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Dec 31, 2012 (V) The Serial - Episode 25 - Part 1. Arshdeep gill Subscribe Unsubscribe 1. 31 Dec 2012 14 054. Karan kundra kritika kamra sommuya seth pooja gor raj singh arora. MOST POPULAR. VIDEOS GALLERIES. Share channel. Tweet Share on Facebook. Dude Pulled Off Acting Like A Blow-Up Doll Amazingly. Karan Kundra is the presenter of this show since season one. Currently, Gumrah: End of Innocence moved to its third season. Gumrah: End of Innocence Season one went on airing weekly with repeat telecasts on Channel V India and Star Plus.
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TV actor Karan Kundra is reuniting with former lady love for Channel V's new show 'The Serial'. But if you're expecting to see some discomfort between them, you're highly mistaken, says Karan. 'Kritika might be seen on the show. She will come on board. But there is no discomfort between us.
We are good friends, and there is no problem in being together on a show,' Karan told IANS. Sparks flew between the two actors when they played onscreen lovers in ' and then in the second season of the show. But they parted ways due to reasons unknown. However, if one is to go by what Karan says, there is no bitterness between the duo.
'All is fine with us. In fact, during the recent Mumbai bandh, we went out for lunch and I even took her to show the first edit of the show 'The Serial'. She liked it, and was clearer about the idea of the show once she watched it.
So let's see, she should soon be on board even though she has a daily soap (') going on,' he said. The format of 'The Serial', which will go on air Monday, is unique - it is a non-fiction property, wherein popular TV actors will play themselves.
Seen through the eyes of a 17-year-old named Rohan, it shows Karan, and Sara Khan among a host of others, unfolding stories of the telly world. Karan, who originally hails from Jalandhar, plays himself - a true-blue Punjabi boy.
But he says this is a bigger challenge than essaying another character on screen. 'When you get to play a character, you can visualise how it would be.
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If it's a loverboy, how he will be, if it's a villain, how he needs to be. But what do you do when you have to play yourself! So it is a big challenge,' said the actor, who is also getting active in the field of Punjabi films. 'I am producing one Punjabi film, and acting in two films. My family is proud and I am also quite proud of myself that I am able to do something to do with my roots,' he added.
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Shaktimaan is an Indian Hindi-language superhero television show that aired on DD 1 from 13 September 1997 to 27 March 2005. Producer Mukesh Khanna played the role of Shaktimaan and his alter ego 'Pandit Gangadhar Vidhyadhar Mayadhar Omkarnath Shastri', a photographer for the newspaper Aaj Ki Aawaz.
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1According to me, the best game under 200 MB is 'Buy a new PC' it was released when your current PC went out of date. You might also try 'upgrade your dying PC' but that I personally prefer the former. Apart from these you might give a chance to Solitaire, Hearts, Minesweeper and chess. They might just work fine on the best graphics settings your PC can afford. Sorry to say but actual games like IGI 2 and Limbo demand more than 200 MB. And you might not get a hang of PvZ for it is highly deplorable. Unfortunately, the two conditions you proposed; good graphics and under 200 MB, do not go well together.
You can have a game with good graphics, but this is very much likely going to be over 200MB, and games which are 200MB and below mostly use pixel graphics, or text-based, even. I recommend you forego the condition of good graphics, as graphics aren’t everything, and there’s a lot more to a game than just how good it looks. For all you know, you’ll have more fun that way too.
Now, coming to games that you could play (hopefully 300 - 400 MB games are fine with you), you have games like:. FTL - Faster Than Light. Into the Breach. Tiny Rails.
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Theory Of Plate Tectonics Study Guide
The Wilson Cycle – What Plate Tectonics Theory Explains About the History of Ocean Basins In the mid 1960s, Tuzo Wilson applied the developing concepts of plate tectonics in a synthesis of how ocean basins formed, evolved, and closed. This is summarized toward the end of Chapter 3. Plate tectonics is the framework in which geologists study and understand the inner workings of the earth. It provides us with a way to tie together what once was considered unrelated geologic.
Diagram of the internal layering of the Earth showing the lithosphere above the asthenosphere (not to scale) Plate tectonics (from the tectonicus, from the: τεκτονικός 'pertaining to building') is a describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the 's, since tectonic processes began on Earth between 3 and 3.5 billion years ago. The model builds on the concept of, an idea developed during the first decades of the 20th century.
The community accepted plate-tectonic theory after was validated in the late 1950s and early 1960s. The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken into. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary:, or., -building, and formation occur along these plate boundaries (or ).
The relative movement of the plates typically ranges from zero to 100 mm annually. Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of. Along convergent boundaries, or one plate moving under another, carries the lower one down into the; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading.
