Editing Plate tectonics (section)

=== Driving forces related to Earth rotation ===
[[Alfred Wegener]], being a [[meteorologist]], had proposed [[tidal force]]s and [[centrifugal force]]s 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.<ref>{{Cite web |title=Alfred Wegener (1880–1930) |url=http://www.ucmp.berkeley.edu/history/wegener.html |url-status=dead |archive-url=https://web.archive.org/web/20171208011353/http://www.ucmp.berkeley.edu/history/wegener.html |archive-date=2017-12-08 |access-date=2010-06-18 |publisher=[[University of California Museum of Paleontology]]}}</ref> 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. In more recent literature, these driving forces are:
# Tidal drag due to the gravitational force the [[Moon]] (and the [[Sun]]) exerts on the crust of Earth.<ref>{{Cite web |last=Neith, Katie |date=April 15, 2011 |title=Caltech Researchers Use GPS Data to Model Effects of Tidal Loads on Earth's Surface |url=http://media.caltech.edu/press_releases/13411 |url-status=dead |archive-url=https://web.archive.org/web/20111019023322/http://media.caltech.edu/press_releases/13411 |archive-date=October 19, 2011 |access-date=August 15, 2012 |publisher=[[California Institute of Technology|Caltech]]}}</ref>
# Global deformation of the [[geoid]] due to small displacements of the rotational pole with respect to Earth's crust.
# Other smaller deformation effects of the crust due to wobbles and spin movements of Earth's rotation on a smaller timescale.

Forces that are small and generally negligible are:

# The [[Coriolis force]].<ref name="Ricard">{{Cite encyclopedia |year=2009 |title=Treatise on Geophysics: Mantle Dynamics |publisher=Elsevier Science |last=Ricard |first=Y. |editor-last=Bercovici |editor-first=David |volume=7 |page=36 |isbn=978-0-444-53580-1 |chapter=2. Physics of Mantle Convection |editor2-last=Schubert |editor2-first=Gerald |chapter-url=https://books.google.com/books?id=bIHNCgAAQBAJ}}</ref><ref name="Glatzmaier2013">{{Cite book |last=Glatzmaier |first=Gary A. |url=https://books.google.com/books?id=RY-GAAAAQBAJ&pg=PR4 |title=Introduction to Modeling Convection in Planets and Stars: Magnetic Field, Density Stratification, Rotation |publisher=[[Princeton University Press]] |year=2013 |isbn=978-1-4008-4890-4 |page=149}}</ref>
# The [[centrifugal force]], which is treated as a slight modification of gravity.<ref name=Ricard/><ref name=Glatzmaier2013/>{{rp|249}}

For these mechanisms to be overall valid, systematic relationships should exist all over the globe between the orientation and kinematics of deformation and the geographical [[latitude|latitudinal]] and [[longitude|longitudinal]] grid of Earth itself. Systematic relations studies in the second half of the nineteenth century and the first half of the twentieth century underlined exactly the opposite: that the plates had not moved in time, that the deformation grid was fixed with respect to Earth's [[equator]] and axis, and that gravitational driving forces were generally acting vertically and caused only local horizontal movements (the so-called pre-plate tectonic, "fixist theories"). Later studies (discussed below on this page), therefore, invoked many of the relationships recognized during this pre-plate tectonics period to support their theories (see reviews of these various mechanisms related to Earth rotation in the work of van Dijk and collaborators).<ref>{{harvnb|van Dijk|1992}}, {{harvnb|van Dijk|Okkes|1990}}.</ref>

==== Possible tidal effect on plate tectonics{{anchor|Tidal effect}} ====
{{see also|Tidal triggering of earthquakes}}

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{{sfn|Moore|1973}} of the [[United States Geological Survey|USGS]] and R. C. Bostrom{{sfn|Bostrom|1971}} 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 has been mainly advocated by Doglioni and co-workers {{Harv|Doglioni|1990}}, such as in a more recent 2006 study,{{sfn|Scoppola|Boccaletti|Bevis|Carminati|2006}} where scientists reviewed and advocated these ideas. It has been suggested in {{Harvtxt|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 Torsvik et al.,{{sfn|Torsvik|Steinberger|Gurnis|Gaina|2010}} 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&nbsp;Ma, is attributed to the increased dominance of the steadily growing and accelerating Pacific plate. The debate is still open, and a 2022 paper by Hofmeister et al.{{Sfn|Hofmeister|Criss|Criss|2022}} revived the idea of the interaction between the Earth's rotation and the Moon as the main driving force for plate movement.