Plate Tectonics Phe

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The tectonic plates of the world were mapped in the

second half of the 20th century.

Remnants of the Farallon Plate, deep in Earth'smantle. It is thought that much of the plate initiallywent under North America (particularly the westernUnited States and southwest Canada) at a veryshallow angle, creating much of the mountainous

terrain in the area (particularly the southern RockyMountains).

Plat e tectonicsFrom Wikipedia, the free encyclo pedia

Plate tecto nics (from the Late Latin tectonicus , fromthe Greek: τεκτονικός "pertaining to building" )[1] is a

scientific theory that describes the large-scale motion of Earth's litho sphere. This theoretical model builds on t heconcept of continental drift which was developedduring the first few decades of the 20th century. Thegeoscientific community accepted the theory after theconcepts of seafloor spreading were later developed inthe late 1950s and early 1960s.

The lithosphe re, which is the ri gid ou termost shell of a planet (on Earth, the crust and upper mantle), is brokenup into tectonic plates. On Earth, there are seven or eight major plates (depending on how they are define d)and many minor plates. Where pla tes meet, their relat ive motion determines the type of bound ary;conv ergent, diver gent, or t ransform. Earthqu akes,volc anic activ ity, mou ntain-build ing, and oc eanictrench formation occur along these plate boundaries.The lateral relative movement of the plates typicallyvaries fro m zero to 10 0 mm annually. [2]

Tectonic plates are composed of oceanic lithosphereand thicker continental lithosphere, each topped by itsown kind of c rust. Along con vergent boundaries,subd uction car ries plates into the mantle; the materia llost is roughl y balanced by the formation of new(oce anic) crust alon g divergent margins by seafloor spre ading. In this way, the total surface of the globeremain s the same. This prediction of plate tectonics isalso referred to as the con veyor b elt principle. Earlier theories (that still have some supporters) proposegradual shrinking (contraction) or gradual expansion of the glo be. [3]

Tectonic plates are able to move because the Earth'slithosphere has greater strength than the underlying asthenosphere. Lateral density variations in the mantleresult 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 indifferences in gravitational forces) and drag, with downward suction, at the subduction zones. Another explanation lies in the different forces generated by the rotation of the globe and the tidal forces of the Sunand Moon. The relative importance of each of these factors and their relationship to each other is unclear,and still the subject of much debate.

http://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Earth%27s_gravity#Variation_in_gravity_and_apparent_gravityhttp://en.wikipedia.org/wiki/Mantle_convectionhttp://en.wikipedia.org/wiki/Mantle_convectionhttp://en.wikipedia.org/wiki/Asthenospherehttp://en.wikipedia.org/wiki/Asthenospherehttp://en.wikipedia.org/wiki/Asthenospherehttp://en.wikipedia.org/wiki/Rocky_Mountainshttp://en.wikipedia.org/wiki/Subductionhttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/File:Farallon_Plate.jpghttp://en.wikipedia.org/wiki/Oceanic_trenchhttp://en.wikipedia.org/wiki/Volcanohttp://en.wikipedia.org/wiki/Oceanic_trenchhttp://en.wikipedia.org/wiki/Mountainhttp://en.wikipedia.org/wiki/Oceanic_trenchhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Transform_faulthttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/List_of_tectonic_plateshttp://en.wikipedia.org/wiki/Seafloor_spreadinghttp://en.wikipedia.org/wiki/Earth_sciencehttp://en.wikipedia.org/wiki/File:Plates_tect2_en.svghttp://en.wikipedia.org/wiki/Continental_drifthttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Lithospherehttp://en.wikipedia.org/wiki/Scientific_theoryhttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Late_Latinhttp://en.wikipedia.org/wiki/Wikipedia:Protection_policy#semihttp://en.wikipedia.org/wiki/Rocky_Mountainshttp://en.wikipedia.org/wiki/File:Farallon_Plate.jpghttp://en.wikipedia.org/wiki/Wikipedia:Protection_policy#semihttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Mountainhttp://en.wikipedia.org/wiki/Farallon_Platehttp://en.wikipedia.org/wiki/Mantle_convectionhttp://en.wikipedia.org/wiki/Earth_sciencehttp://en.wikipedia.org/wiki/Earthquakehttp://en.wikipedia.org/wiki/Seafloor_spreadinghttp://en.wikipedia.org/wiki/Continental_drifthttp://en.wikipedia.org/wiki/Earth%27s_gravity#Variation_in_gravity_and_apparent_gravityhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Volcanohttp://en.wikipedia.org/wiki/Late_Latinhttp://en.wikipedia.org/wiki/Lithospherehttp://en.wikipedia.org/wiki/Asthenospherehttp://en.wikipedia.org/wiki/Oceanic_trenchhttp://en.wikipedia.org/wiki/Transform_faulthttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/File:Plates_tect2_en.svghttp://en.wikipedia.org/wiki/Scientific_theoryhttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Moonhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Subductionhttp://en.wikipedia.org/wiki/List_of_tectonic_plateshttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Drag_(physics)http://en.wikipedia.org/wiki/Suction


