Plate Tectonics Introduction
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Introduction Earth is a dynamic, ever-changing planet If we could go back in time 200 million yours ago there would be no Grand Canyon or Himalayas More over we would find landmasses with unfamiliar shapes Earth scientist have shown that the landmasses are not fixed but slowly migrate across the globe Large landmasses have split apart resulting in the formation of oceans While the floor of the ocean has been recycled back into the Earth’s interior Separate landmasses collided and joined to form a larger continent The movement of earth outer rigid layer generates earthquakes Volcanoes, mountains, new ocean basins Moreover, the changing positions of the continents helps explain ancient climates and distribution of fossils The scientific theory which describes the mobile Earth is called plate tectonics Continental drift A revolution in the Earth sciences begin in the early part of the twentieth century when a radical proposal was mad that the continents drifted about the face of Earth The development of this revolutionary hypothesis, known as continental drift, is credited to Alfred Wagener, a German meteorologist and geophysics Wegener proposed that a supercontinent, which he named Pangaea In addition, Wegener suggested that this supercontinent began breaking into smaller landmasses, which drifter to their present position Fit of the Continents Fossil evidence Evidence from Rocks Paleoclimatic Evidence Wegener first suspected that the continents might have been joined when he noticed the similarities of the coast line of Africa and South America South America and Africa Fossil Evidence Scientist have discovered that fossils of the same ancient plants and animals were found on widely separated continents Why ore fossils of Mesosaurus found on both sides of the South Atlantis but nowhere else in the world Three ideas were proposed to explain the distribution of the fossils Rafting, stepping stone islands, and land bridges Wegener had a better explanation- he proposed the continent of supercontinent Pangaea Evidence from rocks When working a jigsaw puzzle every The picture must be continuous as well The picture that must be matched in the continental drift puzzle is represented by ricks of similar types And mountain belts Mountains of about the same age The mount ranges such as the appellation mountain Paleoclimatic evidence Earth science have learned that between 220 and 300 million years ago vast ice sheets covered extensive portions of earth’s landmasses Evidence called till glaciers leave behind An unsorted mixture of many different sediment sizes Below these layer of till lay bedrock that was scratched and polished by glaciers armed Most glaciers are in an area that you wouldn’t expect Scientist have rejected the idea of the equator becoming cold because during this period large tropical swamps existed in the Northern Hemisphere The lush tropical of these lush swamps eventually became the major coalfields of the eastern United States and Europe. If the coal is under enough pressure the coal will turn in to a diamond Fossils from the coal fields indicate that the environment trees had large fronts Scientist realized that the area containing swamp areas and glacier areas when put together are all in one spot The Great Debate Wegener’s continental drift began to attracted attention in 1924 The continents didn’t break through the ocean floor Harold Jefferson said that the ground under water got softer and moved little by little Continental drift and Paleomagnitism The imputes for renewed interest in continental drift came from studies conduct to determine the intensity of direction Any one who has used a compass knows that Earth’s magnetic fields has a north pole and a south pole that align closely but not exactly Earth’s magnetic field is similar to that produced by a simple bar magnet. The technique used to study ancient magnetic field relies on the fact that some rocks contain iron rich minerals serve as fossil compass Magnetite is found in basaltic rich rocks Magnetic alignment in older lava fields was found to vary widely In The past 500 years the magnetic pull has moved Either the poles had migrated or the continents shifted Poles have remained fixed yet the plates are moving The polar magnetism this alone proved that Pangaea did exist because the lava magnetism created Seafloor spreading One reason that Wagener’s continental drift hypothesis was not widely accepted because there was not much known of the ocean floor The war ships gave echolocation in 1950-1960 as new echolocation sounding technology was developed An echo sounder measures the sound in time and can tell how far is the ocean bottom 1500 meters per second Extensive sampling of the ocean floor did not recover material that was older than 200 million years in age Ridges proposes that ridges are located above upwelling portions of large convection cells in the mantle As rising material spreads laterally seafloor is carried As the crust is pulled apart, molten rock intrudes the fractures Older portions of the seafloor are gradually consumed as they descend into the mantle Plate tectonics: the new paradigm According to the plate tectonics model, the uppermost mantle along with the overlying crust, behaves as a strong, ridged layer known as the lithosphere This rigid outer shell overlies a weaker region in the mantle known as the asthenosphere The temperature and pressure regime in the upper asthenosphere results in a very weak zone that permits the lithosphere to be effectively detached from the layers below. Thus the weak rock within the upper asthenosphere allows Earth’s rigid outer shell to move The lithosphere is broken into numerous segments, called plates, that are in motion with respect to one another, thereby continually changing shape and size