One Plate Of Ocean Crust example essay topic

In the early 1960's, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes. We now know that, directly or indirectly, plate tectonics influences nearly all geologic processes, past and present. Indeed, the notion that the entire Earth's surface is continually shifting has profoundly changed the way we view our world. In geologic terms, a plate is a large, rigid slab of solid rock. The word tectonics comes from the Greek root "to build".

Putting these two words together, we get the term plate tectonics, which refers to how the Earth's surface is built of plates. The theory of plate tectonics states that the Earth's outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. Before the advent of plate tectonics, however, some people already believed that the present-day continents were the fragmented pieces of preexisting larger mandamuses ("supercontinent"). Continental Drift, the theory that continents move slowly about the earth's surface, changing their positions relative to one another and to the poles of the earth.

In the past the theory has been discussed but not generally accepted, most geologists believing the continents to be fixed in place and subject only to vertical movements, such as those observed during mountain uplift. In recent years, however, a sound body of evidence in support of a modified form of the drift theory has been found. Ideas are becoming precise and unified, with emphasis on a moving, evolving ocean floor. The new theory is called plate tectonics. Early Theories Soon after the Atlantic Ocean had been mapped, about three hundred years ago, it was noticed that the opposite coasts had similar shapes, but it was not until the middle of the 19th century that accurate maps were published demonstrating that the two coasts could be fitted together quite closely. Some geologists then suggested that the fit of the coasts was not an accident that the continents were once joined and had subsequently drifted apart.

None of the suggestions were taken seriously. In 1912, however, the German meteorologist Alfred Wegener investigated the fit of the Atlantic coasts more carefully than had his predecessors and grouped all the continents together into one great land mass, which he called Pangaea. He supposed that the mass began to break apart about 200 million years ago. He also showed that some geological features on the opposite coasts could have fitted together, and that there were many striking similarities between the fossil plants and reptiles on the opposite coasts, particularly the coasts of Africa and South America. If the continents were pushed together, the geological, fossil, and other lines of evidence would join together accurately in the way that lines of print on a torn newspaper would join when the paper was reassembled. Wegener also pointed out that ancient climatic zones seemed to have lain in different places from the present zones.

He pointed out that where great ice sheets have melted in recent geological times in Scandinavia and North America, the land is rising as fast as a centimeter a year. This vertical uplift, he said, requires horizontal inflow of matter below and implies that flow and motion do take place within the earth. Wegener's arguments led to heated controversy about continental drift in the 1920's and 1930's. Opponents regarded the idea of continents moving about through solid rock as so preposterous that they ignored all his other arguments, many of which, it is now clear, were essentially correct. Only a few geologists accepted the theory.

Among the first of these was the South African geologist Alex L. Du Toit, who suggested that there had been two ancient continents: the southern continent of Gondwanaland, comprising Antarctica, Australia, the Indian peninsula, Africa, Madagascar, and South America; and the northern continent of Laurasia. Modern Evidence Although Du Toit and the few other advocates of continental drift kept the subject alive, most geologists and geophysicists either ignored or condemned it. However, two new developments changed this situation. One was the study of paleomagnetism, or the magnetism in ancient rocks, carried out from the early 1950's. The other was the discovery, made between 1956 and 1960 by the Americans Maurice Ewing and Bruce C. Herzen, of a continuous mid-ocean ridge, a vast submarine mountain system lying along the middle of the oceans. Related to this system is a line of deep trenches, island arcs, and young mountains, where earthquake activity occurs for example, along the boundaries of the Pacific Ocean.

Certain rocks, when they are formed, are magnetized in the direction of the earth's magnetic field. Examination of this paleomagnetism in rocks of various ages revealed the startling fact that the earth's magnetic field has reversed its direction many times. If a core is drilled through undisturbed rock, one would find that the young rock on top is magnetized in the present normal direction, the older layer underneath is magnetized in the reverse direction, the next layer is again normal, the next layer is again reversed, and so forth. Investigations carried out all over the world show that the earth's magnetic field has reversed direction every few hundred thousand years.