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Contents

1 Key principles

2 Types of plate boundaries

3 Driving forces of plate motion

3.1 Driving forces related to mantle dynamics

3.2 Driving forces related to gravity

3.3 Driving forces related to Earth rotation

3.4 Relative significance of each driving force mechanism

4 Development of the theory

4.1 Summary

4.2 Continental drift

4.3 Floating continents, paleomagnetism, and seismicity zones

4.4 Mid-oceanic ridge spreading and convection

4.5 Magnetic striping

4.6 Definition and refining of the theory

5 Implications for biogeography

6 Plate reconstruction

6.1 Defining plate boundaries

6.2 Past plate motions

6.3 Formation and break-up of continents6.4 Gallery of past configurations

7 Current plates

8 Other celestial bodies (planets, moons)

8.1 Venus

8.2 Mars

8.3 Galilean satellites of Jupiter

8.4 Titan, moon of Saturn

8.5 Exoplanets

9 See also

10 References

10.1 Notes

10.2 Cited books

10.3 Cited articles

11 External links


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11.1 Videos

Key principles

The outer layers of the Earth are divided into the lithosphere and asthenosphere. This is based ondifferences in mechanical properties and in the method for the transfer of heat. Mechanically, thelithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by conduction, whereas the asthenosphere also transfers heat byconvection and has a nearly adiabatic temperature gradient. This division should not be confused with thechemical subdivision of these same layers into the mantle (comprising both the asthenosphere and themantle 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.

The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates ,which ride on the fluid-like (visco-elastic solid) asthenosphere. Plate motions range up to a typical 10– 40 mm/year (Mid-Atlantic Ridge; about as fast as fingernails grow), to about 160 mm/year (Nazca Plate;about as fast as hair grows). [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 crustalmaterial: oceanic crust (in older texts called sima from silicon and magnesium) and continental crust ( sial from silicon and aluminium). Average oceanic lithosphere is typically 100 km (62 mi) thick; [5] its thicknesis 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 mid-ocean ridges and spreads outwards, its thickness is therefore a function of its distance from the mid-ocean ridge where it was formed. For a typical distance that oceanic lithospheremust travel before being subducted, the thickness varies from about 6 km (4 mi) thick at mid-ocean ridgesto greater than 100 km (62 mi) at subduction zones; for shorter or longer distances, the subduction zone(and therefore also the mean) thickness becomes smaller or larger, respectively. [6] Continental lithosphere istypically ~200 km thick, though this varies considerably between basins, mountain ranges, and stablecratonic interiors of continents. The two types of crust also differ in thickness, with continental crust beingconsiderably thicker than oceanic (35 km vs. 6 km). [7]

The location where two plates meet is called a plate boundary . Plate boundaries are commonly associatedwith geological events such as earthquakes and the creation of topographic features such as mountains,volcanoes, mid-ocean 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 discussed in further detail below. Some volcanoes occur in the interiors of plates, andthese have been variously attributed to internal 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 IndianOceans. 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 arcvolcanism and accretion of terranes through tectonic processes, though some of these terranes may containophiolite sequences, which are pieces of oceanic crust considered to be part of the continent when they exitthe standard cycle of formation and spreading centers and subduction beneath continents. Oceanic crust is

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also denser than continental crust owing to their different compositions. Oceanic crust is denser because ithas less silicon and more heavier elements ("mafic") than continental crust ("felsic"). [9] As a result of thisdensity stratification, oceanic crust generally lies below 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 platesmove relative to each other. They are associated with different types of surface phenomena. The differenttypes of plate boundaries are: [11][12]

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.

2. 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.

3. 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., Western South America, and 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., the Andes mountain range in

South America, 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

http://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Japanhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Subductionhttp://en.wikipedia.org/wiki/Island_archttp://en.wikipedia.org/wiki/Sinistralhttp://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/Continental_collisionhttp://en.wikipedia.org/wiki/Aleutian_islandshttp://en.wikipedia.org/wiki/Andeshttp://en.wikipedia.org/wiki/Mafichttp://en.wikipedia.org/wiki/East_Pacific_Risehttp://en.wikipedia.org/wiki/Sea_levelhttp://en.wikipedia.org/wiki/Transform_faulthttp://en.wikipedia.org/w/index.php?title=Mariana_islands&action=edit&redlink=1http://en.wikipedia.org/wiki/Transform_faultshttp://en.wikipedia.org/wiki/Felsichttp://en.wikipedia.org/wiki/Isostasyhttp://en.wikipedia.org/wiki/San_Andreas_Faulthttp://en.wikipedia.org/wiki/Pacific_Platehttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://en.wikipedia.org/wiki/Dextral


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

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.

4. 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.

riving forces of plate motion

Plate tectonics is basically a kinematic phenomenon.

Scientists agree on the observation and deduction thatthe plates have moved with respect to one another butcontinue to debate as to how and when. A major question remains as to what geodynamic mechanismmotors plate movement. Here, science diverges indifferent theories.

