Major Plates of the Lithosphere: Earth's Tectonic Plates - Video & Lesson Transcript | negeriku.info
Isotopic Dating Methods · Other Dating Methods · Understanding Geological Figure A map showing 15 of the Earth's tectonic plates and the Before we talk about processes at plate boundaries, it's important to point out .. or any other resources, write in the names of as many of the plates as you can. The Earth's outer shell, the lithosphere, consisting of the crust and uppermost mantle, is divided into a patchwork of large tectonic plates that move slowly. Plate boundary zones -- broad belts in which boundaries are not well When the continental crust stretches beyond its limits, tension As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved. . Among the three techniques, to date the GPS has been the most.
However, the fact that the North American Plate is nowhere being subducted, although it is in motion, presents a problem. The same holds for the African, Eurasianand Antarctic plates.
Gravitational sliding away from mantle doming: 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. November Learn how and when to remove this template message Alfred Wegenerbeing a meteorologisthad proposed tidal forces and centrifugal forces as the main driving mechanisms behind continental drift ; however, these forces were considered far too small to cause continental motion as the concept was of continents plowing through oceanic crust.
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 sthe oceanic crust is suggested to be in motion with the continents which caused the proposals related to Earth rotation to be reconsidered. In more recent literature, these driving forces are: Tidal drag due to the gravitational force the Moon and the Sun exerts on the crust of the Earth  Global deformation of the geoid 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 Coriolis force   The centrifugal forcewhich is treated as a slight modification of gravity  : 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: Later studies discussed below on this pagetherefore, 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.
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. InGeorge W. 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.
- Minor Tectonic Plates By Size
- Evidence for the theory
- File history
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 study,  scientists reviewed and advocated these earlier proposed ideas.
It has also been suggested recently in Lovett that this observation may also explain why Venus and Mars have no plate tectonics, as Venus has no moon and Mars' moons are too small to have significant tidal effects on the planet.
In a recent paper,  it was suggested that, on the other hand, it can easily be observed that many plates are moving north and eastward, and that the dominantly westward motion of the Pacific Ocean basins derives simply from the eastward bias of the Pacific spreading center which is not a predicted manifestation of such lunar forces.
In the same paper the authors admit, however, that relative to the lower mantle, there is a slight westward component in the motions of all the plates.
The debate is still open. Relative significance of each driving force mechanism The vector of a plate's motion is a function of all the forces acting on the plate; however, therein lies the 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.
How Many Tectonic Plates Are There?
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.
Development of the theory Summary Detailed map showing the tectonic plates with their movement vectors. In line with other previous and contemporaneous proposals, in the meteorologist Alfred Wegener amply described what he called continental drift, expanded in his 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.
Confirmation of their previous contiguous nature also came from the fossil plants Glossopteris and Gangamopterisand the therapsid or mammal-like reptile Lystrosaurusall 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 Alex du Toit put together a mass of such information in his publication Our Wandering Continents, and went further than Wegener in recognising the strong links between the Gondwana fragments. But without detailed evidence and a force sufficient to drive the movement, the theory was not generally accepted: Distinguished scientists, such as Harold Jeffreys and Charles Schuchertwere 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 s, s and s, 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 plates came from paleomagnetism. This is based on the fact that rocks of different ages show a variable magnetic field direction, evidenced by studies since the mid—nineteenth century.
The magnetic north and south poles reverse through time, and, especially important in paleotectonic studies, the relative position of the magnetic north pole varies through time. Initially, during the first half of the twentieth century, the latter phenomenon was explained by introducing what was called "polar wander" see apparent polar wanderi.
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 s it was successfully shown on two occasions that these data could show the validity of continental drift: All this evidence, both from the ocean floor and from the continental margins, made it clear around that continental drift was feasible and the theory of plate tectonics, which was defined in a series of papers between andwas 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 paleogeography and paleobiology.
plate tectonics | Definition, Theory, Facts, & Evidence | negeriku.info
Continental drift Further information: Continental drift In the late 19th and early 20th centuries, geologists assumed that the Earth's major features were fixed, and that most geologic features such as basin development and mountain ranges could be explained by vertical crustal movement, described in what is called the geosynclinal theory.
Generally, this was placed in the context of a contracting planet Earth due to heat loss in the course of a relatively short geological time. Alfred Wegener in Greenland in the winter of — It was observed as early as that the opposite coasts of the Atlantic Ocean—or, more precisely, the edges of the continental shelves —have similar shapes and seem to have once fitted together.
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. Byafter having published a first article in Alfred Wegener was making serious arguments for the idea of continental drift in the first edition of The Origin of Continents and Oceans.
Wegener was not the first to note this Abraham OrteliusAntonio Snider-PellegriniEduard SuessRoberto Mantovani and Frank Bursley Taylor preceded him just to mention a fewbut he was the first to marshal significant fossil and paleo-topographical and climatological evidence to support this simple observation and was supported in this by researchers such as Alex du Toit. Furthermore, when the rock strata of the margins of separate continents are very similar it suggests that these rocks were formed in the same way, implying that they were joined initially.
