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Transcript
Plate Tectonics The Theory Unfolds!!!! 5/23/2017 1 Earth’s Layers 5/23/2017 Earth: built by distinct layers: inner core, outer core, mantle, crust; the crust is the thinnest layer 2 Earth’s Geologic Timeline Pre-Cambrian: Paleozoic: Mesozoic: Cenozoic: 5/23/2017 3 Continents in Motion Alfred Wegener was a German meteorologist that proposed the theory (1912) that the Earth was not fixed - it "moved" on plates. Come to find, in the 1960s, Alfred Wegner´s theory was proven correct. This theory is known as __________________. 5/23/2017 4 Book written by Wegener In 1915, Wegener published his evidence and conclusions in a now classic book, Die entstehung der kontinente und ozeane (The origin of continents and oceans). Wegener proposed that all modern continents were once assembled together in a supercontinent he named Pangaea. 5/23/2017 5 Continental Drift Theory that the continents had once been part of one or more landmasses that had separated and moved apart. They are supposed to have broken up about 200 million years ago. 5/23/2017 6 Pangaea – Means “ All Earth” Wegener proposed that all continents had once been joined in a supercontinent he named Pangaea. Pangaea, he thought, had existed from the primordial earth until the Mesozoic, when it began to break up. Wegener at first considered mantle convection as a possible driving mechanism, but later rejected that in favor of _______________ as the cause for Pangaea's breakup and continental drift. 5/23/2017 7 5/23/2017 8 Panthalassa – Means “All Seas” 245 Million years ago: Pangaea existed when some of the earliest dinosaurs were roaming around this big earth. The land Pangaea was surrounded by a sea called Panthalassa. 5/23/2017 9 5/23/2017 10 Pangaea breaks up Forming: Pangaea started to break up into two smaller supercontinents during the Jurassic period. By the end of the Cretaceous period, the continents were separating into land masses that look like our modern-day continents. 5/23/2017 11 Evidence Supporting Continental Drift 1. These two widely separated continents seem to resemble two separate pieces of a larger jigsaw puzzle. North America, too, seems to mirror the western coastline of Europe. 5/23/2017 12 Evidence Supporting Continental Drift 2. – A small reptile that lived 270 million years ago that was found in Eastern South America and western Africa. Mesosaurus lived near swamps and rivers and it would have been impossible for this reptile to have swam across the Atlantic. 5/23/2017 13 Evidence of Continental Drift 3. Fern fossils have been found in Africa, Australia, India, and Antarctica. 5/23/2017 14 Evidence of Continental Drift 4. Glacial striations on rocks show that glaciers moved from Africa toward the Atlantic Ocean and from the Atlantic Ocean onto South America. Such glaciation is most likely if the Atlantic Ocean were missing and the continents joined. 5/23/2017 15 Evidence of Continental Drift 5. The age and type of rocks in the coastal regions of widely separated areas, western Africa & eastern Brazil, matched closely. Mountain chains such as the Appalachians and Scandanavian Mtns. Of Greenland and Northern Eupope seem to fit closely in age and structure. 5/23/2017 16 5/23/2017 17 5/23/2017 18 Wegener’s Theories Rejected Most scientist rejected Wegener’s theories --------Why ? ---------It was difficult to conceive of large continents plowing through the sea floor to move to new locations. What kind of forces could be strong enough to move such large masses of solid rock over such great distances? While in Wegener’s lifetime, he never found the WHY to why the continents moved. 5/23/2017 19 5/23/2017 20 Wegener suggested that the continents simply plowed through the ocean floor, but Harold Jeffreys, a noted English geophysicist, argued correctly that it was physically impossible for a large mass of solid rock to plow through the ocean floor without breaking up. Recent evidence from ocean floor exploration and other studies has rekindled interest in Wegener's theory, and lead to the development of the theory of plate tectonics. 5/23/2017 21 Definite Proof But the purpose of the Glomar Challenger was scientific exploration. One of the most important discoveries was made during Leg 3. The crew drilled 17 holes at 10 different sites along a oceanic ridge between South America and Africa. The core samples retrieved provided definitive proof for continental drift and seafloor renewal at rift zones. This confirmation of Alfred Wegener's theory of continental drift strengthened the proposal of a single, ancient land mass, which is called Pangaea. 5/23/2017 22 This video can be found on My Big Campus…..It review the material I covered in class 5/23/2017 23 Navy submarine commander during World War II. Harry Hess Hess proposes sea-floor spreading 1960 Suggested that there was actually a break at the center of the ridge known as a ________________________. Magma from deep within the Earth was coming to the surface at this Rift Zone and creating new sea floor. 