The tectonic plates of the world were mapped in thesecond half of the 20th century.

Plate tectonicsFrom Wikipedia, the free encyclopedia

Plate tectonics (from the Late Latin tectonicus, from theGreek: τεκτονικός "pertaining to building")[1] is a scientifictheory describing the large­scale motion of 7 large plates andthe movements of a larger number of smaller plates of theEarth's lithosphere, over the last hundreds of millions of years.The theoretical model builds on the concept of continental driftdeveloped during the first few decades of the 20th century. Thegeoscientific community accepted plate­tectonic theory afterseafloor spreading was validated in the late 1950s and early1960s.

The lithosphere, which is the rigid outermost shell of a planet(the crust and upper mantle), is broken up into tectonic plates.The Earth's lithosphere is composed of seven or eight majorplates (depending on how they are defined) and many minorplates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, ortransform. Earthquakes, volcanic activity, mountain­building, and oceanic trench formation occur along these plateboundaries. The relative movement of the plates typically ranges from zero to 100 mm annually.[2]

Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its ownkind of crust. Along convergent boundaries, subduction carries plates into the mantle; the material lost is roughlybalanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading. In this way, thetotal surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as theconveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradualexpansion of the globe.[3]

Tectonic plates are able to move because the Earth's lithosphere has greater strength than the underlyingasthenosphere. Lateral density variations in the mantle result in convection. Plate movement is thought to be drivenby a combination of the motion of the seafloor away from the spreading ridge (due to variations in topography anddensity of the crust, which result in differences in gravitational forces) and drag, with downward suction, at thesubduction 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 subjectof much debate.

Contents

1 Key principles2 Types of plate boundaries3 Driving forces of plate motion

3.1 Driving forces related to mantle dynamics3.2 Driving forces related to gravity3.3 Driving forces related to Earth rotation3.4 Relative significance of each driving force mechanism

4 Development of the theory4.1 Summary

4.2 Continental drift4.3 Floating continents, paleomagnetism, and seismicity

zones4.4 Mid­oceanic ridge spreading and convection4.5 Magnetic striping4.6 Definition and refining of the theory

5 Implications for biogeography6 Plate reconstruction

6.1 Defining plate boundaries6.2 Past plate motions6.3 Formation and break­up of continents

7 Current plates8 Other celestial bodies (planets, moons)

8.1 Venus8.2 Mars8.3 Icy satellites8.4 Exoplanets

9 See also10 References

10.1 Notes10.2 Cited books10.3 Cited articles

11 External links11.1 Videos

Key principles

The outer layers of the Earth are divided into the lithosphere and asthenosphere. This is based on differences inmechanical properties and in the method for the transfer of heat. Mechanically, the lithosphere is cooler and morerigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heatby conduction, whereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperaturegradient. 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 ofmantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature andpressure.

The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which rideon the fluid­like (visco­elastic solid) asthenosphere. Plate motions range up to a typical 10–40 mm/year (Mid­Atlantic Ridge; about as fast as fingernails grow), to about 160 mm/year (Nazca Plate; about as fast as hairgrows).[4] The driving mechanism behind this movement is described below.

Tectonic lithosphere plates consist of lithospheric mantle overlain by either or both of two types of crustal material:oceanic crust (in older texts called sima from silicon and magnesium) and continental crust (sial from silicon andaluminium). Average oceanic lithosphere is typically 100 km (62 mi) thick;[5] its thickness is a function of its age:as time passes, it conductively cools and subjacent cooling mantle is added to its base. Because it is formed at mid­ocean ridges and spreads outwards, its thickness is therefore a function of its distance from the mid­ocean ridgewhere it was formed. For a typical distance that oceanic lithosphere must travel before being subducted, thethickness varies from about 6 km (4 mi) thick at mid­ocean ridges to greater than 100 km (62 mi) at subductionzones; for shorter or longer distances, the subduction zone (and therefore also the mean) thickness becomes smaller

Transform boundary

or larger, respectively.[6] Continental lithosphere is typically ~200 km thick, though this varies considerablybetween basins, mountain ranges, and stable cratonic interiors of continents. The two types of crust also differ inthickness, with continental crust being considerably thicker than oceanic (35 km vs. 6 km).[7]

The location where two plates meet is called a plate boundary. Plate boundaries are commonly associated withgeological events such as earthquakes and the creation of topographic features such as mountains, volcanoes, mid­ocean ridges, and oceanic trenches. The majority of the world's active volcanoes occur along plate boundaries,with the Pacific Plate's Ring of Fire being the most active and widely known today. These boundaries are discussedin further detail below. Some volcanoes occur in the interiors of plates, and these have been variously attributed tointernal plate deformation[8] and to mantle plumes.

As explained above, tectonic plates may include continental crust or oceanic crust, and most plates contain both.For example, the African Plate includes the continent and parts of the floor of the Atlantic and Indian Oceans. Thedistinction between oceanic crust and continental crust is based on their modes of formation. Oceanic crust isformed at sea­floor spreading centers, and continental crust is formed through arc volcanism and accretion ofterranes through tectonic processes, though some of these terranes may contain ophiolite sequences, which arepieces of oceanic crust considered to be part of the continent when they exit the standard cycle of formation andspreading centers and subduction beneath continents. Oceanic crust is also denser than continental crust owing totheir different compositions. Oceanic crust is denser because it has less silicon and more heavier elements("mafic") than continental crust ("felsic").[9] As a result of this density stratification, oceanic crust generally liesbelow sea level (for example most of the Pacific Plate), while continental crust buoyantly projects above sea level(see the page isostasy for explanation of this principle).

Types of plate boundaries

Three types of plate boundaries exist,[10] with a fourth, mixed type, characterized by the way the plates moverelative to each other. They are associated with different types of surface phenomena. The different types of plateboundaries are:[11][12]

1. Transform boundaries (Conservative) occur where twolithospheric plates slide, or perhaps more accurately, grind pasteach other along transform faults, where plates are neithercreated nor destroyed. The relative motion of the two plates iseither sinistral (left side toward the observer) or dextral (rightside toward the observer). Transform faults occur across aspreading center. Strong earthquakes can occur along a fault.The San Andreas Fault in California is an example of atransform boundary exhibiting dextral motion.

2. Divergent boundaries (Constructive) occur where two platesslide apart from each other. At zones of ocean­to­ocean rifting,divergent boundaries form by seafloor spreading, allowing for the formation of new ocean basin. As theocean plate splits, the ridge forms at the spreading center, the ocean basin expands, and finally, the plate areaincreases causing many small volcanoes and/or shallow earthquakes. At zones of continent­to­continentrifting, divergent boundaries may cause new ocean basin to form as the continent splits, spreads, the centralrift collapses, and ocean fills the basin. Active zones of Mid­ocean ridges (e.g., Mid­Atlantic Ridge and EastPacific Rise), and continent­to­continent rifting (such as Africa's East African Rift and Valley, Red Sea) areexamples of divergent boundaries.

3. Convergent boundaries (Destructive) (or active margins) occur where two plates slide toward each other toform either a subduction zone (one plate moving underneath the other) or a continental collision. At zones ofocean­to­continent subduction (e.g. the Andes mountain range in South America, and the CascadeMountains in Western United States), the dense oceanic lithosphere plunges beneath the less dense continent.Earthquakes trace the path of the downward­moving plate as it

Divergent boundary

Convergent boundary

Plate motion based on Global Positioning System(GPS) satellite data from NASA JPL (http://sideshow.jpl.nasa.gov/mbh/series.html). The vectors showdirection and magnitude of motion.

Earthquakes trace the path of the downward­moving plate as itdescends into asthenosphere, a trench forms, and as thesubducted plate is heated it releases volatiles, mostly water fromhydrous minerals, into the surrounding mantle. The addition ofwater lowers the melting point of the mantle material above thesubducting slab, causing it to melt. The magma that resultstypically leads to volcanism.[13] At zones of ocean­to­oceansubduction (e.g. Aleutian islands, Mariana Islands, and theJapanese island arc), older, cooler, denser crust slips beneath lessdense crust. This causes earthquakes and a deep trench to formin an arc shape. The upper mantle of the subducted plate thenheats and magma rises to form curving chains of volcanicislands. Deep marine trenches are typically associated withsubduction zones, and the basins that develop along the activeboundary are often called "foreland basins". Closure of oceanbasins can occur at continent­to­continent boundaries (e.g.,Himalayas and Alps): collision between masses of graniticcontinental lithosphere; neither mass is subducted; plate edgesare compressed, folded, uplifted.

4. Plate boundary zones occur where the effects of the interactionsare unclear, and the boundaries, usually occurring along a broadbelt, are not well defined and may show various types ofmovements in different episodes.

