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First person to analyze plate tectonics

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a) This page is mainly about what a plate tectonic is, plate boundaries and how they got started. It talks about the origin of the theory and when the movement of plates began to occur.
b) When reviewing the webpage, make sure to take a look at the map of "tectonic plates of the earth". This map shows clear outlines of the plates on the earth's surface. Another important piece of information to look at would be in paragraph 2, line 1-3. This section sums up the plate tectonic theory and how the "Earth's outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core."
c) Knowing the location of the plates is important because it helps to understand why the continents moved the way they did. It mainly has to do with the placement of the plates and without this information trying to understand why the continents moved the way they did would be more challenging. Also understanding the basics of the plate tectonics theory is one of the most important keys to this topic. Having some basic knowledge on the way the plates are set up and how they moved is vital to studying plate tectonics.

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(Image credit: Eileen Devinney/NPS) From the deepest ocean trench to the tallest mountain, plate tectonics explains the features and movement of Earth's surface in the present and the past.

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a) This page mainly focuses on the history of plate tectonics and how they were first analyzed by Alfred Wegener. It also states how Wegener proved his theories with key pieces of information he had discovered. Finally, it talks about his efforts trying to prove the theory of continental drift.
b) When reading over this website, some key points to look at would be in paragragh 2. This paragraph mainly focuses on the important factors leading to the conformation of continental drift. One of the factors being the discovery of fossils of tropical plants and animals in non-tropical areas like Africa. The paragraph continues on about the reasoning that Wegener had behind the discovery of these organisms and how he uses his theories to further prove continental drift had occurred. It also states the reasoning for Wegener hypothesis with ligament reasoning behind each claim.
c) This contains important study information because the claims and points created by Wegener have formed the base behind the modern day theory on plate tectonics. He is a key part is the theories history and this webpage helps to sum up his role and contribution.

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Plate Tectonics: The Rocky History of an Idea

Close examination of a globe often results in the observation that most of the continents seem to fit together like a puzzle: the west African coastline seems to snuggle nicely into the east coast of South America and the Caribbean sea; and a similar fit appears across the Pacific. The fit is even more striking when the submerged continental shelves are compared rather than the coastlines. In 1912 Alfred Wegener (1880-1930) noticed the same thing and proposed that the continents were once compressed into a single protocontinent which he called Pangaea (meaning "all lands"), and over time they have drifted apart into their current distribution. He believed that Pangaea was intact until the late Carboniferous period, about 300 million years ago, when it began to break up and drift apart. However, Wegener's hypothesis lacked a geological mechanism to explain how the continents could drift across the earths surface as he proposed.

Searching for evidence to further develop his theory of continental drift, Wegener came across a paleontological paper suggesting that a land bridge had once connected Africa with Brazil. This proposed land bridge was an attempt to explain the well known paleontological observation that the same fossilized plants and animals from the same time period were found in South America and Africa. The same was true for fossils found in Europe and North America, and Madagascar and India. Many of these organisms could not have traveled across the vast oceans that currently exist. Wegener's drift theory seemed more plausible than land bridges connecting all of the continents. But that in itself was not enough to support his idea. Another observation favoring continental drift was the presence of evidence for continental glaciation in the Pensylvanian period. Striae left by the scraping of glaciers over the land surface indicated that Africa and South America had been close together at the time of this ancient ice age. The same scraping patterns can be found along the coasts of South America and South Africa.

Wegener's drift hypothesis also provided an alternate explanation for the formation of mountains (orogenesis). The theory being discussed during his time was the "Contraction theory" which suggested that the planet was once a molten ball and in the process of cooling the surface cracked and folded up on itself. The big problem with this idea was that all mountain ranges should be approximately the same age, and this was known not to be true. Wegener's explanation was that as the continents moved, the leading edge of the continent would encounter resistance and thus compress and fold upwards forming mountains near the leading edges of the drifting continents. The Sierra Nevada mountains on the Pacific coast of North America and the Andes on the coast of South America were cited. Wegener also suggested that India drifted northward into the asian continent thus forming the Himalayas.

Wegener eventually proposed a mechanism for continental drift that focused on his assertion that the rotation of the earth created a centrifugal force towards the equator. He believed that Pangaea originated near the south pole and that the centrifugal force of the planet caused the protocontinent to break apart and the resultant continents to drift towards the equator. He called this the "pole-fleeing force". This idea was quickly rejected by the scientific community primarily because the actual forces generated by the rotation of the earth were calculated to be insufficient to move continents. Wegener also tried to explain the westward drift of the Americas by invoking the gravitational forces of the sun and the moon, this idea was also quickly rejected. Wegener's inability to provide an adequate explanation of the forces responsible for continental drift and the prevailing belief that the earth was solid and immovable resulted in the scientific dismissal of his theories.

In 1929, about the time Wegener's ideas began to be dismissed, Arthur Holmes elaborated on one of Wegener's many hypotheses; the idea that the mantle undergoes thermal convection. This idea is based on the fact that as a substance is heated its density decreases and rises to the surface until it is cooled and sinks again. This repeated heating and cooling results in a current which may be enough to cause continents to move. Arthur Holmes suggested that this thermal convection was like a conveyor belt and that the upwelling pressure could break apart a continent and then force the broken continent in opposite directions carried by the convection currents. This idea received very little attention at the time.

Not until the 1960's did Holmes' idea receive any attention. Greater understanding of the ocean floor and the discoveries of features like mid-oceanic ridges, geomagnetic anomalies parallel to the mid-oceanic ridges, and the association of island arcs and oceanic trenches occurring together and near the continental margins, suggested convection might indeed be at work. These discoveries and more led Harry Hess (1962) and R.Deitz (1961) to publish similar hypotheses based on mantle convection currents, now known as "sea floor spreading". This idea was basically the same as that proposed by Holmes over 30 years earlier, but now there was much more evidence to further develop and support the idea. To learn more about the current theories which describe the mechanisms behind continental drift go to the "Plate Tectonics: The Mechanism" page.
To learn more about plate tectonics, read the books I used as references listed below:

The New View of the Earth by Seiya Uyeda, 1978 by W.H. Freeman and Co.