Reversals of the magnetic field have left a particularly fortuitous record on the ocean floors. The mid-ocean ridges are found throughout the oceans of the world, and there is reason to believe that they represent places where molten material from the mantle, a deep region of the earth beneath the solid crust, is rising. As it surfaces, the material heaps up to form the ridge, and it also moves out sideways away from the bridge like a pair of giant conveyor belts. At the ridge the rock being formed from mantle material is magnetized in the direction of the magnetic field, and as it moves away from the ridge it carries with it a record of the direction. When the field reverses, the new rock being formed at the ridge is magnetized in the opposite direction, and as it moves away it too carries a record of the direction, opposite to the direction of the previous region. Therefore, one would expect to find alternating regions of normal and reversed magnetic directions symmetrically disposed on both sides of the ridge.

Indeed, this pattern is found. It provides strong evidence for the main mechanism of continental drift that is, spreading of the sea floor as new material wells up from the mantle. Scientists have also used the magnetism in ancient rocks to support in another way the idea that the continents may once have been closer together. Evidence from rocks of the same age in different continents indicates different ancient positions for the earth's magnetic poles.

However, if one hypothetically pushed these continents together, the direction of magnetism in rocks of the same age points to almost identical positions for ancient poles. Thus, one may postulate that the land masses were once joined. The direction of magnetism was fixed as a permanent record in the rocks as they cooled and solidified. Then the continents drifted apart, with the result that the magnetic directions now indicate different pole positions. Modern Theories In one model of continental drift consistent with modern evidence, a current of mantle material rises under an ancient continent, causing it to break apart. The current then spreads out horizontally and carries the pieces of the continent away from each other.

Between the separating pieces an ocean is opened up. In one instance of this, the pieces are South America and Africa; the ocean opened up between them is the Atlantic. Along the middle of the Atlantic lies the Mid-Atlantic Ridge, which represents the region where the mantle current surfaces, forming new oceanic crust and producing much volcanic activity. The horizontal mantle current eventually meets an opposing current, and they both turn downward into the mantle again at the site of one of the trenches mentioned above. Enormous pressures are produced in this region, for the continental crust and the oceanic crust are moving toward each other. (The continental crust is being carried, so to speak, on the back of the mantle current.

On the other hand, the oceanic crust is believed by some geophysicists to be identical with the mantle current it is simply the solid and somewhat altered top layer of the mantle current.) The descending mantle current tends to drag the crust down with it, forming a deep trench or piling up young mountains. At the same time, the continental crust tends to ride over the oceanic crust, for it is the lighter of the two. The trenches may be filled as the advancing edge of the continental crust is thrust up to form mountains, and numerous earthquakes originate from the plane along which the oceanic crust is forced to slip under the continental crust. The Mid-Atlantic Ridge is part of the worldwide system of mid-ocean ridges. It is interesting to note the striking similarity that exists between the shape of the Mid- Atlantic Ridge and the shape of the coastlines on both sides. Indeed, if one were to push the continents bordering the Atlantic together (reversing the drift that is going on at present), the continents would meet at the Mid-Atlantic Ridge and close up on the ocean that now separates them.

Such a model of continental drift is confirmed by many lines of evidence in addition to those already mentioned. If the ocean f floors are spreading, they will be very young near the mid-ocean ridge and progressively older toward the coasts. Thus, although young sediments and young volcanoes can form anywhere on the ocean floors, older sediments and old volcanic islands should only be found toward the coasts. It has become clear through oceano graphic research that no old islands are located near the mid-ocean ridge, but that as the coasts are approached some progressively older islands are found. It has also been shown that the maximum age of sediments decreases toward the mid-ocean ridges, and that the total thickness of sediments increases from zero over the ridges to a few miles near the continents. Plate Tectonics The essential difference between Wegener's original theory of continental drift and the more modern ideas called plate tectonics is that Wegener believed that each continent was propelled like a ship through the solid ocean floor.