5/23/2017 24 Paleomagnetism is a technique used to cross date ocean cores and to establish major intervals over wide areas. By measuring the polarity of the magnetism in samples it is possible to determine the layer in which the Earth’s polarity reverses. Between periods of normal and reversed polarity. 5/23/2017 25 What is Sea-Floor Spreading? In the early 1960s, Princeton geologist Harry Hess proposed the hypothesis of sea-floor spreading, in which basaltic magma from the mantle rises to create new ocean floor at mid-ocean ridges. On each side of the ridge, sea floor moves from the ridge towards the deep-sea trenches, where it is subducted and recycled back into the mantle Types of Boundaries 5/23/2017 27 D i v e r g e n t Boundary 5/23/2017 A divergent boundary occurs where 2 plates are________________. The force associated with this is called – _______________. Example – Mid-Ocean ridges where Sea Floor spreading is occuring. 28 Convergent Boundary: 3 Types A convergent boundary is a boundary between 2 colliding plates. When 2 plates collide one plate may dive under the other plate at a___________________. There are 3 types. 1. Ocean – Ocean Convergence 2. Ocean – Continent Convergence 3. Continent – Continent Convergence 5/23/2017 29 5/23/2017 30 Force associated with Convergent Boundaries What type of force is associated with convergent boundaries? 5/23/2017 31 Ocean – Ocean Convergence 5/23/2017 When two oceanic plates collide creating deep sea trenches. Example: Marianas Trench the deepest part of the Pacific Ocean near the coast of Japan at at 11033 meters (36201 feet) deep. Magma rises to form volcanoes or Island arcs on the ocean floor parallel to the trench. 32 Ocean to Continent Convergence 5/23/2017 The _____________ Oceanic plate descends into the less dense Continental Crust and SUBDUCTS its way down to the Asthenosphere. ___________________ may form Ex: The Andes in South America were created when the Pacific plate ran into the South American plate creating the Andes Mountain Range. 33 New crust is continually being pushed away from divergent boundaries (where sea-floor spreading occurs), increasing Earth's surface. But the Earth isn't getting any bigger. What happens, then, to keep the Earth the same size? 5/23/2017 In locations around the world, ocean crust subducts, or slides under, other pieces of Earth's crust. The boundary where the two plates meet is called a convergent boundary. Deep trenches appear at these boundaries, caused by the oceanic plate bending downward into the Earth.34 Continent to Continent Conv. Continental rocks have low densities in which neither is more dense than the other. This causes them to buckle up and create Mountains when they collide. Very little volcanic activity. Earthquakes are CoMmoN. Ex: Appalachian’s and Himalayas 5/23/2017 35 Convergent – Convergent boundary When two land masses meet neither will slide under the other. Instead, the two crush together at what is known as a convergent boundary. They crumple and fold. Some pieces of land are thrust over or under other pieces. The result is a mountain range. 5/23/2017 36 The ______________, the highest mountains in the world, were created this way. (In fact, they're still growing.) So were the European Alps. Even the Appalachian Mountains formed when two land masses came together. Although with the Appalachians, the crushing ended long ago -- all that's left now are the eroded remnants5/23/2017 of a once high mountain range. 37 Transform Fault Boundary 5/23/2017 Boundaries where plates are sliding past one another in opposite directions or in the same direction but at different rates. The Force associated with this boundary is _____________. Ex: San Andreas Fault in California. YOU GET ________________ !!! 38 Slippin' and a Slidin' Transform boundaries neither create nor consume crust. Rather, two plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk. This sudden jerk creates an earthquake. 5/23/2017 39 5/23/2017 40 Convection Currents 5/23/2017 41 Convection is the____________________________________ ___________________________. When fluid is heated, it expands, lowering the density of the heated material, causing it to rise through the cooler fluid. As it rises, leaving the vicinity of the heat source, in this case, hot magma near the earth's surface, it will cool. When it becomes more dense (because it is cooler) than the surrounding fluid, it will begin to sink.__________________________________ _________________________________. 5/23/2017 42 Arthur Holmes believed a fluid mantle possessed convection currents created by heat trapped beneath the Earth's surface. Holmes hypothesized that convection currents welled up toward the surface and then drug continents across the surface. 5/23/2017 43 Ocean Floor Map