The Earth's Dynamic Systems by W. Kenneth Hamblin, 1975 by Burgess Publishing Co.

Global Tectonics by Philip Kearey & Frederick J. Vine, 1996 by Blackwell Sciences Ltd.

Physical Geology by Carla W. Montgomery, 1987 by Wm. C. Brown Publishers.

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Plate Tectonics: The Rocky History of an Idea Close examination of a globe often results in the observation that most of the continents seem to fit together like a puzzle: the west African coastline seems to snuggle nicely into the east coast of South America and the Caribbean sea; and a similar fit appears across the Pacific.

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3)What can we learn about our world by studying plate tectonics?

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3)What can we learn about our world by studying plate tectonics?

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http://www.thecanadianencyclopedia.ca/en/article/plate-tectonics/
a) This page focuses on the history and the affect plate tectonics has had on the world over time. It talks about the early life and how the world has shaped and changed accourding to the movement of the plates.
b) Specific information to look at when reading over this article would be in the section titled "Seismology and Earth's Interior". It's important because it gives seem insight to the worlds past and how our world today was effect by earthquakes caused by tectonic plates millions of years ago. Also the Plate Movement, Maps located at the top of the article helps to give a visual representation of how plates shaped the world we know today.
c) These areas can be good to look over for study purposes. The map helps to give the reader a clear visual on the worlds relation to plate tectonics. This article also goes into talk about what we can learn from the past, present and future using tracking the plates movements over time.

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Plate tectonics is the theory proposing that Earth's outer rocky shell is divided into seven major and several smaller rigid plates, and that forces generated by heat losses from the planet's interior constantly move the plates about.

Plate tectonics is the theory proposing that Earth's outer rocky shell is divided into seven major and several smaller rigid plates, and that forces generated by heat losses from the planet's interior constantly move the plates about. Plate movements, ongoing over millions of years ( see Geological History), open and close ocean basins, generate volcanoes, raise mountains, facilitate accumulation of mineral and petroleum deposits, and influence evolution and climate change. Friction between plates prevents steady motion and stores energy that is released in sudden movements, causing earthquakes.

History

Early Discoveries and Theories

The discovery of the Americas by early European explorers some 500 years ago led to observations that the coasts of South America and Africa would fit together closely if they were not separated by the Atlantic Ocean. At the time, it was believed that Earth was about 6,000 years old; therefore, it was thought that any separation must have occurred as the result of cataclysmic events at the time of creation.

During the 19th century, geologists suggested that to provide enough time for the great thicknesses of sedimentary rock to have accumulated, Earth must be older than 6,000 years, perhaps hundreds of millions of years old. Conversely, physicists argued that Earth was losing heat to space and that, since no adequate sources of internal energy were known, it must be cooling. They pointed out that, even if Earth had been red-hot when formed, it would have cooled to its present temperature in a few tens of millions of years. They also held that as Earth cooled, contraction wrinkled its surface like the skin of a drying apple, the wrinkles being the mountain belts. In 1896, the discovery of radioactivity led to the realization that radioactive elements are widespread in rocks and could provide an internal heat source. The discovery also led to ways of determining Earth's age at about 4.6 billion years.

Continental Drift

In 1910, American geologist Frank B. Taylor suggested that movements of the continents gave rise to Earth's great mountain belts. In 1912, Alfred Wegener, a German meteorologist, proposed that all continents were merged into a single supercontinent called Pangea, which about 200 million years ago broke apart. Since then the continents have been moving separately through the ocean floors like ships. This theory became known as continental drift. At a major conference in 1926, most authorities rejected Wegener's ideas largely because there was no mechanism known that would allow continents to move through ocean floors. A few supporters held out in areas where evidence for drift was strongest, such as the Alps and South Africa. In the latter, Alexander L. du Toit proposed that Pangea had broken into Gondwanaland in the south and Laurasia in the north before fragmenting into existing continents.

Seismology and Earth's Interior

Nothing has done more to increase our understanding of Earth as a planet than the study of earthquakes, called seismology ( see Geology). Earthquakes were a familiar but little understood phenomenon until, in the late 19th century, the emperor of Japan invited John Milne from England to study them. Milne and his contemporaries produced the first modern seismographs, the first worldwide network for reporting earthquakes and a theory to explain earthquake waves. The improved seismographs enabled the French Rothés, father and son, as well as the Americans Beno Gutenberg and Charles F. Richter, to show that most earthquakes follow the principal mountains and island areas around the Pacific Ocean and the Himalayan and Alpine ranges across Eurasia.

Because the velocities of seismic waves depend on rock and mineral compositions and on changes caused by increasing temperature and pressure with depth, seismology also revealed the nature of Earth's internal structure, which can be visualized as a soft-boiled egg: the shell is a cool, brittle crust of visible rocks, beneath this is a white, thicker mantle of denser rocks, and beneath this the "yolk," i.e. a core rich in liquid iron.

The existence of a readily deformable layer at a depth of a few tens of kilometres beneath the surface is well illustrated by the depression of north-central North America beneath the load of glaciers during the recent ice ages and the uplift of the land since the ice sheets melted ( see Glaciation). The uplift has left beaches raised by hundreds of metres around the shores of the Great Lakes and Hudson Bay.

