GLG101: Physical Geology Lecture Outlines for Exam#3:

G. Calderone- GLG101: Physical Geology Lecture Reviews, Exam#3, August 23, 2011 Page 20 of 20•The Earth's magnetic field occasionally reverses (NOT every 500,000 years though, I don'tcare what your text says) irregular through time. Cause: unknown.•Magnetic field anomaliesBodies of magnetic rock perturb the usual value of the Earth's magnetic field.More magnetic rock beneath the surface magnetized in the direction of the Earth'spresent magnetic field produces positive magnetic anomalies (field strength is higherthan normal)Less magnetic rock beneath the surface OR rock magnetized opposite of the direction ofthe Earth's present magnetic field produces negative gravity anomalies (fieldstrength is less than normal)Magnetic anomalies can be used to locate metal ore bodies or depth to crystalline rock indeep sedimentary basins AND play an important role in the determinations of platemotionsEvidence from meteorites•Origin of meteorites- trajectories place most of them in asteroid belt between Jupiter &Mars. They are thought to represent either a broken up planet or original material of thesolar system that never coalesced into a planet because of Jupiter's enormous gravityfield.•Composition of meteorites- Nickel-iron. Stony- much like Peridotite in compositionPoint: Earth interior is probably made up of similar stuff•Age of meteorites- gives ultimate age of Earth at 4.6 billion years (supported by moonrocks)Summary of Earth's interior•Seismology gives layers of EarthCrust-mantle-outer core-inner coreLithosphere-asthenosphere-lower mantle (= mesosphere)-outer core-inner core•Xenoliths (inclusions), seismology, constrain properties of mantle, meteorites constraincomposition. Mantle is most probably solid (more-or-less) peridotite. Seismology,however, suggests that some composition changes may occur below asthenosphere (400 &670 km discontinuities.•Gravity, seismology, and magnetism constrain properties of core, meteorites constraincomposition. Outer core is most probably liquid iron-nickel. Seismology, however,suggests that innermost core is solid.•Age of meteorites- gives ultimate age of Earth at 4.6 billion years•Summary films: Earth Interior (Earth Revealed)