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CSU NR 150 - Earth's Structure

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NR 150 1st Edition Lecture 4Outline of Last Lecture I. The Age of DiscoveryII. Earth and the OceanIII. The Young EarthOutline of Current Lecture IV. Continental DrifV. Earth’s Structure: 2 approaches to viewing the structureVI. New Technology leads to the explanation of Continental Drif TheoryCurrent LectureI. Continental Drifa. Charles Darwin realized that a balance exists between the tectonic forces that uplif the Andes Mountains and the weathering forces that slowly erode the mountains downb. Alfred Wegeneri. Proposed the theory of continental drif in 1912ii. Realized that all of the continents would fit together into one giant landmass (which he called Pangea) 1. The mountains of Eurasia and North America lined up2. Fossils of animals and plants found at one part of the world could also be found in other parts of the worldiii. Explained his theory by attributing movement to centrifugal forces and inertia/ tidal drag from the Sun and Moon1. This explanation is incorrect and was later disprovediv. He attempted to conduct an expedition to Greenland in 1930 to prove his theory, but he died before the trips completionv. Support for Continental Drif:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.1. Puzzle pieces fit together2. Evidence of similar fossils3. The lining up of mountain rangesvi. Problems with Continental Drif:1. There was no mechanism that Wegener could come with to explain the phenomenonc. Theory of Plate Tectonicsi. Progress was made in understanding that the Earth was density stratified and that the interior of the Earth is hotii. Progress with the Theory of Plate Tectonics came from the study of seismic waves (earthquakes)1. Seismographs: instruments that measure and record seismic activity and earthquakes2. Seismic waves proved Earth’s interior structure3. Surface wavesa. Move along the Earth’s surface, most destructive to propertyb. Travel slowly along the surface and have long wavelengthc. The greater the amplitude of the waves, the greater the damage4. Body Wavesa. P- Waves: compressional waves that changes the volume of rocks (compressed or expanded)i. Can pass through solids, liquids, and gassesii. They are the 1st waves recorded by seismographsiii. Travel quickly, at about 6 km/sb. S-Waves: shear waves, move perpendicular to the direction of wave traveli. Can only pass through solids, not liquids and gassesii. Travel slower than P-Waves (at 3.5 km/s) and are recorded later by seismographsiii. The measurement of seismic waves proved that the Earth was layered1. If the Earth was homogeneous, the seismic waves would radiate from the site of an earthquake through the Earth in straight lines2. P-Waves can penetrate the liquid outer core, but are bent as they move, resulting in shadow zones where seismic activity from an earthquake isn’t detected3. S-Waves cannot travel through the liquid outer core, so their shadow zone is much larger than that of P-WavesII. Earth’s Structure: 2 approaches to viewing the structurea. Chemical Compositioni. Looks at the chemical composition of the Earthii. Results from the accretion process of the young earth and subsequent density stratificationiii. Chemical characteristics of Earth: each layer is composed of different materials1. Crust: uppermost layer, thinnest layera. Oceanic crust: comprised of basaltb. Continental crust: comprised of granite, less dense than basalt2. Mantle: the layer beneath the crusta. Accounts for 68% of the Earth’s mass and *3% of its volumeb. Consists mainly of silicon and oxygen with some oxygen and magnesium3. Core: inner and outer corea. Mainly consists of iron and nickelb. Physical compositioni. Different materials behave differently with depth, properties are affected by temperature, pressure, and depthii. Earth’s interior layers are in a state of isostatic equilibrium (the balanced support of lighter material in a heavier supporting matrixiii. Lithosphere1. The cool, rigid outer layer, about 100-200 km thick2. Comprised of the continental and oceanic crusts and the uppermost cool and rigid portion of the mantleiv. Asthenosphere1. The hot, partially melted, slowly flowing layer of the upper mantlebelow the lithosphere2. Extends to a depth of about 350-650 kmv. Lower Mantle1. Extends to the Earth’s core2. Similar in chemical composition to the asthenosphere (the upper mantle)3. Hotter than the asthenosphere, but not melted due to higher pressure at greater depthsa. Denser material that flows more slowlyvi. Core1. Extremely hot temperatures and high pressure2. Outer core: dense, viscous (slow-flowing) liquid3. Inner core: solid, densest material on EarthIII. New Technology leads to the explanation of Continental Drif Theorya. Wegener’s theory was discarded until new technology came out that was able to prove his hypothesisi. Seismographs revealed a pattern of volcanoes and earthquakesii. Radiometric dating of rocks revealed a surprisingly young oceanic crustiii. Echo sounders revealed the shape of the Mid-Atlantic Ridgeb. Convectioni. Movement within a fluid resulting from differential heating and cooling ofa liquid, hot material rises as cool material fallsii. Provided the mechanism used to prove plate tectonics theoryc. Seafloor spreadingi. Powered by convection currents in the mantleii. Mid-Ocean ridges were the spreading centersiii. Source of new ocean floor rising from the asthenosphereiv. Hot near the ridges due to the rise of lava to create new crust, but as the crust distanced from the ridge the material became denser and the oceanbecame deeperv. The earth isn’t constantly expanding because the spreading is counteracted by subduction zones where oceanic crust is circulated back into the mantled. In 1965: the idea of Continental Drif and Seafloor spreading became better known as the concept of Plate Tectonicsi. The theory was mainly worked on by John Tuzo Wilson at University of


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