Chapter 17 Earth's Interior

Geophysics

the branch of geology that studies the interior of the earth

Seismic waves

vibrations from a large earthquake will pass through the entire earth

Seismic reflection

the return of some waves to the surface after bouncing off a rock layer boundary - sharp boundary between two materials of different densities will reflect seismic waves

Seismic refraction

bending of seismic waves as they pass from one material to another having different seismic wave velocities

Crust

outer layer of rock that forms a thin skin on earth’s surface

Oceanic crust

thinner - composed of mafic rocks

Continental crust

thicker - composed of felsic rocks

Mantle

a thick shell of dense rock that separates the crust above from the core below

Lithosphere

crust and upper mantle

Asthenosphere

lies below the lithosphere and may represent rocks close to its melting point - seismic waves are low in this layer

Core

metallic central zone of earth - S waves pass through the inner core (solid) but not the outer core (liquid)

Seismic shadow zones

when parts of the earth does not recieve seismic waves

P wave shadow zone

caused by refraction of P waves within the earth’s core

S wave shadow zone

suggest outter core is a liquid

Composition of core

iron nickel alloy mixed with small amounts of lighter elements

D layer

marked by great changes in seismic velocity, density, and temperature

Isostasy

equilibrium of adjacent blocks of brittle crust “floating” on upper mantle

Isostatic adjustment

rising or sinking of crustal blocks to achieve isostatic balance - crust will rise when large mass is rapidly removed from the surface as at the end of ice ages - rise of crust after ice sheet removal is called crustal rebound

Gravitational force

determined by the mass and the distance between objects

Gravity meters

detect tiny changes in gravity at earth’s surface related to total mass beneath any given point - gravity slightly higher over dense materials and slightly lower over less dense materials

Curie point

the temperature below which a material becomes magnetized

Magnetic reversals

times when the poles of earth’s magnetic field switch - recorded in magnetic minerals

Paleomagnetism

the study of ancient magnetic fields in rocks,allows reconstruction of plate motions over time

Magnetic anomalies

local increases or decreases in earth’s magnetic field strength -positive and negative magnetic anomalies represent larger and smaller than average local magnetic yield strengths, respectively

Magnetometers

instruments used to measure local magnetic field strength - can detect metallic ore deposits, igneous rocks, and thick layers of non-magnetic sediments beneath earth’s surface

Heat flow

the gradual loss of heat through earth’s surface

Geothermal gradient

temperature increase with depth into the earth