In this way, the total surface of the lithosphere remains the same. This prediction of plate tectonics is also referred to as the conveyor belt principle. Earlier theories, since disproven, proposed gradual shrinking (contraction) or gradual. Tectonic plates are able to move because the Earth's lithosphere has greater than the underlying. Lateral density variations in the mantle result in; that is, the slow creeping motion of Earth's solid mantle. Plate movement is thought to be driven by a combination of the motion of the seafloor away from due to variations in (the ridge is a topographic high) and changes in the crust (density increases as newly formed crust cools and moves away from the ridge).
At subduction zones the relatively cold, dense crust is 'pulled' or sinks down into the mantle over the downward convecting limb of a. Another explanation lies in the different forces generated by tidal forces of the. The relative importance of each of these factors and their relationship to each other is unclear, and still the subject of much debate. Contents. Key principles The are divided into the.
The division is based on differences in and in the method for. The lithosphere is cooler and more rigid, while the asthenosphere is hotter and flows more easily. In terms of heat transfer, the lithosphere loses heat by, whereas the asthenosphere also transfers heat by and has a nearly temperature gradient. This division should not be confused with the chemical subdivision of these same layers into the mantle (comprising both the asthenosphere and the mantle portion of the lithosphere) and the crust: a given piece of mantle may be part of the lithosphere or the asthenosphere at different times depending on its temperature and pressure. The key principle of plate tectonics is that the lithosphere exists as separate and distinct, which ride on the fluid-like ( solid) asthenosphere. Plate motions range up to a typical 10–40 mm/year (; about as fast as grow), to about 160 mm/year (; about as fast as grows). The driving mechanism behind this movement is described below.
Tectonic lithosphere plates consist of lithospheric mantle overlain by one or two types of crustal material: (in older texts called from and ) and ( from silicon and ). Average oceanic lithosphere is typically 100 km (62 mi) thick; 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 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 lithosphere must travel before being subducted, the thickness varies from about 6 km (4 mi) thick at mid-ocean ridges to greater than 100 km (62 mi) at zones; for shorter or longer distances, the subduction zone (and therefore also the mean) thickness becomes smaller or larger, respectively. Continental lithosphere is typically about 200 km thick, though this varies considerably between basins, mountain ranges, and stable interiors of continents. The location where two plates meet is called a plate boundary.
Plate boundaries are commonly associated with geological events such as and the creation of topographic features such as,. The majority of the world's active volcanoes occur along plate boundaries, with the Pacific Plate's being the most active and widely known today. These boundaries are discussed in further detail below. Some volcanoes occur in the interiors of plates, and these have been variously attributed to internal plate deformation and to mantle plumes. As explained above, tectonic plates may include continental crust or oceanic crust, and most plates contain both.
For example, the includes the continent and parts of the floor of the and Oceans. 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 and of through tectonic processes, though some of these terranes may contain sequences, which are pieces of oceanic crust considered to be part of the continent when they exit the standard cycle of formation and spreading centers and subduction beneath continents. Oceanic crust is also denser than continental crust owing to their different compositions. Oceanic crust is denser because it has less silicon and more heavier elements (') than continental crust ('). As a result of this density stratification, oceanic crust generally lies below (for example most of the ), while continental crust buoyantly projects above sea level (see the page for explanation of this principle).
Types of plate boundaries. Convergent boundary. (Conservative) occur where two lithospheric plates slide, or perhaps more accurately, grind past each other along, where plates are neither created nor destroyed. The relative motion of the two plates is either (left side toward the observer) or (right side toward the observer). Transform faults occur across a spreading center.
Strong earthquakes can occur along a fault. The in California is an example of a transform boundary exhibiting dextral motion. (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. As the ocean plate 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., the and ), and continent-to-continent rifting (such as Africa's and Valley and the Red Sea), are examples of divergent boundaries. (Destructive) (or active margins) occur where two plates slide toward each other to form either a zone (one plate moving underneath the other) or a. At zones of ocean-to-continent subduction (e.g. The mountain range in South America, and the Cascade Mountains in Western United States), the dense oceanic lithosphere plunges beneath the less dense continent. Earthquakes trace the path of the downward-moving plate as it descends into asthenosphere, a trench forms, and as the subducted plate is heated it releases volatiles, mostly water from, into the surrounding mantle.
The addition of water lowers the melting point of the mantle material above the subducting slab, causing it to melt. The magma that results typically leads to volcanism.
At zones of ocean-to-ocean subduction (e.g., and the ), older, cooler, denser crust slips beneath less dense crust. This motion causes earthquakes and a deep trench to form in an arc shape.
The upper mantle of the subducted plate then heats and magma rises to form curving chains of volcanic islands. Deep marine trenches are typically associated with subduction zones, and the basins that develop along the active boundary are often called 'foreland basins'.
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. 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. Driving forces of plate motion.
Plate motion based on Global Positioning System (GPS) satellite data from NASA. The vectors show direction and magnitude of motion. It has generally been accepted that tectonic plates are able to move because of the relative density of oceanic lithosphere and the relative weakness of the asthenosphere.