Driving forces of plate motion

It has generally been accepted that tectonic plates are able tomove because of the relative density of oceanic lithosphereand the relative weakness of the asthenosphere. Dissipationof heat from the mantle is acknowledged to be the originalsource of the energy required to drive plate tectonics throughconvection or large scale upwelling and doming. The currentview, though still a matter of some debate, asserts that as aconsequence, a powerful source of plate motion is generateddue to the excess density of the oceanic lithosphere sinking insubduction zones. When the new crust forms at mid­oceanridges, this oceanic lithosphere is initially less dense than theunderlying asthenosphere, but it becomes denser with age asit conductively cools and thickens. The greater density of oldlithosphere relative to the underlying asthenosphere allows itto sink into the deep mantle at subduction zones, providingmost of the driving force for plate movement. The weaknessof the asthenosphere allows the tectonic plates to move easilytowards a subduction zone.[14] Although subduction isthought to be the strongest force driving plate motions, it cannot be the only force since there are plates such as theNorth American Plate which are moving, yet are nowhere being subducted. The same is true for the enormousEurasian Plate. The sources of plate motion are a matter of intensive research and discussion among scientists. Oneof the main points is that the kinematic pattern of the movement itself should be separated clearly from the possiblegeodynamic mechanism that is invoked as the driving force of the observed movement, as some patterns may be

explained by more than one mechanism.[15] In short, the driving forces advocated at the moment can be dividedinto three categories based on the relationship to the movement: mantle dynamics related, gravity related (mostlysecondary forces).

Driving forces related to mantle dynamics

For much of the last quarter century, the leading theory of the driving force behind tectonic plate motionsenvisaged large scale convection currents in the upper mantle, which can be transmitted through the asthenosphere.This theory was launched by Arthur Holmes and some forerunners in the 1930s[16] and was immediatelyrecognized as the solution for the acceptance of the theory as originally discussed in the papers of Alfred Wegenerin the early years of the century. However, despite its acceptance, it was long debated in the scientific communitybecause the leading ("fixist") theory still envisaged a static Earth without moving continents up until the majorbreakthroughs of the early sixties.

Two­ and three­dimensional imaging of Earth's interior (seismic tomography) shows a varying lateral densitydistribution throughout the mantle. Such density variations can be material (from rock chemistry), mineral (fromvariations in mineral structures), or thermal (through thermal expansion and contraction from heat energy). Themanifestation of this varying lateral density is mantle convection from buoyancy forces.[17]

How mantle convection directly and indirectly relates to plate motion is a matter of ongoing study and discussionin geodynamics. Somehow, this energy must be transferred to the lithosphere for tectonic plates to move. There areessentially two main types of forces that are thought to influence plate motion: friction and gravity.

Basal drag (friction): Plate motion driven by friction between the convection currents in the asthenosphereand the more rigid overlying lithosphere.Slab suction (gravity): Plate motion driven by local convection currents that exert a downward pull on platesin subduction zones at ocean trenches. Slab suction may occur in a geodynamic setting where basal tractionscontinue to act on the plate as it dives into the mantle (although perhaps to a greater extent acting on both theunder and upper side of the slab).

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

In the theory of plume tectonics developed during the 1990s, a modified concept of mantle convection currents isused. It asserts that super plumes rise from the deeper mantle and are the drivers or substitutes of the majorconvection cells. These ideas, which find their roots in the early 1930s with the so­called "fixistic" ideas of theEuropean and Russian Earth Science Schools, find resonance in the modern theories which envisage hotspots/mantle plumes which remain fixed and are overridden by oceanic and continental lithosphere plates overtime and leave their traces in the geological record (though these phenomena are not invoked as real drivingmechanisms, but rather as modulators). Modern theories that continue building on the older mantle domingconcepts and see plate movements as a secondary phenomena are beyond the scope of this page and are discussedelsewhere (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 justbelow 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.[18] Recent research, based onthree­dimensional computer modeling, suggests that plate geometry is governed by a feedback between mantleconvection patterns and the strength of the lithosphere.[19]

Driving forces related to gravity

Forces related to gravity are usually invoked as secondary phenomena within the framework of a more generaldriving 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 higherelevation of plates at ocean ridges.[20] As oceanic lithosphere is formed at spreading ridges from hot mantlematerial, it gradually cools and thickens with age (and thus adds distance from the ridge). Cool oceanic lithosphereis significantly denser than the hot mantle material from which it is derived and so with increasing thickness itgradually subsides into the mantle to compensate the greater load. The result is a slight lateral incline withincreased 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 nothingis "pushing" horizontally and tensional features are dominant along ridges. It is more accurate to refer to thismechanism as gravitational sliding as variable topography across the totality of the plate can vary considerably andthe topography of spreading ridges is only the most prominent feature. Other mechanisms generating thisgravitational secondary force include flexural bulging of the lithosphere before it dives underneath an adjacentplate which produces a clear topographical feature that can offset, or at least affect, the influence of topographicalocean ridges, and mantle plumes and hot spots, which are postulated to impinge on the underside of tectonic plates.

Slab­pull: Current scientific opinion is that the asthenosphere is insufficiently competent or rigid to directly causemotion by friction along the base of the lithosphere. Slab pull is therefore most widely thought to be the greatestforce acting on the plates. In this current understanding, plate motion is mostly driven by the weight of cold, denseplates sinking into the mantle at trenches.[21] Recent models indicate that trench suction plays an important role aswell. 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 theplates is the existence of large scale asthenosphere/mantle domes which cause the gravitational sliding oflithosphere plates away from them. This gravitational sliding represents a secondary phenomenon of this basicallyvertically oriented mechanism. This can act on various scales, from the small scale of one island arc up to thelarger scale of an entire ocean basin.[22]

Driving forces related to Earth rotation

Alfred Wegener, being a meteorologist, had proposed tidal forces and pole flight force as the main drivingmechanisms behind continental drift; however, these forces were considered far too small to cause continentalmotion as the concept then was of continents plowing through oceanic crust.[23] Therefore, Wegener later changedhis position and asserted that convection currents are the main driving force of plate tectonics in the last edition ofhis 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 motionwith the continents which caused the proposals related to Earth rotation to be reconsidered. In more recentliterature, these driving forces are:

1. Tidal drag due to the gravitational force the Moon (and the Sun) exerts on the crust of the Earth[24]2. Global deformation of the geoid due to small displacements of rotational pole with respect to the Earth'scrust;

3. Other smaller deformation effects of the crust due to wobbles and spin movements of the Earth rotation on asmaller time scale.

Forces that are small and generally negligible are:

1. The Coriolis force[25][26]

2. The centrifugal force, which is treated as a slight modification of gravity[25][26]:249

For these mechanisms to be overall valid, systematic relationships should exist all over the globe between theorientation 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 thetwentieth century underline exactly the opposite: that the plates had not moved in time, that the deformation gridwas fixed with respect to the Earth equator and axis, and that gravitational driving forces were generally actingvertically and caused only local horizontal movements (the so­called pre­plate tectonic, "fixist theories"). Laterstudies (discussed below on this page), therefore, invoked many of the relationships recognized during this pre­plate tectonics period to support their theories (see the anticipations and reviews in the work of van Dijk andcollaborators).[27]

Of the many forces discussed in this paragraph, tidal force is still highly debated and defended as a possibleprinciple driving force of plate tectonics. The other forces are only used in global geodynamic models not usingplate tectonics concepts (therefore beyond the discussions treated in this section) or proposed as minor modulationswithin the overall plate tectonics model.

In 1973, George W. Moore[28] of the USGS and R. C. Bostrom[29] presented evidence for a general westward driftof 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. Asthe Earth spins eastward beneath the moon, the moon's gravity ever so slightly pulls the Earth's surface layer backwestward, just as proposed by Alfred Wegener (see above). In a more recent 2006 study,[30] scientists reviewed andadvocated these earlier proposed ideas. It has also been suggested recently in Lovett (2006) that this observationmay also explain why Venus and Mars have no plate tectonics, as Venus has no moon and Mars' moons are toosmall to have significant tidal effects on the planet. In a recent paper,[31] it was suggested that, on the other hand, itcan easily be observed that many plates are moving north and eastward, and that the dominantly westward motionof the Pacific Ocean basins derives simply from the eastward bias of the Pacific spreading center (which is not apredicted manifestation of such lunar forces). In the same paper the authors admit, however, that relative to thelower mantle, there is a slight westward component in the motions of all the plates. They demonstrated though thatthe westward drift, seen only for the past 30 Ma, is attributed to the increased dominance of the steadily growingand accelerating Pacific plate. The debate is still open.

Relative significance of each driving force mechanism

The vector of a plate's motion is a function of all the forces acting on the plate; however, therein lies the problemregarding the degree to which each process contributes to the overall motion of each tectonic plate.

