Lecture 4 - LECTURE NOTES - GEOSCIENCES 40 (Marone/Arthur)...

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LECTURE NOTES -- GEOSCIENCES 40 (Marone/Arthur) Sep 8 2005, Lecture 4 Sea Floor Spreading Earth's surface is in motion! Recall: THE "WILSON CYCLE" (CREATION AND DESTRUCTION OF OCEAN BASIN) SUPPORT FOR SEA FLOOR SPREADING -Magnetic "stripes" on seafloor What Is Driving All This Commotion? Heat flow from within the Earth drives plate motions Plates are the brittle layer (~ 100 km thick) that is carried on more ductile region below (asthenosphere) Motion is driven by heat flow out of Earth Earth's interior is VERY HOT! Mantle Convection internal heat engine radioactive decay Three main forces that move plates 1. Ridge Push 2. Basal drag 3. Trench Pull EARTH'S MAGNETIC FIELD The Dipole Field (see diagram) -A giant bar (dipole) magnet along spin axis -Magnetic "force" lines (Today "Normal") --"enter" at North Pole parallel to spin axis --"exit" at South Pole parallel to spin axis --force line angle w/ surface of earth progressively horizontal towards equator -Many rocks record orientation of ancient magnetic field (polarity or paleolatitude) Polarity Reversals -Earth's field orientation flips periodically (N magnetic pole and S magnetic pole switch); -Related to circulation of molten outer core -Polarity flips recorded in remanent magnetism
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This note was uploaded on 03/30/2008 for the course GEOSC 040 taught by Professor Arthur during the Fall '08 term at Pennsylvania State University, University Park.

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Lecture 4 - LECTURE NOTES - GEOSCIENCES 40 (Marone/Arthur)...

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