Recognition that material could move laterally out from beneath the load of ice, much as water is displaced by a boat, and return when the load was removed, led to a second set of terms for Earth's outer rock layers based on rock strength. The relatively cool, stiff and mechanically strong outermost rocky layer, which includes the crust and uppermost parts of the mantle, is the lithosphere (rock sphere). In thickness it varies from over 200 km beneath the old, cold parts of continents, such as the Canadian Shield, to a few kilometres below parts of the ocean floors. Gradationally below this is the asthenosphere (weak sphere), the mechanically weak, ductile layer mostly in the upper mantle that can flow at rates of a few centimetres per year.

Ocean Floors

The collection of information about the deep ocean floors began in the mid-19th century, when Commodore Matthew F. Maury, US Navy, made soundings across the Atlantic Ocean. These soundings revealed that the central part is shallower than the rest. The Challenger Expedition (1872-76) showed this shallower region was part of a great ridge, called the Mid-Atlantic Ridge, which lay along the axis of the ocean. Later expeditions found ridges in other oceans and located deep trenches off the continental coasts and the convex sides of arcuate volcanic island chains around the Pacific Ocean.

Enough was known, even in 1910, for American geologist Frank Taylor to propose that the Mid-Atlantic Ridge was a rift with the crust moving away from it on both sides. In the 1920s, Canadian geologist Reginald A. Daly speculated that the mountain chains of the western Americas were caused by the sliding of the continental masses towards the Pacific, with the Atlantic opening behind. In England, Arthur Holmes in 1931 suggested that radioactive heating caused convection currents within Earth's mantle that rose beneath the ocean floor, spread out in opposite directions and eventually descended at the trenches. Unfortunately, until instruments were developed to permit detailed measurements, little firm evidence was available to permit general acceptance of these ideas.

This changed, starting with echo sounders in the 1930s and towed magnetometers used to detect submarines during the Second World War, which allowed ocean floors to be mapped in detail by remote sensing. In 1956, Maurice Ewing and Bruce Heezen of Columbia University noticed that some earthquakes coincided with the crests of known oceanic ridges. By 1960, they had established the existence of Earth's longest mountain chain, winding its way for 60,000 km down the axis of the Atlantic Ocean, around South Africa to the middle of the Indian Ocean. One branch follows the Gulf of Aden northward into the Red Sea and another passes south of Australia and New Zealand to cross the Pacific and join the San Andreas Fault at the head of the Gulf of California. The ridge rises to form islands such as Iceland, the Azores and Easter Island.

Great Faults and Fracture Zones

Californian oceanographers observed that the crests of oceanic ridges were intersected at intervals and offset by as much as hundreds of kilometres on great fracture zones that resembled faults, but appeared to end abruptly at continents. These submarine features added fuel to arguments about observed amounts of offset on huge faults recognized on land, such as that recognized in 1936 by Canadian Clifford H. Stockwell near Great Slave Lake.

In 1946, geologists in Scotland and New Zealand proposed that huge faults with lateral offsets of over 100 km crossed those countries, beginning and ending in the sea. In 1953, California geologists showed that rocks on either side of the San Andreas Fault, which began in the Gulf of California and ended in the Pacific off Cape Mendocino, were offset from one another by 560 km. These discoveries posed a problem for believers in a rigid Earth, because they could not explain such large offsets or how such large faults could be terminated.

Rock Magnetism

Earth's magnetic poles coincide approximately with the geographic poles of rotation that locate the axis upon which Earth spins. Early in the 20th century it was demonstrated that many rocks acquired a weak magnetization at the time they formed, a force they retain permanently. It is believed that the Earth's magnetic field imparts this magnetization.

Because the inclination of the magnetic field varies systematically from steep at high latitudes to shallow at low latitudes, measurement of the magnetic direction within a rock potentially can locate the position of the magnetic pole at the time the rock formed.

In 1954, British geophysicist Keith Runcorn found that pole positions obtained from rocks of different age plotted at different locations along what became known as a polar-wandering curve. Further work showed that polar-wandering curves from other continents were different from one another, but if the positions of the continents were restored to something like those suggested by Wegener, the curves came together. Their discovery provided quantitative evidence for continental drift and inaugurated a gradual change of opinion, which, over the next two decades, led most Earth scientists to accept continental drift, although a mechanism for moving continents still had to be found.

Early studies showed that some rocks were magnetized in a reverse direction from the present magnetic field, and in the 1920s Japanese geophysicist Motonori Matuyama recognized that reversals were of different ages: periodically, the north magnetic pole becomes the south magnetic pole and vice versa. Reversal ages are now well known and occur at irregular intervals from a few thousand to millions of years, with about 200 happening in the last 100 million years. In 1961, American Arthur Raff and Englishman Ronald Mason published a map of the ocean floor off the west coast of North America between latitudes 52º and 40º. The map featured orderly patterns of stripes of higher magnetic intensity alternating with ones of low intensity, and the symmetry of stripes on opposite sides of a ridge that was segmented and offset by transverse fracture zones. This map was seminal in formulation of plate tectonic theory.

Overview of Plate Tectonics

The essential difference between the theories of plate tectonics and continental drift is that the latter assumed continents moved through the ocean floors. According to plate tectonics, both continents and ocean floors are integral parts of the "cracked egg-shell" of rigid but mobile lithospheric plates that overlie the ductile asthenosphere. Knowledge about the nature of the ocean floors - which occupy over 60 per cent of Earth's surface - was the major contributor to the theory. Plates have three kinds of boundaries: divergent plate, transform fault and convergent plate.