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

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, for instance,is essentially surrounded by zones of subduction (the so­called Ring of Fire) and moves much faster than the platesof the Atlantic basin, which are attached (perhaps one could say 'welded') to adjacent continents instead ofsubducting plates. It is thus thought that forces associated with the downgoing plate (slab pull and slab suction) arethe driving forces which determine the motion of plates, except for those plates which are not being subducted.[21]This view however has been contradicted by a recent study which found that the actual motions of the Pacific Plate

Detailed map showing the tectonic plates with theirmovement vectors.

and other plates associated with the East Pacific Rise do not correlate mainly with either slab pull or slab push, butrather with a mantle convection upwelling whose horizontal spreading along the bases of the various plates drivesthem along via viscosity­related traction forces.[32] The driving forces of plate motion continue to be activesubjects of on­going research within geophysics and tectonophysics.

Development of the theory

Summary

In line with other previous and contemporaneous proposals,in 1912 the meteorologist Alfred Wegener amply describedwhat he called continental drift, expanded in his 1915 bookThe Origin of Continents and Oceans[33] and the scientificdebate started that would end up fifty years later in the theoryof plate tectonics.[34] Starting from the idea (also expressedby his forerunners) that the present continents once formed asingle land mass (which was called Pangea later on) thatdrifted apart, thus releasing the continents from the Earth'smantle and likening them to "icebergs" of low density granitefloating on a sea of denser basalt.[35] Supporting evidence forthe idea came from the dove­tailing outlines of SouthAmerica'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 andGangamopteris, and the therapsid or mammal­like reptile Lystrosaurus, all widely distributed over South America,Africa, Antarctica, India and Australia. The evidence for such an erstwhile joining of these continents was patentto field geologists working in the southern hemisphere. The South African Alex du Toit put together a mass ofsuch information in his 1937 publication Our Wandering Continents, and went further than Wegener in recognisingthe 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 thecrust could move around. Distinguished scientists, such as Harold Jeffreys and Charles Schuchert, were outspokencritics 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 formerreached important milestones proposing that convection currents might have driven the plate movements, and thatspreading may have occurred below the sea within the oceanic crust. Concepts close to the elements nowincorporated in plate tectonics were proposed by geophysicists and geologists (both fixists and mobilists) likeVening­Meinesz, Holmes, and Umbgrove.

One of the first pieces of geophysical evidence that was used to support the movement of lithospheric plates camefrom paleomagnetism. This is based on the fact that rocks of different ages show a variable magnetic fielddirection, evidenced by studies since the mid–nineteenth century. The magnetic north and south poles reversethrough time, and, especially important in paleotectonic studies, the relative position of the magnetic north polevaries through time. Initially, during the first half of the twentieth century, the latter phenomenon was explained byintroducing what was called "polar wander" (see apparent polar wander), i.e., it was assumed that the north polelocation 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".

Alfred Wegener in Greenland in thewinter of 1912­13.

During the late 1950s it was successfully shown on two occasions that these data could show the validity ofcontinental drift: by Keith Runcorn in a paper in 1956 ,[36] and by Warren Carey in a symposium held in March1956.[37]

The second piece of evidence in support of continental drift came during the late 1950s and early 60s from data onthe bathymetry of the deep ocean floors and the nature of the oceanic crust such as magnetic properties and, moregenerally, with the development of marine geology[38] which gave evidence for the association of seafloorspreading along the mid­oceanic ridges and magnetic field reversals, published between 1959 and 1963 by Heezen,Dietz, Hess, Mason, Vine & Matthews, and Morley.[39]

Simultaneous advances in early seismic imaging techniques in and around Wadati­Benioff zones along the trenchesbounding many continental margins, together with many other geophysical (e.g. gravimetric) and geologicalobservations, showed how the oceanic crust could disappear into the mantle, providing the mechanism to balancethe 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 thatcontinental drift was feasible and the theory of plate tectonics, which was defined in a series of papers between1965 and 1967, was born, with all its extraordinary explanatory and predictive power. The theory revolutionizedthe Earth sciences, explaining a diverse range of geological phenomena and their implications in other studies suchas paleogeography and paleobiology.

Continental drift

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

It was observed as early as 1596 that the opposite coasts of the AtlanticOcean—or, more precisely, the edges of the continental shelves—havesimilar shapes and seem to have once fitted together.[40]

Since that time many theories were proposed to explain this apparentcomplementarity, but the assumption of a solid Earth made these variousproposals difficult to accept.[41]

The discovery of radioactivity and its associated heating properties in1895 prompted a re­examination of the apparent age of the Earth.[42] Thishad previously been estimated by its cooling rate under the assumptionthat the Earth's surface radiated like a black body.[43] Those calculationshad implied that, even if it started at red heat, the Earth would havedropped to its present temperature in a few tens of millions of years. Armed with the knowledge of a new heatsource, scientists realized that the Earth would be much older, and that its core was still sufficiently hot to beliquid.

By 1915, after having published a first article in 1912,[44] Alfred Wegener was making serious arguments for theidea of continental drift in the first edition of The Origin of Continents and Oceans.[33] In that book (re­issued infour successive editions up to the final one in 1936), he noted how the east coast of South America and the westcoast of Africa looked as if they were once attached. Wegener was not the first to note this (Abraham Ortelius,Antonio Snider­Pellegrini, Eduard Suess, Roberto Mantovani and Frank Bursley Taylor preceded him just to

Global earthquake epicenters, 1963–1998

mention a few), but he was the first to marshal significant fossil and paleo­topographical and climatologicalevidence 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 rockswere formed in the same way, implying that they were joined initially. For instance, parts of Scotland and Irelandcontain rocks very similar to those found in Newfoundland and New Brunswick. Furthermore, the CaledonianMountains of Europe and parts of the Appalachian Mountains of North America are very similar in structure andlithology.

However, his ideas were not taken seriously by many geologists, who pointed out that there was no apparentmechanism for continental drift. Specifically, they did not see how continental rock could plow through the muchdenser rock that makes up oceanic crust. Wegener could not explain the force that drove continental drift, and hisvindication did not come until after his death in 1930.

Floating continents, paleomagnetism, and seismicity zones

As it was observed early that although granite existed oncontinents, seafloor seemed to be composed of denser basalt,the prevailing concept during the first half of the twentiethcentury 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 waspresent under the continents. It therefore looked apparent thata layer of basalt (sial) underlies the continental rocks.

However, based on abnormalities in plumb line deflection bythe Andes in Peru, Pierre Bouguer had deduced that less­dense mountains must have a downward projection into thedenser layer underneath. The concept that mountains had"roots" was confirmed by George B. Airy a hundred yearslater, during study of Himalayan gravitation, and seismic studies detected corresponding density variations.Therefore, by the mid­1950s, the question remained unresolved as to whether mountain roots were clenched insurrounding basalt or were floating on it like an iceberg.

During the 20th century, improvements in and greater use of seismic instruments such as seismographs enabledscientists to learn that earthquakes tend to be concentrated in specific areas, most notably along the oceanictrenches and spreading ridges. By the late 1920s, seismologists were beginning to identify several prominentearthquake zones parallel to the trenches that typically were inclined 40–60° from the horizontal and extendedseveral hundred kilometers into the Earth. These zones later became known as Wadati­Benioff zones, or simplyBenioff zones, in honor of the seismologists who first recognized them, Kiyoo Wadati of Japan and Hugo Benioffof the United States. The study of global seismicity greatly advanced in the 1960s with the establishment of theWorldwide Standardized Seismograph Network (WWSSN)[45] to monitor the compliance of the 1963 treatybanning above­ground testing of nuclear weapons. The much improved data from the WWSSN instrumentsallowed seismologists to map precisely the zones of earthquake concentration worldwide.

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 movedthrough different climatic zones during the past. Furthermore, paleomagnetic data had shown that the magneticpole 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,[36] and successive papers by him and hisstudents Ted Irving (who was actually the first to be convinced of the fact that paleomagnetism supportedcontinental drift) and Ken Creer.

This was immediately followed by a symposium in Tasmania in March 1956.[46] In this symposium, the evidencewas used in the theory of an expansion of the global crust. In this hypothesis the shifting of the continents can besimply explained by a large increase in size of the Earth since its formation. However, this was unsatisfactorybecause 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 showthat the evidence was equally in support of continental drift on a globe with a stable radius.

During the thirties up to the late fifties, works by Vening­Meinesz, Holmes, Umbgrove, and numerous othersoutlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the Englishgeologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea, and in 1928 thatconvection currents within the mantle might be the driving force.[47] Often, these contributions are forgottenbecause:

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 withoutcontinental drift or an expanding Earth.They were published during an episode of extreme political and economic instability that hamperedscientific communication.Many were published by European scientists and at first not mentioned or given little credit in the papers onsea floor spreading published by the American researchers in the 1960s.

