SCI102 Chapter 12

Terms in this set (39)

3 interior layers of the Earth
crust, mantle, and core
what established the 3 layers?
gravity and chemical segregation
mineral and phase changes
the density of rocks increases toward the center of the planet due to gravity
seismic velocities
-seismic waves travel fastest in stiff (rigid) rocks
-velocities vary based on composition of the rocks
interactions between seismic waves and Earth's layers
-seismic waves reflect and refract as they pass through the different layers of Earth
-allow us to "see" inside the Earth
when are seismic waves reflected and refracted?
when the waves hit a boundary between different Earth materials
oceanic crust
-forms at mid-ocean ridges
-averages 7 km thick
-composed of basalt and gabbro
-average density is 3.0 g/cm3
continental crust
-heterogenous structure and composition
-averages 40 km thick
-average density of 2.7 g/cm3
the Moho
the boundary between the crust and the mantle discovered in 1909 through the jump in velocity of P waves below the base of the continents
what happens to seismic waves at the Moho?
-p waves velocities abruptly increase
-waves refract as they cross the Moho
mantle
-makes up 82% of Earth's volume and is nearly 2900 km thick
-extends from Moho to liquid outer core
-solid rock layer composed of silicate minerals rich in iron and magnesium
upper mantle
-extends from the Moho to 660 km deep
-composed of peridotite, an iron and magnesium rich rock
lithospheric mantle
the uppermost part of the mantle and ranges in thickness from a few km to 200 km
asthenosphere
a weak layer beneath the lithospheric mantle
transition zone
the lower portion of the upper mantle ranges between 410 and 660 km depth
lower mantle
-extends from the transition zone to the liquid core (2900 km deep)
-occupies 56% of Earth's volume
D" layer
-the boundary between the rocky lower mantle and the liquid outer core
-cool regions are thought to be the remnants of subjected lithospheric plates
-hot regions are thought to be the start of deep mantle plumes
the core mantle boundary
has shadow zones beyond 100 degrees from an epicenter, where p and s waves are absent or weak
shadow zone
-s waves cannot travel through liquid
-p waves are considerably refracted through liquid
outer core
-liquid, based on the absence of s waves traveling through the core
-density of 9.9 g/cm3
-composed mostly of iron with some nickel
-2270 km thick
inner core
-solid, dense sphere
-density of 13 g/cm3
-is growing as Earth cools at the expense of the outer core
-rotates faster, and moves independently of, the crust and mantle
inner core-outer core boundary
some p waves are strongly refracted by a sudden increase in velocity at a boundary within Earth's core
heat flow from hotter regions to colder regions
-core is 5500 degrees celsius
-surface is 15 degrees celsius
-heat flows from the core to the surface
-flow is highest near mid ocean rigids
-flow is lowest at the deep abyssal plains
how did Earth get so hot?
-1st stage lasted 50 million years when temperatures increased rapidly
-2nd stage involves the slow cooling over the next 4.5 billion years
how does heat travel through Earth?
-conduction and convection which occur within Earth's interior
-radiation which transports heat away from Earth's surface to space
convection
-the transfer of heat where hot materials replace cold material (or vice versa)
-primary heat transfer within Earth
-cycles occur within the mantle and the outer crust
viscosity
a material's resistance to flow
conduction
-the transfer of heat through a material
-occurs through the collision of atoms or through the flow of electrons
-not an efficient way to move heat through most of Earth
where are conduction and convection important?
-conduction= solid inner core
-convection= from the inner to the outer core
geothermal gradient
the profile of Earth's temperature at each depth
Earth's temperature profile
-crust= 30 degrees celsius per km of depth
-mantle= .3 degrees celsius per km
-base of lithosphere= roughly 1400 degrees
-base of mantle= roughly 2500 degrees
-Earth's center= roughly 5500 degrees
what does Earth's rotation cause?
a centrifugal force that is proportional to the distance from the axis of rotation
how does Earth's shape affect gravity?
the oblate ellipsoid (bulges at the equator) shape results in a weaker gravity at the equator
seismic tomography
involves collection data at many different seismic stations to "see" parts of Earth's interior in 3 dimensions
how are 3 dimensional changes in composition and density detected?
-gravity measurements and can be viewed using seismology
-identifies regions where p and s waves travel faster or slower than average
-variations in p and s wave velocities allow scientists to image subjecting plates and mantle plumes
Earth's magnetic field
produced by convection of liquid iron in the outer core
geodynamo
-the magnetic field caused by spiraling columns of rising electrically charged fluid in the outer core
how is Earth's magnetic field measured?
-declination measures the direction of magnetic north pole with respect to the geographic north pole
-inclination measures the downward tilt of the magnetic lines
magnetic reversals
-the magnetic field randomly reverses and north and south poles swap direction
-reversals take only a few thousand years
-discovery of reversals have been extremely important to the foundation of the theory of plate tectonics
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