Is acknowledged to be the original source of the energy required to drive plate tectonics through convection or large scale upwelling and doming. The current view, though still a matter of some debate, asserts that as a consequence, a powerful source of plate motion is generated due to the excess density of the oceanic lithosphere sinking in subduction zones.
When the new crust forms at mid-ocean ridges, this oceanic lithosphere is initially less dense than the underlying asthenosphere, but it becomes denser with age as it conductively cools and thickens. The greater of old lithosphere relative to the underlying asthenosphere allows it to sink into the deep mantle at subduction zones, providing most of the driving force for plate movement. The weakness of the asthenosphere allows the tectonic plates to move easily towards a subduction zone. Although subduction is thought to be the strongest force driving plate motions, it cannot be the only force since there are plates such as the North American Plate which are moving, yet are nowhere being subducted. The same is true for the enormous.
The sources of plate motion are a matter of intensive research and discussion among scientists. One of the main points is that the of the movement itself should be separated clearly from the possible geodynamic mechanism that is invoked as the driving force of the observed movement, as some patterns may be explained by more than one mechanism. In short, the driving forces advocated at the moment can be divided into three categories based on the relationship to the movement: mantle dynamics related, gravity related (mostly secondary forces), and earth rotation related.
Driving forces related to mantle dynamics. Main article: For much of the last quarter century, the leading theory of the driving force behind tectonic plate motions envisaged large scale convection currents in the upper mantle, which can be transmitted through the asthenosphere. This theory was launched by and some forerunners in the 1930s and was immediately recognized as the solution for the acceptance of the theory as originally discussed in the papers of in the early years of the century. However, despite its acceptance, it was long debated in the scientific community because the leading theory still envisaged a static Earth without moving continents up until the major breakthroughs of the early sixties. Two- and three-dimensional imaging of Earth's interior shows a varying lateral density distribution throughout the mantle. Such density variations can be material (from rock chemistry), mineral (from variations in mineral structures), or thermal (through thermal expansion and contraction from heat energy). The manifestation of this varying lateral density is from buoyancy forces.
How mantle convection directly and indirectly relates to plate motion is a matter of ongoing study and discussion in geodynamics. Somehow, this must be transferred to the lithosphere for tectonic plates to move. There are essentially two main types of forces that are thought to influence plate motion:. 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. May occur in a geodynamic setting where basal tractions continue to act on the plate as it dives into the mantle (although perhaps to a greater extent acting on both the under and upper side of the slab). Lately, the convection theory has been much debated, as modern techniques based on 3D seismic tomography still fail to recognize these predicted large scale convection cells; therefore, alternative views have been proposed: In the theory of developed during the 1990s, a modified concept of mantle convection currents is used.
It asserts that super plumes rise from the deeper mantle and are the drivers or substitutes of the major convection cells. These ideas, which find their roots in the early 1930s with the so-called 'fixistic' ideas of the European and Russian Earth Science Schools, find resonance in the modern theories which envisage or which remain fixed and are overridden by oceanic and continental lithosphere plates over time and leave their traces in the geological record (though these phenomena are not invoked as real driving mechanisms, but rather as modulators). Modern theories that continue building on the older mantle doming concepts and see plate movements as a secondary phenomena are beyond the scope of this article and are discussed elsewhere (for example on the article). Another theory is that the mantle flows neither in cells nor large plumes but rather as a series of channels just below the Earth's crust, which then provide basal friction to the lithosphere.
This theory, called 'surge tectonics', became quite popular in geophysics and geodynamics during the 1980s and 1990s. Recent research, based on three-dimensional computer modeling, suggests that plate geometry is governed by a feedback between mantle convection patterns and the strength of the lithosphere. Driving forces related to gravity Forces related to gravity are usually invoked as secondary phenomena within the framework of a more general driving mechanism such as the various forms of mantle dynamics described above. Gravitational sliding away from a spreading ridge: According to many authors, plate motion is driven by the higher elevation of plates at ocean ridges.
As oceanic lithosphere is formed at spreading ridges from hot mantle material, it gradually cools and thickens with age (and thus adds distance from the ridge). Cool oceanic lithosphere is significantly denser than the hot mantle material from which it is derived and so with increasing thickness it gradually subsides into the mantle to compensate the greater load.
The result is a slight lateral incline with increased distance from the ridge axis. This force is regarded as a secondary force and is often referred to as '. This is a misnomer as nothing is 'pushing' horizontally and tensional features are dominant along ridges. It is more accurate to refer to this mechanism as gravitational sliding as variable topography across the totality of the plate can vary considerably and the topography of spreading ridges is only the most prominent feature.
Other mechanisms generating this gravitational secondary force include flexural bulging of the lithosphere before it dives underneath an adjacent plate which produces a clear topographical feature that can offset, or at least affect, the influence of topographical ocean ridges, and and hot spots, which are postulated to impinge on the underside of tectonic plates. Slab-pull: Current scientific opinion is that the asthenosphere is insufficiently competent or rigid to directly cause motion by friction along the base of the lithosphere. Is therefore most widely thought to be the greatest force acting on the plates. In this current understanding, plate motion is mostly driven by the weight of cold, dense plates sinking into the mantle at trenches. Recent models indicate that plays an important role as well.