Divergent Plate Boundaries

Spreading ridges, or divergent plate boundaries, are places where plates move apart and grow by addition of basalt from the mantle. In 1960, American Harry H. Hess elaborated on Holmes's idea of mantle convection cells. He suggested that the ascending arm of a convection cell rises beneath the ridge in the eastern Pacific Ocean and splits the ridge apart, allowing basaltic lava to extrude and solidify to form new ocean floor. The ocean floors on either side of the ridge move away to eventually sink at the deep ocean trenches and disappear into the mantle beneath the mountain belts and island arcs bordering the Pacific.

In 1963, Canadians Lawrence W. Morley and Andre Larochelle first showed that long lines of magnetic anomalies form parallel stripes situated symmetrically along both sides of the crest of the Mid-Atlantic Ridge, and realized that the stripes were caused by reversals in Earth's magnetic field. Their ideas seemed so strange that two reputable journals rejected their paper. However, later that year, Fred Vine and Drummond H. Matthews in Britain published similar observations from the Indian Ocean, which they also interpreted as the result of reversals in Earth's field. As basaltic lava extrudes along the rift at the ridge crest and solidifies, it "freezes in" the direction of the ambient magnetic field. Therefore spreading is recorded by the "bar code" of normal and reversed magnetic anomalies on the ocean floor. This result was quickly accepted with ocean floor mapping supplemented in 1968 by the US's Deep Sea Drilling Program, which collected rock samples from the ocean floor for analysis and isotopic dating. The oldest ocean floor is a little less than 200 million years old and located near the Mariana Islands in the western Pacific Ocean.

Transform Fault Boundaries

The second type of plate boundary occurs where plates slide past one another along transform faults. A plot of earthquake locations superimposed on the sea-floor map off the North American Pacific coast, noted earlier, showed that the southern tip of the spreading ridge that lay offshore between northernmost California and southwest British Columbia is connected via the San Andreas Fault to the main Pacific spreading ridge off Central America. Hence, the spreading of the ridge system evidently controls lateral movement on the connecting fault.

The connection of one spreading ridge to another via an active fault led John Tuzo Wilson in 1965 to recognize that this was a special kind of fault he called a transform fault because it transforms one kind of plate boundary into another. It explains the origin of the great fracture zones that cross ocean floors. For example, in the Atlantic the mid-ocean ridge does not follow the same curved shape as the coasts of Brazil and Africa, but is broken into a series of short segments, each fairly straight and each end of which is offset by a fracture zone that ends abruptly at the continents. The spreading ridges form at right angles to the direction of separation of the continents and are broken and offset from one another at intervals by fracture zones that form parallel to the motion of the continents. Only those parts of the fracture zone that connect the spreading ridges are active and generate earthquakes. Their inactive continuations, between ridge and continent, record earlier spreading back to initial separation of the continents. The segmentation of the oceanic crust along spreading ridges and transform faults reflect accommodation of the blocks of growing oceanic floor to the spherical surface of Earth as the Americas rotated away from Africa and Eurasia.

Convergent Plate Boundaries

Third, convergent plate boundaries are where plates come together and one plate dives beneath another along a subduction zone to disappear into the mantle. Before the Second World War, Kiyoo Wadati in Japan and Hugo Benioff in California located the positions of earthquake sources, or foci, beneath the chains of volcanic islands in the western Pacific Ocean and the mountains bordering the eastern Pacific. The foci define surfaces that extend downward from the oceanic trenches to depths of as much as 700 km, and dip away from the ocean at angles ranging from about 65º in the western Pacific to 30º below the mountains. The earthquakes apparently were generated by movement on gigantic reverse faults as the Pacific Ocean floor was overridden by surrounding regions.

Ocean floor mapping shows that over the last 90 million years an average of 3.4 km2 per year has been added to Earth's surface area at spreading ridges. Because Earth evidently is not swelling like an inflating balloon, the enormous volume of new lithosphere generated must be balanced by the return of a comparable amount to the mantle. As ocean floors move away from spreading ridges at rates of between mostly three and 10 cm per year they cool by conduction at the rock-water interface. As they cool, they gradually become denser and subside so that ocean floors can be thought of as the top surfaces of giant convection cells. Eventually the oceanic lithosphere becomes so dense that it sinks at the oceanic trenches into the mantle along subduction zones. These are the descending limbs of the convection cells, located by the reverse faults recognized by Wadati and Benioff.

Because of convective circulation, ocean floors are constantly being renewed. As continental rocks are less dense and more buoyant than those of ocean floors, the continents are not readily subducted but instead are moved around Earth's surface on constantly growing and disappearing oceanic conveyer belts, like scum in a pot of boiling dirty water. This provides explanations for "continental drift" and why continents contain many rocks up to 2.5 billion years old and even a few nearly 4 billion years old, whereas no ocean floors are older than 200 million years.

As the ocean floor starts to subduct, in places material is scraped off and accreted to the overriding plate to form distinctive bodies of disrupted ocean floor rocks, which underlie much of New Zealand, parts of Japan, California and southern Alaska. Elsewhere, the base of the overriding plate may be thinned by a process called subduction erosion. As ocean floor rocks continue to sink along subduction zones to depths of about 100 to 250 km, they release superheated water, which rises and lowers the melting point of rocks in the overlying lithosphere. Molten rocks that reach the surface form the chains of volcanoes around the Pacific Ocean that give rise to the name Ring of Fire, while those that cool and solidify in the crust form great bodies of granitic rock such as those in the Coast Mountains of British Columbia. The rising heat also thins and weakens the lithosphere, so that under lateral compression it can be deformed and thickened to build mountain chains like the Andes and Cordillera. The depth to which subducting rocks sink is debated. Some suggest that it is only to the 700 km depth recorded by earthquakes. Others use a technique called seismic tomography, based on the fact that the rates of seismic wave transmission are faster in the cooler subducting slab than the enclosing hot mantle. Seismic tomographic images show plates descending to near the core-mantle boundary; ocean floor rocks that 100 million years ago were disappearing beneath western North America now lie 2,800 km below the eastern seaboard of the continent.