Many geologists thought this impossible. The theory of plate tectonics holds that the entire crust of the earth is broken into six large pieces (plates) and many smaller ones. Any plate may consist, in part, of ocean floor and, in part, of a continent or islands. The boundaries between plates are the mid-ocean ridges, where new oceanic crust is formed and plates move apart; ocean trenches and young mountains, where plates come together and older ocean crust is overridden and returned to the interior; and large faults, such as the San Andrea in California, along which one plate moves horizontally past another. An example of a plate is the Africa plate bounded on the west, south, and east by the mid- ocean Atlantic Ridge, the southern and Indian Oceans, and the Red Sea and, on the north, by the faults and young mountains extending from the Red Sea north along the Jordan Valley to Turkey and by the young alpine mountains of the Mediterranean region extended by submarine faults from Morocco to the Azores. Thus, Africa is carried like a raft embedded in a larger plate, not propelled as an isolated continent.

Although Wegener and Du Toit proposed that the primitive continents began to break up about 200 million years ago, there is much evidence that drift began long before then, and that continental blocks have slowly been moving about the earth's surface throughout much of geological time. It seems that before the continents drifted apart and opened up the Atlantic, they had drifted together and closed up an earlier ocean. Another place where continents seem to have bumped into each other and piled up mountains between them is the Himalayas, which may have been produced when the Indian Peninsula detached itself from Gondwanaland and gradually drifted into Asia. resource Copyright 1996 P.F. Collier, A Division of Newfield Publications, Inc. J. Tubo Wilson, Continental Drift, ., Vol. 7, Colliers Encyclopedia CD-ROM, 02-28-1996. With the theory of plate tectonics, geologists can explain a host of phenomena, from earthquakes to the origin of mountain ranges.

Oddly enough, there is one feature of Earth's surface that the theory, fails to explain@ the size of the crustal plates themselves. The theory predicts that a large number of relatively small plates should cover Earth's surface rather than the few large plates that are observed. Hans-Peter Bunge, a geod y-namic ist at Los Alamos National Laboratory, may have found a way to make theory jibe with observation. The theoretical problem is fairly straightforward: the continental and oceanic plates ride on a 1,800-mile-thick layer of hot, churning mantle rock.

The flowing mantle is driven by heat from Earth's molten core. Like boiling water in a pot, the mantle rock should flow roughly in a circular pattern: as hot rock rises and cool rock sinks, the horizontal extent of the flow should be about the same length as the 1,800-mile depth of the flow. But the horizontal flow - as marked by the boundaries of the tectonic plates at Earths surface - is not 1,800 miles wide but closer to 6,000 miles, on average. Most geologists have assumed that the steely tensile strength of crustal plates might be squashing the mantle flow, making it spread out near Earth's surface. But Bunge has used a supercomputer to create a highly realistic three-dimensional model of mantle flow, and he's shown that it is independent of the plates.

The shape of the flow seems to depend entirely on how friction in the mantle increases with depth. Bunge generated two plate less models of the mantle one of which assumed uniform mantle friction, and another in which mantle friction increased markedly with depth, the result of pressure compressing the rock. Only the latter model duplicated real- world mantle flow even in the absence of surface plates. Because the mantle meets less resistance to its flow near the surface, it spreads out, distorting what would otherwise be the neat, nearly circular flow pattern predicted by theory. To test whether the mantle's squashed pattern might also be caused by the plates themselves, Bunge imposed 6,000-mile-wide extra-strong plates on both models. Again, only the model with increasing friction showed realistic mantle flow.

"We are the first to move the problem away from the plates and back to the mantle", says Bunge. "By making this one assumption, we turn a fairly unrealistic model into a very realistic one". resource COPYRIGHT 1996 Walt Disney Company Vol. 17, Discover Magazine, 12-01-1996, pp 26 (2). SCIENCE'S CENTURY Alfred Wegener understood the Earth better than anyone else of his era. But few other scientists understood him.