Mid­oceanic ridge spreading and convection

In 1947, a team of scientists led by Maurice Ewing utilizing the Woods Hole Oceanographic Institution's researchvessel Atlantis and an array of instruments, confirmed the existence of a rise in the central Atlantic Ocean, andfound that the floor of the seabed beneath the layer of sediments consisted of basalt, not the granite which is themain constituent of continents. They also found that the oceanic crust was much thinner than continental crust. Allthese new findings raised important and intriguing questions.[48]

The new data that had been collected on the ocean basins also showed particular characteristics regarding thebathymetry. One of the major outcomes of these datasets was that all along the globe, a system of mid­oceanicridges was detected. An important conclusion was that along this system, new ocean floor was being created,which led to the concept of the "Great Global Rift". This was described in the crucial paper of Bruce Heezen(1960),[49] which would trigger a real revolution in thinking. A profound consequence of seafloor spreading is thatnew crust was, and still is, being continually created along the oceanic ridges. Therefore, Heezen advocated the so­called "expanding Earth" hypothesis of S. Warren Carey (see above). So, still the question remained: how can newcrust be continuously added along the oceanic ridges without increasing the size of the Earth? In reality, thisquestion had been solved already by numerous scientists during the forties and the fifties, like Arthur Holmes,Vening­Meinesz, Coates and many others: The crust in excess disappeared along what were called the oceanictrenches, where so­called "subduction" occurred. Therefore, when various scientists during the early sixties startedto 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 ReserveRear Admiral, and Robert S. Dietz, a scientist with the U.S. Coast and Geodetic Survey who first coined the termseafloor spreading. Dietz and Hess (the former published the same idea one year earlier in Nature,[50] but prioritybelongs to Hess who had already distributed an unpublished manuscript of his 1962 article by 1960)[51] were

Seafloor magnetic striping.

among the small handful who really understood the broad implications of sea floor spreading and how it wouldeventually agree with the, at that time, unconventional and unaccepted ideas of continental drift and the elegantand mobilistic models proposed by previous workers like Holmes.

In the same year, Robert R. Coats of the U.S. Geological Survey described the main features of island arcsubduction in the Aleutian Islands. His paper, though little noted (and even ridiculed) at the time, has since beencalled "seminal" and "prescient". In reality, it actually shows that the work by the European scientists on islandarcs and mountain belts performed and published during the 1930s up until the 1950s was applied and appreciatedalso in the United States.

If the Earth's crust was expanding along the oceanic ridges, Hess and Dietz reasoned like Holmes and others beforethem, it must be shrinking elsewhere. Hess followed Heezen, suggesting that new oceanic crust continuouslyspreads away from the ridges in a conveyor belt–like motion. And, using the mobilistic concepts developed before,he correctly concluded that many millions of years later, the oceanic crust eventually descends along thecontinental margins where oceanic trenches – very deep, narrow canyons – are formed, e.g. along the rim of thePacific Ocean basin. The important step Hess made was that convection currents would be the driving force in thisprocess, arriving at the same conclusions as Holmes had decades before with the only difference that the thinningof the ocean crust was performed using Heezen's mechanism of spreading along the ridges. Hess thereforeconcluded that the Atlantic Ocean was expanding while the Pacific Ocean was shrinking. As old oceanic crust is"consumed" in the trenches (like Holmes and others, he thought this was done by thickening of the continentallithosphere, not, as now understood, by underthrusting at a larger scale of the oceanic crust itself into the mantle),new magma rises and erupts along the spreading ridges to form new crust. In effect, the ocean basins areperpetually being "recycled," with the creation of new crust and the destruction of old oceanic lithosphereoccurring simultaneously. Thus, the new mobilistic concepts neatly explained why the Earth does not get biggerwith sea floor spreading, why there is so little sediment accumulation on the ocean floor, and why oceanic rocksare much younger than continental rocks.

Magnetic striping

Beginning in the 1950s, scientists like Victor Vacquier, using magneticinstruments (magnetometers) adapted from airborne devices developedduring World War II to detect submarines, began recognizing odd magneticvariations across the ocean floor. This finding, though unexpected, was notentirely surprising because it was known that basalt—the iron­rich,volcanic rock making up the ocean floor—contains a strongly magneticmineral (magnetite) and can locally distort compass readings. Thisdistortion was recognized by Icelandic mariners as early as the late 18thcentury. More important, because the presence of magnetite gives the basaltmeasurable magnetic properties, these newly discovered magneticvariations provided another means to study the deep ocean floor. Whennewly formed rock cools, such magnetic materials recorded the Earth'smagnetic field at the time.

As more and more of the seafloor was mapped during the 1950s, the magnetic variations turned out not to berandom or isolated occurrences, but instead revealed recognizable patterns. When these magnetic patterns weremapped over a wide region, the ocean floor showed a zebra­like pattern: one stripe with normal polarity and theadjoining stripe with reversed polarity. The overall pattern, defined by these alternating bands of normally andreversely polarized rock, became known as magnetic striping, and was published by Ron G. Mason and co­workersin 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.[52]

A demonstration of magneticstriping. (The darker the coloris, the closer it is to normalpolarity)

The discovery of magnetic striping called for an explanation. In the early 1960sscientists such as Heezen, Hess and Dietz had begun to theorise that mid­oceanridges mark structurally weak zones where the ocean floor was being ripped intwo lengthwise along the ridge crest (see the previous paragraph). New magmafrom deep within the Earth rises easily through these weak zones and eventuallyerupts along the crest of the ridges to create new oceanic crust. This process, atfirst denominated the "conveyer belt hypothesis" and later called seafloorspreading, operating over many millions of years continues to form new oceanfloor all across the 50,000 km­long system of mid­ocean ridges.

Only four years after the maps with the "zebra pattern" of magnetic stripes werepublished, the link between sea floor spreading and these patterns was correctlyplaced, independently by Lawrence Morley, and by Fred Vine and DrummondMatthews, in 1963,[53] now called the Vine­Matthews­Morley hypothesis. Thishypothesis linked these patterns to geomagnetic reversals and was supported by several lines of evidence:[54]

1. the stripes are symmetrical around the crests of the mid­ocean ridges; at or near the crest of the ridge, therocks are very young, and they become progressively older away from the ridge crest;

2. the youngest rocks at the ridge crest always have present­day (normal) polarity;3. stripes of rock parallel to the ridge crest alternate in magnetic polarity (normal­reversed­normal, etc.),suggesting that they were formed during different epochs documenting the (already known from independentstudies) normal and reversal episodes of the Earth's magnetic field.

By explaining both the zebra­like magnetic striping and the construction of the mid­ocean ridge system, theseafloor spreading hypothesis (SFS) quickly gained converts and represented another major advance in thedevelopment of the plate­tectonics theory. Furthermore, the oceanic crust now came to be appreciated as a natural"tape recording" of the history of the geomagnetic field reversals (GMFR) of the Earth's magnetic field. Today,extensive studies are dedicated to the calibration of the normal­reversal patterns in the oceanic crust on one handand known timescales derived from the dating of basalt layers in sedimentary sequences (magnetostratigraphy) onthe other, to arrive at estimates of past spreading rates and plate reconstructions.

Definition and refining of the theory

After all these considerations, Plate Tectonics (or, as it was initially called "New Global Tectonics") becamequickly accepted in the scientific world, and numerous papers followed that defined the concepts:

In 1965, Tuzo Wilson who had been a promotor of the sea floor spreading hypothesis and continental driftfrom the very beginning[55] added the concept of transform faults to the model, completing the classes offault types necessary to make the mobility of the plates on the globe work out.[56]A symposium on continental drift was held at the Royal Society of London in 1965 which must be regardedas the official start of the acceptance of plate tectonics by the scientific community, and which abstracts areissued as Blacket, Bullard & Runcorn (1965). In this symposium, Edward Bullard and co­workers showedwith a computer calculation how the continents along both sides of the Atlantic would best fit to close theocean, which became known as the famous "Bullard's Fit".In 1966 Wilson published the paper that referred to previous plate tectonic reconstructions, introducing theconcept of what is now known as the "Wilson Cycle".[57]In 1967, at the American Geophysical Union's meeting, W. Jason Morgan proposed that the Earth's surfaceconsists of 12 rigid plates that move relative to each other.[58]Two months later, Xavier Le Pichon published a complete model based on 6 major plates with their relativemotions, which marked the final acceptance by the scientific community of plate tectonics.[59]

In the same year, McKenzie and Parker independently presented a model similar to Morgan's usingtranslations and rotations on a sphere to define the plate motions.[60]

Implications for biogeography

Continental drift theory helps biogeographers to explain the disjunct biogeographic distribution of present­day lifefound on different continents but having similar ancestors.[61] In particular, it explains the Gondwanan distributionof ratites and the Antarctic flora.