It is generally accepted that tectonic plates are able tomove because of the relative density of oceaniclithosphere and the relative weakness of theasthenosphere. Dissipation of heat from the mantle isacknowledged to be the original source of the energyrequired 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 aconsequence, a powerful source of plate motion isgenerated due to the excess density of the oceaniclithosphere sinking in subduction zones. When the new crust forms at mid-ocean ridges, this oceaniclithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age as itconductively cools and thickens. The greater density of old lithosphere relative to the underlyingasthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving

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force for plate movement. The weakness of the asthenosphere allows the tectonic plates to move easilytowards a subduction zone. [13] Although subduction is believed to be the strongest force driving platemotions, it cannot be the only force since there are plates such as the North American Plate which aremoving, 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 isthat the kinematic pattern of the movement itself should be separated clearly from the possible geodynamicmechanism that is invoked as the driving force of the observed movement, as some patterns may be

explained by more than one mechanism.[14]

In short, the driving forces advocated at the moment can bedivided into three categories based on the relationship to the movement: mantle dynamics related, gravityrelated (mostly secondary forces), and Earth rotation related.

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 are transmitted through theasthenosphere. This theory was launched by Arthur Holmes and some forerunners in the 1930s [15] and wasimmediately recognized as the solution for the acceptance of the theory as originally discussed in the papersof Alfred Wegener in the early years of the century. However, despite its acceptance, it was long debated inthe scientific community because the leading ("fixist") theory still envisaged a static Earth without movingcontinents up until the major breakthroughs of the early sixties.

Two- and three-dimensional imaging of Earth's interior (seismic tomography) shows a varying lateraldensity 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 fromheat energy). The manifestation of this varying lateral density is mantle convection from buoyancyforces. [16]

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

Basal drag (friction): Plate motion driven by friction between the convection currents in the

asthenosphere and the more rigid overlying lithosphere.

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 agreater 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 seismictomography still fail to recognize these predicted large scale convection cells. Therefore, alternative viewshave been proposed:

In the theory of plume tectonics developed during the 1990s, a modified concept of mantle convectioncurrents 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

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"fixistic" ideas of the European and Russian Earth Science Schools, find resonance in the modern theorieswhich envisage hot spots/mantle plumes which remain fixed and are overridden by oceanic and continentallithosphere plates over time and leave their traces in the geological record (though these phenomena are notinvoked as real driving mechanisms, but rather as modulators). Modern theories that continue building onthe older mantle doming concepts and see plate movements as a secondary phenomena are beyond thescope 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 channelsust 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. [17]

Driving forces related to gravity

Forces related to gravity are usually invoked as secondary phenomena within the framework of a moregeneral 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.[18]

As oceanic lithosphere is formed at spreading ridges fromhot mantle material, it gradually cools and thickens with age (and thus adds distance from the ridge). Cooloceanic lithosphere is significantly denser than the hot mantle material from which it is derived and so withincreasing thickness it gradually subsides into the mantle to compensate the greater load. The result is aslight 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 asnothing is "pushing" horizontally and tensional features are dominant along ridges. It is more accurate torefer to this mechanism as gravitational sliding as variable topography across the totality of the plate canvary 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 beforeit dives underneath an adjacent plate which produces a clear topographical feature that can offset, or at leastaffect, the influence of topographical ocean ridges, and mantle plumes and hot spots, which are postulatedto impinge on the underside of tectonic plates.

Slab-pull: Current scientific opinion is that the asthenosphere is insufficiently competent or rigid to directlycause motion by friction along the base of the lithosphere. Slab pull is therefore most widely thought to bethe greatest force acting on the plates. In this current understanding, plate motion is mostly driven by theweight of cold, dense plates sinking into the mantle at trenches. [19] Recent models indicate that trenchsuction plays an important role as well. However, as the North American Plate is nowhere being subducted,

et 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 drivingmechanisms of the plates is the existence of large scale asthenosphere/mantle domes which cause thegravitational 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 smallscale of one island arc up to the larger scale of an entire ocean basin. [20]

Driving forces related to Earth rotation

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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 causecontinental motion as the concept then was of continents plowing through oceanic crust. [21] Therefore,Wegener later changed his position and asserted that convection currents are the main driving force of platetectonics in the last edition of his book in 1929.

However, in the plate tectonics context (accepted since the seafloor spreading proposals of Heezen, Hess,Dietz, Morley, Vine, and Matthews (see below) during the early 1960s), oceanic crust is suggested to be inmotion with the continents which caused the proposals related to Earth rotation to be reconsidered. In morerecent 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 [22]

2. Shear strain of the Earth globe due to N-S compression related to its rotation and modulations;

3. Pole flight force: equatorial drift due to rotation and centrifugal effects: tendency of the plates to

move from the poles to the equator (" Polflucht ");

4. The Coriolis effect acting on plates when they move around the globe;

5. Global deformation of the geoid due to small displacements of rotational pole with respect to theEarth's crust;

6. Other smaller deformation effects of the crust due to wobbles and spin movements of the Earth

rotation on a smaller time scale.