For instance, parts of Scotland and Ireland contain rocks very similar to those found in Newfoundland and New Brunswick.
Furthermore, the Caledonian Mountains of Europe and parts of the Appalachian Mountains of North America are very similar in structure and lithology.
However, his ideas were not taken seriously by many geologists, who pointed out that there was no apparent mechanism for continental drift. Specifically, they did not see how continental rock could plow through the much denser rock that makes up oceanic crust.
Wegener could not explain the force that drove continental drift, and his vindication did not come until after his death in Most earthquakes occur in narrow belts that correspond to the locations of lithospheric plate boundaries. Map of earthquakes in As it was observed early that although granite existed on continents, seafloor seemed to be composed of denser basaltthe prevailing concept during the first half of the twentieth century was that there were two types of crust, named "sial" continental type crust and "sima" oceanic type crust.
Furthermore, it was supposed that a static shell of strata was present under the continents. It therefore looked apparent that a layer of basalt sial underlies the continental rocks. However, based on abnormalities in plumb line deflection by the Andes in Peru, Pierre Bouguer had deduced that less-dense mountains must have a downward projection into the denser layer underneath. The concept that mountains had "roots" was confirmed by George B. Airy a hundred years later, during study of Himalayan gravitation, and seismic studies detected corresponding density variations.
Therefore, by the mids, the question remained unresolved as to whether mountain roots were clenched in surrounding basalt or were floating on it like an iceberg. During the 20th century, improvements in and greater use of seismic instruments such as seismographs enabled scientists to learn that earthquakes tend to be concentrated in specific areas, most notably along the oceanic trenches and spreading ridges.
These zones later became known as Wadati—Benioff zones, or simply Benioff zones, in honor of the seismologists who first recognized them, Kiyoo Wadati of Japan and Hugo Benioff of the United States.
The study of global seismicity greatly advanced in the s with the establishment of the Worldwide Standardized Seismograph Network WWSSN  to monitor the compliance of the 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.
North American and South American Plates At the start of this lesson, we identified some major land masses found on Earth. This gets us closer to understanding the location of the major tectonic plates, but it doesn't share the whole story. This is because tectonic plates can contain both continental crust and oceanic crust.
Therefore, some of the plates may contain land, but others may be located underwater or be a mix of both. Take the North American plate for example. It is one of the major plates of the lithosphere and extends from the middle of the Atlantic Ocean to the West Coast of North America. The same can be said for the South American plate, which is another of the seven major plates and extends from the middle of the Atlantic Ocean to the west coast of South America.
Pacific Plate So, you can see below that the North and South American plates contain oceanic crust, even though they are named for the main continent they encompass. In fact, six of the seven major tectonic plates are named after the continents they contain. The one exception is the Pacific plate, which lies beneath the Pacific Ocean.
NAME: DATE: Review: Plate Tectonics/Layers of the Earth Label the
Not only is this the only major tectonic plate that is mainly underwater, it is also the largest, spanning over million square kilometers. The majority of plates are named after the continents they contain.
African Plate - 61, sq km The African plate is the fourth largest tectonic plate with an estimated area of 61, square kilometers. Most of the African continent is on the African Plate.
Notably, the Italian island of Sicily is also a part of the African Plate. Antarctic Plate - 60, sq km The Antarctic Plate encompasses the entire continent of Antarctica, as well as the nearby oceans. It is the fifth largest plate on earth. Indo-Australian Plate - 58, sq km The Indo-Australian Plate was formed out of a merger of the Australian and Indian plates millions of years ago. When the Eursian Plate and the Indo-Australian plate collided many many years ago, the Himilaya mountains were formed.
Some scientists believe that the Indian Plate and the Australian Plate are actually separate plates, and have been for millions of years.
South American Plate - 43, sq km The South American plate is a major tectonic plate that covers 43 million square kilometers around South America and the surrounding Atlantic Ocean. Plate motions between the South American Plate, which moves westward, and the nearby minor plate, the Nazca Plate, has been causing the formation of volcanoes as well as the heightening of the Andes Mountains. Currently, the Somali Plate is moving away from continental Africa at a very small pace which equates to around 20 millimetres per annum.
Nazca Plate - 15, sq km The second largest of all minor plates, the Nazca Plate, stretches for This location has been responsible for the number of volcanic islands and mountainous landscapes on the western coast of South America. Philippine Sea Plate - 5, sq km The Philippine Sea Plate comprises of over 5 million square km of ocean space adjacent to the Philippines, in the Philippine Sea.
The plate also touches upon both Taiwan and Japan in its northern reaches. Arabian Plate - 5, sq km The Arabian Plate measures for 5 million km squared, mostly across the Arabian Peninsula.