However, the fact that the is nowhere being subducted, although it is in motion, presents a problem. The same holds for the African, and plates.
Gravitational sliding away from mantle doming: According to older theories, one of the driving mechanisms of the plates is the existence of large scale asthenosphere/mantle domes which cause the gravitational sliding of lithosphere plates away from them. This gravitational sliding represents a secondary phenomenon of this basically vertically oriented mechanism. This can act on various scales, from the small scale of one island arc up to the larger scale of an entire ocean basin. Driving forces related to Earth rotation. This section needs additional citations for.
Unsourced material may be challenged and removed. (November 2015) , being a, had proposed and as the main driving mechanisms behind; however, these forces were considered far too small to cause continental motion as the concept was of continents plowing through oceanic crust. Therefore, Wegener later changed his position and asserted that convection currents are the main driving force of plate tectonics in the last edition of his book in 1929. However, in the plate tectonics context (accepted since the proposals of Heezen, Hess, Dietz, Morley, Vine, and Matthews (see below) during the early 1960s), the oceanic crust is suggested to be in motion with the continents which caused the proposals related to Earth rotation to be reconsidered. In more recent literature, these driving forces are:.
Tidal drag due to the gravitational force the (and the ) exerts on the crust of the. Global deformation of the due to small displacements of the rotational pole with respect to the Earth's crust;.
Other smaller deformation effects of the crust due to wobbles and spin movements of the Earth rotation on a smaller time scale. Forces that are small and generally negligible are:. The. The, which is treated as a slight modification of gravity: 249 For these mechanisms to be overall valid, systematic relationships should exist all over the globe between the orientation and kinematics of deformation and the geographical and grid of the Earth itself. Ironically, these systematic relations studies in the second half of the nineteenth century and the first half of the twentieth century underline exactly the opposite: that the plates had not moved in time, that the deformation grid was fixed with respect to the Earth and axis, and that gravitational driving forces were generally acting vertically and caused only local horizontal movements (the so-called pre-plate tectonic, 'fixist theories'). Later studies (discussed below on this page), therefore, invoked many of the relationships recognized during this pre-plate tectonics period to support their theories (see the anticipations and reviews in the work of van Dijk and collaborators).
Of the many forces discussed in this paragraph, tidal force is still highly debated and defended as a possible principal driving force of plate tectonics. The other forces are only used in global geodynamic models not using plate tectonics concepts (therefore beyond the discussions treated in this section) or proposed as minor modulations within the overall plate tectonics model.
In 1973, George W. Moore of the and R. Bostrom presented evidence for a general westward drift of the Earth's lithosphere with respect to the mantle. He concluded that tidal forces (the tidal lag or 'friction') caused by the Earth's rotation and the forces acting upon it by the Moon are a driving force for plate tectonics. As the Earth spins eastward beneath the moon, the moon's gravity ever so slightly pulls the Earth's surface layer back westward, just as proposed by Alfred Wegener (see above).
In a more recent 2006 study, scientists reviewed and advocated these earlier proposed ideas. It has also been suggested recently in that this observation may also explain why and have no plate tectonics, as Venus has no moon and Mars' moons are too small to have significant tidal effects on the planet. In a recent paper, it was suggested that, on the other hand, it can easily be observed that many plates are moving north and eastward, and that the dominantly westward motion of the Pacific Ocean basins derives simply from the eastward bias of the Pacific spreading center (which is not a predicted manifestation of such lunar forces). In the same paper the authors admit, however, that relative to the lower mantle, there is a slight westward component in the motions of all the plates. They demonstrated though that the westward drift, seen only for the past 30 Ma, is attributed to the increased dominance of the steadily growing and accelerating Pacific plate. The debate is still open.
Relative significance of each driving force mechanism The of a plate's motion is a function of all the forces acting on the plate; however, therein lies the problem regarding 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 various processes actively driving each individual plate. One method of dealing with this problem is to consider the relative rate at which each plate is moving as well as the evidence related to the significance of each process to the overall driving force on the plate. 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 so-called Ring of Fire) and moves much faster than the plates of the Atlantic basin, which are attached (perhaps one could say 'welded') to adjacent continents instead of subducting plates. It is thus thought that forces associated with the downgoing plate (slab pull and slab suction) are the driving forces which determine the motion of plates, except for those plates which are not being subducted.
