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Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, the process of subduction, or one plate moving under another, carries the edge of the lower one down into the mantle; the area of material lost is balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total geoid surface area of the lithosphere remains constant. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual expansion of the globe.
Continental Drift and Plate Tectonics mobi download book
Alfred Wegener, being a meteorologist, had proposed tidal forces and centrifugal forces as the main driving mechanisms behind continental drift; however, these forces were considered far too small to cause continental motion as the concept was of continents plowing through oceanic crust. 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.
Of the many forces discussed above, tidal force is still highly debated and defended as a possible principal driving force of plate tectonics. 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. Moore of the USGS and R. C. Bostrom presented evidence for a general westward drift of Earth's lithosphere with respect to the mantle, based on the steepness of the subduction zones (shallow dipping towards the east, steeply dipping towards the west). They concluded that tidal forces (the tidal lag or "friction") caused by Earth's rotation and the forces acting upon it by the Moon are a driving force for plate tectonics. As Earth spins eastward beneath the Moon, the Moon's gravity ever so slightly pulls Earth's surface layer back westward, just as proposed by Alfred Wegener (see above). Since 1990 this theory is mainly advocated by Doglioni and co-workers (Doglioni 1990), such as in a more recent 2006 study, where scientists reviewed and advocated these ideas. It has been suggested in Lovett (2006) that this observation may also explain why Venus and Mars have no plate tectonics, as Venus has no moon and Mars' moons are too small to have significant tidal effects on the planet. In a paper by  it was suggested that, on the other hand, it can easily be observed that many plates are moving north and eastward, and that the dominantly westward motion of the Pacific Ocean basins derives simply from the eastward bias of the Pacific spreading center (which is not a predicted manifestation of such lunar forces). In the same paper the authors admit, however, that relative to the lower mantle, there is a slight westward component in the motions of all the plates. They demonstrated though that the westward drift, seen only for the past 30 Ma, is attributed to the increased dominance of the steadily growing and accelerating Pacific plate. The debate is still open, and a recent paper by Hofmeister et al. (2022)  revived the idea advocating again the interaction between the Earth's rotation and the Moon as main driving forces for the plates.
The development of the theory of Plate Tectonics was the scientific and cultural change which developed through the acceptance the plate tectonics theory which went through a development 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.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.
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.
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 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. Wegener was not the first to note this (Abraham Ortelius, Antonio Snider-Pellegrini, Eduard Suess, Roberto Mantovani and Frank Bursley Taylor preceded him just to mention a few), but he was the first to marshal significant fossil and paleo-topographical and climatological evidence to support this simple observation (and was supported in this by researchers such as Alex du Toit). Furthermore, when the rock strata of the margins of separate continents are very similar it suggests that these rocks were formed in the same way, implying that they were joined initially. For instance, parts of Scotland and Ireland contain rocks very similar to those found in Newfoundland and New Brunswick. Furthermore, the Caledonian Mountains of Europe and parts of the Appalachian Mountains of North America are very similar in structure and lithology.
The question particularly intrigued Harry Hammond Hess, a Princeton University geologist and a Naval Reserve Rear Admiral, and Robert S. Dietz, a scientist with the U.S. Coast and Geodetic Survey who first coined the term seafloor spreading. Dietz and Hess (the former published the same idea one year earlier in Nature, but priority belongs to Hess who had already distributed an unpublished manuscript of his 1962 article by 1960) were among the small number who really understood the broad implications of sea floor spreading and how it would eventually agree with the, at that time, unconventional and unaccepted ideas of continental drift and the elegant and mobilistic models proposed by previous workers like Holmes.
The main objective of this article is to offer a different approach towards understanding the conflict around the acceptance of the continental drift theory, less grounded on rational explanations about the inherent weight of evidence and more concerned about the cultural and social contexts that shaped this debate. It is important to advise that this does not imply to reject the role of evidence in the acceptance of the plate tectonic theory, but to focus on its social and cultural backgrounds. I do not pretend to argue that evidence has no role; rather, I criticise perspectives that only focus on evidence while explaining the social acceptance of the theory since such explanation tends to conceive the scientific community as a purely logical organism. On the contrary, I am highlighting the importance of broader cultural frameworks.
The fact that in the 1960s the tectonic plate theory was accepted and, having this theory, similar ideas to those stated by Wegener in 1912, made scientific community consider him the father of the continental drift theory. However, other predecessors of the same idea can be found such as Taylor, Mantovani and Pickering.Footnote 6 This could allow us to think of the continental drift theory as a simultaneous discovery. Indeed, as Merton had already pointed out, simultaneous discoveries happen so often in science that they are the rule rather than the exception (Merton 1961, 480). Some well-known examples are those of Darwin and Wallace in discovering the evolutionary theory; Newton and Leibniz in the calculus theory; Euler and Lagrange regarding the solution to the variation calculus, among others. To establish the actual discoverer of a scientific fact is indeed arbitrary since there is always previous background which may be considered valuable in contributing to the discovery. As regards this issue, in 1980 Joseph Stigler proposed that no scientific discovery is named after its original discoverer arguing that it is always possible to find out previous discoverers who have remained in the shadows, without receiving any credit for their research (Stigler 1999, 277).
On the other hand, mobilism imagines its object as something in permanent change whose continuous interactions redefine it every time. Fixists find it natural to see the same structure over time, and label as extravagant all theories whose object is continuously moving. For mobilists, the only fix element to be found is change.Footnote 11 Both styles of thought coexisted for centuries providing a general background for the acceptance/rejection of the continental drift theory.
Ignoring mobilists contributions on the subject for hundreds of years: Neglecting authors who have been sustaining mobilists arguments and evidence concerning continental drift theory is not merely a curious phenomenon or a problem of communication of ideas, but part of the same conflict between styles of thought. Ignoring challenging positions is a possible reaction of a dominant style of thought against an anomaly, as well as questioning its validity, exposing its problems or offering other explanations against it.
Indeed, there is still a fixist style of thought in geology, and some of it appears in the New Concepts in Global Tectonics Group (Pratt 2006). Since 1996, this group of Earth scientists carry out periodical conferences and publishes their own journal with a dissident perspective: they argue that plate tectonics theory was developed in the 1960s by young inexperienced geologists with a simplistic view and that all existing data was just swept aside. Interestingly, this anti-continental drift group is linked with a religious movement, which is coherent with the essentialist aspects of fixism style of thought (see Exploring theosophy: The synthesis of science, religion and philosophy, at: Accessed 26 January 2019. Links between anti-continental drifts and religious positions may also be found at: -drift-plate-tectonics-bible. Accessed 26 January 2019). A similar situation may be described for creationists, who found certain institutions within the United States that allow them to develop their ideas and reproduce them, despite the overwhelming consensus among the scientific community towards evolution.