Seven major lithospheric plates are recognized South American plate North American plate Pacific plate Australian- Indian plates Antarctic plate Eurasian plate And African plate The largest is the Pacific plate which encompasses a significant portion of the Pacific Ocean basin Most of the large plates include an entire continent plus a large area of ocean floor. Intermediate size plate include Philippian plate Arabian plate Scotia plate Caribbean plat Nazca plate Cocos plate And Juan de Fuca plate Interactions of the plates sre n there boundaries There are three types of plate boundaries Divergent plate boundaries where two plates move apart resulting in upwelling of material from the mantle the create new seafloor Convergent plate boundaries: where two plates move together, resulting in oceanic lithosphere descending beneath an overriding plate, eventually to be reabsorbed into the mantel Although the total surface area of Earth does not change The individual plate may diminish or grow in size The Antarctic plate is mostly bounded by divergent boundaries and is growing larger The pacific plate is shrinking The African plate will eventually split Every plate has all three plate boundaries Divergent plate boundaries Most divergent plate boundaries are located along the crest of oceanic crust Oceanic ridges Along a well developed divergent plate boundaries the sea floor is elevated forming the oceanic ridge The oceanic ridge represents 20% of Earth’s surface The ocean ridge can be 1000 to 4000 km wide Along the axis of some ridges segments is a deep down faulted stretch called a rift valley The average spreading is 5 cm slow is 2cm The oldest ocean floor is 200 million years old The ocean is growing symmetrically Continental rift Spreading centers mostly under water Continental rifting =extensional forces, up warping Faulting the rift is up warping the rift valley creating a continent like the Red sea Also like lake Victoria Earth’s interior 2/6/13 Heat from the Earth’s interior is the major source of energy for the movement of Earth’s outer shell Scientist have determined the Earth’s interior is divided into four layers The inner core is a solid iron rich sphere having a diameter of 2432 kilometers (1511 miles) The outer core is a liquid metallic layer that is about 2270 km (1410 miles) Earth’s magnetic field is thought to be generated by vigorous churning of the iron-rich material in the hot, fluid outer core. Movement of outer core creates the magnetic field. The mantle is a solid rocky layer having a thickness of about 2885km (1789 miles. Over 82 percent of Earth’s volume is contained within the mantle, a thick shell of rock composed of silicate materials that are rich in iron and magnesium The outer crust is a very thin outer layer that ranges from 7-70km The crust is made up of two crusts oceanic (basalt) and continental (granite) The continental crust is about 35-70 km Oceanic crust is about 7km (5 miles) Continental rocks are less dense than oceanic crust There is an Asthenosphere and a lithosphere Asthenosphere is located within the upper mantle between 100 to 600 km and is composed of hot rocky material that the movment is very slow The lithosphere is part of the crust and goes lower Behaves as a strong ridged layer because it is composed of solid rock Weak rock allows the ridged outer shell to move Convergent plate boundaries 2/27/13 Convergent plate margins occur where two plates collide and the motion is accommodated by on plate sliding under Also called Subduction zones because the lithosphere is descending in to the asthenosphere Deep ocean trenches develop between two convergent plates The oceanic plate is more dense than the continental plate so the plate descend in to the asthenosphere Some oceanic plate descends fairly beep sometimes Density of the plate is what determines which goes under (more compact and temperature change) As it gets older the oceanic plate will more likely sink because it is more cool Older oceanic plate will descend almost 90 degree because of the density   
as one is decending the plate pulls the continent with it. It changes position. There are three types of convergent boundaries Oceanic and oceanic Oceanic and continental Continental and continental Oceanic continental convergence When the oceanic lithosphere go 100 km the plate rock starts to melt Peridotite has low water content Different amounts of water in rock effects how it melts Seismic evidence predicts that under average conditions of temperature and pressure the upper mantle consists of solid There are different depths to melt different times 100 km melts wet peridotite at roughly 400 degrees Hot mixture gradually rises toward the surface in tear shape form Basaltic magma separates from the un-melted components and continues to ascent Basaltic magma rises to the surface because it is less dense and hot Magma sometimes melt other continental rock Andesitic magma reaches the surface they erupt explosively generating large columns of ash Andesitic rock name came from the Andes mountains in south America Directory: file -> fetch fetch -> 11 th Lit Semester 1 Final Study Guide!!! fetch -> Industrial Revolution Inventors fetch -> Analysis for Galveston Hurricane of 1900 fetch -> The Illuminators (Team 2) 1900 Galveston Hurricane Cycle a team Assignment fetch -> Team csi-utb ruth Reyes Jose Ferrer fetch -> Galveston Hurricane of 1900 Cycle a-teacher as a Problem Solver fetch -> Is Climate Change Starting a New Dust Bowl? Cycle A fetch -> What makes a storm a hurricane fetch -> The 1950s were the "Happy Days" because it was a time of economic prosperity, technology development, new entertainment, new fashion and family growth. The 1950s was a great time fetch -> Sputnik and The Dawn of the Space Age Download 27.42 Kb. Share with your friends:
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