This view however has been contradicted by a recent study which found that the actual motions of the Pacific Plate and other plates associated with the East Pacific Rise do not correlate mainly with either slab pull or slab push, but rather with a mantle convection upwelling whose horizontal spreading along the bases of the various plates drives them along via viscosity-related traction forces. The driving forces of plate motion continue to be active subjects of on-going research within. Development of the theory. Detailed map showing the tectonic plates with their movement vectors. In line with other previous and contemporaneous proposals, in 1912 the meteorologist amply described what he called continental drift, expanded in his 1915 book The Origin of Continents and Oceans and the scientific debate started that would end up fifty years later in the theory of plate tectonics. Starting from the idea (also expressed by his forerunners) that the present continents once formed a single land mass (which was called later on) that drifted apart, thus releasing the continents from the Earth's mantle and likening them to 'icebergs' of low density floating on a sea of denser. Supporting evidence for the idea came from the dove-tailing outlines of South America's east coast and Africa's west coast, and from the matching of the rock formations along these edges.
Confirmation of their previous contiguous nature also came from the fossil plants and, and the or, all widely distributed over South America, Africa, Antarctica, India, and Australia. The evidence for such an erstwhile joining of these continents was patent to field geologists working in the southern hemisphere. The South African 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 fragments. But without detailed evidence and a force sufficient to drive the movement, the theory was not generally accepted: the Earth might have a solid crust and mantle and a liquid core, but there seemed to be no way that portions of the crust could move around.
Distinguished scientists, such as and, 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 and 1940s, the former reached important milestones proposing that 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 plates came from. This is based on the fact that rocks of different ages show a variable direction, evidenced by studies since the mid–nineteenth century. The magnetic north and south poles reverse through time, and, especially important in paleotectonic studies, the relative position of the magnetic north pole varies through time. Initially, during the first half of the twentieth century, the latter phenomenon was explained by introducing what was called 'polar wander' (see ), i.e., it was assumed that the north pole location had been shifting through time. An alternative explanation, though, was that the continents had moved (shifted and rotated) relative to the north pole, and each continent, in fact, shows its own 'polar wander path'.
During the late 1950s it was successfully shown on two occasions that these data could show the validity of continental drift: by Keith Runcorn in a paper in 1956, and by Warren Carey in a symposium held in March 1956. The second piece of evidence in support of continental drift came during the late 1950s and early 60s from data on the bathymetry of the deep and the nature of the oceanic crust such as magnetic properties and, more generally, with the development of which gave evidence for the association of seafloor spreading along the and, published between 1959 and 1963 by Heezen, Dietz, Hess, Mason, Vine & Matthews, and Morley. Simultaneous advances in early imaging techniques in and around along the trenches bounding many continental margins, together with many other geophysical (e.g. Gravimetric) and geological observations, showed how the oceanic crust could disappear into the mantle, providing the mechanism to balance the extension of the ocean basins with shortening along its margins.
All this evidence, both from the ocean floor and from the continental margins, made it clear around 1965 that continental drift was feasible and the theory of plate tectonics, which was defined in a series of papers between 1965 and 1967, was born, with all its extraordinary explanatory and predictive power. The theory revolutionized the Earth sciences, explaining a diverse range of geological phenomena and their implications in other studies such as. Continental drift. Alfred Wegener in Greenland in the winter of 1912–13. It was observed as early as 1596 that the opposite of the Atlantic Ocean—or, more precisely, the edges of the —have similar shapes and seem to have once fitted together. Since that time many theories were proposed to explain this apparent complementarity, but the assumption of a solid Earth made these various proposals difficult to accept.
The discovery of and its associated properties in 1895 prompted a re-examination of the apparent. This had previously been estimated by its cooling rate under the assumption that the Earth's surface radiated like a. Those calculations had implied that, even if it started at, the Earth would have dropped to its present temperature in a few tens of millions of years.
Armed with the knowledge of a new heat source, scientists realized that the Earth would be much older, and that its core was still sufficiently hot to be liquid. By 1915, after having published a first article in 1912, Alfred Wegener was making serious arguments for the idea of continental drift in the first edition of The Origin of Continents and Oceans.
In that book (re-issued in four successive editions up to the final one in 1936), he noted how the east coast of and the west coast of looked as if they were once attached. Wegener was not the first to note this (, and preceded him just to mention a few), but he was the first to marshal significant and paleo-topographical and climatological evidence to support this simple observation (and was supported in this by researchers such as ). Furthermore, when the rock of the margins of separate continents are very similar it suggests that these rocks were formed in the same way, implying that they were joined initially. For instance, parts of and contain rocks very similar to those found in. Furthermore, the of Europe and parts of the of North America are very similar in.
However, his ideas were not taken seriously by many geologists, who pointed out that there was no apparent mechanism for continental drift. Specifically, they did not see how continental rock could plow through the much denser rock that makes up oceanic crust. Wegener could not explain the force that drove continental drift, and his vindication did not come until after his death in 1930.
