Introduction: The Beginning of the “Continental Drift Theory” In the center of the 18th century. James Hutton proposed a theory. uniformitarianism ; “the nowadays is the key to the past” . It held that procedures such as geologic forces- gradual and catastrophic-occurring in the present were the same that operated in the yesteryear. ( Matt Rosenberg. 2004 ) This theory coincides with the theory of Continental Drift that was foremost proposed by Abraham Ortelius in December 1596. who suggested that North. South America. Africa and Eurasia were one time connected but had been torn apart by temblors and inundations.
He besides discovered that the seashores of the eastern portion of South America and the western seashores of Africa fit together like a saber saw mystifier and this fit becomes particularly outstanding as the borders of the Continental shelves have similar forms and therefore. look to be one time fitted together. ( Figure 1. 1 and Figure 1. 2 ) The similarity of southern continents’ geological formations had led Roberto Mantovani to theorize that all continents had one time been a supercontinent and was smaller in its volume than it is now. Through volcanic activity. crevices are created in the crust doing this continent to interrupt apart. However. this theory. known as the Expanding Earth Theory has since been proven wrong.
The Theory of Continental Drift
In 1912. The Theory of Continental Drift was intensively developed by Alfred Wegener. who claimed that the universe was made up of a individual mammoth supercontinent named Pangea since the Permian period. 250 million old ages ago. It began organizing at the beginning of the Carboniferous period. 365 million old ages ago. when Gondwana collided into Laurussia bring forthing the Appalachian mountain belt in eastern North America and shutting in Paleo-Tethys Ocean and modern land mass became exposed to air. Alexander Du Toit so suggested that 145-200 million old ages ago. in the in-between Jurassic Period. Pangea started interrupting up into two smaller supercontinents. Laurasia in the Northern hemisphere and Gondwana in the southern hemisphere. with Tethys Sea and North Atlantic Ocean dividing the two supercontinents.
The late Jurassic epoch began the formation of the Rocky Mountains and Sierra Nevada mountains. In the Cretaceous Period. 65 million old ages ago. the two supercontinents so began break uping into the present seven continents. ( USGS. 2012 ) The Tethys Sea that lay between the two land masss was subducted beneath Eurasia. organizing the lower Atlantic Ocean. Finally. it disappeared. ( Nelson Thomas. 2007 ) ( Figure 2 ) Wegener proposed that continents were traveling at about one pace per century and supported this theory with several points of grounds.
Evidence back uping the Theory of Continental Drift ( Alfred Wegener and Du Toit ) Alfred Wegener matched up coastlines. and he realized that by suiting the Continental shelves together. cratons formed a immediate form across the boundary of South America and Africa. ( Lois Van Wagner. 2013 ) He realized that mountain ranges that ended at one coastline seemed to get down once more on another such as antediluvian mountains in South Africa that align with the mountains in close Buenos Aires in Argentina. ( Sant. Joseph. 2012 ) He discovered angleworms of the household Megascolecina. who are improbable to be long-distance migrants. were found in dirts of all the Gondwanaland continents. ( kangarooistan. 2009 ) This indistinguishable species could non hold arisen on different continents without some fluctuations. ( WiseGeek. 2010 ) Fossil remains of a prehistoric reptilian known as the Mesosaurus had been uncovered on both sides of the South Atlantic seashores. yet the animal was unable to swim across the Atlantic Ocean. ( Lois Van Wagner. 2013 ) Fossils of the land reptilian. Lystrosaurus were discovered in South America. Africa and Antarctica. ( Sant. Joseph. 2012 ) .
He besides discovered the dodo works Glossopteris was distributed throughout India. South America. Southern Africa. Australia and Antarctica. ( USGS. 2012 ) ( Figure 3 ) Alexander Du Toit traveled to Brazil and Argentina where he found similarities in the dodos and stone strata to those found in South Africa such as the fossilised remains of Mesosaurus in fresh H2O sedimentations. dune sedimentations capped by basalt flows. tillite and coal beds. Similar beds of stone were formed in Antarctica. Australia. South America. Africa and India. ( Figure 4 ) Widespread distribution of Permo-Carboniferous glacial deposits in South America. Africa. Madagascar. Arabia. India. Antarctica and Australia and striations that indicated glacial flow off from the equator and towards the poles were discovered and supported the theory of Continental Drift which proposed that southern continents were one time located over the South Pole part and covered by ice sheets. ( Lois Van Wagner. 2013 ) ( Figure 4 )
He besides discovered a basal bed of shale scratched by glaciers and covered by beds of tillite in South Africa. a continent of a tropical equatorial clime. Tillites and varves dating back to 2 billion old ages ago. were found in Canada and India. bespeaking glaciation on a world-wide graduated table. Such tillites were found on all major continents except Antarctica. which has been the most extended glacial continent in earth’s history. ( kangarooistan. 2009 ) Additionally. dodos of tropical workss in the signifier of coal sedimentations were found in Antarctica which implies that Antarctica had to be closer to the Equator. ( USGS. 2012 ) This survey of alterations in clime taken on the graduated table of the full history of Earth is known as palaeoclimatology. Sediments of rifting have proved the floating apart of Pangea.