For these mechanisms to be overall valid, systematic relationships should exist all over the globe betweenthe orientation and kinematics of deformation and the geographical latitudinal and longitudinal grid of theEarth itself. Ironically, these systematic relations studies in the second half of the nineteenth century and thefirst 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 drivingforces were generally acting vertically and caused only local horizontal movements (the so-called pre-platetectonic, "fixist theories"). Later studies (discussed below on this page), therefore, invoked many of therelationships recognized during this pre-plate tectonics period to support their theories (see the anticipationsand reviews in the work of van Dijk and collaborators). [23]

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 notusing plate tectonics concepts (therefore beyond the discussions treated in this section) or proposed asminor modulations within the overall plate tectonics model.

In 1973, George W. Moore [24] of the USGS and R. C. Bostrom [25] presented evidence for a generalwestward drift of the Earth's lithosphere with respect to the mantle. He concluded that tidal forces (the tidallag or "friction") caused by the Earth's rotation and the forces acting upon it by the Moon are a driving forcefor plate tectonics. As the Earth spins eastward beneath the moon, the moon's gravity ever so slightly pullsthe Earth's surface layer back westward, just as proposed by Alfred Wegener (see above). In a more recent2006 study, [26] scientists reviewed and advocated these earlier proposed ideas. It has also been suggestedrecently in Lovett (2006) that this observation may also explain why Venus and Mars have no platetectonics, as Venus has no moon and Mars' moons are too small to have significant tidal effects on the

planet. In a recent paper, [27] it was suggested that, on the other hand, it can easily be observed that many

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came from the dove-tailing outlines of South America's east coast and Africa's west coast, and from thematching of the rock formations along these edges. Confirmation of their previous contiguous nature alsocame 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. Theevidence for such an erstwhile joining of these continents was patent to field geologists working in thesouthern 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 generallyaccepted: the Earth might have a solid crust and mantle and a liquid core, but there seemed to be no waythat portions of the crust could move around. Distinguished scientists, such as Harold Jeffreys and CharlesSchuchert, were outspoken critics of continental drift.

Despite much opposition, the view of continental drift gained support and a lively debate started between"drifters" or "mobilists" (proponents of the theory) and "fixists" (opponents). During the 1920s, 1930s and1940s, 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.

One of the first pieces of geophysical evidence that was used to support the movement of lithospheric platescame from paleomagnetism. This is based on the fact that rocks of different ages show a variable magneticfield direction, evidenced by studies since the mid–nineteenth century. The magnetic north and south polesreverse through time, and, especially important in paleotectonic studies, the relative position of themagnetic 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 eachcontinent, in fact, shows its own "polar wander path". During the late 1950s it was successfully shown ontwo occasions that these data could show the validity of continental drift: by Keith Runcorn in a paper in1956, [31] and by Warren Carey in a symposium held in March 1956. [32]

The second piece of evidence in support of continental drift came during the late 1950s and early 60s fromdata 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 [33] which gave evidence for theassociation 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. [34]

Simultaneous advances in early seismic imaging techniques in and around Wadati-Benioff zones along thetrenches bounding many continental margins, together with many other geophysical (e.g. gravimetric) andgeological observations, showed how the oceanic crust could disappear into the mantle, providing themechanism 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 1965that 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. The theory

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Alfred Wegener in Greenland in thewinter of 1912-13.

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, andthat most geologic features such as basin development and mountain ranges could be explained by verticalcrustal movement, described in what is called the geosynclinal theory. Generally, this was placed in thecontext of a contracting 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 theAtlantic Ocean—or, more precisely, the edges of the continentalshelves—have similar shapes and seem to have once fittedtogether. [35]

Since that time many theories were proposed to explain thisapparent complementarity, but the assumption of a solid Earth

made these various proposals difficult to accept.[36]

The discovery of radioactivity and its associated heating propertiesin 1895 prompted a re-examination of the apparent age of theEarth. [37] This had previously been estimated by its cooling rateand assumption the Earth's surface radiated like a black body. [38]

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,[39]

Alfred Wegener was making serious argumentsfor the idea of continental drift in the first edition of The Origin of Continents and Oceans .[28] In that book (re-issued in four successive editions up to the final one in 1936), he noted how the east coast of SouthAmerica and the west coast of Africa looked as if they were once attached. Wegener was not the first tonote 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 inthis by researchers such as Alex du Toit). Furthermore, when the rock strata of the margins of separatecontinents are very similar it suggests that these rocks were formed in the same way, implying that theywere 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 theAppalachian 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 noapparent mechanism for continental drift. Specifically, they did not see how continental rock could plowthrough the much denser rock that makes up oceanic crust. Wegener could not explain the force that drovecontinental drift, and his vindication did not come until after his death in 1930.