Floating continents, paleomagnetism, and seismicity zones. Map of earthquakes in 2016 As it was observed early that although existed on continents, seafloor seemed to be composed of denser, the prevailing concept during the first half of the twentieth century was that there were two types of crust, named 'sial' (continental type crust) and 'sima' (oceanic type crust). Furthermore, it was supposed that a static shell of strata was present under the continents. It therefore looked apparent that a layer of basalt (sial) underlies the continental rocks. However, based on abnormalities in by the in Peru, had deduced that less-dense mountains must have a downward projection into the denser layer underneath. The concept that mountains had 'roots' was confirmed by a hundred years later, during study of gravitation, and seismic studies detected corresponding density variations. Therefore, by the mid-1950s, the question remained unresolved as to whether mountain roots were clenched in surrounding basalt or were floating on it like an iceberg.
During the 20th century, improvements in and greater use of seismic instruments such as enabled scientists to learn that earthquakes tend to be concentrated in specific areas, most notably along the and spreading ridges. By the late 1920s, seismologists were beginning to identify several prominent earthquake zones parallel to the trenches that typically were inclined 40–60° from the horizontal and extended several hundred kilometers into the Earth. These zones later became known as Wadati–Benioff zones, or simply Benioff zones, in honor of the seismologists who first recognized them, of Japan and of the United States. The study of global seismicity greatly advanced in the 1960s with the establishment of the Worldwide Standardized Seismograph Network (WWSSN) to monitor the compliance of the 1963 treaty banning above-ground testing of nuclear weapons. The much improved data from the WWSSN instruments allowed seismologists to map precisely the zones of earthquake concentration worldwide. Meanwhile, debates developed around the phenomena of polar wander.
Since the early debates of continental drift, scientists had discussed and used evidence that polar drift had occurred because continents seemed to have moved through different climatic zones during the past. Furthermore, paleomagnetic data had shown that the magnetic pole had also shifted during time.
Reasoning in an opposite way, the continents might have shifted and rotated, while the pole remained relatively fixed. The first time the evidence of magnetic polar wander was used to support the movements of continents was in a paper by in 1956, and successive papers by him and his students (who was actually the first to be convinced of the fact that paleomagnetism supported continental drift) and Ken Creer.
This was immediately followed by a symposium in in March 1956. In this symposium, the evidence was used in the theory of an. In this hypothesis the shifting of the continents can be simply explained by a large increase in size of the Earth since its formation. However, this was unsatisfactory because its supporters could offer no convincing mechanism to produce a significant expansion of the Earth. Certainly there is no evidence that the moon has expanded in the past 3 billion years; other work would soon show that the evidence was equally in support of continental drift on a globe with a stable radius.
During the thirties up to the late fifties, works by, Holmes, and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the, and in 1928 that convection currents within the mantle might be the driving force. Often, these contributions are forgotten because:. At the time, continental drift was not accepted.
Some of these ideas were discussed in the context of abandoned fixistic ideas of a deforming globe without continental drift or an expanding Earth. They were published during an episode of extreme political and economic instability that hampered scientific communication. Many were published by European scientists and at first not mentioned or given little credit in the papers on sea floor spreading published by the American researchers in the 1960s. Mid-oceanic ridge spreading and convection. Further information on Mid-ocean ridge: In 1947, a team of scientists led by utilizing the 's research vessel Atlantis and an array of instruments, confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath the layer of sediments consisted of basalt, not the granite 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. The new data that had been collected on the ocean basins also showed particular characteristics regarding the 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 '. This was described in the crucial paper of (1960), 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 ' hypothesis of S. Warren Carey (see above). So, still the question remained: how can new crust be continuously added along the oceanic ridges without increasing the size of the Earth?
The Theory Of Plate Tectonics Answers
In reality, this question had been solved already by numerous scientists during the forties and the fifties, like Arthur Holmes, Vening-Meinesz, Coates and many others: The crust in excess disappeared along what were called the oceanic trenches, where so-called 'subduction' occurred. Therefore, when various scientists during the early sixties started to reason on the data at their disposal regarding the ocean floor, the pieces of the theory quickly fell into place.
The question particularly intrigued, a geologist and a Naval Reserve Rear Admiral, and, a scientist with the who first coined the term seafloor spreading. Dietz and Hess (the former published the same idea one year earlier in, but priority belongs to Hess who had already distributed an unpublished manuscript of his 1962 article by 1960) 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.
In the same year, of the U.S. Geological Survey described the main features of subduction in the. 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 scientists on island arcs and mountain belts performed and published during the 1930s up until the 1950s was applied and appreciated also in the United States. If the Earth's crust was expanding along the oceanic ridges, Hess and Dietz reasoned like Holmes and others before them, it must be shrinking elsewhere. Hess followed Heezen, suggesting that new oceanic crust continuously spreads 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 the continental margins where oceanic trenches – very deep, narrow canyons – are formed, e.g. The important step Hess made was that convection currents would be the driving force in this process, arriving at the same conclusions as Holmes had decades before with the only difference that the thinning of the ocean crust was performed using Heezen's mechanism of spreading along the ridges. Hess therefore concluded that the Atlantic Ocean was expanding while the was shrinking. As old oceanic crust is 'consumed' in the trenches (like Holmes and others, he thought this was done by thickening of the continental lithosphere, 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 are perpetually being 'recycled,' with the creation of new crust and the destruction of old oceanic lithosphere occurring simultaneously. Thus, the new mobilistic concepts neatly explained why the Earth does not get bigger with sea floor spreading, why there is so little sediment accumulation on the ocean floor, and why oceanic rocks are much younger than continental rocks.