Plate reconstruction

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

Defining plate boundaries

Current plate boundaries are defined by their seismicity.[62] Past plate boundaries within existing plates areidentified from a variety of evidence, such as the presence of ophiolites that are indicative of vanished oceans.[63]

Past plate motions

Tectonic motion first began around three billion years ago.[64]

Various types of quantitative and semi­quantitative information are available to constrain past plate motions. Thegeometric fit between continents, such as between west Africa and South America is still an important part of platereconstruction. Magnetic stripe patterns provide a reliable guide to relative plate motions going back into theJurassic period.[65] The tracks of hotspots give absolute reconstructions, but these are only available back to theCretaceous.[66] Older reconstructions rely mainly on paleomagnetic pole data, although these only constrain thelatitude and rotation, but not the longitude. Combining poles of different ages in a particular plate to produceapparent polar wander paths provides a method for comparing the motions of different plates through time.[67]

Additional evidence comes from the distribution of certain sedimentary rock types,[68] faunal provinces shown byparticular fossil groups, and the position of orogenic belts.[66]

Formation and break­up of continents

The movement of plates has caused the formation and break­up of continents over time, including occasionalformation of a supercontinent that contains most or all of the continents. The supercontinent Columbia or Nunaformed during a period of 2,000 to 1,800 million years ago and broke up about1,500 to 1,300 million years ago.[69] The supercontinent Rodinia is thought to have formed about 1 billion yearsago and to have embodied most or all of Earth's continents, and broken up into eight continents around600 million years ago. The eight continents later re­assembled into another supercontinent called Pangaea; Pangaeabroke up into Laurasia (which became North America and Eurasia) and Gondwana (which became the remainingcontinents).

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

Current plates

Depending on how they aredefined, there are usually sevenor eight "major" plates: African,Antarctic, Eurasian, NorthAmerican, South American,Pacific, and Indo­Australian. Thelatter is sometimes subdividedinto the Indian and Australianplates.

There are dozens of smallerplates, the seven largest of whichare the Arabian, Caribbean, Juande Fuca, Cocos, Nazca,Philippine Sea and Scotia.

The current motion of thetectonic plates is todaydetermined by remote sensingsatellite data sets, calibrated with ground station measurements.

Other celestial bodies (planets, moons)

The appearance of plate tectonics on terrestrial planets is related to planetary mass, with more massive planets thanEarth expected to exhibit plate tectonics. Earth may be a borderline case, owing its tectonic activity to abundantwater [70] (silica and water form a deep eutectic.)

Venus

Venus shows no evidence of active plate tectonics. There is debatable evidence of active tectonics in the planet'sdistant past; however, events taking place since then (such as the plausible and generally accepted hypothesis thatthe Venusian lithosphere has thickened greatly over the course of several hundred million years) has madeconstraining the course of its geologic record difficult. However, the numerous well­preserved impact craters havebeen utilized as a dating method to approximately date the Venusian surface (since there are thus far no knownsamples of Venusian rock to be dated by more reliable methods). Dates derived are dominantly in the range500 to 750 million years ago, although ages of up to 1,200 million years ago have been calculated. This researchhas led to the fairly well accepted hypothesis that Venus has undergone an essentially complete volcanicresurfacing at least once in its distant past, with the last event taking place approximately within the range ofestimated surface ages. While the mechanism of such an impressive thermal event remains a debated issue inVenusian 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 waterto be present.[71][72] The Earth's crust is soaked with water, and water plays an important role in the development ofshear zones. Plate tectonics requires weak surfaces in the crust along which crustal slices can move, and it maywell be that such weakening never took place on Venus because of the absence of water. However, someresearchers 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.[73]Scientists today disagree, and think that it was created either by upwelling within the Martian mantle thatthickened the crust of the Southern Highlands and formed Tharsis[74] or by a giant impact that excavated theNorthern Lowlands.[75]

Valles Marineris may be a tectonic boundary.[76]

Observations made of the magnetic field of Mars by the Mars Global Surveyor spacecraft in 1999 showed patternsof magnetic striping discovered on this planet. Some scientists interpreted these as requiring plate tectonicprocesses, such as seafloor spreading.[77] However, their data fail a "magnetic reversal test", which is used to see ifthey were formed by flipping polarities of a global magnetic field.[78]

Icy satellites

Some of the satellites of Jupiter have features that may be related to plate­tectonic style deformation, although thematerials and specific mechanisms may be different from plate­tectonic activity on Earth. On 8 September 2014,NASA reported finding evidence of plate tectonics on Europa, a satellite of Jupiter—the first sign of suchgeological activity on another world other than Earth.[79]

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.[80]

Exoplanets

On Earth­sized planets, plate tectonics is more likely if there are oceans of water; however, in 2007, twoindependent teams of researchers came to opposing conclusions about the likelihood of plate tectonics on largersuper­earths[81][82] with one team saying that plate tectonics would be episodic or stagnant[83] and the other teamsaying that plate tectonics is very likely on super­earths even if the planet is dry.[70]

See also

References

Notes

Conservation of angular momentumGeological history of Earth ­ includes timeline ofplate configurationsGeosyncline theoryGPlates, desktop software for the interactivevisualization of plate­tectonics.List of plate tectonics topics

List of plate tectonics topicsList of submarine topographical featuresSupercontinent cycleTectonicsAtmospheric circulation

1. Little, Fowler & Coulson 1990.2. Read & Watson 1975.3. Scalera & Lavecchia 2006.4. Zhen Shao 1997, Hancock, Skinner & Dineley 2000.

5. Turcotte & Schubert 2002, p. 5.6. Turcotte & Schubert 2002.7. Turcotte & Schubert 2002, p. 3.8. Foulger 2010.9. Schmidt & Harbert 1998.10. Meissner 2002, p. 100.11. "Plate Tectonics: Plate Boundaries". platetectonics.com. Retrieved 12 June 2010.12. "Understanding plate motions". USGS. Retrieved 12 June 2010.13. Grove, Timothy L.; Till, Christy B.; Krawczynski, Michael J. (8 March 2012). "The Role of H2O in Subduction Zone

Magmatism". Annual Review of Earth and Planetary Sciences. 40 (40): 413–439. Bibcode:2012AREPS..40..413G.doi:10.1146/annurev­earth­042711­105310. Retrieved 14 January 2016.

14. Mendia­Landa, Pedro. "Myths and Legends on Natural Disasters: Making Sense of Our World". Retrieved 2008­02­05.15. van Dijk 1992, van Dijk & Okkes 1991.16. Holmes, Arthur (1931). "Radioactivity and Earth Movements" (PDF). Transactions of the Geological Society of Glasgow.

Geological Society of Glasgow: 559–606.17. Tanimoto & Lay 2000.18. Meyerhoff et al. 1996.19. Mallard, Claire; Coltice, Nicolas; Seton, Maria; Müller, R. Dietmar; Tackley, Paul J. (2016). "Subduction controls the

distribution and fragmentation of Earth's tectonic plates". Nature. 535 (7610): 140–143. Bibcode:2016Natur.535..140M.doi:10.1038/nature17992. ISSN 0028­0836.

20. Spence 1987, White & McKenzie 1989.21. Conrad & Lithgow­Bertelloni 2002.22. Spence 1987, White & Mckenzie 1989, Segev 2002.23. "Alfred Wegener (1880­1930)". University of California Museum of Paleontology.24. Neith, Katie (April 15, 2011). "Caltech Researchers Use GPS Data to Model Effects of Tidal Loads on Earth's Surface".

Caltech. Retrieved August 15, 2012.25. Ricard, Y. (2009). "2. Physics of Mantle Convection". In David Bercovici; Gerald Schubert. Treatise on Geophysics:

Mantle Dynamics. 7. Elsevier Science. p. 36. ISBN 9780444535801.26. Glatzmaier, Gary A. (2013). Introduction to Modeling Convection in Planets and Stars: Magnetic Field, Density

Stratification, Rotation. Princeton University Press. p. 149. ISBN 9781400848904.27. van Dijk 1992, van Dijk & Okkes 1990.28. Moore 1973.29. Bostrom 1971.30. Scoppola et al. 2006.31. Torsvik et al. 2010.32. ["Kinematics and dynamics of the East Pacific Rise linked to a stable, deep­mantle upwelling", Rowley et al, Science

Advances 23 Dec 2016:Vol. 2, no. 12, e1601107, DOI: 10.1126/sciadv.1601107]33. Wegener 1929.34. Hughes 2001a.35. Wegener 1966, Hughes 2001b.36. Runcorn 1956.37. Carey 1956.38. see for example the milestone paper of Lyman & Fleming 1940.39. Korgen 1995, Spiess & Kuperman 2003.40. Kious & Tilling 1996.41. Frankel 1987.42. Joly 1909.43. Thomson 1863.44. Wegener 1912.45. Stein & Wysession 2009, p. 2646. Carey 1956; see also Quilty 2003.47. Holmes 1928; see also Holmes 1978, Frankel 1978.48. Lippsett 2001, Lippsett 2006.49. Heezen 1960.50. Dietz 1961.51. Hess 1962.52. Mason & Raff 1961, Raff & Mason 1961.

