GEOL 120 1nd Edition Lecture 3Outline of Last Lecture II. The Red ShifIII.How the universe evolved IV.Gravitational Forcea.Origin of matterV.Solar SystemVI.Earth’s Mechanical LayersOutline of Current Lecture VII. Wegner’s observationVIII. Harry HessIX. Seafloor spreading and subductionX. Oceanic ridges XI. SeamountsXII. Oceanic TrenchesXIII. Seafloor spreading hypothesisXIV.Earth magnetic FieldCurrent LectureI. Wegener’s observationsa. Glacial Depositsi. Distribution explained if they formed on Pangaea b. Indicated by specific Rock typesi. Make more sense if continents were in positions different from today when they formedc. Fossil distributioni. Animals that could not have crossed oceans are found on different continentsii. Unique plants are found on all southern continents d. Matching rock assemblagesi. Rocks comprising discontinuous mountain belts align when continents aremoved to earlier positionse. Wegener’s Failingsi. Could not explain HOW or WHY continents drifed apartThese 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.II. Harry Hessa. 1968- model of Earth’s 20 platesi. Plate tectonics (widely accepted)1. One of the most influential theories of how the earth worksa. Explains earthquakes, volcanismIII. Seafloor spreading & subductiona. Seafloor spreading:i. Shallow oceanic crust allows molten magma to rise to surface along ocean ridges & widens seafloorii. Creates new crust and forces older crust to move literallyb. Subductioni. Forces crust back into lithosphere at ocean trenchesIV. Oceanic Ridgesa. Segmented linear highsi. Ofen symmetric1. Mid-Atlantic ride is best known2. Offset by fracture zonesii. Measurement of heat flowing through the Earth’s crust show that more heat escapes through oceanic ridgesV. Seamountsa. Isolated submarine mountains of volcanic origini. Show crustal movement over a “hotspot” in crustii. Ofen occur in linear chains, some of which breach the surface of the oceanVI. Oceanic Trenchesa. Lowest places on earthb. Found adjacent and parallel to volcanic chainsi. Continental mountain chainsii. Island arcsVII. The Seafloor spreading Hypothesisa. Oceanic crust is made at ridges and destroyed at trenchesb. These processes result in continental movement above the mantleVIII. Earth’s Magnetic fielda. Two key characteristic that vary with positioni. Declinationii. InclinationIX. Magnetism in Sedimentary Rocksa. Magnetic sediment grains orient themselves parallel to Earth’s local magnetic field as they Seattle through waterb. Atoms in magnetic minerals align as they precipitate in the pore spaces of rocks as groundwater passes throughX. Putting It all Togethera. Wegener proposed Pangea hypothesis using observationi. Fit of continents ii. Locations of past glaciationsiii. Climate belt distributionsiv. Fossil distributions v. Matiching geologic unitsb. Harry Hess proposed seafloor spreading as a mechanism to explain Wegener's observations n Bathymetric observations gave clues to physical processes that may be responsible for seafloor spreading n Ocean-ridges n Deep ocean trenches adjacent to volcanic arcs n Seamounts with active volcanism and a trail of inactive volcanic islands (remember Hawaii!) n Paleomagnetism documents seafloor spreading n The result of a spreading seafloor is continental drif! n BUT THIS IS STILL INCOMPLETE! n How do theseobservations and hypothesis interact with the lithospheric mantle and