Editing Plate tectonics (section)

=== Summary ===
[[File:Tectonic plates boundaries physical World map Wt 180degE centered-en.svg|thumb|upright=1.35|right|Detailed map showing the tectonic plates with their movement vectors]]
The development of the theory of plate tectonics was the scientific and cultural change which occurred during a period of 50 years of scientific debate. The event of the acceptance itself was a [[paradigm shift]] and can therefore be classified as a scientific revolution,<ref>{{Cite journal |last1=Casadevall |first1=Arturo |last2=Fang |first2=Ferric C. |date=1 March 2016 |title=Revolutionary Science |journal=[[mBio]] |volume=7 |issue=2 |pages=e00158–16 |doi=10.1128/mBio.00158-16 |pmc=4810483 |pmid=26933052}}</ref> now described as the [[Plate Tectonics Revolution]].

Around the start of the twentieth century, various theorists unsuccessfully attempted to explain the many geographical, geological, and biological continuities between continents. 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.<ref>{{Cite web |last=Hughes |first=Patrick |date=8 February 2001 |title=Alfred Wegener (1880–1930): A Geographic Jigsaw Puzzle |url=http://earthobservatory.nasa.gov/Features/Wegener/wegener_2.php |access-date=2007-12-26 |website=On the Shoulders of Giants |publisher=Earth Observatory, [[NASA]] |quote=... on January 6, 1912, Wegener... proposed instead a grand vision of drifting continents and widening seas to explain the evolution of Earth's geography.}}</ref>

Wegener expanded his theory in his 1915 book ''The Origin of Continents and Oceans''.{{sfn|Wegener|1929}} Starting from the idea (also expressed by his forerunners) that the present continents once formed a single land mass (later called [[Pangaea]]), Wegener suggested that these separated and drifted apart, likening them to "icebergs" of low density [[sial]] floating on a sea of denser [[Sima (geology)|sima]].<ref>{{Cite web |last=Hughes |first=Patrick |date=8 February 2001 |title=Alfred Wegener (1880–1930): The origin of continents and oceans |url=http://earthobservatory.nasa.gov/Features/Wegener/wegener_4.php |access-date=2007-12-26 |website=On the Shoulders of Giants |publisher=Earth Observatory, [[NASA]] |quote=By his third edition (1922), Wegener was citing geological evidence that some 300{{nbsp}}million years ago all the continents had been joined in a supercontinent stretching from pole to pole. He called it Pangaea (all lands),...}}</ref>{{sfn|Wegener|1966}} Supporting evidence for the idea came from the dove-tailing outlines of South America's east coast and Africa's west coast [[Antonio Snider-Pellegrini]] had drawn on his maps, and from the matching of the rock formations along these edges. Confirmation of their previous contiguous nature also came from the fossil plants ''[[Glossopteris]]'' and ''[[Gangamopteris]]'', and the [[therapsid]] or [[mammal-like reptile]] ''[[Lystrosaurus]]'', all widely distributed over South America, Africa, Antarctica, India, and Australia. The evidence for such an erstwhile joining of these continents was patent to field geologists working in the southern hemisphere. 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 but mostly because of the lack of a reasonable physically supported mechanism. Earth might have a solid crust and mantle and a liquid core, but there seemed to be no way that portions of the crust could move around. Many distinguished scientists of the time, such as [[Harold Jeffreys]] and [[Charles Schuchert]], were outspoken critics of continental drift.

Despite much opposition, the view of continental drift gained support and a lively debate started between "drifters" or "mobilists" (proponents of the theory) and "fixists" (opponents). During the 1920s, 1930s and 1940s, the former reached important milestones proposing that [[convection current]]s might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust. Concepts close to the elements of plate tectonics were proposed by geophysicists and geologists (both fixists and mobilists) like Vening-Meinesz, Holmes, and Umbgrove. In 1941, [[Otto Ampferer]] described, in his publication "Thoughts on the motion picture of the Atlantic region",<ref>[[Otto Ampferer]]: ''[https://www.zobodat.at/pdf/SBAWW_150_0019-0035.pdf Thoughts on the motion picture of the Atlantic region].'' Sber. österr. Akad. Wiss., math.-naturwiss. KL, 150, 19–35, 6 figs., Vienna 1941.</ref> processes that anticipated [[seafloor spreading]] and [[subduction]].<ref>{{Cite journal |last1=Dullo |first1=Wolf-Christian |last2=Pfaffl |first2=Fritz A. |date=28 March 2019 |title=The theory of undercurrent from the Austrian alpine geologist Otto Ampferer (1875–1947): first conceptual ideas on the way to plate tectonics |url=https://cdnsciencepub.com/doi/full/10.1139/cjes-2018-0157 |journal=[[Canadian Journal of Earth Sciences]] |volume=56 |issue=11 |pages=1095–1100 |bibcode=2019CaJES..56.1095D |doi=10.1139/cjes-2018-0157 |s2cid=135079657}}</ref><ref>Karl Krainer, Christoph Hauser: ''[https://www2.uibk.ac.at/downloads/c715/geoalp_sbd1_07/krainer_hauser.pdf Otto Ampferer (1875-1947): pioneer in geology, mountaineer, collector and draughtsman]''. In: Geo. Alp Sonderband 1, 2007, pp. 94–95.</ref> One of the first pieces of geophysical evidence that was used to support the movement of lithospheric plates came from [[paleomagnetism]]. This is based on the fact that rocks of different ages show a variable [[magnetic field]] direction, evidenced by studies since the mid–nineteenth century. The magnetic north and south poles reverse through time, and, especially important in paleotectonic studies, the relative position of the magnetic north pole varies through time. Initially, during the first half of the twentieth century, the latter phenomenon was explained by introducing what was called "polar wander" (see [[apparent polar wander]]) (i.e., it was assumed that the north pole location had been shifting through time). An alternative explanation, though, was that the continents had moved (shifted and rotated) relative to the north pole, and each continent, in fact, shows its own "polar wander path". During the late 1950s, it was successfully shown on two occasions that these data could show the validity of continental drift: by Keith Runcorn in a paper in 1956,{{sfn|Runcorn|1956}} and by Warren Carey in a symposium held in March 1956.{{sfn|Carey|1958}}

The second piece of evidence in support of continental drift came during the late 1950s and early 60s from data on the bathymetry of the deep [[ocean floor]]s and the nature of the oceanic crust such as magnetic properties and, more generally, with the development of [[marine geology]]<ref>see for example the milestone paper of {{Harvnb|Lyman|Fleming|1940}}.</ref> which gave evidence for the association of seafloor spreading along the [[mid-oceanic ridge]]s and [[Geomagnetic reversal|magnetic field reversals]], published between 1959 and 1963 by Heezen, Dietz, Hess, Mason, Vine & Matthews, and Morley.<ref>{{Harvnb|Korgen|1995}}, {{Harvnb|Spiess|Kuperman|2003}}.</ref>

Simultaneous advances in early [[seismic]] imaging techniques in and around [[Wadati–Benioff zone]]s along the trenches bounding many continental margins, together with many other geophysical (e.g., gravimetric) and geological observations, showed how the oceanic crust could disappear into the mantle, providing the mechanism to balance the extension of the ocean basins with shortening along its margins.

All this evidence, both from the ocean floor and from the continental margins, made it clear around 1965 that continental drift was feasible. The theory of plate tectonics was defined in a series of papers between 1965 and 1967. The theory revolutionized the Earth sciences, explaining a diverse range of geological phenomena and their implications in other studies such as [[paleogeography]] and [[paleobiology]].