Cited books

53. Vine & Matthews 1963.54. See summary in Heirzler, Le Pichon & Baron 196655. Wilson 1963.56. Wilson 1965.57. Wilson 1966.58. Morgan 1968.59. Le Pichon 1967.60. McKenzie & Parker 1967.61. Moss & Wilson 1998.62. Condie 1997.63. Lliboutry 2000.64. Kranendonk, V.; Martin, J. (2011). "Onset of Plate Tectonics". Science. 333 (6041): 413–414.

Bibcode:2011Sci...333..413V. doi:10.1126/science.1208766. PMID 21778389.65. Torsvik, Trond Helge. "Reconstruction Methods". Retrieved 18 June 2010.66. Torsvik 2008.67. Butler 1992.68. Scotese, C.R. (2002­04­20). "Climate History". Paleomap Project. Retrieved 18 June 2010.69. Zhao 2002, 200470. Valencia, O'Connell & Sasselov 2007.71. Kasting 1988.72. Bortman, Henry (2004­08­26). "Was Venus alive? "The Signs are Probably There" ". Astrobiology Magazine. Retrieved

2008­01­08.73. Sleep 1994.74. Zhong & Zuber 2001.75. Andrews­Hanna, Zuber & Banerdt 2008.76. Wolpert, Stuart (August 9, 2012). "UCLA scientist discovers plate tectonics on Mars". Yin, An. UCLA. Retrieved

August 13, 2012.77. Connerney et al. 1999, Connerney et al. 200578. Harrison 2000.79. Dyches, Preston; Brown, Dwayne; Buckley, Michael (8 September 2014). "Scientists Find Evidence of 'Diving' Tectonic

Plates on Europa". NASA. Retrieved 8 September 2014.80. Soderblom et al. 2007.81. Valencia, Diana; O'Connell, Richard J. (2009). "Convection scaling and subduction on Earth and super­Earths". Earth

and Planetary Science Letters. 286 (3–4): 492–502. Bibcode:2009E&PSL.286..492V. doi:10.1016/j.epsl.2009.07.015.82. van Heck, H. J.; Tackley, P.J. (2011). "Plate tectonics on super­Earths: Equally or more likely than on Earth". Earth and

Planetary Science Letters. 310 (3–4): 252–261. Bibcode:2011E&PSL.310..252V. doi:10.1016/j.epsl.2011.07.029.83. C. O'Neill, A. Lenardic Geological consequences of super­sized Earths (http://www.agu.org/pubs/crossref/2007/2007GL0

30598.shtml) GEOPHYSICAL RESEARCH LETTERS 34: L19204 doi:10.1029/2007GL030598 (https://dx.doi.org/10.1029%2F2007GL030598)

Butler, Robert F. (1992). "Applications topaleogeography". Paleomagnetism: Magnetic domainsto geologic terranes (PDF). Blackwell. ISBN 0­86542­070­X. Retrieved 18 June 2010.Carey, S. W. (1958). "The tectonic approach tocontinental drift". In Carey, S.W. Continental Drift—Asymposium, held in March 1956. Hobart: Univ. ofTasmania. pp. 177–363. Expanding Earth from p. 311to p. 349.Condie, K.C. (1997). Plate tectonics and crustalevolution (4th ed.). Butterworth­Heinemann. p. 282.ISBN 978­0­7506­3386­4. Retrieved 2010­06­18.Foulger, Gillian R. (2010). Plates vs Plumes: AGeological Controversy. Wiley­Blackwell. ISBN 978­1­4051­6148­0.

Frankel, H. (1987). "The Continental Drift Debate". InH.T. Engelhardt Jr; A.L. Caplan. ScientificControversies: Case Solutions in the resolution andclosure of disputes in science and technology.Cambridge University Press. ISBN 978­0­521­27560­6.Hancock, Paul L.; Skinner, Brian J.; Dineley, David L.(2000). The Oxford Companion to The Earth. OxfordUniversity Press. ISBN 0­19­854039­6.Hess, H. H. (November 1962). "History of OceanBasins" (PDF). In A. E. J. Engel; Harold L. James; B.F. Leonard. Petrologic studies: a volume to honor of A.F. Buddington. Boulder, CO: Geological Society ofAmerica. pp. 599–620.Holmes, Arthur (1978). Principles of Physical Geology(3 ed.). Wiley. pp. 640–641. ISBN 0­471­07251­6.

Cited articles

Joly, John (1909). Radioactivity and Geology: AnAccount of the Influence of Radioactive Energy onTerrestrial History. London: Archibald Constable.p. 36. ISBN 1­4021­3577­7.Kious, W. Jacquelyne; Tilling, Robert I. (February2001) [1996]. "Historical perspective". This DynamicEarth: the Story of Plate Tectonics (Online ed.). U.S.Geological Survey. ISBN 0­16­048220­8. Retrieved2008­01­29. "Abraham Ortelius in his work ThesaurusGeographicus... suggested that the Americas were 'tornaway from Europe and Africa... by earthquakes andfloods... The vestiges of the rupture reveal themselves,if someone brings forward a map of the world andconsiders carefully the coasts of the three [continents].'"Lippsett, Laurence (2006). "Maurice Ewing and theLamont­Doherty Earth Observatory". In WilliamTheodore De Bary; Jerry Kisslinger; Tom Mathewson.Living Legacies at Columbia. Columbia UniversityPress. pp. 277–297. ISBN 0­231­13884­9. Retrieved2010­06­22.Little, W.; Fowler, H.W.; Coulson, J. (1990). OnionsC.T., ed. The Shorter Oxford English Dictionary: onhistorical principles. II (3 ed.). Clarendon Press.ISBN 978­0­19­861126­4.Lliboutry, L. (2000). Quantitative geophysics andgeology. Springer. p. 480. ISBN 978­1­85233­115­3.Retrieved 2010­06­18.McKnight, Tom (2004). Geographica: The completeillustrated Atlas of the world. New York: Barnes andNoble Books. ISBN 0­7607­5974­X.* Meissner, Rolf(2002). The Little Book of Planet Earth. New York:Copernicus Books. p. 202. ISBN 978­0­387­95258­1.Meyerhoff, Arthur Augustus; Taner, I.; Morris, A. E.L.; Agocs, W. B.; Kamen­Kaye, M.; Bhat, MohammadI.; Smoot, N. Christian; Choi, Dong R. (1996). DonnaMeyerhoff Hull, ed. Surge tectonics: a new hypothesisof global geodynamics. Solid Earth Sciences Library. 9.Springer Netherlands. p. 348. ISBN 978­0­7923­4156­7.Moss, S.J.; Wilson, M.E.J. (1998). "Biogeographicimplications from the Tertiary palaeogeographicevolution of Sulawesi and Borneo" (PDF). In Hall R;Holloway JD. Biogeography and Geological Evolutionof SE Asia (PDF). Leiden, The Netherlands: Backhuys.pp. 133–163. ISBN 90­73348­97­8.Oreskes, Naomi, ed. (2003). Plate Tectonics: AnInsider's History of the Modern Theory of the Earth.Westview. ISBN 0­8133­4132­9.

