User:Rectified/Critcism of Plate Tectonics

Supposed remnants of the Farallon Plate, deep in Earth's mantle, reconstructed from seismic data. In Plate Tectonics, it is thought that much of the plate initially went under North America (particularly the western United States and southwest Canada) at a very shallow angle, creating much of the mountainous terrain in the area (particularly the southern Rocky Mountains).

In Plate Tectonics, oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. Persistent giant currents in molten rock propel the continents across the globe.

An animation showing the movement of the continents from the separation of Pangaea until the present day

Notice there is no way for India to cross the Indian Ocean without leaving a trail of colored stripes behind it perpendicular to the motion. Compare to Pangaea animation

Plate tectonics is a scientific theory that purports to describes the large-scale motion of Earth's lithosphere. This theoretical model builds on the concept of continental drift, which was first proposed in 1598 AD, and further developed during the first few decades of the 20th century. Members of the geoscientific community who wished to complete their degrees and continue receiving government grants accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s.

Like many other contemporary scientific theories promoted by paid academicians, Plate Tectonics is in a state of siege and crisis. It has too many internal contradictions. There are too many observations that falsify it. The prime mover cannot be located. The necessary loss of surface area in subduction zones, needed to offset the seafloor spreading, cannot be found. For these reasons and others, Plate Tectonics is a disputed theory.

In Plate Tectonics, the lithosphere, which is the rigid outermost shell of Earth (the crust and upper mantle), is broken up into tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries. The lateral relative movement of the plates typically ranges from zero to 100 mm annually.

Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, the total surface of the globe remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Other theories propose gradual shrinking (contraction) or gradual expansion of the globe to account for the motion of the continents.

Tectonic plates are said to be able to move because the Earth's lithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge (due to variations in topography and density of the crust, which result in differences in gravitational forces) and drag, with downward suction, at the subduction zones. Another explanation lies in the different forces generated by tidal forces of the Sun and Moon. The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate.

The quickest way to see the major inconsistencies in Plate Tectonics mappings is to compare the reconstruction of Pangaea with the map of the ocean floor. The floor has been mapped with enough detail to show the relative ages of its different parts. If Pangaea had collected together on one side of the Earth, then the other side, where the Pacific Ocean is now, should be of a much older age. The map shows it to be of the same range of ages, mostly about 0-200 Million years. It also shows a tremendous expansion of the area of the Pacific, not a contraction.

There are many different attempts at a Pangaea reconstruction. Almost all of them require the excision of Central America and the Caribbean Sea in addition to other, smaller adjustments. The Carribean is one of the oldest seas on Earth. It cannot have been erased. Central America also does not have geological evidence of an origin less than 200 million radioisotope-years ago, or a creation of its southern portions since then. But without these excisions, Pangaea cannot be assembled.

India would have to travel at a relatively high speed from Africa to Asia, jumping across the expansion gap that runs north-south. This should have left a "wake", a series of chevron-shaped colored stripes across the ocean floor, with the younger, red and orange stripes near the southern coast of India. The map shows the opposite- the floor off the coast of India is blue and green, the oldest.

Key principles

The outer layers of the Earth are divided into the thin lithosphere and the asthenosphere, the thick rock layer beneath the lithosphere. This is based on differences in mechanical properties and in the method for the transfer of heat. Mechanically, the lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily. The picture is of a thin rigid plate riding on a "sea" of molten rock, driven here and there by convection currents in the molten asthenosphere. This is claimed to be the result of gigantic "convection cells", spanning the continents and operating for millions of years within the asthenosphere. These convection cells have never been observed, nor does the greater part of the asthenosphere appear to be molten enough to support currents running through it.

In terms of heat transfer, the more rigid lithosphere loses heat by conduction, whereas the asthenosphere also transfers heat by convection and is thought to have a nearly adiabatic temperature gradient. This division should not be confused with the chemical subdivision of these same layers into the mantle (comprising both the asthenosphere and the mantle portion of the lithosphere) and the crust: a given piece of mantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature and pressure.

Tectonic plates may include continental crust or oceanic crust, and most plates are said to contain both. The distinction between oceanic crust and continental crust is based on their modes of formation. Oceanic crust is formed at sea-floor spreading centers, and continental crust is formed through arc volcanism and accretion of terranes through tectonic processes.

Oceanic crust is also denser than continental crust owing to their different compositions. Oceanic crust is denser because it has less silicon and more heavier elements. Plate tectonic theorists claim that as a result of this density difference, oceanic crust generally lies below sea level, while continental crust buoyantly projects above sea level (see the page isostasy for an explanation of this principle). But water is many times less dense than either ocean or continental rock, so that explanation is unsatisfactory. Also, the prime mover of plate tectonics does not need the presence of the oceans. It would either work or not regardless of whether water were present (although water is invoked as an auxiliary to lubricate the subduction process.

Experiment. I'm going through the article in a mirroring fashion, rebutting each fanciful claim as it shows up, leaving the parts intact that are not being rebutted, stripping out excess. I may add/remove sections or not, but would rather not. Isostasy revisit.

Arguments against plate tectonics

• The continents do not actually fit together without severe 'cutting' and 'pasting'.