When the former Tethys Ocean that once lay between the Indian and Eurasian continents closed over 40 million years ago by subduction beneath what is now Tibet, collision between the buoyant continents piled up the Himalayas and raised the Tibetan Plateau. How then did the North American Cordillera and the Andes form when there were no continental collisions, merely the Americas overriding Pacific Ocean lithosphere? In places, fragments of mainly former volcanic island chains are embedded in the mountains, but none are large enough to have raised continental-scale mountain belts. Mountain building was initiated when the Atlantic Ocean started to open, and it seems that the westward drive of the Americas was so rapid that Pacific lithosphere could not subduct fast enough to get out of the way, and so the continent in effect collided with the ocean floor, much as suggested by some early "continental drifters." This is happening today, where the Pacific Plate dives northward beneath Alaska and raises the highest mountains in North America.

Rifting

In 1930, German geologist Hans Cloos drew attention to the association of faults, earthquakes and volcanoes along the Rhine and East African rift valleys. Volcanism and upward doming are greatest at triple points, places where three plates meet. For example, the Ethiopian highlands are where the Red Sea, Gulf of Aden and East African Rift valley come together. They are linked by the Red Sea, which has opened in the last 10 million years to the mountains of Sinai where the north end of the Red Sea and gulfs of Suez and Aqaba meet. This relationship suggests that oceans start to form where rifts connect a series of volcanic centres and that the rifts spread to form widening oceans. When this happens a fourth type of boundary is created within a plate along the boundary between high-standing continent and low-standing ocean floor. Here great thicknesses of sediment eroded from the continent are deposited on the adjacent ocean floor. Today, such deposits lie off the eastern seaboard of North America, where rifting that started some 200 million years ago led to opening of the North Atlantic Ocean. An ancient example of such a boundary, formed between about 500 and 200 million years ago, is preserved in the Canadian Rocky Mountains.

Hot Spots

Hot spots form above cylindrical columns with mushroom-shaped heads called mantle plumes that rise beneath oceans and continents by convection originating from deep within the mantle. Some, like Hawaii or Yellowstone, are isolated within plates; others, like Iceland and Tristan da Cunha, lie along mid-ocean ridges. At surface, hot spots are marked by extrusion of voluminous amounts of lava, and associated with trails of extinct volcanic islands or lava fields. These become progressively older away from the active hot spot and form as the lithosphere moves across the head of the mantle plume. A single trail extends north north-westward for over 30º of latitude from Hawaii and formed as the Pacific Plate moved in that direction over the plume. A double trail forms the Walvis and Rio Grande ridges in the South Atlantic Ocean, which extend from the Tristan da Cunha islands above the present plume head to the coasts of Africa and South America, where volcanic rocks 130 million years old mark the ends of the trails. This relationship supports the view that 130 million years ago a hot spot formed beneath Gondwana and, linked by rift valleys to other hot spots, eventually determined the location of the Atlantic Ocean.

Present System of Plates

Earth's surface is broken into seven major plates and many smaller ones. The Pacific Plate, the largest, consists entirely of oceanic lithosphere with the exception of Baja California in Mexico and southwestern California, whereas the African, Antarctic, Eurasian, Indian and North and South American plates contain both continental and oceanic lithosphere.

The pattern is slowly, but ceaselessly, changing. Most changes are gradual, but occasional plate reorganizations take place. One may be happening today within the Indian Ocean in reaction to the 40 million year long collision between India and Tibet, and another in the geologically-rapid changing geography of southeastern Asia, where the continent of Australia, part of the Indian Plate, drives northward into the Indonesian complex of volcanic islands, continental fragments and small ocean basins. No parts of the Atlantic or Indian oceans are more than 180 million years old; the Red Sea and Gulf of Aden are about 10 million years old; the East African Rift valleys are younger still and are only beginning to open. Even though the Pacific Ocean is spreading at a rate three times that of the Atlantic, it is diminishing in area as it is being overridden by surrounding plates.

Earlier Cycles of Ocean and Mountain Building

The present oceans, with the exception of the Pacific, mark only the last part of a cycle that began when the supercontinent Pangea broke apart 200 million years ago. The ancestor of the Pacific was the "superocean" called Panthalassa, which occupied over half Earth's surface when Pangea existed. If the two sides of the North Atlantic are reassembled, it is clear that the Scandinavian, Scottish, Appalachian and Moroccan mountains once formed a single chain in the heart of Pangea. This chain was created when former oceans closed, only to open later, roughly in the same place, to form the present Atlantic.

About 1,000 years ago, all continents were assembled into a supercontinent called Rodinia, which fragmented some 700 million years ago into continents that then recombined about 300 million years ago into Pangea. The cyclic opening and closing of ocean basins has been called the Wilson Cycle by Kevin Burke and William Kidd. The linear patterns and associations of rocks characteristic of those formed during plate tectonic processes are different in the Archean, before about 2.5 billion years ago, indicating that tectonic processes operating then were different.

Consequences of Plate Tectonic Activity

Aspects of plate tectonics of direct concern are earthquakes, tsunamis and volcanoes, most of which are generated at plate boundaries. Earthquakes happen all the time, but the largest are generated where plates come together. Friction causes converging plates to stick; stress accumulates over periods that may amount to hundreds of years until the stored energy is suddenly released in a major earthquake. There is evidence for a succession of big earthquakes just offshore between northern California and northern Vancouver Island, where the small Juan de Fuca Plate is being overridden by the big North American Plate. The last major earthquake was in 1700, and one is predicted to occur in the next 50 years. Such earthquakes may cause the seabed and coast to suddenly subside or rise and the displaced seawater to generate tsunamis. The type of volcanic activity that often accompanies plate convergence may be explosive and destructive, as in the 1980 eruption of Mount St Helens, Oregon.