Read, Herbert Harold; Watson, Janet (1975).Introduction to Geology. New York: Halsted. pp. 13–15.ISBN 978­0­470­71165­1. OCLC 317775677.Schmidt, Victor A.; Harbert, William (1998). "TheLiving Machine: Plate Tectonics". Planet Earth and theNew Geosciences (3 ed.). p. 442. ISBN 0­7872­4296­9.Retrieved 2008­01­28.Schubert, Gerald; Turcotte, Donald L.; Olson, Peter(2001). Mantle Convection in the Earth and Planets.Cambridge: Cambridge University Press. ISBN 0­521­35367­X.Stanley, Steven M. (1999). Earth System History. W.H.Freeman. pp. 211–228. ISBN 0­7167­2882­6.Sverdrup, H. U., Johnson, M. W. and Fleming, R. H.(1942). The Oceans: Their physics, chemistry andgeneral biology. Englewood Cliffs: Prentice­Hall.p. 1087.Thompson, Graham R. & Turk, Jonathan (1991).Modern Physical Geology. Saunders CollegePublishing. ISBN 0­03­025398­5.Torsvik, Trond Helge; Steinberger, Bernhard(December 2006). "Fra kontinentaldrift tilmanteldynamikk" [From Continental Drift to MantleDynamics]. Geo (in Norwegian). 8: 20–30. Retrieved22 June 2010., translation: Torsvik, Trond Helge;Steinberger, Bernhard (2008). "From Continental Driftto Mantle Dynamics" (PDF). In Trond Slagstad; RolvDahl Gråsteinen. Geology for Society for 150 years ­The Legacy after Kjerulf. 12. Trondheim: NorgesGeologiske Undersokelse. pp. 24–38 [NorwegianGeological Survey, Popular Science].Turcotte, D.L.; Schubert, G. (2002). "Plate Tectonics".Geodynamics (2 ed.). Cambridge University Press.pp. 1–21. ISBN 0­521­66186­2.Wegener, Alfred (1929). Die Entstehung der Kontinenteund Ozeane (4 ed.). Braunschweig: Friedrich Vieweg &Sohn Akt. Ges. ISBN 3­443­01056­3.Wegener, Alfred (1966). The origin of continents andoceans. Biram John (translator). Courier Dover. p. 246.ISBN 0­486­61708­4.Winchester, Simon (2003). Krakatoa: The Day theWorld Exploded: August 27, 1883. HarperCollins.ISBN 0­06­621285­5.Stein, Seth; Wysession, Michael (2009). AnIntroduction to Seismology, Earthquakes, and EarthStructure. Chichester: John Wiley & Sons. ISBN 978­1­4443­1131­0.

Andrews­Hanna, Jeffrey C.; Zuber, Maria T.; Banerdt,W. Bruce (2008). "The Borealis basin and the origin ofthe martian crustal dichotomy". Nature. 453 (7199):1212–5. Bibcode:2008Natur.453.1212A.doi:10.1038/nature07011. PMID 18580944.

Blacket, P.M.S.; Bullard, E.; Runcorn, S.K., eds.(1965). A Symposium on Continental Drift, held in 28October 1965. Philosophical Transactions of the RoyalSociety A. 258. The Royal Society of London. p. 323.

Bostrom, R.C. (31 December 1971). "Westwarddisplacement of the lithosphere". Nature. 234 (5331):536–538. Bibcode:1971Natur.234..536B.doi:10.1038/234536a0.Connerney, J.E.P.; Acuña, M.H.; Wasilewski, P.J.;Ness, N.F.; Rème H.; Mazelle C.; Vignes D.; Lin R.P.;Mitchell D.L.; Cloutier P.A. (1999). "MagneticLineations in the Ancient Crust of Mars". Science. 284(5415): 794–798. Bibcode:1999Sci...284..794C.doi:10.1126/science.284.5415.794. PMID 10221909.Connerney, J.E.P.; Acuña, M.H.; Ness, N.F.;Kletetschka, G.; Mitchell D.L.; Lin R.P.; Rème H.(2005). "Tectonic implications of Mars crustalmagnetism". Proceedings of the National Academy ofSciences. 102 (42): 14970–14975.Bibcode:2005PNAS..10214970C.doi:10.1073/pnas.0507469102. PMC 1250232 .PMID 16217034.Conrad, Clinton P.; Lithgow­Bertelloni, Carolina(2002). "How Mantle Slabs Drive Plate Tectonics".Science. 298 (5591): 207–9.Bibcode:2002Sci...298..207C.doi:10.1126/science.1074161. PMID 12364804.Archived from the original on September 20, 2009.Dietz, Robert S. (June 1961). "Continent and OceanBasin Evolution by Spreading of the Sea Floor".Nature. 190 (4779): 854–857.Bibcode:1961Natur.190..854D. doi:10.1038/190854a0.van Dijk, Janpieter; Okkes, F.W. Mark (1990). "Theanalysis of shear zones in Calabria; implications for thegeodynamics of the Central Mediterranean". RivistaItaliana di Paleontologia e Stratigrafia. 96 (2–3): 241–270.van Dijk, J.P.; Okkes, F.W.M. (1991). "Neogenetectonostratigraphy and kinematics of Calabrian Basins:implications for the geodynamics of the CentralMediterranean". Tectonophysics. 196: 23–60.Bibcode:1991Tectp.196...23V. doi:10.1016/0040­1951(91)90288­4.van Dijk, Janpieter (1992). "Late Neogene fore­arcbasin evolution in the Calabrian Arc (CentralMediterranean). Tectonic sequence stratigraphy anddynamic geohistory. With special reference to thegeology of Central Calabria". Geologica Ultraiectina.92: 288.Frankel, Henry (July 1978). "Arthur Holmes andcontinental drift". The British Journal for the History ofScience. 11 (2): 130–150.doi:10.1017/S0007087400016551. JSTOR 4025726.Harrison, C.G.A. (2000). "Questions About MagneticLineations in the Ancient Crust of Mars". Science. 287(5453): 547a. doi:10.1126/science.287.5453.547a.Heezen, B. (1960). "The rift in the ocean floor".Scientific American. 203 (4): 98–110.doi:10.1038/scientificamerican1060­98.

Heirtzler, James R.; Le Pichon, Xavier; Baron, J.Gregory (1966). "Magnetic anomalies over theReykjanes Ridge". Deep­Sea Research. 13 (3): 427–432. Bibcode:1966DSROA..13..427H.doi:10.1016/0011­7471(66)91078­3.Holmes, Arthur (1928). "Radioactivity and Earthmovements". Transactions of the Geological Society ofGlasgow. 18: 559–606.Hughes, Patrick (8 February 2001). "Alfred Wegener(1880­1930): A Geographic Jigsaw Puzzle". On theshoulders of giants. Earth Observatory, NASA.Retrieved 2007­12­26. "... on January 6, 1912,Wegener... proposed instead a grand vision of driftingcontinents and widening seas to explain the evolution ofEarth's geography."Hughes, Patrick (8 February 2001). "Alfred Wegener(1880­1930): The origin of continents and oceans". Onthe Shoulders of Giants. Earth Observatory, NASA.Retrieved 2007­12­26. "By his third edition (1922),Wegener was citing geological evidence that some 300million years ago all the continents had been joined in asupercontinent stretching from pole to pole. He called itPangaea (all lands),..."Kasting, James F. (1988). "Runaway and moistgreenhouse atmospheres and the evolution of Earth andVenus". Icarus. 74 (3): 472–494.Bibcode:1988Icar...74..472K. doi:10.1016/0019­1035(88)90116­9. PMID 11538226.Korgen, Ben J. (1995). "A voice from the past: JohnLyman and the plate tectonics story" (PDF).Oceanography. The Oceanography Society. 8 (1): 19–20. doi:10.5670/oceanog.1995.29.Lippsett, Laurence (2001). "Maurice Ewing and theLamont­Doherty Earth Observatory". Living Legacies.Retrieved 2008­03­04.Lovett, Richard A (24 January 2006). "Moon IsDragging Continents West, Scientist Says". NationalGeographic News.Lyman, J.; Fleming, R.H. (1940). "Composition ofSeawater". Journal of Marine Research. 3: 134–146.Mason, Ronald G.; Raff, Arthur D. (1961). "Magneticsurvey off the west coast of the United States between32°N latitude and 42°N latitude". Bulletin of theGeological Society of America. 72 (8): 1259–1266.Bibcode:1961GSAB...72.1259M. doi:10.1130/0016­7606(1961)72[1259:MSOTWC]2.0.CO;2. ISSN 0016­7606.Mc Kenzie, D.; Parker, R.L. (1967). "The NorthPacific: an example of tectonics on a sphere". Nature.216 (5122): 1276–1280.Bibcode:1967Natur.216.1276M.doi:10.1038/2161276a0.Moore, George W. (1973). "Westward Tidal Lag as theDriving Force of Plate Tectonics". Geology. 1 (3): 99–100. Bibcode:1973Geo.....1...99M. doi:10.1130/0091­7613(1973)1<99:WTLATD>2.0.CO;2. ISSN 0091­7613.

