Geology Chapter 17

T/F: Most of the evidence for magnetic reversals comes from lava flows on the continents

True

T/F: Seismic waves travel faster in oceanic crust than in continental crust

True

T/F: The Moho separates the crust from the mantle

True

T/F: The asthenosphere may be a partially melted crystal and liquid slush

True

T/F: The average heat flow of the continents is the same as the average heat flow of the sea floor

True

T/F: The presence of an S-wave shadow zone implies that the Earth's core is liquid

True

T/F: The rise of the surface of the crust after removal of glacial ice known as isostatic rebound

True

a deviation from average reading is called a(n) ---

anomaly

the --- is a low velocity seismic zone

asthenosphere

--- is a circulation pattern in which low-density material rises and high-density material sinks

convection

Iron-nickel meteorites are an important source of information regarding the composition of Earth's ---

core

the P-wave shadow zone can be explained by the refraction of P-waves at the ---

core-mantle boundary

The rise of the crust after removal of ice is called ---

crustal rebound

heat flow --- the crest of the mid-oceanic ridges

decreases away from

recently, geologists have been analyzing --- generated by tidal friction, ocean waves, and storms to gain an even more detailed image of the crust and upper mantle

energy waves

a --- is a tool used to study the gravitational attraction between Earth and a mass within the instrument

gravity meter

high --- is usually an indication of a magma body or still-cooling pluton near the surface

heat flow

the gradual loss of heat through the Earth's surface is called ---

heat flow

a gravity meter registers --- over ore bodies

increased gravity

--- is a balance or equilibrium of adjacent blocks of brittle crust floating on the upper mantle

isostasy

--- predicts that the higher a mountain range extends above sea level the deeper it extends into the mantle

isostatic adjustment

what is the asthenosphere?

it is the zone of weakness in the mantle on which the lithosphere moves

one widely accepted hypothesis is that the Earth's magnetic field is created by Electric currents within the ---

liquid outer core

the crust and upper mantle form the ---

lithosphere

a region of magnetic force, called the --- surround the earth

magnetic field

a cavity or body of low-density material causes a --- pull on a gravity meter relative to average crust

weaker

the magnetic poles are displaced about --- degrees from the geographic poles

11.5

the average temperature increase in the shallow crust (the geothermal gradient) is about --- degrees C per kilometer

25

a gravity reading lower than the normal regional gravity indicates that a region is ---

being held down

--- indicates that the core of the Earth is a liquid

the S-wave shadow zone

the upper mantle consists of ---

ultramafic rocks

as lava cools below the --- point, a record of the Earth's magnetic field is permanently trapped in the rock

Curie

the --- is the transition zone at the core-mantle boundary

D layer

T/F: A region held down out of isostatic equilibrium produces a negative gravity anomaly

False

T/F: Generally, seismic wave velocity decreases with depth

False

T/F: Geologists think that the asthenosphere is molten

False

T/F: The concept of isostatic adjustments implies that all mountains extend to the same depth in the mantle

False

--- is the branch of geology that applies physical laws and principles to study Earth

Geophysics

the boundary that separates the crust from the mantle is the ---

Mohorovicic discontinuity

because --- can be accurately calculated, the size and shape of the core can be determined

P-wave paths

the study of ancient magnetic fields is called ---

paleomagnetism

at a pressure equivalent to a depth of 670 km the mineral olivine collapses to form ---

perovskite

the bending of seismic waves as they pass from one material to another is called seismic ---

refraction

the rock record for tens of millions of years indicates that the Earth's magnetic field ---

reverses polarity about every 500,000 years

--- is the return of some of the energy of a seismic wave to the Earth's surface after it bounces off a rock boundary

seismic reflection

detailed images provided by ---- suggest that the mantle is heterogeneous, probably due to variations in temperature, composition, and density

seismic reflection

the boundary between the core and the mantle is marked by great changes in ---

seismic velocity, density, and temperature are all correct

hot mantle rock rising slowly by convection under parts of the ocean explains

the unexpectedly high heat flow under the oceans

continental crust is --- relative to oceanic crust

thicker

oceanic crust is --- continental crust

thinner than

seismic P-waves --- through continental crust relative to oceanic crust

travel slower