginning to identify several prominent earthquake zones parallel to the trenches that typically were inclined 40–60° from the horizontal and extended several hundred kilometers into the Earth.
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.
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.
Therefore, Wegener later changed his position and asserted that convection currents are the main driving force of plate tectonics in the last edition of his book in 1929. However, in the plate tectonics context (accepted since the seafloor spreading proposals of Heezen, Hess, Dietz, Morley, Vine, and Matthews (see below) during the early 1960s), the oceanic crust is suggested to be in motion with the continents which caused the proposals related to Earth rotation to be reconsidered.
This theory was launched by Arthur Holmes and some forerunners in the 1930s and was immediately recognized as the solution for the acceptance of the theory as originally discussed in the papers of Alfred Wegener in the early years of the century.
These ideas find their roots in the early 1930s in the works of Beloussov and van Bemmelen, which were initially opposed to plate tectonics and placed the mechanism in a fixistic frame of verticalistic movements.
During the 1920s, 1930s and 1940s, the former reached important milestones proposing that convection currents might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust.
Wegener could not explain the force that drove continental drift, and his vindication did not come until after his death in 1930. ===Floating continents, paleomagnetism, and seismicity zones=== As it was observed early that although granite existed on continents, seafloor seemed to be composed of denser basalt, the prevailing concept during the first half of the twentieth century was that there were two types of crust, named "sial" (continental type crust) and "sima" (oceanic type crust).
In reality, it actually shows that the work by the European scientists on island arcs and mountain belts performed and published during the 1930s up until the 1950s was applied and appreciated also in the United States. If the Earth's crust was expanding along the oceanic ridges, Hess and Dietz reasoned like Holmes and others before them, it must be shrinking elsewhere.
In that book (re-issued in four successive editions up to the final one in 1936), he noted how the east coast of South America and the west coast of Africa looked as if they were once attached.
The South African Alex du Toit put together a mass of such information in his 1937 publication Our Wandering Continents, and went further than Wegener in recognising the strong links between the Gondwana fragments. Wegener's work was initially not widely accepted, in part due to a lack of detailed evidence.
During the 1920s, 1930s and 1940s, the former reached important milestones proposing that convection currents might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust.
The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s. The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken into tectonic plates.
In reality, it actually shows that the work by the European scientists on island arcs and mountain belts performed and published during the 1930s up until the 1950s was applied and appreciated also in the United States. If the Earth's crust was expanding along the oceanic ridges, Hess and Dietz reasoned like Holmes and others before them, it must be shrinking elsewhere.
When newly formed rock cools, such magnetic materials recorded the Earth's magnetic field at the time. As more and more of the seafloor was mapped during the 1950s, the magnetic variations turned out not to be random or isolated occurrences, but instead revealed recognizable patterns.
The first time the evidence of magnetic polar wander was used to support the movements of continents was in a paper by Keith Runcorn in 1956, and successive papers by him and his students Ted Irving (who was actually the first to be convinced of the fact that paleomagnetism supported continental drift) and Ken Creer. This was immediately followed by a symposium in Tasmania in March 1956.
The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s. The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken into tectonic plates.
Therefore, Wegener later changed his position and asserted that convection currents are the main driving force of plate tectonics in the last edition of his book in 1929. However, in the plate tectonics context (accepted since the seafloor spreading proposals of Heezen, Hess, Dietz, Morley, Vine, and Matthews (see below) during the early 1960s), the oceanic crust is suggested to be in motion with the continents which caused the proposals related to Earth rotation to be reconsidered.
The study of global seismicity greatly advanced in the 1960s with the establishment of the Worldwide Standardized Seismograph Network (WWSSN) to monitor the compliance of the 1963 treaty banning above-ground testing of nuclear weapons.
Therefore, when various scientists during the early 1960s started to reason on the data at their disposal regarding the ocean floor, the pieces of the theory quickly fell into place. The question particularly intrigued Harry Hammond Hess, a Princeton University geologist and a Naval Reserve Rear Admiral, and Robert S.
In the early 1960s scientists such as Heezen, Hess and Dietz had begun to theorise that mid-ocean ridges mark structurally weak zones where the ocean floor was being ripped in two lengthwise along the ridge crest (see the previous paragraph).
Mason and co-workers in 1961, who did not find, though, an explanation for these data in terms of sea floor spreading, like Vine, Matthews and Morley a few years later. The discovery of magnetic striping called for an explanation.
The study of global seismicity greatly advanced in the 1960s with the establishment of the Worldwide Standardized Seismograph Network (WWSSN) to monitor the compliance of the 1963 treaty banning above-ground testing of nuclear weapons.
In this symposium, Edward Bullard and co-workers showed with a computer calculation how the continents along both sides of the Atlantic would best fit to close the ocean, which became known as the famous "Bullard's Fit". In 1966 Wilson published the paper that referred to previous plate tectonic reconstructions, introducing the concept of what is now known as the "Wilson Cycle". In 1967, at the American Geophysical Union's meeting, W.
In this symposium, Edward Bullard and co-workers showed with a computer calculation how the continents along both sides of the Atlantic would best fit to close the ocean, which became known as the famous "Bullard's Fit". In 1966 Wilson published the paper that referred to previous plate tectonic reconstructions, introducing the concept of what is now known as the "Wilson Cycle". In 1967, at the American Geophysical Union's meeting, W.
The other forces are only used in global geodynamic models not using plate tectonics concepts (therefore beyond the discussions treated in this section) or proposed as minor modulations within the overall plate tectonics model. In 1973, George W.
This theory, called "surge tectonics", was popularized during the 1980s and 1990s.
Alternative views have been proposed. ====Plume tectonics==== In the theory of plume tectonics followed by numerous researchers during the 1990s, a modified concept of mantle convection currents is used.
This theory, called "surge tectonics", was popularized during the 1980s and 1990s.
However, some researchers remain convinced that plate tectonics is or was once active on this planet. ===Mars=== Mars is considerably smaller than Earth and Venus, and there is evidence for ice on its surface and in its crust. In the 1990s, it was proposed that Martian Crustal Dichotomy was created by plate tectonic processes.
Scientists today disagree, and think that it was created either by upwelling within the Martian mantle that thickened the crust of the Southern Highlands and formed Tharsis or by a giant impact that excavated the Northern Lowlands. Valles Marineris may be a tectonic boundary. Observations made of the magnetic field of Mars by the Mars Global Surveyor spacecraft in 1999 showed patterns of magnetic striping discovered on this planet.
On 8 September 2014, NASA reported finding evidence of plate tectonics on Europa, a satellite of Jupiter—the first sign of subduction activity on another world other than Earth. Titan, the largest moon of Saturn, was reported to show tectonic activity in images taken by the Huygens probe, which landed on Titan on January 14, 2005. ===Exoplanets=== On Earth-sized planets, plate tectonics is more likely if there are oceans of water.
In a more recent 2006 study, scientists reviewed and advocated these earlier proposed ideas.
On 8 September 2014, NASA reported finding evidence of plate tectonics on Europa, a satellite of Jupiter—the first sign of subduction activity on another world other than Earth. Titan, the largest moon of Saturn, was reported to show tectonic activity in images taken by the Huygens probe, which landed on Titan on January 14, 2005. ===Exoplanets=== On Earth-sized planets, plate tectonics is more likely if there are oceans of water.
Movie. Multiple videos of plate tectonic movements Quartz December 31, 2015 Geodynamics Geology theories Seismology Lithosphere
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