The rifting that formed the South Atlantic Ocean began tardily in the Mesozoic Period when Africa and South America began to draw apart. Water from the south so flowed in over clip. therefore organizing the evaporites now found along the coastlines at that place. ( Lois Van Wagner. 2013 ) ( Figure 5 ) However. Wegener believed that merely the continents were traveling and they plowed through the stones of the ocean basins. ( Colliers Encyclopedia. 1996 ) Harold Jeffreys so argued that it is impossible for continents to interrupt through solid stone without interrupting apart. ( USGS. 2012 ) Wegener besides claimed that the centrifugal force of the spinning planet had forced the continents sideways. analogue to the equator ; tidal draw from the Sun and Moon had caused sidelong motion. ( Sant. Joseph. 2012 ) His orders of magnitude were excessively weak. Therefore. his theory was dismissed. ( Lois Van Wagner. 2013 ) Further development and support of the “Continental Drift Theory” in the sixtiess After World War 2. the U. S. Office of Naval Research intensified attempts in ocean-floor function. taking to the find of the Middle atlantic Ridge to be portion of a continous system of mid-oceanic ridges on all ocean floors. motivating Harry H. Hess to propose the theory of sea-floor spreading.
The oldest dodos found in ocean deposits were merely 180 million old ages old and small deposit were accumulated on the ocean floor. Therefore. he suggested that seafloors were no more than a few hundred million old ages old. significantly younger than Continental land due to hot magma lifting from volcanically active mid-oceanic ridges. distributing sideways. chilling on the seafloor’s surface due to cooler temperatures of the sea. solidifying to make new seafloor. thereby forcing the tectonic home bases apart. ( Edmond A. Mathez. 2000 ) The realisation that the form of the Middle atlantic Ridge and the Atlantic Coast are strikingly similar substantiated the claim that the continents had been joined together at the Middle atlantic Ridge. ( J. Tuzo Wilson. 1996 ) ( Figure 6 )
The cause of the Continental impetus that Wegener was unable to explicate had been farther researched on by Arthur Holmes who claimed that the motion of continents was the consequence of convection currents driven by the thermic convection in the heat of the inside of the Earth. viz. the mantle. The heat beginning of the mantle comes from radiation decay in the nucleus. ( Figure 7 ) At constructive home base boundaries. run basalt flows out on either side of the ridge and cools with the Fe atoms in the basalt alining with the earth’s magnetic field which reverses way every few hundred thousand old ages. ( Lois Van Wagner. 2013 ) Due to magma chilling. the mutual opposition of stones will be recorded at the clip it was formed. ( Figure 8. 1 )
In 1950. research workers of paleomagnetism discovered that there were jumping parts of normal and reversed magnetic waies symmetrically disposed on both sides of the Middle atlantic Ridge –magnetic denudation. ( J. Tuzo Wilson. 1996 ) Harry H. Hess’ theory was therefore proven by the magnetic anomalousnesss in the pelagic crust. ( Nelson Thomas. 2007 ) ( Figure 8. 2 ) It was besides discovered that the youngest stones were closest to the mid-oceanic Ridge and the oldest stones were near the seashores of the continents. When scientists began roll uping magnetic informations for North America and Europe. they discovered the north pole seemed to be traveling about over clip. ( ALLA. 2009 ) However. when informations from other continents was collected for the same clip frames. it showed different polar locations. therefore back uping that continents were traveling approximately.
The Theory of Plate Architectonicss
The theory of home base tectonics held that the Earth’s lithosphere. the Earth’s crust and the topmost mantle. is broken into seven macro-plates and about 12 smaller 1s. averaging 50 stat mis in breadth. ( U. S. Dept. of the Interior. Geological Survey. 2007 ) Any home base may dwell of both pelagic crust and Continental crust. ( Colliers Encyclopedia. 1996 ) ( Figure 9 ) It suggests that the ocean floor began to distribute at constructive home base boundaries. and continents. bing on “plates” . moved due to convection currents in the mantle and changeless sea-floor spreading. ( The Columbia Electronic Encyclopedia. 2011 ) . They drag and move home bases above them due to lifting magma distributing out beneath the earth’s crust. As two pelagic home bases move apart. magma from the underlying asthenosphere mantle wells up from pelagic ridges and becomes stiff plenty to fall in the geosphere of the home bases on either side of the home base boundary. making new seafloor and finally. an ocean is opened up. ( J. Tuzo Wilson. 1996 ) ( Figure 10 ) Examples are the Atlantic Ocean formed between South America and Africa.