Floating continents, paleomagnetism, and seismicity zones

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Global earthquake epicenters, 1963–1998

As it was observed early that although granite existedon continents, seafloor seemed to be composed of denser basalt, the prevailing concept during the firsthalf of the twentieth century was that there were twotypes of crust, named "sial" (continental type crust) and"sima" (oceanic type crust). Furthermore, it wassupposed 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 linedeflection by the Andes in Peru, Pierre Bouguer haddeduced that less-dense mountains must have adownward projection into the denser layer underneath. The concept that mountains had "roots" wasconfirmed by George B. Airy a hundred years later, during study of Himalayan gravitation, and seismicstudies detected corresponding density variations. Therefore, by the mid-1950s, the question remainedunresolved as to whether mountain roots were clenched in surrounding basalt or were floating on it like aniceberg.

During the 20th century, improvements in and greater use of seismic instruments such as seismographsenabled scientists to learn that earthquakes tend to be concentrated in specific areas, most notably along theoceanic 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 horizontaland 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, KiyooWadati of Japan and Hugo Benioff of the United States. The study of global seismicity greatly advanced inthe 1960s with the establishment of the Worldwide Standardized Seismograph Network (WWSSN) [40] tomonitor the compliance of the 1963 treaty banning above-ground testing of nuclear weapons. The muchimproved data from the WWSSN instruments allowed seismologists to map precisely the zones of earthquake concentration world wide.

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 continentsseemed to have moved through different climatic zones during the past. Furthermore, paleomagnetic datahad shown that the magnetic pole had also shifted during time. Reasoning in an opposite way, thecontinents might have shifted and rotated, while the pole remained relatively fixed. The first time theevidence of magnetic polar wander was used to support the movements of continents was in a paper byKeith Runcorn in 1956, [31] and successive papers by him and his students Ted Irving (who was actually thefirst 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. [41] In this symposium, theevidence was used in the theory of an expansion of the global crust. In this hypothesis the shifting of thecontinents 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 significantexpansion of the Earth. Certainly there is no evidence that the moon has expanded in the past 3 billion

ears; other work would soon show that the evidence was equally in support of continental drift on a globewith a stable radius.

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During the thirties up to the late fifties, works by Vening-Meinesz, Holmes, Umbgrove, and numerousothers 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 in1928 that convection currents within the mantle might be the driving force. [42] Often, these contributionsare 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 globewithout 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

In 1947, a team of scientists led by Maurice Ewing utilizing the Woods Hole Oceanographic Institution'sresearch vessel Atlantis and an array of instruments, confirmed the existence of a rise in the central AtlanticOcean, and found that the floor of the seabed beneath the layer of sediments consisted of basalt, not thegranite which is the main constituent of continents. They also found that the oceanic crust was much thinner than continental crust. All these new findings raised important and intriguing questions. [43]

The new data that had been collected on the ocean basins also showed particular characteristics regardingthe bathymetry. One of the major outcomes of these datasets was that all along the globe, a system of mid-oceanic ridges 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), [44] which would trigger a real revolution in thinking. 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 withoutincreasing the size of the Earth? In reality, this question had been solved already by numerous scientistsduring the forties and the fifties, like Arthur Holmes, Vening-Meinesz, Coates and many others: The crustin excess disappeared along what were called the oceanic trenches, where so-called "subduction" occurred.Therefore, when various scientists during the early sixties started to reason on the data at their disposalregarding 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 NavalReserve Rear Admiral, and Robert S. Dietz, a scientist with the U.S. Coast and Geodetic Survey who firstcoined the term seafloor spreading . Dietz and Hess (the former published the same idea one year earlier in

Nature ,[45] but priority belongs to Hess who had already distributed an unpublished manuscript of his 1962article by 1960) [46] were among the small handful who really understood the broad implications of sea floor spreading and how it would eventually agree with the, at that time, unconventional and unaccepted ideas of continental drift and the elegant and mobilistic models proposed by previous workers like Holmes.

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Seafloor magnetic striping.

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

been called "seminal" and "prescient". In reality, it actually shows that the work by the European scientistson island arcs and mountain belts performed and published during the 1930s up until the 1950s was appliedand appreciated also in the United States.

If the Earth's crust was expanding along the oceanic ridges, Hess and Dietz reasoned like Holmes andothers before them, it must be shrinking elsewhere. Hess followed Heezen, suggesting that new oceaniccrust continuously spreads away from the ridges in a conveyor belt–like motion. And, using the mobilisticconcepts developed before, he correctly concluded that many millions of years later, the oceanic crusteventually descends along the continental margins where oceanic trenches – very deep, narrow canyons – are formed, e.g. along the rim of the Pacific Ocean basin. The important step Hess made was thatconvection currents would be the driving force in this process, arriving at the same conclusions as Holmeshad decades before with the only difference that the thinning of the ocean crust was performed usingHeezen's mechanism of spreading along the ridges. Hess therefore concluded that the Atlantic Ocean wasexpanding while the Pacific Ocean was shrinking. As old oceanic crust is "consumed" in the trenches (likeHolmes and others, he thought this was done by thickening of the continental lithosphere, not, as nowunderstood, by underthrusting at a larger scale of the oceanic crust itself into the mantle), new magma risesand 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 occurringsimultaneously. Thus, the new mobilistic concepts neatly explained why the Earth does not get bigger withsea 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, usingmagnetic instruments (magnetometers) adapted from airbornedevices developed during World War II to detect submarines, beganrecognizing odd magnetic variations across the ocean floor. Thisfinding, though unexpected, was not entirely surprising because itwas known that basalt—the iron-rich, volcanic rock making up theocean floor—contains a strongly magnetic mineral (magnetite) andcan locally distort compass readings. This distortion was recognized