Wegener was an astronomer, balloonist, explorer and meteorologist. In his spare time he investigated paleontology, geophysics and geology. The scope of his studies enabled him to deduce that the map of the world was not a timeless portrait, but a still-frame from a moving picture. Continents and oceans were not fixed features of the Earth's surface, Wegener argued. Instead the continents wandered about the globe, closing some oceans while opening new ones. As a child could see at a glance, Africa and South America looked like adjoining pieces of a puzzle.

Wegener put the whole picture together. The new Earth conceived by Wegener was half a century ahead of its time. He published his major work describing continental drift t in 1915; it was the mid-'60's before geologists generally realized that he was, in essence, right. By then Wegener's drift theory, in its modern version known as plate tectonics, had begun to explain many of the Earth's deepest mysteries from how mountains form to why earthquakes cluster in specific seismic regions. And it united the understanding of the history of life with the physics of the Earth. "Plate tectonics has greatly affected the whole of geological development", says Stanford University geophysicist George Thompson.

"Plate tectonics brought us all together. Physics and chemistry, and biology, geology and paleontology, all turned out to be interlinked in ways that we really didn't suspect before plate tectonics". Plate tectonics was not the 20th century's only contribution to the new understanding of the Earth. When the century began, nobody knew how old the Earth was or much about its inner structure.

By the 1950's, though, geologists had established that the Earth was born 4.6 billion years ago and was built in layers an outer crust and an inner mantle surrounding a metallic core. But at mid-century many mysteries remained. The revival of Wegener's idea soon thereafter solved most of them, transforming earth science textbooks into their current form. Wegener, born in Berlin in 1880, earned a degree in astronomy and then lectured on meteorology and participated in a couple of expeditions to Greenland. By 1910, he later wrote, he had begun to suspect that the continents surrounding the Atlantic Ocean had once been joined, and he published that idea in 1912. A more complete account of his theory came in a 1915 book, The Origin of Continents and Oceans, written during a "prolonged sick-leave" caused by a bullet wound to the neck that he suffered as a German military officer in World War I. In that book Wegener alleged that all the Earth's continents had once been joined in a single supercontinent, Pangaea, that split into pieces millions of years ago.

Wegener's book marshaled abundant evidence in favor of what became known as the "drift theory". Certain fossils in South America and Africa showed striking similarities, Wegener observed, and many rock formations seemed to match at various points along the two shorelines. Biologists explained the fossil evidence by supposing that a land bridge had once connected the two continents. But Wegener argued that a sunken land bridge of the needed size would have raised the Earth's ocean levels above all the continents.

Furthermore, he said, such a large land mass couldn't sink to begin with. The notion of a permanent fixed map of the world's continents must therefore be wrong, Wegener asserted. "The continents must have shifted", he wrote. "South America must have lain alongside Africa and formed a unified block which was split in two in the Cretaceous; the two parts must then have become increasingly separated over a period of millions of years like pieces of a cracked ice floe in water". Wegener's theory also addressed the mystery of mountain building. A century ago, geologists thought that mountain ranges were wrinkles formed as a hot Earth cooled and shrank.

The American geologist Joseph Le Conte, in a 1900 article in Appleton's Popular Scientific Monthly, noted that the main problem in understanding mountain building was establishing the cause of sideways pressure. "The most obvious and as yet the most probable view is that it is the result of the secular contraction of the earth which has gone on throughout the whole history, and is still going on", Le Conte wrote. Or as Wegener himself described it, "Just as a dying apple acquires surface wrinkles by loss of internal water, the earth is supposed to form mountains by surface folding as it cools and therefore shrinks internally". But the "contraction" theory assumed that the Earth is always cooling, whereas the Earth actually has a constant source of internal heat from radioactive elements (discovered only recently), Wegener pointed out.