Morgan, W. Jason (1968). "Rises, Trenches, GreatFaults, and Crustal Blocks" (PDF). Journal ofGeophysical Research. 73 (6): 1959–1982.Bibcode:1968JGR....73.1959M.doi:10.1029/JB073i006p01959.Le Pichon, Xavier (15 June 1968). "Sea­floor spreadingand continental drift". Journal of Geophysical Research.73 (12): 3661–3697. Bibcode:1968JGR....73.3661L.doi:10.1029/JB073i012p03661.Quilty, Patrick G.; Banks, Maxwell R. (2003). "SamuelWarren Carey, 1911­2002". Biographical memoirs.Australian Academy of Science. Retrieved 2010­06­19."This memoir was originally published in HistoricalRecords of Australian Science (2003) 14 (3)."Raff, Arthur D.; Mason, Roland G. (1961). "Magneticsurvey off the west coast of the United States between40°N latitude and 52°N latitude". Bulletin of theGeological Society of America. 72 (8): 1267–1270.Bibcode:1961GSAB...72.1267R. doi:10.1130/0016­7606(1961)72[1267:MSOTWC]2.0.CO;2. ISSN 0016­7606.Runcorn, S.K. (1956). "Paleomagnetic comparisonsbetween Europe and North America". Proceedings,Geological Association of Canada. 8 (1088): 7785.Bibcode:1965RSPTA.258....1R.doi:10.1098/rsta.1965.0016.Scalera, G. & Lavecchia, G. (2006). "Frontiers in earthsciences: new ideas and interpretation". Annals ofGeophysics. 49 (1). doi:10.4401/ag­4406 (inactive2017­01­16).Scoppola, B.; Boccaletti, D.; Bevis, M.; Carminati, E.;Doglioni, C. (2006). "The westward drift of thelithosphere: A rotational drag?". Geological Society ofAmerica Bulletin. 118: 199–209.Bibcode:2006GSAB..118..199S. doi:10.1130/B25734.1.Segev, A (2002). "Flood basalts, continental breakupand the dispersal of Gondwana: evidence for periodicmigration of upwelling mantle flows (plumes)" (PDF).EGU Stephan Mueller Special Publication Series. 2:171–191. doi:10.5194/smsps­2­171­2002. Retrieved5 August 2010.Sleep, Norman H. (1994). "Martian plate tectonics".Journal of Geophysical Research. 99: 5639.Bibcode:1994JGR....99.5639S.doi:10.1029/94JE00216.Soderblom, Laurence A.; Tomasko, Martin G.;Archinal, Brent A.; Becker, Tammy L.; Bushroe,Michael W.; Cook, Debbie A.; Doose, Lyn R.;Galuszka, Donna M.; Hare, Trent M.; Howington­Kraus, Elpitha; Karkoschka, Erich; Kirk, Randolph L.;Lunine, Jonathan I.; McFarlane, Elisabeth A.; Redding,Bonnie L.; Rizk, Bashar; Rosiek, Mark R.; See,Charles; Smith, Peter H. (2007). "Topography andgeomorphology of the Huygens landing site on Titan".Planetary and Space Science. 55 (13): 2015–2024.Bibcode:2007P&SS...55.2015S.doi:10.1016/j.pss.2007.04.015.

Spence, William (1987). "Slab pull and theseismotectonics of subducting lithosphere" (PDF).Reviews of Geophysics. 25 (1): 55–69.Bibcode:1987RvGeo..25...55S.doi:10.1029/RG025i001p00055.Spiess, Fred; Kuperman, William (2003). "The MarinePhysical Laboratory at Scripps" (PDF). Oceanography.The Oceanography Society. 16 (3): 45–54.doi:10.5670/oceanog.2003.30.Tanimoto, Toshiro; Lay, Thorne (7 November 2000)."Mantle dynamics and seismic tomography".Proceedings of the National Academy of Sciences. 97(23): 12409–12410. Bibcode:2000PNAS...9712409T.doi:10.1073/pnas.210382197. PMC 34063 .PMID 11035784.Thomson, W (1863). "On the secular cooling of theearth". Philosophical Magazine. 4 (25): 1–14.doi:10.1080/14786446308643410 (inactive 2017­01­16).Torsvik, Trond H.; Steinberger, Bernhard; Gurnis,Michael; Gaina, Carmen (2010). "Plate tectonics andnet lithosphere rotation over the past 150 My" (PDF).Earth and Planetary Science Letters. 291: 106–112.Bibcode:2010E&PSL.291..106T.doi:10.1016/j.epsl.2009.12.055. Retrieved 18 June2010.Valencia, Diana; O'Connell, Richard J.; Sasselov,Dimitar D (November 2007). "Inevitability of PlateTectonics on Super­Earths". Astrophysical JournalLetters. 670 (1): L45–L48. arXiv:0710.0699 .Bibcode:2007ApJ...670L..45V. doi:10.1086/524012.Vine, F.J.; Matthews, D.H. (1963). "Magneticanomalies over oceanic ridges". Nature. 199 (4897):947–949. Bibcode:1963Natur.199..947V.doi:10.1038/199947a0.Wegener, Alfred (6 January 1912). "Die Herausbildungder Grossformen der Erdrinde (Kontinente undOzeane), auf geophysikalischer Grundlage" (PDF).Petermanns Geographische Mitteilungen. 63: 185–195,253–256, 305–309.White, R.; McKenzie, D. (1989). "Magmatism at riftzones: The generation of volcanic continental marginsand flood basalts". Journal of Geophysical Research.94: 7685–7729. Bibcode:1989JGR....94.7685W.doi:10.1029/JB094iB06p07685.Wilson, J.T. (8 June 1963). "Hypothesis on the Earth'sbehaviour". Nature. 198 (4884): 849–865.Bibcode:1963Natur.198..925T. doi:10.1038/198925a0.Wilson, J. Tuzo (July 1965). "A new class of faults andtheir bearing on continental drift" (PDF). Nature. 207(4995): 343–347. Bibcode:1965Natur.207..343W.doi:10.1038/207343a0. Archived from the original(PDF) on August 6, 2010.Wilson, J. Tuzo (13 August 1966). "Did the Atlanticclose and then re­open?" (PDF). Nature. 211 (5050):676–681. Bibcode:1966Natur.211..676W.doi:10.1038/211676a0.

The Wikibook HistoricalGeology has a page on thetopic of: Plate tectonics:overview

Wikimedia Commons hasmedia related to Platetectonics.

External links

This Dynamic Earth: The Story of Plate Tectonics (http://pubs.usgs.gov/gip/dynamic/dynamic.html). USGS.Understanding Plate Tectonics (http://pubs.usgs.gov/publications/text/understanding.html). USGS.The PLATES Project (http://www.ig.utexas.edu/research/projects/plates/). Jackson School of Geosciences.An explanation of tectonic forces (http://www.tectonic­forces.org).Example of calculations to show that Earth Rotation could be adriving force.Bird, P. (2003); An updated digital model of plate boundaries (http://peterbird.name/publications/2003_PB2002/2003_PB2002.htm).Map of tectonic plates (http://snobear.colorado.edu/Markw/Mountains/03/week3.html).MORVEL plate velocity estimates and information (http://www.geology.wisc.edu/~chuck/MORVEL/). C.DeMets, D. Argus, & R. Gordon.Mollewide Plate Tectonic Maps (http://cpgeosystems.com/mollglobe.html) ­ continental maps at variouspoints in the past

Videos

Khan Academy Explanation of evidence (https://www.youtube.com/watch?v=6EdsBabSZ4g)750 million years of global tectonic activity (http://www.ucmp.berkeley.edu/geology/tectonics.html). Movie.Multiple videos of plate tectonic movements (http://qz.com/577842/scientists­have­used­groundbreaking­technology­to­figure­out­how­the­earth­looked­a­billion­years­ago/) Quartz December 31, 2015

Retrieved from "https://en.wikipedia.org/w/index.php?title=Plate_tectonics&oldid=767376644"

Categories: Plate tectonics Geology theories Seismology Geodynamics

This page was last modified on 25 February 2017, at 14:57.Text is available under the Creative Commons Attribution­ShareAlike License; additional terms may apply.By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademarkof the Wikimedia Foundation, Inc., a non­profit organization.

Zhen Shao, Huang (1997). "Speed of the ContinentalPlates". The Physics Factbook.Zhao, Guochun, Cawood, Peter A., Wilde, Simon A.,and Sun, M. (2002). "Review of global 2.1–1.8 Gaorogens: implications for a pre­Rodiniasupercontinent". Earth­Science Reviews. 59: 125–162.Bibcode:2002ESRv...59..125Z. doi:10.1016/S0012­8252(02)00073­9.

Zhao, Guochun, Sun, M., Wilde, Simon A., and Li,S.Z. (2004). "A Paleo­Mesoproterozoic supercontinent:assembly, growth and breakup". Earth­Science Reviews.67: 91–123. Bibcode:2004ESRv...67...91Z.doi:10.1016/j.earscirev.2004.02.003.Zhong, Shijie; Zuber, Maria T. (2001). "Degree­1mantle convection and the crustal dichotomy on Mars".Earth and Planetary Science Letters. 189: 75–84.Bibcode:2001E&PSL.189...75Z. doi:10.1016/S0012­821X(01)00345­4.