New stone is created by volcanism at mid-oceanic ridges and returned to the Earth’s mantle at pelagic trenches where the denser home base is subducted under the other. coercing the earth’s crust back into the mantle. ( J. Tuzo Wilson. 1996 ) This procedure is known as the ridge push and slab-pull. ( Figure 11 ) Different home base tectonics motion and subsequent tectonic activities Transform home base motion doing temblors: Seismic waves interrupting the continents in the signifier of temblors are due to the great sum of emphasis and energy built up by the clash of the traveling home bases. particularly during transform plate motion. where home bases slide past each other in a grinding. shearing mode and signifier tear mistakes ( Columbia Electronic Encyclopedia. 2011 ) . ( Figure 12. 1 ) There is gradual bending of stones before the malleable bound of stones is exceeded. doing the home bases to lock and the mistake to interrupt. taking to sudden release of stored energy. doing temblors. ( Nelson Thomas. 2007 )
An illustration is the strike-slip mistake. San Andreas Fault in California. ( Figure 12. 2 ) ( WiseGeek. 2010 ) Oceanic and Oceanic convergent home base motion: Other grounds of home base tectonics motion are most of the world’s active vents located along or near the boundaries between switching home bases known as plate-boundary vents. ( J. Tuzo Wilson. 1996 ) When two pelagic home bases collided. the denser home base will subduct under the other. organizing a deep pelagic trench and signifier magma through hydration or decompression thaw. The magma being less dense than the environing mantle. rises and flights to the sea-floor through clefts in the earth’s crust. organizing pigboat vents that rise above H2O to organize a concatenation of volcanic islands known as island discharge. such as the Japan Islands. ( Figure 13 ) Examples would be the Pacific Plate subducting underneath the North American Plate making the Kuril Trench and the Japan Trench that can be found along the Pacific Ring of Fire.
Many vents such as Mount St. Helens. Mount Fuji in Japan and Mount Pinatubo in the Phillipines are located along the margin of the Pacific Ocean Basin where boundaries of several home bases such as the Nazca and the Cocos Plate are found. organizing the Ring of Fire. ( Fraser Cain. 2009 ) ( Figure 14 ) Volcanoes formed non due to tectonic activities: 5 per cent of the world’s vents are formed at stray “hot spots” and many intra-plate vents organize approximately additive ironss along the center of pelagic home bases. ( The Columbia Electronic Encyclopedia. 2011 ) Examples are the Yellowstone National park and Hawaiian Islands. an intra-plate volcanic concatenation developed by the Pacific home base passing over a deep. stationary “hot spot” . located 60 km beneath the contemporary place of the Island of Hawaii. Heat from this hot spot produced a changeless beginning of basaltic magma by partially runing the overruling Pacific Plate.
This magma rises through the mantle to break out onto the seafloor. organizing an active seamount. Over clip. infinite eruptions caused the seamount to turn until it eventually emerges above sea degree to organize island vents. The go oning plate motion finally carries the island vent off from the hot spot. cutting it off from the “hot spot” and making another island vent. This rhythm is repeated. organizing the Hawaiian Islands. ( U. S. Dept. of the Interior. Geological Survey. 2007 ) ( Figure 15 ) Continental and Continental convergent home base motion: Continental fold mountain scopes are grounds of two Continental home bases that are thick and floaty therefore. forestalling both home bases from subducting. Alternatively. the two home bases collide into each other organizing fold mountain ranges in a procedure known as orogenesis.
An illustration is the high lift of the Tibetan tableland. fringed to the South by the Himalayas as the borders of the Indian and Eurasia home base buckle. upheaval. crease and deform. Mt. Everest is the highest acme on Earth. yet Yellowband limestone that was originally portion of the shallow seals of the Tethys Ocean was found on Mount Everest at a tallness of 8462m. ( Figure 16 ) Eastern malayo-polynesian and Continental convergent home base motion: Mountains are formed when pelagic crust is subducted under a Continental crust. ensuing in thaw of stone. therefore volcanic activity and doing the Continental crust to deform. rise and buckle upwards under compressional forces.
Examples are the Andes Mountain. the Chile-Peru Trench and the upheaval of the Rockies and Appalachians in the yesteryear. ( The Columbia Electronic Encyclopedia. 2007 ) The Table Mountains was formed about 250 million old ages ago. due to the Pacific home base subducting under the North American home base. ( Mary Ann Resendes. 2012 ) therefore making the Sierra Nevada foothills. later making the Cape of Good Hope as the ocean erodes the soft sandstone of Table Mountains on the seashore. ( National Geographic. 1996 )
Other tectonic activities such as the Wadati-Benioff zones. that are temblor zones parallel to pelagic trenches are besides formed at such subduction zones and inclined from 40 to 60 grades from the horizontal. widening several hundred kilometers into the mantle. ( Figure 17 ) Continental and Continental divergent home base motion: When two Continental crusts are pulled apart due to tensional forces. the country sinks and forms a rift vale and sea such as the East African Rift Valley and the Red Sea that runs from the Jordan Valley and into East Africa. already dotted with vents such as Hermon. This is due to the country being stretched. doing the crustal stuff to thin. weaken and sink due to lowered denseness. ( Figure 18 )
Besides. isostasy takes topographic point wherever a big sum of weight such as the crease mountain scopes created from home base tectonics motions is formed or glaciers. pushes down the Earth’s crust and creates a little dent. Isostasy besides takes topographic point at divergent home base boundaries when a big sum of weight is removed from an country. doing that part of the Earth’s crust to lift. Therefore. equilibrium in the earth’s crust is achieved such that forces promoting land masss balances those be givening to deject land masss. ( Learning Network. 1998 ) ( Figure 19 )