Even before Wegener, others had raised objections to the shrinkage theory of mountain building. Le Conte contended that many of the objections had been answered. "But the complete answer to others must be left to the next century", he presciently wrote. That complete answer came in the form of plate tectonics: The force forming mountains comes from the collision between massive plates segments of the Earth's rocky outer layer.

In the current picture, that outer layer is known as the lithosphere; its plates glide over a plastic like inner layer called the asthenosphere. Some of the plates carry continents; some are mostly ocean. The boundaries where plates come together are the scene of violent geological activity, such as volcanoes and earthquakes. A typical plate boundary is the mid-Atlantic ridge, an undersea mountain range that pokes above the water as Iceland. At the crack between plates, magma from the Earth's depths rises into the water and cools, generating new ocean floor and driving the plates apart in the process.

Thus the Atlantic (and Iceland) is widening, at a rate of 2 centimeters per year. At other plate boundaries, such as the deep trenches of the western Pacific, one plate of ocean crust dives under another into the Earth, where it melts and then rises to fuel volcanic activity. Mountain ranges typically rise where plates smash together. This plate tectonic picture came together in the '60's; the secret to that success was a message written in the ocean floor by magnetic rocks. At mid-ocean ridges, magma flowing from the Earth's interior cools to form new ocean floor.

Magnetic particles in the magma are locked into place as the rock solidifies, pointing in the direction of the Earth's magnetic field, like a compass needle. Measurements of such magnetism revealed a strange pattern: The ocean floor was "painted" by magnetic stripes. A strip of ocean floor containing magnetic particles pointing in one direction adjoined a strip with particles pointing in the opposite direction. It was as if a compass needle pointed south instead of north. Other research showed that the Earth's magnetic filed has a habit of flipping from north-pointing to south-pointing every half million years or so. The stripes on the ocean floor revealed the timing of its creation.

New sea floor spread outward from the ridges; magnetic particles lined up depending on the direction of the Earth's magnetic field when they cooled. The key scientific paper linking the magnetic stripe pattern to the timing of the sea floor spreading came in 1963 by geoscientists Drummond Matthews and Fred Vine of Cambridge University in England. (Lawrence Morley of the Geological Survey of Canada had proposed a similar connection, but his paper was rejected.) "That was an enormous breakthrough", says Stanford's Thompson. By 1966, new evidence on magnetic reversals confirmed the Matthews-Vine idea.

Since then many details have been worked out about how plate tectonics rules the globe, with numerous modifications and complications but in essence confirming the general picture. "This was such a revolutionary, simple explanation that there are still people who don't accept it", says Thompson. But the vast majority of experts now agree that Wegener has been vindicated, decades after his death in 1930 during another Greenland expedition. Fortunately, Wegener's idea didn't die with him. Thompson remembers attending seminars as a graduate student in the '40's where drift theory was often discussed. "People would examine the evidence that existed at that time in considerable detail, and people argued on both sides", Thompson recalls.

"But there wasn't anything that would attract a graduate student to get busy and study it further, because there were no tools, no means to get at it quantitatively. "We recognized that Wegener had something, and that it was a possibility, but we didn't understand the mechanism. And there was no way to test the hypotheses... as to how it might work". But the magnetic stripes provided something that could be studied, once the technology existed to measure sea floor magnetism.

What was obvious to Wegener finally found a way into the mainstream scientific system. And today it's obvious to nearly everybody. "Students now accept continental drift", Thompson said. "And they look at us and say, How could you be so stupid not to have recognized this?" resource (c) 1999 The Dallas Morning News.

