BAESi Plate Tectonics JonH

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Information about BAESi Plate Tectonics JonH
Travel-Nature

Published on December 23, 2008

Author: aSGuest7880

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BAESI: Earth and Life Through Time : BAESI: Earth and Life Through Time Plate Tectonics Overview Jonathan Hendricks SJSU Department of Geology jhendricks@sjsugeology.org Plate Tectonics Overview : Plate Tectonics Overview Lecture Overview: Have the positions of continents moved through time? What is the history of the idea of continental drift? How does plate tectonics work? How do plates interact at their boundaries? Plate Tectonics : Slide shows an image of one tectonic plate being subducted beneath another. Plate Tectonics Plate Tectonics: The scientific theory that the surface of the Earth (lithosphere) is divided into plates that move relative to one another and that interact at their boundaries. Image from USGS Map of the World : Map of the World Slide shows a satellite map of the world. Image from NASA History of Plate Tectonics : History of Plate Tectonics Slide shows two images made by geographer Antonio Snider-Pellegrini, 1858. One shows the continents separated. The other shows North and South America connected with Europe and Africa. Maps by geographer Antonio Snider-Pellegrini, 1858 Glossopteris – “Seed Fern” : Slide shows a photo of a Glossopteris fossil, as well as locations on the world map where Glossopteris fossils have been found. Glossopteris – “Seed Fern” Stars show places where Glossopteris fossils have been found. Image from USGS Image from NASA Glossopteris Flora and Land Bridges? : Slide shows a photo of a Glossopteris fossil, as well as locations on the world map where Glossopteris fossils have been found. A circle shows the position of the ancient land mass known as “Gondwana”. Glossopteris Flora and Land Bridges? “Gondwana” Was sea level lower during late Paleozoic? Image from USGS Image from NASA Alfred Wegener (1880-1930) : Slide shows a photograph of Alfred Wegener. Alfred Wegener (1880-1930) German meteorologist who proposed idea of “continental drift”: idea that continents moved (and continue to move) horizontally over the surface of the Earth. In 1915 presented evidence for a single supercontinent, which he called Gondwana. Early evidence presented by Wegener and other workers (especially Alexander du Toit) in support of continental drift: Continental fit. Rock sequences. Glacial flow directions. Rift valleys. Distributions of fossils. Image from USGS Glacial Flow Directions : Glacial Flow Directions Slide shows two images. One shows a picture of scratch marks on rocks caused by glacial flow. The second shows ancient glacial flow directions on the modern world map. The third shows that the glacial flow directions in the southern continents only make sense if the continents were once connected. Image from USGS Image from NASA Rift Valleys of Africa : Rift Valleys of Africa Slide shows two images. One is a map of northeastern Africa showing the positions of major rift valleys. The second shows a satellite photo of a rift valley. From NASA Image from USGS Fossil Evidence : Fossil Evidence Slide shows the distributions of Glossopteris, Lystrosaurus, and Mesosaurus fossils when the southern continents are reunited as Gondwana. History of Plate Tectonics : History of Plate Tectonics Despite the extensive evidence that the positions of the continents have changed through time, most geologists rejected the idea of continental drift. This was because there was no known mechanism that could produce such change. Interior of the Earth : Interior of the Earth Inner core: mostly solid iron Outer core: mostly liquid iron Mantle: rocky material Crust: Oceanic crust Continental crust Pressure increases with depth. Slide shows two figures that detail the different parts of the interior of the Earth Images from USGS Earth’s Magnetism : Earth’s Magnetism Motion of iron-rich outer core creates a magnetic field. Earth acts like giant bar magnet with N and S poles. Geographic and magnetic poles offset. Slide shows a cartoon image of Earth’s magnetic field. Image from USGS Magnetism is Recorded in Rocks : Magnetism is Recorded in Rocks Some rocks contain iron minerals. These minerals align themselves to Earth’s magnetic field as the rock forms. Iron particles in sedimentary rock align as they fall out of suspension from water. Iron particles in magma (igneous rocks) align before the magma cools. “Frozen” orientations preserve record of the ancient orientations of Earth’s magnetic field. Study of the Seafloor : Study of the Seafloor The seafloor became much better explored during the 1940-1960’s. WWII, sonar. Complex topography. Mid-oceanic ridges with central furrow. Volcanoes often associated with ridges. Slide shows an artist’s painting of the Mid-Atlantic Ridge. Image from USGS Harry H. Hess & Seafloor Spreading : Slide shows a photograph of Harry Hess. Harry H. Hess & Seafloor Spreading Hess’ Hypothesis of Seafloor Spreading: 1962 Continental and oceanic crust move together. New oceanic crust forms from rising magma at mid-continental ridges Oceanic crust moves away from ridge as it cools. Mechanism: thermal convection. Image from USGS Thermal Convection : Thermal Convection Thermal convection is thought to be the process driving the movement of plates. Earth is hotter (due to radioactive decay - fission) in some portions of the deep mantle than in others. This causes the