On the positive side, many kinds of mineral deposits are generated by plate tectonic activity. Hot springs carrying metal sulphides accompany spreading ridges, and when the hot water enters cold seawater, sulphides are precipitated as lead and zinc and sulphide ores around the spring. The chains of volcanic and plutonic rocks above subduction zones host widespread deposits of copper, molybdenum and gold, such as those mined in the Cordillera and Andes. During mountain building, any fluids containing metal sulphides may be squeezed laterally and concentrated in chemically favourable settings. The thick sedimentary deposits formed within plates at continent-ocean boundaries, such as those flanking the Atlantic Ocean, contain accumulations of hydrocarbons.

Collision between continents allows life forms to migrate from one continent to another and, with subsequent continental separation, to evolve independently into different species. The movement of continents causes climates to change and is at least partly responsible for periodic ice ages. In some continental configurations, ocean currents that flow between warm equatorial regions and cool high-latitude regions distribute heat and give rise to equable climates. In other configurations, such as Antarctica, which is almost entirely surrounded by spreading ridges, currents flow around it so the continent loses heat and an ice age results.

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Plate tectonics is the theory proposing that Earth's outer rocky shell is divided into seven major and several smaller rigid plates, and that forces generated by heat losses from the planet's interior constantly move the plates about.

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https://commons.bcit.ca/civil/students/earthquakes/unit1_02.htm
a) This page is mostly about the effect of earthquakes on our world. It talks about what places in Canada get hit harder with earthquakes. Also it brings up the magnitude and volume of major earthquakes that an impact on Canada over the past 150 years.
b) When reading over this article on earthquakes, the important points to look at would be the maps provided with locations of past earthquakes. This can help us understand why different areas experience more earthquakes. We also can connect it back to the location of the plate tectonics.
c) Understanding why earthquakes happen more often in certain areas can help when analyzing our world and it's affect from plate tectonics and how it has helped shape the continents we know day. When studying you may ask yourself how do natural disasters affect movement of our continents?

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Unit1: Earthquakes/The Seismicity of Canada

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In the past, some parts of Canada have experienced more and larger earthquakes than others. Western Canada, and particularly the territory of British Columbia, is considered to be the most seismically prone area of Canada. Boundary between the North American and Pacific tectonic plates occurs along the west coast of the United States, Mexico and Canada.

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5)The ring of fire         http://www.cnn.com/2017/09/08/world/ring-of-fire-explainer/index.html

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5)The ring of fire         http://www.cnn.com/2017/09/08/world/ring-of-fire-explainer/index.html

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a) This page talks about the ring of fire why it is a target point for earthquakes. Most of the important information is not found written in the article but provided in the video linked at the top. It explains how the movement of plates cause over 90% of the worlds earthquakes.
b) The most important points from this article can be found in the video linked at the top and the photos provided. Both these points help sum up the ring of fire to someone who's just starting to learn bout it.
c) This is an important piece of study material because earthquakes have shaped our world in so many ways. Being able to find out why plate tectonics play such a role in the location of earthquakes can help us better understand the placement of these plates and there effects.

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The 40,000-kilometer (25,000-mile) area stretches from the boundary of the Pacific Plate and the smaller plates such as the Philippine Sea plate to the Cocos and Nazca Plates that line the edge of the Pacific Ocean.

About 80% of all earthquakes strike in the Ring of Fire, according to Hongfeng Yang, a seismologist at the Chinese University of Hong Kong.

People are most at risk in Chile, Japan, the US west coast, and other island nations including the Solomon Islands to the western seaboard of North and South Americas.

They are at risk because they lie on subduction zones that are locked so tectonic energy must be released by large earthquakes.

How did the Ring of Fire form?

Tectonic plates are massive slabs of the Earth's crust. These move constantly above the mantle -- a layer of solid and molten rock below the Earth's crust.

The Ring of Fire was formed as oceanic plates slid under continental plates.

Volcanoes along the Ring of Fire are formed when one plate is shoved under another into the mantle -- a solid body of rock between the Earth's crust and the molten iron core -- through a process called subduction.

Large earthquakes -- which risk triggering tsunamis -- also occur in subduction zones.

How are earthquakes triggered?

Earthquakes represent the energy release from the interior of the Earth, where huge amount of heat is stored.

The heat drives the plates to move. When two plates move against one another and produce friction, it causes energy to build up. When the energy is released it triggers an earthquake.

"It takes tens of thousands of years for the energy to build up, but only a matter of seconds for it to be released," said Hongfeng Yang, a seismologists at the Chinese University of Hong Kong.

Tectonic plates usually move an average of a few centimeters each year, but when an earthquake strikes, they can move several meters per second.

Can earthquakes be predicted along the Ring of Fire?

As with Friday's earthquake off the west coast of Mexico, seismologists can't yet predict when or where earthquakes will strike, or how large they will be.

Some researchers argue that there are certain conditions -- such as hydraulic fracturing when we drill deep into the sea to extract energy resources -- induce earthquakes. But there's no hard scientific evidence to back this up.

Correction: A previous version of a map above incorrectly identified the location of the Ring of Fire. It has been corrected.

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The 40,000-kilometer (25,000-mile) area stretches from the boundary of the Pacific Plate and the smaller plates such as the Philippine Sea plate to the Cocos and Nazca Plates that line the edge of the Pacific Ocean. About 80% of all earthquakes strike in the Ring of Fire, according to Hongfeng Yang, a seismologist at the Chinese University of Hong Kong.

