GEOL 102 1st Edition Lecture 3Outline of Last Lecture NoneOutline of Current Lecture I. Continental DrifII. Compositional EarthIII. Observations of the SeafloorIV. Plate TectonicsCurrent LectureI. Continental DrifAlfred Wegener suggests that continents are not fixed, but that they migrateEvidence: Fit of continental coastlinesGlacial depositsGeologic evidence of climatic zonesFossil evidence: distribution along now-far coastsII. Compositional EarthCrust: Density is 2.6 gm/cm cubed, thickness is 30-40 km (continental)Density is 3 gm/cm cubed, thickness is 25-10 km (oceanic)Mantle: density is 5 gm/cm cubedOuter Core: Very DenseThese 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.Inner Core: very, very denseRheology: material behavior, lithosphere is brittle and breaks under stress, asthenosphere flowsIII. Observations of the SeafloorFractures along mid-ocean ridgesOceanic islands, seamounts, guyots, trenches High heat flow at mid-ocean ridges Breakthrough of sea-floor understanding came with magnetic anomalies Molten rock cools and preserves properties of the prevailing fieldStrength, orientation, and polarity of the earth’s magnetic field varies with timeIV. The theory of plate tectonics emerges in the 1960sPlates move relative to each otherGeologic activity is focused at plate boundariesDivergent: moving away, home to mid-ocean ridgesAsthenosphere upwells, forms magma, creates crustLithosphere cools and thickens away from ridge axisConvergent: moving towards each other, crust is consumedHappens at oceanic-continental and continental-continentalPartial melting arc volcanism, accretionary prisms, quakesTransform: sliding along, crust not created or
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