• The reconstruction of super-continent Pangaea requires cutting away major land masses such as Central America, which show no signs of being recent.

• If the continents had all gathered together on one side of the Earth to form the super-continent Pangaea, the planet's center of gravity would have shifted towards the single continent. The waters of the world-ocean would have followed, flooding almost the entire continental mass to many hundreds of meters depth, and leaving evidence of that behind.

• The floor of the Pacific Ocean is as young as the Atlantic. The old continents would have had to have swept the older floor away, then quickly come around to join each other as Pangaea before the new Pacific floor could age.

• The solid roots of the continents extend hundreds of kilometers downward, as evidenced by deep earthquakes. They are not like thin rafts floating on an ocean of molten rock.

• There is no viable mechanism, proposed or observed, that can explain the motion of the continents (this is mostly admitted by the proponents).

• There is no geological evidence that India was ever separate from Asia. There is no seam between the two. This was extensively researched in situ by Carey.

• There are no discontinuous seams in the basement geology at most of the proposed convergent zones.

• There are about 3.5 km² of new ocean floor calculated to be added each year at the seafloor spreading rifts. An equal amount of area would have to be subtracted in the subduction zones to keep the total surface area of the Earth the same. No such reliable accounting of subduction exists.

• The total length of the lines of subduction should be somewhat similar to the total of lines of rifting. For each km of rift, there should be some comparable length of subduction. There is not, the rifts exceed the proposed subduction by inordinate amounts

• With a few possible exceptions (Juan De Fuca Plate?), no subduction has been observed at the putative subduction zones.

• There are no observed accretion wedges at subduction boundaries.

• When a thin oceanic plate collides with a thick, continental plate, the thin plate should do most of the buckling and consequent mountain-building on the ocean side, for the same reason that a car colliding with a brick wall does most of the crumpling.

• There is no observed subduction in subduction zones, unlike the observed and celebrated spreading at mid-ocean rifts.

• The continents would have had to have destroyed by subduction nearly all of the ocean floor of the Earth over the past 200 million years, since most of it is younger than that.

• The mechanical ideas of 'conveyor belt' transport do not work out, from considerations of friction, compression, boundary layer shear, power, etc.

• The convection-cell idea goes against the theory of convection (Raleigh criterion).

• The mid-Pacific expansion ridge has the continents going the wrong direction.

• Antarctica has no place to move to or from. It is surrounded by expansion joints, seafloor spreading rifts. So are all the other continents, less obviously. This is partially admitted by the proponents.

Types of plate boundaries

Main article: List of tectonic plate interactions

Three types of plate boundaries exist, with a fourth, mixed type, characterized by the way the plates move relative to each other. They are associated with different types of surface phenomena. The different types of plate boundaries are:

1. Transform boundaries (Conservative) occur where two lithospheric plates slide, or perhaps more accurately, grind past each other along transform faults, where plates are neither created nor destroyed. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer). Transform faults occur across a spreading center. Strong earthquakes can occur along a fault. The San Andreas Fault in California is an example of a transform boundary exhibiting dextral motion.

1. Divergent boundaries (Constructive) occur where two plates slide apart from each other. At zones of ocean-to-ocean rifting, divergent boundaries form by seafloor spreading, allowing for the formation of new ocean basin. As the continent splits, the ridge forms at the spreading center, the ocean basin expands, and finally, the plate area increases causing many small volcanoes and/or shallow earthquakes. At zones of continent-to-continent rifting, divergent boundaries may cause new ocean basin to form as the continent splits, spreads, the central rift collapses, and ocean fills the basin. Active zones of Mid-ocean ridges (e.g., Mid-Atlantic Ridge and East Pacific Rise), and continent-to-continent rifting (such as Africa's East African Rift and Valley, Red Sea) are examples of divergent boundaries.

1. Convergent boundaries (Destructive) (or active margins) occur where two plates slide toward each other to form either a subduction zone (one plate moving underneath the other) or a continental collision. At zones of ocean-to-continent subduction (e.g. the Andes mountain range in South America, and the Cascade Mountains in Western United States), the dense oceanic lithosphere plunges beneath the less dense continent. Earthquakes then trace the path of the downward-moving plate as it descends into asthenosphere, a trench forms, and as the subducted plate partially melts, magma rises to form continental volcanoes. At zones of ocean-to-ocean subduction (e.g. Aleutian islands, Mariana islands, and the Japanese island arc), older, cooler, denser crust slips beneath less dense crust. This causes earthquakes and a deep trench to form in an arc shape. The upper mantle of the subducted plate then heats and magma rises to form curving chains of volcanic islands. Deep marine trenches are typically associated with subduction zones, and the basins that develop along the active boundary are often called "foreland basins". The subducting slab contains many hydrous minerals which release their water on heating. This water then causes the mantle to melt, producing volcanism. Closure of ocean basins can occur at continent-to-continent boundaries (e.g., Himalayas and Alps): collision between masses of granitic continental lithosphere; neither mass is subducted; plate edges are compressed, folded, uplifted.

1. Plate boundary zones occur where the effects of the interactions are unclear, and the boundaries, usually occurring along a broad belt, are not well defined and may show various types of movements in different episodes.