by Icelandic mariners as early as the late 18th century. Moreimportant, because the presence of magnetite gives the basaltmeasurable magnetic properties, these newly discovered magneticvariations provided another means to study the deep ocean floor.When newly formed rock cools, such magnetic materials recorded the Earth's magnetic field at the time.

As more and more of the seafloor was mapped during the 1950s, the magnetic variations turned out not to be random or isolated occurrences, but instead revealed recognizable patterns. When these magnetic patterns were mapped over a wide region, the ocean floor showed a zebra-like pattern: one stripe withnormal polarity and the adjoining stripe with reversed polarity. The overall pattern, defined by thesealternating bands of normally and reversely polarized rock, became known as magnetic striping, and was

published by Ron G. Mason and co-workers in 1961, who did not find, though, an explanation for thesedata in terms of sea floor spreading, like Vine, Matthews and Morley a few years later. [47]

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A demonstration of magneticstriping. (The darker the color is, the closer it is to normal

polarity)

The discovery of magnetic striping called for an explanation. In the early1960s scientists such as Heezen, Hess and Dietz had begun to theorisethat mid-ocean ridges mark structurally weak zones where the oceanfloor was being ripped in two lengthwise along the ridge crest (see the

previous paragraph). New magma from deep within the Earth riseseasily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. This process, at first denominatedthe "conveyer belt hypothesis" and later called seafloor spreading,operating over many millions of years continues to form new ocean floor all across the 50,000 km-long system of mid-ocean ridges.

Only four years after the maps with the "zebra pattern" of magneticstripes were published, the link between sea floor spreading and these

patterns was correctly placed, independently by Lawrence Morley, and by Fred Vine and Drummond Matthews, in 1963, [48] now called the Vine-Matthews-Morley hypothesis.This hypothesis linked these patterns to geomagnetic reversals and was supported by several lines of evidence: [49]

1. the stripes are symmetrical around the crests of the mid-ocean ridges; at or near the crest of the ridge,

the rocks are very young, and they become progressively older away from the ridge crest;

2. the youngest rocks at the ridge crest always have present-day (normal) polarity;

3. stripes of rock parallel to the ridge crest alternate in magnetic polarity (normal-reversed-normal, etc.),

suggesting that they were formed during different epochs documenting the (already known from

independent studies) normal and reversal episodes of the Earth's magnetic field.

By explaining both the zebra-like magnetic striping and the construction of the mid-ocean ridge system, theseafloor spreading hypothesis (SFS) quickly gained converts and represented another major advance in thedevelopment of the plate-tectonics theory. Furthermore, the oceanic crust now came to be appreciated as anatural "tape recording" of the history of the geomagnetic field reversals (GMFR) of the Earth's magneticfield. Today, extensive studies are dedicated to the calibration of the normal-reversal patterns in the oceaniccrust on one hand and known timescales derived from the dating of basalt layers in sedimentary sequences(magnetostratigraphy) on the 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") became quickly 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

drift from the very beginning [50] added the concept of transform faults to the model, completing the

classes of fault types necessary to make the mobility of the plates on the globe work out. [51]

A symposium on continental drift was held at the Royal Society of London in 1965 which must be

regarded as the official start of the acceptance of plate tectonics by the scientific community, and

which abstracts are issued as Blacket, Bullard & Runcorn (1965). In this symposium, Edward Bullard

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and co-workers showed with a computer calculation how the continents along both sides of the

Atlantic would best fit to close the ocean, which became known as the famous "Bullard's Fit".

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". [52]

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. [53]

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 the scientific community of plate

tectonics. [54]

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. [55]

Implications for biogeography

Continental drift theory helps biogeographers to explain the disjunct biogeographic distribution of presentday life found on different continents but having similar ancestors. [56] In particular, it explains theGondwanan distribution of ratites and the Antarctic flora.