formation of convection cells that drag along overlying lithospheric plates - acts like conveyor belts. Think about a container full of boiling water. Slide shows two images. One is a cross-section through the Earth showing how convection cells in the mantle may operate. The other shows a container of boiling water. Images from USGS Testing Hess’ Hypothesis : Testing Hess’ Hypothesis How could one test Hess’ hypothesis of seafloor spreading? What pattern should one find on either side of mid-ocean ridge systems if Hess’ hypothesis is true? Slide shows an image of the Mid-Atlantic Ridge. Image from Google Earth Magnetic Reversals : Magnetic Reversals The polarity of Earth’s magnetic field has “flipped” many times throughout the geologic past. The reason(s) why are not at all clear. Durations of “normal” and “reversed” polarity highly variable in length. Test of Hess’ Hypothesis : Test of Hess’ Hypothesis During the early 1960’s, it was discovered that changes in Earth’s magnetic polarity have been recorded into rocks on the seafloor (oceanic crust) as they cooled. Symmetrical banding on each side of mid-oceanic ridge systems. Younger rock near ridge, older away. Slide shows two images that illustrate magnetic reversals on either side of a mid-ocean ridge. These reversals form symmetrical patterns on each side of the mid-ocean ridge. Images from USGS Ages of the World’s Ocean Basins : Ages of the World’s Ocean Basins Slide has one image showing the ages of different oceanic crust rocks in the world’s ocean basins. Image from USGS Hess’ Hypothesis Was NOT FalsifiedEnough support has since been provided for plate tectonics that the idea is now accepted as a unifying theory for geology.Simple idea with great explanatory power. : Hess’ Hypothesis Was NOT FalsifiedEnough support has since been provided for plate tectonics that the idea is now accepted as a unifying theory for geology.Simple idea with great explanatory power. Major Plates of the World : Major Plates of the World Slide shows the major plates of the world. Image from USGS Plates Interact at Their Boundaries : Plates Interact at Their Boundaries Slide shows a figure that details where recent earthquakes have occurred. Most occurred near plate boundaries. Image from USGS; Earthquakes over last 30 days (http://neic.usgs.gov/neis/qed/) Different Plate Boundaries : Three major types of plate boundaries: Divergent - plates diverge from each other. Convergent - plates converge toward each other. Oceanic-Continental - oceanic crust (denser) subducts (goes under) beneath continental crust. Continental-Continental - neither body of continental crust subducts (equal density). Transform - plates slide past each other. Different Plate Boundaries Different Plate Boundaries : Slide shows a figure that provides an overview of the three major types of plate boundaries: divergent plate boundaries, convergent plate boundaries, and transform plate boundaries. Different Plate Boundaries Image from USGS Divergent Plate Boundary : Divergent Plate Boundary Slide shows two images. The first shows a picture that illustrates a divergent plate boundary. The second shows the mid-Atlantic ridge system. Image from Google Earth Image from USGS Mid-Atlantic Ridge Oceanic-Continental Convergent Plate Boundary : Oceanic-Continental Convergent Plate Boundary Andes, South America Slide shows two images. On is an illustration of a oceanic-continental convergent boundary. The second is an image of the west coast of South America, which is an oceanic-continental convergent boundary. Image from Google Earth Image from USGS Continental-Continental Convergent Plate Boundary : Slide shows three images. One is an illustration of a continental-continental convergent boundary. The second is an image of the Himalayan mountains, which is an example of a continental-continental convergent boundary. The third is a cartoon that shows how India crashed into Asia. Continental-Continental Convergent Plate Boundary Himalaya Mountains, Asia Image from Google Earth Image from USGS Image from USGS Transform Plate Boundary : Transform Plate Boundary Slide shows two images, both of which illustrate the positions of transform plate boundaries near the northwest coast of the United States. Image from Google Earth Northwestern United States Image from USGS San Andreas Fault Earth Today : Earth Today Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Cretaceous : Earth in the Cretaceous Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Jurassic : Earth in the Jurassic GONDWANA: South America, Africa, Antarctica, India, and Australia Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Permian : Earth in the Permian SUPERCONTINENT OF PANGEA!! Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Devonian : Earth in the Devonian Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Ordovician : Earth in the Ordovician Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Cambrian : Earth in the Cambrian Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in the Late Proterozoic : Earth in the Late Proterozoic Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth Today : Earth Today Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in 150 Million Years : Earth in 150 Million Years Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com) Earth in 250 Million Years : Earth in 250 Million Years Plate tectonic maps and Continental drift animations by C. R. Scotese, PALEOMAP Project (www.scotese.com)

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