Magnetic striping. Further information: Beginning in the 1950s, scientists like, using magnetic instruments adapted from airborne devices developed during to detect, began recognizing odd magnetic variations across the ocean floor. This finding, though unexpected, was not entirely surprising because it was known that basalt—the iron-rich, volcanic rock making up the ocean floor—contains a strongly magnetic mineral and can locally distort compass readings.
This distortion was recognized by Icelandic mariners as early as the late 18th century. More important, because the presence of magnetite gives the basalt measurable magnetic properties, these newly discovered magnetic variations provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials recorded the 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 -like pattern: one stripe with normal polarity and the adjoining stripe with reversed polarity. The overall pattern, defined by these alternating bands of normally and reversely polarized rock, became known as magnetic striping, and was published by and co-workers in 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. The discovery of magnetic striping called for an explanation. In the early 1960s scientists such as Heezen, Hess and Dietz had begun to theorise that mid-ocean ridges mark structurally weak zones where the ocean floor was being ripped in two lengthwise along the ridge crest (see the previous paragraph). New from deep within the Earth rises easily through these weak zones and eventually erupts along the crest of the ridges to create new oceanic crust. This process, at first denominated the '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 magnetic stripes were published, the link between sea floor spreading and these patterns was correctly placed, independently by, and by and, in 1963, now called the. Main article: Reconstruction is used to establish past (and future) plate configurations, helping determine the shape and make-up of ancient supercontinents and providing a basis for paleogeography. Defining plate boundaries Current plate boundaries are defined by their seismicity. Past plate boundaries within existing plates are identified from a variety of evidence, such as the presence of that are indicative of vanished oceans. Past plate motions Tectonic motion is believed to have begun around 3 to 3.5 billion years ago. Various types of quantitative and semi-quantitative information are available to constrain past plate motions. The geometric fit between continents, such as between west Africa and South America is still an important part of plate reconstruction.
Magnetic stripe patterns provide a reliable guide to relative plate motions going back into the period. The tracks of hotspots give absolute reconstructions, but these are only available back to the.
Older reconstructions rely mainly on paleomagnetic pole data, although these only constrain the latitude and rotation, but not the longitude. Combining poles of different ages in a particular plate to produce apparent polar wander paths provides a method for comparing the motions of different plates through time. Additional evidence comes from the distribution of certain types, faunal provinces shown by particular fossil groups, and the position of. Formation and break-up of continents The movement of plates has caused the formation and break-up of continents over time, including occasional formation of a that contains most or all of the continents. The supercontinent or Nuna formed during a period of and broke up about.
The supercontinent is thought to have formed about 1 billion years ago and to have embodied most or all of Earth's continents, and broken up into eight continents around million years ago. The eight continents later re-assembled into another supercontinent called; Pangaea broke up into (which became North America and Eurasia) and (which became the remaining continents).
The, the world's tallest mountain range, are assumed to have been formed by the collision of two major plates. Before uplift, they were covered by the. Current plates. Depending on how they are defined, there are usually seven or eight 'major' plates:,. The latter is sometimes subdivided into the and plates.
There are dozens of smaller plates, the seven largest of which are the,. The current motion of the tectonic plates is today determined by remote sensing satellite data sets, calibrated with ground station measurements. Other celestial bodies (planets, moons) The appearance of plate tectonics on is related to planetary mass, with expected to exhibit plate tectonics. Earth may be a borderline case, owing its tectonic activity to abundant water (silica and water form a deep ).
See also: Venus shows no evidence of active plate tectonics. There is debatable evidence of active tectonics in the planet's distant past; however, events taking place since then (such as the plausible and generally accepted hypothesis that the Venusian lithosphere has thickened greatly over the course of several hundred million years) has made constraining the course of its geologic record difficult. However, the numerous well-preserved have been utilized as a to approximately date the Venusian surface (since there are thus far no known samples of Venusian rock to be dated by more reliable methods). Dates derived are dominantly in the range, although ages of up to million years ago have been calculated.
Theory Of Plate Tectonics Study Guide Answers
This research has led to the fairly well accepted hypothesis that Venus has undergone an essentially complete volcanic resurfacing at least once in its distant past, with the last event taking place approximately within the range of estimated surface ages. While the mechanism of such an impressive thermal event remains a debated issue in Venusian geosciences, some scientists are advocates of processes involving plate motion to some extent. One explanation for Venus's lack of plate tectonics is that on Venus temperatures are too high for significant water to be present.