Plate reconstruction

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

Defining plate boundaries

Current plate boundaries are defined by their seismicity. [57] Past plate boundaries within existing plates areidentified from a variety of evidence, such as the presence of ophiolites that are indicative of vanishedoceans. [58]

Past plate motions

Tectonic motion first began around three billion years ago. [59]

Various types of quantitative and semi-quantitative information are available to constrain past platemotions. The geometric fit between continents, such as between west Africa and South America is still animportant part of plate reconstruction. Magnetic stripe patterns provide a reliable guide to relative platemotions going back into the Jurassic period. [60] The tracks of hotspots give absolute reconstructions, butthese are only available back to the Cretaceous. [61] Older reconstructions rely mainly on paleomagnetic poledata, 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

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the motions of different plates through time. [62] Additional evidence comes from the distribution of certainsedimentary rock types, [63] faunal provinces shown by particular fossil groups, and the position of orogenic

belts. [61]

Formation and break-up of continents

The movement of plates has caused the formation and break-up of continents over time, includingoccasional formation of a supercontinent that contains most or all of the continents. The supercontinentColumbia or Nuna formed during a period of 2,000 to 1,800 million years ago and broke up about1,500 to 1,300 million years ago. [64] The supercontinent Rodinia is thought to have formed about 1 billion

ears ago and to have embodied most or all of Earth's continents, and broken up into eight continentsaround 600 million years ago. The eight continents later re-assembled into another supercontinent calledPangaea; 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 twomajor plates. Before uplift, they were covered by the Tethys Ocean.

Gallery of past configurations

Interpretive simulation of past continental movement and shorelines, with time given in millions of yearsago (Ma). For more complete timeline of images, see Gallery of continental movement.

500 Ma

400 Ma

Current 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 sometimessubdivided 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.

Other celestial

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bodies (planets,moons)

The appearance of platetectonics on terrestrial

planets is related to planetary mass, with moremassive planets thanEarth expected to exhibit

plate tectonics. Earth may be a borderline case,owing its tectonic activityto abundant water [65]

(silica and water form adeep eutectic.)

VenusVenus 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 acceptedhypothesis that the Venusian lithosphere has thickened greatly over the course of several hundred million

ears) 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). Datesderived are dominantly in the range 500 to 750 million years ago, although ages of up to1,200 million years ago have been calculated. This research has led to the fairly well accepted hypothesisthat Venus has undergone an essentially complete volcanic resurfacing at least once in its distant past, withthe last event taking place approximately within the range of estimated surface ages. While the mechanismof such an impressive thermal event remains a debated issue in Venusian geosciences, some scientists areadvocates of processes involving plate motion to some extent.

One explanation for Venus' lack of plate tectonics is that on Venus temperatures are too high for significantwater to be present. [66][67] The Earth's crust is soaked with water, and water plays an important role in thedevelopment of shear zones. Plate tectonics requires weak surfaces in the crust along which crustal slicescan 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

Mars is considerably smaller than Earth and Venus, and there is evidence for ice on its surface and in itscrust.

In the 1990s, it was proposed that Martian Crustal Dichotomy was created by plate tectonic processes. [68]

Scientists today disagree, and believe that it was created either by upwelling within the Martian mantle thatthickened the crust of the Southern Highlands and formed Tharsis [69] or by a giant impact that excavated

http://en.wikipedia.org/wiki/Tharsishttp://en.wikipedia.org/wiki/Myrhttp://en.wikipedia.org/wiki/Dating_methodshttp://en.wikipedia.org/wiki/Eutectichttp://en.wikipedia.org/wiki/Martian_dichotomyhttp://en.wikipedia.org/wiki/Shear_zonehttp://en.wikipedia.org/wiki/Super-Earthhttp://en.wikipedia.org/wiki/Impact_craterhttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Terrestrial_planethttp://tools.wmflabs.org/timescale/?Ma=500%E2%80%93750http://en.wikipedia.org/wiki/File:Plate_tectonics_map.gifhttp://tools.wmflabs.org/timescale/?Ma=1,200http://en.wikipedia.org/wiki/Myr


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the Northern Lowlands. [70]

Valles Marineris may be a tectonic boundary. [71]

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 platetectonic processes, such as seafloor spreading. [72] 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. [73]

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 8September 2014, NASA reported finding evidence of plate tectonics on Europa, a satellite of Jupiter - thefirst sign of such geological activity on another world other than Earth. [74]

Titan, moon of Saturn

Titan, the largest moon of Saturn, was reported to show tectonic activity in images taken by the HuygensProbe, which landed on Titan on January 14, 2005. [75]

Exoplanets

On Earth-sized 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 onlarger super-earths [76][77] with one team saying that plate tectonics would be episodic or stagnant [78] and th

other team saying that plate tectonics is very likely on super-earths even if the planet is dry. [65]

See also

References

Notes

Geological history of Earth

Geosyncline theory

List of plate tectonics topics

Supercontinent cycle

Conservation of angular momentumList of submarine topographical features

Tectonics

http://en.wikipedia.org/wiki/Mars_Global_Surveyorhttp://en.wikipedia.org/wiki/Vastitas_Borealishttp://en.wikipedia.org/wiki/Angular_momentum#Conservation_of_angular_momentumhttp://en.wikipedia.org/wiki/List_of_plate_tectonics_topicshttp://en.wikipedia.org/wiki/Valles_Marinerishttp://en.wikipedia.org/wiki/Super-earthhttp://en.wikipedia.org/wiki/Saturnhttp://en.wikipedia.org/wiki/Supercontinent_cyclehttp://en.wikipedia.org/wiki/Huygens_Probehttp://en.wikipedia.org/wiki/Geosynclinehttp://en.wikipedia.org/wiki/Titan_(moon)http://en.wikipedia.org/wiki/Europa_(moon)http://en.wikipedia.org/wiki/List_of_submarine_topographical_featureshttp://en.wikipedia.org/wiki/Jupiterhttp://en.wikipedia.org/wiki/Galilean_satelliteshttp://en.wikipedia.org/wiki/Tectonicshttp://en.wikipedia.org/wiki/Geological_history_of_Earth


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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.