All Rights Reserved Tom Siegfried / Science Editor of The Dallas Morning News, A GOOD FIT: View of continents in motion pulled Earth puzzle together., The Dallas Morning News, 03-15-1999, pp 7 D. Continental drift is a geological theory which proposes that the relative positions of the continents on the earth's surface have changed considerably through geologic time. Though first proposed by American geologist Frank Burnley Taylor in a lecture in 1908, the first detailed theory of continental drift was put forth by German meteorologist and geophysicist Alfred Wegener in 1912. On the basis of geology, biology, climatology, and the alignment of the continental shelf rather than the coastline, he believed that during the late Paleozoic and early Mesozoic eras, about 275 to 175 million years ago, all the continents were united into a vast supercontinent, which he called Pangaea. Later, Pangaea broke into two supercontinent al masses -- Laurasia to the north, and Gondwanaland to the south.

The present continents began to split apart in the latter Mesozoic era about 100 million years ago, drifting to their present positions. As additional evidence he cited the unusual presence of coal deposits in South Polar regions, glacial features in present-day equatorial regions, and the jigsaw fit of the opposing Atlantic continental shelves. He also pointed out that a plastic, fluid layer in the earth's interior must exist to accommodate vertical adjustments caused by the creation of new mountains and by the wearing down of old mountains by erosion. He postulated that the earth's rotation caused horizontal adjustment of rock in this plastic layer, which caused the continents to drift. The frictional drag along the leading edges of the drifting continents results in mountain building. Wegener's theory stirred considerable controversy during the 1920's.

South African geologist A.L. Du toit, in 1921, strengthened the argument by adding more exacting details that correlated geological and paleontological similarities on both sides of the Atlantic. In 1928, Scottish geologist Arthur Holmes suggested that thermal convection in the mantle was the mechanism that drove the continental movements. American geologist David Griggs performed scale model experiments to show the mantle movements. The theory of continental drift was not generally accepted, particularly by American geologists, until the 1950's and 60's, when a group of British geophysicists reported on magnetic studies of rocks from many places and from each major division of geologic time. They found that for each continent, the magnetic pole had apparently changed position through geologic time, forming a smooth curve, or pole path, particular to that continent.

The pole paths for Europe and North America could be made to coincide by bringing the continents together. resource Copyright (c) 1993, Columbia University Press. Licensed from Ler nout & Haus pie Speech Products USA, Inc. All rights reserved. continental drift., The Columbia Encyclopedia, Fifth Edition, 01-01-1993 Continents on the Move Earth Explorer Continents on the Move A time-lapse movie of earth's history compressed into a few minutes would show continents smashing into each other and mountains being pushed up on some parts of earth, while other continents just slide past each other. A few continents would rip apart, and vast oceans would rush in to fill the gap. According to the theory of plate tectonics, the earth's surface has been shaped and molded in this way over millions of years. The earth's crust is not just one unbroken covering, but a series of continually moving slabs (called plates) consisting of land or ocean floor.

As the plates move, their edges can ram into each other, causing spectacular volcanoes and earthquakes. The plates float on the earth's mantle, a hotter and more fluid layer of rock. Below the mantle is earth's hottest part -- the dense core. As the earth's core heats the bottom of the mantle, columns of hot rock rise slowly to the top.

At the same time, columns of cooler, denser (and heavier) rock at the top gradually sink to the bottom at another part of the mantle. This movement produces circular currents that carry the floating plates -- as a conveyor belt in a supermarket carries food. Plates move very slowly, generally creeping along at a rate of up to 5 centimeters (2 in) a year. That's about as fast as your fingernails grow.

Plates are made up of either of two different crust types: continental and oceanic. The crust that forms the continents is thicker and lighter than the crust that forms the ocean floor. Most plates consist of both crust types. When oceanic crust collides with continental crust, the oceanic crust generally is subducted -- that is, it slides -- under the continent. The leading edge of subducted crust melts into earth's mantle. The molten rock is lighter than the solid rock of the continent that is on top of it, so it rises and melts through the continental crust, often causing volcanoes and earthquakes.

Such movement is now occurring (among other places) along the Ring of Fire of the Pacific Rim and along the Mediterranean Belt that stretches from central Asia to southern Europe. Slip-Slidin' Away In some places, plates grind past each other. The San Andreas fault in California is the boundary between two such sliding plates. The North American plate carries most of North America, and the Pacific plate carries the Pacific Ocean floor and a small slice of North America, including part of California.

