BYU - PHY S 100 - Class Notes - Week 12

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School: Brigham Young University

Department: OTHER

Course: Physical Science

Professor: Patricia Ackroyd

Term: Spring 2017

Name: Chapter 26, Week 12 Notes

Description: The mechanical and compositional layers of the earth, including evidence for these layers

Uploaded: 12/10/2017

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Chapter 26: the Earth's Interior Evidence from Direct Observation • Places where rocks that were deep within the Earth are now exposed on the surface • Crust: uppermost layer, rock foundations of continents and oceans   • Mantle: layer below earth's curse, peridotites form here (denser than basalt and granite of crust)    Evidence from Meteorites • Stony chondrites: made up of same materials from which earth and other planets were made • Stony achondrites: pieces from top layers of planets, separated into layers and then broken up    Evidence from Earth's Mass and Density • F = GmM/ d^2 • Mass: 5.973 * 10^24 kilograms • Density: 5.5 g/cm^3  (density tells us about the rocks that make up earth!)    Evidence from Seismology • Earth's crust is actually pretty elastic • Faults: created by elastic rebound (stress of lithosphere makes it rupture and rebound like a
rubber band) • Seismic waves: produced by earthquakes o Tectonic plates grind against each other. Pressure underneath snaps a section of plate,
creating shock waves • Compression waves: P-waves • Shear waves: S-waves • Surface waves: slowest and last to arrive, cause devastating tsunamis, create most earthquake
damage, only travel in solids • Focus: where earthquake originates    (epicenter: point on surface directly above focus) • Seismic discontinuity o Place where velocities of seismic waves change abruptly (proof that density of rock changes
abruptly with depth) • Shadow zones (no seismic waves) is proof of boundary between solid mantle and liquid layer
below (outer core)    Evidence from Earth's Magnetic Field • Curie temperature: at 760 degrees C, iron loses its magnetism…so how is Earth's magnetic field
produced, if not in the core? • Convection between top and bottom of outer core, iron atoms move as electrical conductors o Electrical currents in outer core --> magnetic field    Mechanical Layers of Earth • Refers to the physical behavior of the rocks in the layers Lithosphere: outermost rigid, brittle, skin-like layer • From surface to uppermost part of mantle • Granite in continental crust, basalt in oceanic crust, and peridotite in mantle

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