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https://www.universetoday.com/39760/plate-boundaries/
a) This website talks about the 3 main types of plate boundaries. Divergent, Convergent and Transform boundaries.
b) This article is relatively short so almost every paragraph has some type of relative information on the topic. Mainly focus on reading about how the plate boundaries move (direction) and they effect of different boundaries.
c) This is important information to study because often people assume all plates move the same and have the some standards. In this article it explains that there is 3 types of plate boundaries and why it's important to understand the difference between all 3.

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In Plate Tectonic Theory, the lithosphere is broken into tectonic plates, which undergo some large scale motions. The boundary regions between plates are aptly called plate boundaries. Based upon their motions with respect to one another, these plate boundaries are of three kinds: divergent, convergent, and transform.

Divergent Boundaries:

Divergent boundaries are those that move away from one another. When they separate, they form what is known as a rift. As the gap between the two plates widen, the underlying layer may be soft enough for molten lava underneath to push its way upward. This upward push results in the formation of volcanic islands. Molten lava that succeeds in breaking free eventually cools and forms part of the ocean floor.

Some formations due to divergent plate boundaries are the Mid-Atlantic Ridge and the Gakkel Ridge. On land, you have Lake Baikal in Siberia and Lake Tanganyika in East Africa.

Convergent Boundaries:

Convergent boundaries are those that move towards one another. When they collide, subduction usually takes place. That is, the denser plate gets subducted or goes underneath the less dense one. Sometimes, the plate boundaries also experience buckling. Convergent boundaries are responsible for producing the deepest and tallest structures on Earth.

Among those that have formed due to convergent plate boundaries are K2 and Mount Everest, the tallest peaks in the world. They formed when the Indian plate got subducted underneath the Eurasian plate. Another extreme formation due to the convergent boundary is the Mariana Trench, the deepest region on Earth.

Transform Boundaries:

Transform boundaries are those that slide alongside one another. Lest you imagine a slippery, sliding motion, take note that the surfaces involved are exposed to huge amounts of stress and strain and are momentarily held in place. As a result, when the two plates finally succeed in moving with respect to one another, huge amounts of energy are released. This causes earthquakes.

The San Andreas fault in North America is perhaps the most popular transform boundary. Transform boundary is also known as transform fault or conservative plate boundary.

Movements of the plates are usually just a few centimeters per year. However, due to the huge masses and forces involved, they typically result in earthquakes and volcanic eruptions. If the interactions between plate boundaries involve only a few centimeters per year, you could just imagine the great expanse of time it had to take before the land formations we see today came into being.

You can read more about plate boundaries here in Universe Today. Here are the links:

Here are the links of two more articles from USGS:

Here are two episodes at Astronomy Cast that you might want to check out as well:

Sources:
Plate Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html

boundaries, convergent, divergent boundaries, plate boundaries transform, plate tectonics

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What are Plate Boundaries? - Universe Today

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In Plate Tectonic Theory, the lithosphere is broken into tectonic plates, which undergo some large scale motions. The boundary regions between plates are aptly called plate boundaries. Based upon their motions with respect to one another, these plate boundaries are of three kinds: divergent, convergent, and transform.

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a) This article talks about the contribution made to the plate tectonic theory by  J. Tuzo Wilson.
b) Paragraph 1 is probably the most key point to this article. It sums up J. Tuzo Wilson's discovery and why he believed certain areas formed due to the movement of a plate over a stationary "hotspot" in the mantle.
c) Knowing about J. Tuzo Wilson's contribution to the plate tectonics can help better understand the modern version of the theory. He provides more proof to his theory and helps further expand the theory first developed by Alfred Wegener.

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J. Tuzo Wilson [This Dynamic Earth, USGS]

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Canadian geophysicist J. Tuzo Wilson was also pivotal in advancing the plate-tectonics theory. Intrigued by Wegener's notion of a mobile Earth and influenced by Harry Hess' exciting ideas, Wilson was eager to convert others to the revolution brewing in the earth sciences in the early 1960s.

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https://www.livescience.com/37706-what-is-plate-tectonics.html
by Becky Oskin, March 21, 2016
http://www.ucmp.berkeley.edu/geology/techist.html
by Anne Weil, August 22, 1992
http://www.thecanadianencyclopedia.ca/en/article/plate-tectonics/
by J.W.H. MONGER, J. TUZO WILSON, May 2,
https://commons.bcit.ca/civil/students/earthquakes/unit1_02.htm
by BCIT
http://www.cnn.com/2017/09/08/world/ring-of-fire-explainer/index.html
by Emiko Jozuka, September 20, 2017
https://www.universetoday.com/39760/plate-boundaries/
by John Carl Villanueva, 2009
http://pubs.usgs.gov/gip/dynamic/Wilson.html
by USGS
https://www.nationalgeographic.com/environment/natural-disasters/volcanoes/
by National Geographic

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1)Q: What is plate tectonics?
A: Plate tectonics is basically a theory that explains the structure of the earth's crust and how plates below the earths surface move and shape the world we know today.
2) Q: What is the history of the theory of Plate Tectonics?
A: The history of plate tectonics starts with a man named Alfred Wegener who first analyzed the movement of the plates. Over time discovered more and more proof of the movement of plates and created the base of what we know today as "the modern theory of plate tectonics'
3) Q: What can we learn about our world by studying plate tectonics?
A: We can learn about why our continents are shaped the way they are, causes of earthquakes and other natural disasters, how to plan for disasters before they happen based on plate movement, etc.

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a) This website talks about how volcanoes occur and how they are made.
b) Focus on the parish titled "how volcanos are made". this paragraph talks about the build up underground and the effects volcanoes can have on people. Also watch the video provided at the top. It helps explain why the movement of plates below the surface have an effect on why volcanoes occur.
c) Knowing why volcanoes occur is important because it shows us another effect of the movement of tectonic plates. It can help us when studying the different types of plates and there effects.