The Earth's crust is soaked with water, and water plays an important role in the development of. Plate tectonics requires weak surfaces in the crust along which crustal slices can move, and it may well be that such weakening never took place on Venus because of the absence of water. However, some researchers remain convinced that plate tectonics is or was once active on this planet. See also: 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 was created by plate tectonic processes. Scientists today disagree, and think that it was created either by upwelling within the Martian that thickened the crust of the Southern Highlands and formed or by a giant impact that excavated the. May be a tectonic boundary. Observations made of the magnetic field of Mars by the spacecraft in 1999 showed patterns of magnetic striping discovered on this planet. Some scientists interpreted these as requiring plate tectonic processes, such as seafloor spreading. However, their data fail a 'magnetic reversal test', which is used to see if they were formed by flipping polarities of a global magnetic field. Icy satellites Some of the of have features that may be related to plate-tectonic style deformation, although the materials and specific mechanisms may be different from plate-tectonic activity on Earth.
On 8 September 2014, NASA reported finding evidence of plate tectonics on, a satellite of Jupiter—the first sign of subduction activity on another world other than Earth., the largest moon of, was reported to show tectonic activity in images taken by the, which landed on Titan on January 14, 2005. Exoplanets On Earth-sized planets, plate tectonics is more likely if there are oceans of water. However, in 2007, two independent teams of researchers came to opposing conclusions about the likelihood of plate tectonics on larger with one team saying that plate tectonics would be episodic or stagnant and the other team saying that plate tectonics is very likely on super-earths even if the planet is dry. Consideration of plate tectonics is a part of the. – The large-scale movement of, a process which distributes thermal energy about the Earth's surface. – The sequence of major geological events in Earth's past.
– An obsolete geological concept to explain orogens before the theory of plate tectonics was developed. – Open-source application software for interactive plate-tectonic reconstructions. – Oceanic landforms and topographic elements. – The quasi-periodic aggregation and dispersal of Earth's continental crust. – The processes that control the structure and properties of the Earth's crust and its evolution through time References Notes.
Fill in the table below. In the column on the right, put the following examples: Himalayas, Andes, Japan, Indonesia, Mid-Atlantic ridge, Mt.
Helens, San Andreas fault in California. Boundary Type Direction of movement Resulting Features Example in the world Ocean-ocean convergent Trench, volcanic island chains, earthquakes Japan, Indonesia Ocean-continent convergent Trench, volcanoes, folded mountain belts, earthquakes Mt. Helens, Andes Continent-continent convergent High folded mountain belts Himalayas Divergent Mid-ocean ridges, rift valleys, earthquakes Mid-atlantic ridge Transform Earthquakes San Andreas fault 8. What evidence caused Alfred Wegener to develop his hypothesis of Continental Drift (4 things)? The shape of the continents, matching mountain ranges on different continents, matching fossils, and glacier evidence.
Cipher Wheel Template Guide
Cipher Disk Templates. Create out your own cipher disks. View a printable version of Cipher Disk 1 and Cipher Disk 2. Print out each cipher disk, paste on card stock, cutout, and assemble your own set of cipher disks.
It is time to keep your messages away from prying eyes. Are you interested in finding out more about ciphers and codes? Book by David Kahn is what I would start with. How to make a cipher wheel Here are 6 material you will require in making a cipher wheel.
Cipher Disk Template
Glue stick. Pen or pencil.
Paper fastener or split pin. Cipher wheel template. How to make a cipher wheel (using premade template). Print off the cipher wheel.
Blank Cipher Wheel Template
Then cut the wheels out and glue them onto the card with the glue stick. Carefully cut both of the cipher wheels out. Then write the alphabet in the outer boxes of both the small and large wheel.
Using a sharp pencil, punch a hole through the center of both wheels. Then push the paper fastener through the smaller wheel and then through the larger wheel. Then open the split pin at the back so that the wheel are fastened together. How to make a cipher wheel (from scratch).
You need two concentric circles; one should be larger than the other. Then punch a hole in the middle of both and attach with a brass fastener so the inner wheel can move independent of the outer wheel. Then divide the entire circle into 26 sections. You can use a protractor to divide the circle into equal segments of about 13.8 degrees each.
Then write the letters of the alphabet, in order, on both circles. Then decide on the key to use for encoding your message. Finally turn the inner wheel based on the key.
To encrypt, look at the inner wheel and write down the letter that matches on the outer wheel. How to encrypt using cipher wheel First, choose a key to use. To encode, simply align the circles so there is the same letter on the outer and on the inner circle. Plaintext: Kifanga. Thus, ciphertext: dbytgzt How to decrypt using cipher wheel Simply move the inner circle the number of times based on the key used to encode the message. Then, to decode look at the encrypted letter on the inner circle and write down the letter on the outer circle above it.
Do this for the entire letters to get the original message at the end. What are the variants of the cipher wheel Cipher discs have many variations based on the basic design.
For example, instead of numbers only, one can use combinations of numbers on the outer disk with each combination corresponding to a letter.
