GEO 101N 1st Edition Lecture 5Outline of Last Lecture I. Magnetic Field continuedII. Plate TectonicsIII. Alfred WegnerOutline of Current Lecture IV. New Observational Dataa. Harry Hessb. SonarV.Discovery of Sea Floor SpreadingVI. Magnetic FieldCurrent LectureI. 1940’s View of Eartha. No view of the oceanic topographyb. No maps showed anything except blue for waterII. Harry Hess a. Princeton Geology Professorb. Joined the Navy for/during WWIIc. Was in command of a troop carrier that was tasked with sonar mapping of possible landing sitesd. Left sonar on as often as possible and kept his data, compiled it after the war back @ PrincetonIII. Sonara. Bouncing sound waves off objects to get a map of shapeThese 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.b. Delineated bathymetric (depth/shape) featuresIV. Ocean Crusta. By the 1950’s scientists learnedi. Ocean floor is covered in sedimentii. Thickest near the continents/thinnest near mid-oceanic ridgesiii. Ocean crust is mafic (basalt and gabbro); no granite or metamorphic rockiv. High heat flow @ mid-oceanic ridgesV. Hess’s Theory- called “Sea-floor Spreading” (Hess/Dietz concept)a. Upwelling mantle erupts @ mid-oceanic ridgesb. New crust moves away from ridges gathering sediment over timec. @ trenches the sea floor dives back under the mantled. This became a potential mechanism for sea floor spreading/”continental drift”VI. Magnetic Polesa. The magnetic poles intersect the Earths surface just like the geographic poles doi. Magnetic N & S poles both existii. Near but not aligned with the geographic polesiii. Move constantlyVII. Paleomagnetisma. Rock magnetism can be measured in the labb. “fossil magnetism” = paleomagnetismc. Iron (Fe) preserves infoi. Declination and inclination preserved in rocksVIII. Earths Magnetism Fielda. Geographic and magnetic poles are not parallelb. A compass points to magnetic N not geographic Nc. Difference between geo and mag is called “declination”d. Angle differentiation between magnetic field &earths surface is “inclination”IX. Magnetic Reversalsa. Are geologically rapidb. Time between reversals varies from 10,000 to 25 million yearsc. Can be used as time markersd. Can take anywhere from 100 to 1000 years to