Three types of plate boundary. The "accretion wedge" is shown on the right, where the upper layers of sediment are scraped off and left behind as the basement rock is subducted. With small, possible exceptions, no accretion wedges have been observed.

The Pacific plate is claimed to be subducted beneath the Mariana Plate, creating the Mariana Trench. This diagram is misleading. The "trench" is a broad valley, about 60 km across, with gently sloping sides. No accretion wedge has been found. No "suture" or "seam" between Asia and the Pacific Ocean basin has been found in this valley.

Driving forces of plate motion

Plate motion based on Global Positioning System (GPS) satellite data from NASA JPL. The vectors show direction and magnitude of motion.

It is claimed that tectonic plates are able to move horizontally because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere. Deep earthquake data refutes that.

Dissipation of heat from the mantle is acknowledged to be the original source of the energy required to drive plate tectonics through convection or large scale upwelling and doming. The current view, though still a matter of some debate, asserts that as a consequence, a powerful source of plate motion is generated due to the excess density of the oceanic lithosphere sinking in subduction zones. When the new crust forms at mid-ocean ridges, this oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age as it conductively cools and thickens. The greater density of old lithosphere relative to the underlying asthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving force for plate movement THIS IS THE SLAB-PULL THEORY, WHICH RELIES ON THE TENSILE STRENGTH OF ROCK AND ON LESS-DENSE MATERIAL SINKING UNDERNEATH MORE-DENSE MATERIAL. The weakness of the asthenosphere (BELIED BY EARTHQUAKE DATA) allows the tectonic plates to move easily towards a subduction zone. Although subduction is thought to be the strongest force driving plate motions, it cannot be the only force since there are plates such as the North American Plate which are moving, yet are nowhere being subducted. The same is true for the enormous Eurasian Plate. The sources of plate motion are a matter of intensive research and discussion among scientists. One of the main points is that the kinematic pattern of the movement itself should be separated clearly from the possible geodynamic mechanism that is invoked as the driving force of the observed movement, as some patterns may be explained by more than one mechanism. In short, the driving forces advocated at the moment can be divided into three categories based on the relationship to the movement: mantle dynamics related, gravity related (mostly secondary forces) WHAT IS THE THIRD CATEGORY?.

Driving forces related to mantle dynamics

Main article: Mantle convection

Previously, the leading theory of the driving force behind tectonic plate motions envisaged large scale convection currents in the upper mantle which are transmitted through the asthenosphere. This theory was launched in the 1930s and was immediately seized upon 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. However, despite its seeming acceptance, it is still debated in the scientific community. There are many problems with the idea, not the least of which is the lack of any observed convection currents.

The special pleadings in the case of India illustrates the problem. After a period of quiescence, a giant convection cell spanning thousands of kilometers would have to have been established, for no apparent reason, that would split off the entire mass of India from Africa, then drive it northeast across the Indian Ocean in a straight line at a high rate of speed without veering, there to collide with the Asian landmass. Not only does the driving convection cell have to come from nothing, it has to either ride along underneath India for the entire journey, or it has to span the entire distance like the luggage handler at an airport, all while persisting for millions of years. If it rides along underneath India, there has to be something else pushing it along as well, another conveyor belt to convey the Indian conveyor belt. If it is big enough to convey India without moving itself, then there should be many other observable effects in the geology of the surrounding terrain. In any case, the Indian convection cell needs another driver, one which also cannot be located.

Two- and three-dimensional imaging of Earth's interior (seismic tomography) shows a varying lateral density distribution throughout the mantle. Such density variations can be material (from rock chemistry), mineral (from variations in mineral structures), or thermal (through thermal expansion and contraction from heat energy). The manifestation of this varying lateral density is claimed to somehow cause mantle convection from buoyancy forces.

How mantle convection directly and indirectly relates to plate motion is unresolved. Somehow, this force would have to be transferred to the lithosphere for tectonic plates to move. The rising current would have to transition to a horizontal current sheet moving underneath the entire continent, acting in concert over thousands of kilometers. If only part of the continent had a current sheet, it would be torn apart as part of it moved and another part stood still.

THE CONVECTION CURRENT WOULD NOT ONLY HAVE TO MOVE LATERALLY, IT WOULD HAVE TO MOVE "IN CONCERT WITH ITSELF" OVER MILLIONS OS SQUARE KM, OVER MILLIONS OF YEARS, AND DO SO WITHOUT CRUMPLING UP THE CONTINENT. A DELICATE OPERATION. 

The case of North and South America illustrate this problem. Both continents appear to be moving westward, together, relative to Europe and Africa. The convection-cell conveyor belt that they are imagined to ride on would have to span the entire distance from northern Canada to the southern tip of South America, while also stretching along the entire underside of both continents, along with the half of the Atlantic ocean basin on their side of the mid-Atlantic ridge. This giant convection cell, spanning a large part of the entire surface of the Earth, would have had to maintain this concerted action over tens of millions of years.

There are essentially two types of forces that are thought to [THE ARTICLE IS RIFE WITH THESE SPECULATIONS] influence plate motion: friction and gravity.

