Chapter 12: Earth's Interior

asthenosphere

A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is easily deformed.

seismic topography

A technique that uses differences in the travel time of seismic waves produced by earthquakes and recorded on seismographs to construct three-dimensional images of Earth's interior.

transition zone

An area between two geographic regions that has characteristics of both.

Describe how Earth's inner core grows in size.

As Earth cools, iron began to crystallize and core grows. Liquid outer core allows it some space.

How do S waves "tell us" the mantle is solid?

B/c they go through it but then are blocked my liquid outer core

Distinguish between conduction and convection.

Conduction-the transfer of heat through matter by molecular activity Convection-transfer of heat by mass movement or circulation of a substance

lithospheric mantle

Earth's crust and that portion of the uppermost mantle directly below the crust, extending down about 45 mi. Some sources use this term to refer to the entire Earth.

What occurs during a magnetic reversal?

Earths magnetic field reverses polarity so the north needle on a compass would point south. during:the strength of the magnetic field decreases to about 10% and poles locations begin to wander.

True or False: No seismic waves arrive in the shadow zone? Explain.

F. Some do. All S do not because they dont travel through liquid but most P waves get refracted similar to how light passes from air to water

What is the importance of determining the cross-over distance? (See Figure 12.8)

It is important to find the thickness of crust for any location. refracted waves enter mantle, seismographs near the center record waves first then seis mos further from center record waves 2nd. pt at which both waves arrive at same time is cross-over

upper mantle

Layer of the earth directly below the crust that is made up of a mixture of elements which makes it soft and plastic.

What mineral phase changes occur at the top and botton of the transition zone?

Olivine. in the top it converts to B-spinel and in the bottom it converts to more compact ringwoodite

mantle

One of Earth's compositional layers. The solid rocky shell that extends from the base of the crust to a depth of 2900 kilometers.

Would you expect to find a large layer of iron ore underground in a region with a positive or negative gravity anomaly? Explain.

Positive because this is where thick, dense volcanic rocks filled a rupture in the crust more than a billion years ago.

geodynamo

The global geosystem that produces Earth's magnetic field, driven by convection in the outer core.

geothermal gradient or geotherm

The gradual increase in temperature with depth in the crust. The average is 30 degrees Celsius per kilometer in the upper crust.

core

The innermost later of Earth based on composition. It is thought to be largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfate.

lower mantle

The part of the mantle that extends from the core-mantle boundary to a depth of 600 kilometers. Also known as the Mesophere.

lithosphere

The rigid outer layer of Earth, including the crust and upper mantle.

inner core

The solid innermost later of Earth, about 1216 kilometers in radius.

convection

The transfer of heat by the mass movement or circulation of a substance.

conduction

The transfer of heat through matter by molecular activity.

If there were a lot of water in Earth's mantle, in what layer could it most likely reside?

The transition zone within the upper mantle

crust

The very thin outermost layer of Earth.

Why is Earth's core one-sixth of Eath's volume but one-third of its mass?

b/c it is composed mostly of iron which is the most dense of the common elements.

Why does the mid-Atlantic ridge appear as a slow seismic velocity anomaly in Figure 12.20?

b/c it is hotter and more tectonically alive making this portion weaker and warmer which slows S waves

Why is conduction more important than convection within Earth's crust?

b/c the iron-rich material in core is too dense to intrude (convect) into less thermal rocks. for the thermal energy to leave the core, it must conduct across the core-mantle boundary and up through the D layer. after upper mantle, conducts in lithosphere

Why is convection an inefficient means of heat transfer to materials with high viscosity?

b/c these materials resist flow/are too strong to flow and thus do not move the heat in a fluid-like manner

Why is seismology responsible for gasoline prices being more affordable than they might be without seismology?

b/c without it a huge number of wells would have to be randomly drilled to find oil. seismology helps find structures where petroleum may be trapped

Why is the lithosphere stiffer than the asthenosphere?

bc its temp is much colder than its melting temp.

Why would tectonic plates have a hard time moving if it were not for the existence of the asthenosphere?

bc the asthenosphere is weaker and softer bc it is close to melting temp

How is the D'' layer similar to the lithosphere?

both have large variations in composition and temperature

What prevents Earth from being a cold, motionless sphere of totally solid rock and metal?

convection with mantle, sinks cold oceanic lithosphere back into deep mantle

Why might a magnetic reversal be dangerous to humans?

could cause health hazards w/ excess ionized materials

Why is heat flow from Earth's surface not evenly distributed?

earth loses most of its heat near mid ocean ridges where magma rises toward the surface to fill the cracks where tectonic plates pull apart. Continents lose heat faster than old oceanic seafloor bc they contain higher amounts of heat producing isotopes

What happens to rock in regions where the geotherm crosses above the melting point curve?

it begins to soften and weaken

Earth once rotated much faster than it currently does. How would Earth's shape have been different in the past?

it would have been more rounded than ellipsoid (poked out on sides)

D'' layer

A region in roughly the lowermost 200 kilometers of the mantle where P-waves experience a sharp decrease in velocity.

viscosity

A measure of a fluid's resistance to flow.

What are the two major reasons for the increase in density with depth within Earth's mantle?

1) Compression resulting from increased pressure 2) Mineral phase change

List three ways that oceanic crust and continental crust differ. Where is the thickest crust found? The thinnest crust?

1. Oceanic crust is created at mid-ocean ridges, continental varies 2. Oceanic crust has similar composition and thickness throughout while in continental it varies. 3. Oceanic crust averages 7 km thick while cont is 40-70

What are the three driving forces of convection in the outer core?

1.heat conducts out of core into mantle, outermost core cools,becomes denser and sinks 2.crystallization of solid iron sinks to form inner core,leaves behind fluids, drives chem. convection 3.radioactive isotopes in core that drive thermal convection

Describe the heat sources that caused Earth to get very hot early in its history?

1st stage involved rapid increase in internal temp. earth formed through collisions of baby planets.more collisions=more kinetic energy. as earth grew, temp increased, contained many short lived radioactive isotopes (released radiogenic heat)

outer core

A layer beneath the mantle about 2270 kilometers which, which has the properties of liquid.

What role does gravity play in the layering of planets?

Solid Iron (the heaviest) makes up the core. The outer core is made of liquid iron. The Lower mantle is a solid rocky mantle. Upper mantle is lighter and rocky. Gravity causes respective layering.

What layer of Earth has the greatest volume?

The Lower Mantle. perovskite is the single most abundant material within the earth

Moho

The boundary separating the crust and the mantle, discernible by an increase in seismic velocity.