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15. Holmes, Arthur (1931). "Radioactivity and Earth Movements"

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16. Tanimoto & Lay 2000.

17. Smoot et al. 1996.

18. Spence 1987, White & McKenzie 1989.

19. Conrad & Lithgow-Bertelloni 2002.

20. Spence 1987, White & Mckenzie 1989, Segev 2002.21. "Alfred Wegener (1880-1930)" (http://www.ucmp.berkeley.edu/history/wegener.html). University of California

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22. Neith, Katie (April 15, 2011). "Caltech Researchers Use GPS Data to Model Effects of Tidal Loads on Earth's

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23. van Dijk 1992, van Dijk & Okkes 1990).

24. Moore 1973.

25. Bostrom 1971.

26. Scoppola et al. 2006.

27. Torsvik et al. 2010.

28. Wegener 1929.

29. Hughes 2001a.

30. Wegener 1966, Hughes 2001b.

31. Runcorn 1956.

32. Carey 1956.

33. see for example the milestone paper of Lyman & Fleming 1940.

34. Korgen 1995, Spiess & Kuperman 2003.

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35. Kious & Tilling 1996.

36. Frankel 1987.

37. Joly 1909.

38. Thomson 1863.

39. Wegener 1912.

40. Stein & Wysession 2009, p. 26

41. Carey 1956; see also Quilty 2003.

42. Holmes 1928; see also Holmes 1978, Frankel 1978.

43. Lippsett 2001, Lippsett 2006.

44. Heezen 1960.

45. Dietz 1961.

46. Hess 1962.

47. Mason & Raff 1961, Raff & Mason 1961.

48. Vine & Matthews 1963.

49. See summary in Heirzler, Le Pichon & Baron 1966

50. Wilson 1963.51. Wilson 1965.

52. Wilson 1966.

53. Morgan 1968.

54. Le Pichon 1967.

55. McKenzie & Parker 1967.

56. Moss & Wilson 1998.

57. Condie 1997.

58. Lliboutry 2000.

59. Kranendonk, V.; Martin, J. (2011). "Onset of Plate Tectonics". Science 333 (6041): 413–414.doi:10.1126/science.1208766 (https://dx.doi.org/10.1126%2Fscience.1208766). PMID 21778389

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60. Torsvik, Trond Helge. "Reconstruction Methods"

(http://www.geodynamics.no/GMAP/Methods/Introduction_to_Methods.htm). Retrieved 18 June 2010.

61. Torsvik 2008.

62. Butler 1992.

63. Scotese, C.R. (2002-04-20). "Climate History" (http://www.scotese.com/climate.htm). Paleomap Project .

Retrieved 18 June 2010.

64. Zhao 2002, 2004

65. Valencia, O'Connell & Sasselov 2007.

66. Kasting 1988.

67. Bortman, Henry (2004-08-26). "Was Venus alive? "The Signs are Probably There" "

(http://www.space.com/scienceastronomy/venus_life_040826.html). Astrobiology Magazine. Retrieved

2008-01-08.

68. Sleep 1994.

69. Zhong & Zuber 2001.

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71. Wolpert, Stuart (August 9, 2012). "UCLA scientist discovers plate tectonics on Mars"

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72. Connerney et al. 1999, Connerney et al. 2005

73. Harrison 2000.

74. Dyches, Preston; Brown, Dwayne; Buckley, Michael (8 September 2014). "Scientists Find Evidence of 'Diving'

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75. Soderblom et al. 2007.

76. Convection scaling and subduction on Earth and super-Earths

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Earth and Planetary Science Letters, Volume 286, Issues 3–4, 15 September 2009, Pages 492–502,

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77. Plate tectonics on super-Earths: Equally or more likely than on Earth

(http://www.sciencedirect.com/science/article/pii/S0012821X11004559),http://dx.doi.org/10.1016/j.epsl.2011.07.029, Earth and Planetary Science Letters, Volume 310, Issues 3–4, 15

October 2011, Pages 252–261, H.J. van Heck, P.J. Tackley

78. GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L19204, 4 PP., 2007, doi:10.1029/2007GL030598,

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Butler, Robert F. (1992). "Applications to paleogeography". Paleomagnetism: Magnetic domains to geologicterranes (http://www.geo.arizona.edu/Paleomag/book/chap10.pdf). Blackwell. ISBN 0-86542-070-X. Retrieved

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