• Basal drag (friction): Plate motion driven by friction between the convection currents in the asthenosphere and the more rigid overlying lithosphere. [BOUNDARY-LAYER STRUCTURE AND THEORY NEGATES THIS IDEA.]
• Slab suction (gravity): Plate motion driven by local convection currents that exert a downward pull on plates in subduction zones at ocean trenches. Slab suction may occur in a geodynamic setting where basal tractions continue to act on the plate as it dives into the mantle (although perhaps to a greater extent acting on both the under and upper side of the slab).

Lately, the convection theory has been much debated as modern techniques based on 3D seismic tomography still fail to recognize these predicted large scale convection cells. [BA DA BING]. Therefore, alternative views have been proposed:

In the theory of plume tectonics developed during the 1990s, a modified concept of mantle convection currents is used. It asserts that super plumes rise from the deeper mantle and are the drivers or substitutes of the major convection cells. These ideas, which find their roots in the early 1930s with the so-called "fixistic" ideas of the European and Russian Earth Science Schools, find resonance in the modern theories which envisage hot spots/mantle plumes which remain fixed and are overridden by oceanic and continental lithosphere plates over time and leave their traces in the geological record (though these phenomena are not invoked as real driving mechanisms, but rather as modulators) [TRANSLATION: HOT SPOTS CAN'T CAUSE CONTINENTS TO MOVE]. Modern theories that continue building on the older mantle doming concepts and see plate movements as a secondary phenomena are beyond the scope of this page and are discussed elsewhere (for example on the plume tectonics page).

Another theory is that the mantle flows neither in cells nor large plumes but rather as a series of channels just below the Earth's crust, which then provide basal friction to the lithosphere. This theory, called "surge tectonics", became quite popular in geophysics and geodynamics during the 1980s and 1990s.

Driving forces related to gravity

Forces related to gravity are usually invoked as secondary phenomena within the framework of a more general driving mechanism such as the various forms of mantle dynamics described above.

Gravitational sliding away from a spreading ridge: According to many authors, plate motion is driven by the higher elevation of plates at ocean ridges. As oceanic lithosphere is formed at spreading ridges from hot mantle material, it gradually cools and thickens with age (and thus adds distance from the ridge). Cool oceanic lithosphere is significantly denser than the hot mantle material from which it is derived and so with increasing thickness it gradually subsides into the mantle to compensate the greater load. The result is a slight lateral incline with increased distance from the ridge axis.

This force is regarded as a secondary force and is often referred to as "ridge push". This is a misnomer as nothing is "pushing" horizontally and tensional features are dominant along ridges. It is more accurate to refer to this mechanism as gravitational sliding as variable topography across the totality of the plate can vary considerably and the topography of spreading ridges is only the most prominent feature. Other mechanisms generating this gravitational secondary force include flexural bulging of the lithosphere before it dives underneath an adjacent plate which produces a clear topographical feature that can offset, or at least affect, the influence of topographical ocean ridges, and mantle plumes and hot spots, which are postulated to impinge on the underside of tectonic plates.

Slab-pull: Current scientific opinion is that the asthenosphere is insufficiently competent or rigid to directly cause motion by friction along the base of the lithosphere. Slab pull is therefore most widely thought to be the greatest force acting on the plates. In this current understanding, plate motion is mostly driven by the weight of cold, dense plates sinking into the mantle at trenches [NO SUCH PROCESS HAS EVER BEEN OBSERVED]. Recent models indicate that trench suction plays an important role as well. However, as the North American Plate is nowhere being subducted, yet it is in motion presents a problem. The same holds for the African, Eurasian, and Antarctic plates.

Gravitational sliding away from mantle doming: According to older theories, one of the driving mechanisms of the plates is the existence of large scale asthenosphere/mantle domes which cause the gravitational sliding of lithosphere plates away from them. This gravitational sliding represents a secondary phenomenon of this basically vertically oriented mechanism. This can act on various scales, from the small scale of one island arc up to the larger scale of an entire ocean basin.

Driving forces related to Earth rotation

Alfred Wegener had proposed tidal forces and pole flight force as the main driving mechanisms behind continental drift; however, these forces were considered far too small to cause continental motion as the concept then was of continents plowing through oceanic crust.

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), 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:

1. Tidal drag due to the gravitational force the Moon (and the Sun) exerts on the crust of the Earth[TIDAL THEORY IS ALSO IN DISARRAY]
2. Global deformation of the geoid due to small displacements of rotational pole with respect to the Earth's crust;
3. Other smaller deformation effects of the crust due to wobbles and spin movements of the Earth rotation on a smaller time scale.

Forces that are small and generally negligible are:

1. The Coriolis force

The Coriolis force is invoked extensively when describing the motion of large air masses in the Earth's atmosphere and major currents in the ocean. By extension, it should be of major importance for modeling the purported convection cells in the asthenosphere, which are of a similar scale. They have to reject it as a causal agent because the movement of the continents contradicts. If a Coriolis force were active in creating the Atlantic Ocean, then North America would be moving and rotating in directions opposite to South America, since they are mostly in opposite hemispheres. As these continents are observed to both be moving away from Europe and Africa at an even rate and with negligible rotation, a Coriolis force cannot be the cause.