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Volcanoes are Earth's geologic architects. They've created more than 80 percent of our planet's surface, laying the foundation that has allowed life to thrive. Their explosive force crafts mountains as well as craters. Lava rivers spread into bleak landscapes. But as time ticks by, the elements break down these volcanic rocks, liberating nutrients from their stony prisons and creating remarkably fertile soils that have allowed civilizations to flourish.

There are volcanoes on every continent, even Antarctica. Some 1,500 volcanoes are still considered potentially active around the world today; 161 of those-over 10 percent-sit within the boundaries of the United States.

But each volcano is different. Some burst to life in explosive eruptions, like the 1991 eruption of Mount Pinatubo, and others burp rivers of lava in what's known as an effusive eruption, like the 2018 activity of Hawaii's Kilauea volcano. These differences are all thanks to the chemistry driving the molten activity. Effusive eruptions are more common when the magma is less viscous, or runny, which allows gas to escape and the magma to flow down the volcano's slopes. Explosive eruptions, however, happen when viscous molten rock traps the gasses, building pressure until it violently breaks free.

How do volcanoes form?

The majority of volcanoes in the world form along the boundaries of Earth's tectonic plates-massive expanses of our planet's lithosphere that continually shift, bumping into one another. When tectonic plates collide, one often plunges deep below the other in what's known as a subduction zone.

As the descending landmass sinks deep into the Earth, temperatures and pressures climb, releasing water from the rocks. The water slightly reduces the melting point of the overlying rock, forming magma that can work its way to the surface-the spark of life to reawaken a slumbering volcano.

Not all volcanoes are related to subduction, however. Another way volcanoes can form is what's known as hotspot volcanism. In this situation, a zone of magmatic activity-or a hotspot-in the middle of a tectonic plate can push up through the crust to form a volcano. Although the hotspot itself is thought to be largely stationary, the tectonic plates continue their slow march, building a line of volcanoes or islands on the surface. This mechanism is thought to be behind the Hawaii volcanic chain.

Where are all these volcanoes?

Some 75 percent of the world's active volcanoes are positioned around the ring of fire, a 25,000-mile long, horseshoe-shaped zone that stretches from the southern tip of South America across the West Coast of North America, through the Bering Sea to Japan, and on to New Zealand.

This region is where the edges of the Pacific and Nazca plates butt up against an array of other tectonic plates. Importantly, however, the volcanoes of the ring aren't geologically connected. In other words, a volcanic eruption in Indonesia is not related to one in Alaska, and it could not stir the infamous Yellowstone supervolcano.

What are some of the dangers from a volcano?

Volcanic eruptions pose many dangers aside from lava flows. It's important to heed local authorities' advice during active eruptions and evacuate regions when necessary.

One particular danger is pyroclastic flows, avalanches of hot rocks, ash, and toxic gas that race down slopes at speeds as high as 450 miles an hour. Such an event was responsible for wiping out the people of Pompeii and Herculaneum after Mount Vesuvius erupted in A.D. 79.

Similarly, volcanic mudflows called lahars can be very destructive. These fast-flowing waves of mud and debris can race down a volcano's flanks, burying entire towns.

Ash is another volcanic danger. Unlike the soft, fluffy bits of charred wood left after a campfire, volcanic ash is made of sharp fragments of rocks and volcanic glass each less than two millimeters across. The ash forms as the gasses within rising magma expand, shattering the cooling rocks as they burst from the volcano's mouth. It's not only dangerous to inhale, it's heavy and builds up quickly. Volcanic ash can collapse weak structures, cause power outages, and is a challenge to shovel away post-eruption.

Can we predict volcanic eruptions?

Volcanoes give some warning of pending eruption, making it vital for scientists to closely monitor any volcanoes near large population centers. Warning signs include small earthquakes, swelling or bulging of the volcano's sides, and increased emission of gasses from its vents. None of those signs necessarily mean an eruption is imminent, but they can help scientists evaluate the state of the volcano when magma is building.

However, it's impossible to say exactly when, or even if, any given volcano will erupt. Volcanoes don't run on a timetable like a train. This means it's impossible for one to be "overdue" for eruption -no matter what news headlines say.

What is the largest eruption in history?

The deadliest eruption in recorded history was the 1815 explosion of Mount Tabora in Indonesia. The blast was one of the most powerful ever documented and created a caldera -essentially a crater-4 miles across and more than 3,600 feet deep. A superheated plume of hot ash and gas shot 28 miles into the sky, producing numerous pyroclastic flows when it collapsed.

The eruption and its immediate dangers killed around 10,000 people. But that wasn't its only impact. The volcanic ash and gas injected into the atmosphere obscured the sun and increased the reflectivity of Earth, cooling its surface and causing what's known as the year without a summer. Starvation and disease during this time killed some 82,000 more people, and the gloomy conditions are often credited as the inspiration for gothic horror tales, such as Mary Shelley's Frankenstein.

Although there have been several big eruptions in recorded history, volcanic eruptions today are no more frequent than there were a decade or even a century ago. At least a dozen volcanoes erupt on any given day. As monitoring capacity for-and interest in-volcanic eruptions increases, coverage of the activity more frequently appears in the news and on social media. As Erik Klemetti, associate professor of geosciences at Denison University, writes in The Washington Post: "The world is not more volcanically active, we're just more volcanically aware."

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Volcanoes are Earth's geologic architects. They've created more than 80 percent of our planet's surface, laying the foundation that has allowed life to thrive. Their explosive force crafts mountains as well as craters. Lava rivers spread into bleak landscapes.

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Movement of continents over millions of years 

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Movement of continents over millions of years 

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Magnitude of earthquakes in Canada over past 150 years 

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Magnitude of earthquakes in Canada over past 150 years 