The Pacific plate moves about 5 centimeters (2 in) northward each year. The edges of the plates are not smooth, and the plates can sometimes snag on each another. Pressure builds until the plates lurch past each other and an earthquake rocks the land. The San Francisco earthquake of 1906 opened a 5.5-meter (18-ft) gap in a road that crossed the San Andreas fault. When two plates of continental crust crash head on, neither can sink into the earth's mantle. The force of the collision squeezes the crust, folding it and pushing it up into mountain ranges.

That is one way that fossils of sea creatures can turn up at the tops of mountains. When the continental collision pushes up the shallow sea floor along the edges of a continent, fossilized remains of dead marine organisms in rocks are carried up into the new mountain ranges. If some plates melt down into the mantle while others get pushed up, it would seem that the earth should shrink. But our planet stays about the same size because new crust forms where plates move apart. Molten rock from the mantle wells up between them and sticks to the outer edges of the plates that are separating, in a process called sea-floor spreading. Eruptions from a network of volcanic ridges along the bottom of the oceans also continually adds to the ocean floor.

An underwater mountain system in the Atlantic Ocean rises high enough in seven places to form groups of islands, including Iceland. These mountains (the Mid-Atlantic Ridge) are wedging North America and Europe farther apart, but at a snail's pace. The two continents have moved about 15 meters (50 ft) since Christopher Columbus arrived in the Americas in 1492. From One Into Many All of earth's present continents formed a single huge supercontinent called Pangaea (meaning "all land") more than 200 million years ago. Gradually, convection currents in the mantle beneath Pangaea tore the supercontinent apart. The separate land masses slowly evolved into the seven continents we know today.

You can see roughly how the continents once fit together by looking at a map of the world. The pointed east side of South America seems to fit into the indented west side of Africa as neatly as two pieces of a puzzle. In fact, the fossil remains of Mesosaurus, a small reptile that lived 270 million years ago, are found only at the precise spots on the two continents where they fit together, and nowhere else in the world. Many formations such as mountain ranges and diamond mines also continue from one continent to the next, like separated puzzle pieces.

Using the theory of plate tectonics, prospectors who find fossil fuels or mineral deposits on one continent may find similar deposits across the ocean on another continent. A New Pangaea? The theory of plate tectonics, which provides insight into earth's geologic history, also may help predict the future. Scientists think that in 10 million years, Los Angeles, which is on the Pacific plate, will lie alongside San Francisco, which is on the North American plate. In 50 million years, Africa will probably be split in two. Its Great Rift Valley marks the boundary where two continental plates are pulling apart.

The split will gash the face of Africa from the Red Sea to Mozambique. And 200 million years from now, scientists predict that all the continents may come back together to form a new supercontinent. Copyright 1995, Enter active, Inc., All rights reserved. Author not available, Continents on the Move., Earth Explorer, 02-01-1995 PLATE TECTONIC EARTH PLANET MODEL Abstract An Earth planet model based on the science of plate tectonics. Accordingly, the model (10) includes a plurality of curved members (12), each curved member representing one of Earth's crustal tectonic plates. Each plate member (12) is formed of a durable, lightweight plastic material and molded in raised and indented relief to illustrate such tectonic features as subduction zones, collision zones, mid-ocean ridges, island chains, island arcs, continental shelves, terrestrial and ocean floor topography, and the like.

Plates (12) are attached to the exterior of a base globe (14) forming, as a whole, the surface layer of Earth, or lithosphere. The base globe itself consists of a plurality of spheroidal members, an inner core (22), an outer core (20), and a mantle (18), representing Earth's internal strata. The assembled model is positioned on a supporting pedestal (11) for display or demonstration. The pedestal includes a simple rotary mechanism which allows rotation of the model.