1. The centrifugal force, which is treated as a slight modification of gravity

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 latitudinal and longitudinal grid of the Earth itself. Ironically, these systematic relations studies in the second half of the nineteenth century and the first half of the twentieth century underline exactly the opposite: that the plates had not moved in time, that the deformation grid was fixed with respect to the Earth 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 the anticipations and reviews in the work of van Dijk and collaborators).

Of the many forces discussed in this paragraph, tidal force is still highly debated and defended as a possible principle driving force of plate tectonics. The other forces are only used in global geodynamic models not using plate tectonics concepts 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 the Earth's lithosphere with respect to the mantle. He concluded that tidal forces (the tidal lag or "friction") caused by the Earth's rotation and the forces acting upon it by the Moon are a driving force for plate tectonics. As the Earth spins eastward beneath the moon, the moon's gravity ever so slightly pulls the Earth's surface layer back westward, just as proposed by Alfred Wegener (see above). In a more recent 2006 study, scientists reviewed and advocated these earlier proposed ideas. It has also been suggested recently 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 recent paper, 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.

Relative significance of each driving force mechanism

The vector of a plate's motion is claimed to be a function of all the forces acting on the plate; however, therein lies both the problem regarding the degree to which each process contributes to the overall motion of each tectonic plate, as well as the validity of assigning a force-summation vector to an extensive, deformable body.

[SAME OBJECTION ABOUT SUMMATION OF CONVECTION CURRENTS NOTED ABOVE]

The diversity of geodynamic settings and the properties of each plate result from the impact of the various processes actively driving each individual plate. One method of dealing with this problem is to consider the relative rate at which each plate is moving as well as the evidence related to the significance of each process to the overall driving force on the plate.

The Pacific Plate is relatively much thinner and more fragile than an eggshell. The material properties of basalt and eggshell are similar within an order of magnitude (eggshell may be the stronger of the two, particularly in toughness and tensile strength). A thin plate, both plastically-deformable and at the same time brittle (depending on length and time scales) cannot be forced to move against external resistance without causing it to fail in some fashion. A force-summation vector implies a single-point of net force, which would immediately destroy that region of the plate. To prevent that, the translating force has to be distributed across the entire plate, to within a few plate thicknesses. The convection cell, or whatever other motive cause, has to therefore also be distributed across most of the area of the plate. For this case of a "fast-moving" Pacific Plate, its underlying convection cell would be even larger than the one needed to propel the Americas. None of these giant cell motions have been reproduced in a physical demonstration system.

One of the most significant correlations discovered to date is that lithospheric plates attached to downgoing (subducting) plates move much faster than plates not attached to subducting plates.

The Pacific plate is claimed to be essentially surrounded by zones of subduction (the so-called Ring of Fire), but most of the eastern side of it is an expansion zone, as can be seen on the Age of the Ocean Floors map.

and moves much faster than the plates of the Atlantic basin, which are attached to adjacent continents instead of subducting plates. It is thus thought that forces associated with the downgoing plate (slab pull and slab suction) are the driving forces which determine the motion of plates, except for those plates which are not being subducted.

The driving forces of plate motion continue to be active subjects of on-going research within geophysics and tectonophysics because the original proposals of convection have been shown to be unworkable. This is why ideas like "slab suction" are entertained.

Development of the theory

Further information: Timeline of the development of tectonophysics

Detailed map showing the tectonic plates with their movement vectors.

Detailed map showing the tectonic plates with their movement vectors.

Summary

In line with other previous and contemporaneous proposals, in 1912 the meteorologist Alfred Wegener amply described what he called continental drift, expanded in his 1915 book The Origin of Continents and Oceans and the scientific debate started that would end up fifty years later in the theory of plate tectonics. Starting from the idea (also expressed by his forerunners) that the present continents once formed a single land mass (which was called Pangea later on) that drifted apart, thus releasing the continents from the Earth's mantle and likening them to "icebergs" of low density granite floating on a sea of denser basalt [SLAB PULL PROBLEM AGAIN. IF IT'S LESS DENSE, HOW CAN IT SINK BELOW THE MORE DENSE?]. Supporting evidence for the idea came from the dove-tailing outlines of South America's east coast and Africa's west coast, 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. [TRUE] 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.

But without detailed evidence and a force sufficient to drive the movement, the theory was not generally accepted: the 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. Distinguished scientists, such as Harold Jeffreys and Charles Schuchert, were outspoken critics of continental drift. [AND CAREY, WHO COINED THE TERM PLATE TECTONICS, THEN DISAVOWED IT]

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 currents might have driven the plate movements, and that spreading may have occurred below the sea within the oceanic crust. Concepts close to the elements now incorporated in plate tectonics were proposed by geophysicists and geologists (both fixists and mobilists) like Vening-Meinesz, Holmes, and Umbgrove. [CONVECTION VIOLATES RALEIGH CRITERION]

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, and by Warren Carey in a symposium held in March 1956.

[PALEOMAGETIC MAPS OF THE OCEAN FLOOR ALSO SHOW RELATIVE AGES. THES DO NOT CORRESPOND IN ANY WAY TO THE IDEA OF CONTINENTAL DRIFT. IN PARTICULAR, THEY DO NOT LINE UP WITH THE PROPOSED SUBDUCTION ZONES, THERE ARE NO JOINTS, DISCONTINUITIES, UNCONFORMITIES, IN THOSE PLACES.]

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 floors and the nature of the oceanic crust such as magnetic properties and, more generally, with the development of marine geology which gave evidence for the association of seafloor spreading along the mid-oceanic ridges and magnetic field reversals, published between 1959 and 1963 by Heezen, Dietz, Hess, Mason, Vine & Matthews, and Morley.

[OBSERVATION OF SEAFLOOR SPREADING SUPPORTS PT, NOT-OBSERVATION OF SUBDUCTION DOES NOT.]

Simultaneous advances in early seismic imaging techniques in and around Wadati-Benioff zones 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 and the theory of plate tectonics, which was defined in a series of papers between 1965 and 1967, was born, with all its extraordinary explanatory and predictive power. [NOT TRUE. THE THEORY IS CONTINUOUSLY ALTERED TO POST-PREDICT AND POST-EXPLAIN] The theory revolutionized the Earth sciences, explaining a diverse range of geological phenomena and their implications in other studies such as paleogeography and paleobiology.

Continental drift

In the late 19th and early 20th centuries, geologists assumed that the Earth's major features were fixed, and that most geologic features such as basin development and mountain ranges could be explained by vertical crustal movement, described in what is called the geosynclinal theory. Generally, this was placed in the context of a contracting planet Earth due to heat loss in the course of a relatively short geological time.

Alfred Wegener in Greenland in the winter of 1912-13.

It was observed as early as 1596 that the opposite coasts of the Atlantic Ocean—or, more precisely, the edges of the continental shelves—have similar shapes and seem to have once fitted together.

Since that time many theories were proposed to explain this apparent complementarity, but the assumption of a solid Earth made these various proposals difficult to accept.

The discovery of radioactivity and its associated heating properties in 1895 prompted a re-examination of the apparent age of the Earth. This had previously been estimated by its cooling rate and assumption the Earth's surface radiated like a black body. Those calculations had implied that, even if it started at red heat, the Earth would have dropped to its present temperature in a few tens of millions of years. 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 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.

However, his ideas were not taken seriously by many geologists, who pointed out that there was no apparent mechanism for continental drift. Specifically, they did not see how continental rock could plow through the much denser rock that makes up 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

Global earthquake epicenters, 1963–1998

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). Furthermore, it was supposed that a static shell of strata was present under the continents. It therefore looked apparent that a layer of basalt (sial) underlies the continental rocks.

However, based on abnormalities in plumb line deflection by the Andes in Peru, Pierre Bouguer had deduced that less-dense mountains must have a downward projection into the denser layer underneath. The concept that mountains had "roots" was confirmed by George B. Airy a hundred years later, during study of Himalayan gravitation, and seismic studies detected corresponding density variations. Therefore, by the mid-1950s, the question remained unresolved as to whether mountain roots were clenched in surrounding basalt or were floating on it like an iceberg.

During the 20th century, improvements in and greater use of seismic instruments such as seismographs enabled scientists to learn that earthquakes tend to be concentrated in specific areas, most notably along the oceanic trenches and spreading ridges. 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. These zones later became known as Wadati-Benioff zones, or simply Benioff zones, in honor of the seismologists who first recognized them, Kiyoo Wadati of Japan and Hugo Benioff of the United States. 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. The much improved data from the WWSSN instruments allowed seismologists to map precisely the zones of earthquake concentration worldwide.

[3D RECONSTRUCTIONS OF CLAIMED W-B ZONES DO NOT SHOW A CORRELATION WITH PROPOSED LINES OF SUBDUCTION. INSTEAD, THE EARTHQUKES LOCI RESEMBLE SCATTER PLOTS.]

Meanwhile, debates developed around the phenomena of polar wander. Since the early debates of continental drift, scientists had discussed and used evidence that polar drift had occurred because continents seemed to have moved through different climatic zones during the past. Furthermore, paleomagnetic data had shown that the magnetic pole had also shifted during time. Reasoning in an opposite way, the continents might have shifted and rotated, while the pole remained relatively fixed. 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. In this symposium, the evidence was used in the theory of an expansion of the global crust. In this hypothesis the shifting of the continents can be simply explained by a large increase in size of the Earth since its formation. However, this was unsatisfactory because its supporters could offer no convincing mechanism to produce a significant expansion of the Earth. Certainly there is no evidence that the moon has expanded in the past 3 billion years; other work would soon show that the evidence was equally in support of continental drift on a globe with a stable radius. [NEITHER EXPANDING EARTH NOR PT HAVE A CREDIBLE, OBSERVED MECHANISM. THEY ARE ON EQUAL FOOTING HERE.]

During the thirties up to the late fifties, works by Vening-Meinesz, Holmes, Umbgrove, and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. 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. Often, these contributions are forgotten because:

• At the time, continental drift was not accepted.
• Some of these ideas were discussed in the context of abandoned fixistic ideas of a deforming globe without continental drift or an expanding Earth.
• They were published during an episode of extreme political and economic instability that hampered scientific communication.
• Many were published by European scientists and at first not mentioned or given little credit in the papers on sea floor spreading published by the American researchers in the 1960s.

Mid-oceanic ridge spreading and convection

the floor of the seabed beneath the layer of sediments consist of basalt, not the granite which is the main constituent of continents. The oceanic crust is much thinner than continental crust.

All along the globe, a system of mid-oceanic ridges was detected where new ocean floor was being created, which led to the concept of the "Great Global Rift" described in the crucial paper of Bruce Heezen (1960),. A profound consequence of seafloor spreading is that new crust was, and still is, being continually created along the oceanic ridges. Therefore, Heezen advocated the so-called "expanding Earth" hypothesis of S. Warren Carey (see above). So, still the question remained: how can new crust be continuously added along the oceanic ridges without increasing the size of the Earth? In reality, this question had been solved already by numerous scientists during the forties and the fifties, like Arthur Holmes, Vening-Meinesz, Coates and many others: The crust in excess disappeared along what were called the oceanic trenches, where so-called "subduction" occurred.

Harry Hammond Hess ... understood the broad implications of sea floor spreading and how it would eventually agree with the ideas of continental drift

It agrees with one-half of some of the ideas of continental drift.

If the Earth's crust was expanding along the oceanic ridges, it must be shrinking elsewhere

in order to preserve the idea that the Earth has been about the same size it is now, for millions of years. 

Hess suggested that new oceanic crust continuously spreads away from the ridges in a conveyor belt–like motion. many millions of years later, the oceanic crust eventually descends along the continental margins where oceanic trenches – very deep, narrow canyons – are formed, e.g. along the rim of the Pacific Ocean basin.

Not all continental margins which are said to be subduction zones are "trenches". Trenches, in at least the most famous case of the Mariana Trench, are wide valleys with gently sloping sides and flat bottoms.

The important step Hess made was that convection currents would be the driving force in this process,

convection currents appear to be going out of fashion.

... the thinning of the ocean crust was performed using Heezen's mechanism of spreading along the ridges.

Doesn't make sense. The new crust is thinnest at the ridge and thickens as it cools and moves away from the ridge.

Hess concluded that the Atlantic Ocean was expanding while the Pacific Ocean was shrinking.

Hess didn't have the Age of the Ocean Floor map, which wasn't made until 2-3 decades later. It shows that the Pacific expanded far more than the Atlantic in the same time frame. This could happen if the subduction rate were higher than the expansion rate.

As old oceanic crust is "consumed" in the trenches new magma rises and erupts along the spreading ridges to form new crust. In effect, the ocean basins are perpetually being "recycled," with the creation of new crust and the destruction of old oceanic lithosphere occurring simultaneously. The... Earth does not get bigger with sea floor spreading, why there is so little sediment accumulation on the ocean floor, and why oceanic rocks are much younger than continental rocks.

Definition and refining of the theory

After some consideration, Plate Tectonics (initially called "New Global Tectonics") became quickly accepted by scientists who wished to retain their positions and income streams. Numerous taxpayer-funded papers followed that defined the concepts:

• In 1965, Tuzo Wilson who had been a promotor of the sea floor spreading hypothesis and continental drift added the concept of transform faults to the model.
• A symposium on continental drift was held at the Royal Society of London in 1965 which is promoted as the official start of the acceptance of plate tectonics by funded scientists.
• 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. Jason Morgan proposed that the Earth's surface consists of 12 rigid plates that move relative to each other.
• Two months later, Xavier Le Pichon published a complete model based on 6 major plates with their relative motions, which marked the final acceptance by tenured and funded scientists of plate tectonics, in a kind of bandwagon effect.
• In the same year, McKenzie and Parker independently presented a model similar to Morgan's using translations and rotations on a sphere to define the plate motions.

Since that time, no alternative models are allowed to be funded within academia and government.

Implications for biogeography

Continental drift theory helps biogeographers explain the disjunct biogeographic distribution of past and present-day life found on different continents but having similar characteristics. For one example of many, it is used to explain the ancient distribution of ratites and the Antarctic flora. This is one of the pieces of non-exclusive supporting evidence for Plate Tectonics.

Plate reconstruction

Main article: Plate reconstruction

Reconstruction is used to establish past (and future) plate configurations, helping determine the shape and make-up of ancient supercontinents and providing a basis for paleogeography.

Defining plate boundaries

Current plate boundaries are defined by their seismicity. [BUT NOT BY RELATIVE MOTION ACROSS A LINE OF SUBDUCTION] Past plate boundaries within existing plates are identified from a variety of evidence, such as the presence of ophiolites that are indicative of vanished oceans.

Past plate motions

Tectonic motion first began around three billion years ago.

Various types of quantitative and semi-quantitative information are available to constrain past plate motions. The geometric fit between continents, such as between west Africa and South America is still an important part of plate reconstruction. Magnetic stripe patterns provide a reliable guide to relative plate motions going back into the Jurassic period. The tracks of hotspots give absolute reconstructions, but these are only available back to the Cretaceous. Older reconstructions rely mainly on paleomagnetic pole data, although these only constrain the latitude and rotation, but not the longitude. Combining poles of different ages in a particular plate to produce apparent polar wander paths provides a method for comparing the motions of different plates through time. Additional evidence comes from the distribution of certain sedimentary rock types, faunal provinces shown by particular fossil groups, and the position of orogenic belts.

Formation and break-up of continents

The movement of plates has caused the formation and break-up of continents over time, including occasional formation of a supercontinent that contains most or all of the continents. The supercontinent Columbia or Nuna formed during a period of 2,000 to 1,800 million years ago and broke up about 1,500 to 1,300 million years ago. The supercontinent Rodinia is thought to have formed about 1 billion years ago and to have embodied most or all of Earth's continents, and broken up into eight continents around 600 million years ago. The eight continents later re-assembled into another supercontinent called Pangaea; Pangaea broke up into Laurasia (which became North America and Eurasia) and Gondwana (which became the remaining continents).

The Himalayas, the world's tallest mountain range, are assumed to have been formed by the collision of two major plates. Before uplift, they were covered by the Tethys Ocean.

Current plates

Main article: List of tectonic plates

Depending on how they are defined, there are usually seven or eight "major" plates: African, Antarctic, Eurasian, North American, South American, Pacific, and Indo-Australian. The latter is sometimes subdivided into the Indian and Australian plates.

There are dozens of smaller plates, the seven largest of which are the Arabian, Caribbean, Juan de Fuca, Cocos, Nazca, Philippine Sea and Scotia.

The current motion of the tectonic plates is today determined by remote sensing satellite data sets, calibrated with ground station measurements. [THESE CANNOT BE USED FOR UNDERSEA MOTION]

Other celestial bodies (planets, moons)

The appearance of plate tectonics on terrestrial planets is related to planetary mass, with more massive planets than Earth expected to exhibit plate tectonics. Earth may be a borderline case, owing its tectonic activity to abundant water (silica and water form a deep eutectic.)

Venus

See also: Geology of Venus

Venus shows no evidence of active plate tectonics. There is debatable evidence of active tectonics in the planet's distant past; however, events taking place since then (such as the plausible and generally accepted hypothesis that the Venusian lithosphere has thickened greatly over the course of several hundred million years) has made constraining the course of its geologic record difficult. However, the numerous well-preserved impact craters have been utilized as a dating method to approximately date the Venusian surface (since there are thus far no known samples of Venusian rock to be dated by more reliable methods). Dates derived are dominantly in the range 500 to 750 million years ago, although ages of up to 1,200 million years ago have been calculated. This research has led to the fairly well accepted hypothesis that Venus has undergone an essentially complete volcanic resurfacing at least once in its distant past, with the last event taking place approximately within the range of estimated surface ages. While the mechanism of such an impressive thermal event remains a debated issue in Venusian geosciences, some scientists are advocates of processes involving plate motion to some extent.

One explanation for Venus's lack of plate tectonics is that on Venus temperatures are too high for significant water to be present. The Earth's crust is soaked with water, and water plays an important role in the development of shear zones. Plate tectonics requires weak surfaces in the crust along which crustal slices can move, and it may well be that such weakening never took place on Venus because of the absence of water. However, some researchers remain convinced that plate tectonics is or was once active on this planet.

Mars

See also: Geology of 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. Some scientists interpreted these as requiring plate tectonic processes, such as seafloor spreading. However, their data fail a "magnetic reversal test", which is used to see if they were formed by flipping polarities of a global magnetic field.

Galilean satellites of Jupiter

Some of the satellites of Jupiter have features that may be related to plate-tectonic style deformation, although the materials and specific mechanisms may be different from plate-tectonic activity on Earth. On 8 September 2014, NASA reported finding evidence of plate tectonics on Europa, a satellite of Jupiter—the first sign of such geological activity on another world other than Earth.

Titan, moon of Saturn

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.

[PURE SPECULATION, THIS WHOLE SECTION]

Exoplanets

On Earth-sized planets, plate tectonics is more likely if there are oceans of water; however, in 2007, two independent teams of researchers came to opposing conclusions about the likelihood of plate tectonics on larger super-earths with one team saying that plate tectonics would be episodic or stagnant and the other team saying that plate tectonics is very likely on super-earths even if the planet is dry.

See also

• Conservation of angular momentum
• Geological history of Earth
• Geosyncline theory
• GPlates, desktop software for the interactive visualization of plate-tectonics.
• List of plate tectonics topics
• List of submarine topographical features
• Supercontinent cycle
• Tectonics

References

Cited books

• Expanding Earth from p. 311 to p. 349.
• *
• , translation:

External links

• This Dynamic Earth: The Story of Plate Tectonics. USGS.
• Understanding Plate Tectonics. USGS.
• The PLATES Project. Jackson School of Geosciences.
• An explanation of tectonic forces. Example of calculations to show that Earth Rotation could be a driving force.
• Bird, P. (2003); An updated digital model of plate boundaries.
• Map of tectonic plates.
• MORVEL plate velocity estimates and information. C. DeMets, D. Argus, & R. Gordon.
• Mollewide Plate Tectonic Maps - continental maps at various points in the past

Videos

• Khan Academy Explanation of evidence
• 750 million years of global tectonic activity. Movie.
• Multiple videos of plate tectonic movements Quartz December 31, 2015