Term
| Major processes that have contributed to Earth’s internal heat: |
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Definition
–Heat released by colliding particles during the formation of Earth
–Heat released during gravitational contraction of the early Earth
–Heat emitted by radioactive decay of unstable isotopes within the Earth
–Early impact with a Mars-sized object
–Heat released as iron crystallized to form the solid inner core |
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Term
| Planetesimals Aggregated into |
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Definition
| Form Larger Bodies ~4.6 B.Y. Ago |
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Term
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Definition
| Form Planets, Including Earth |
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Term
| Collision caused extensive |
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Definition
| heating and melting of the Earth and impactor; Moon formed from material ejected into space |
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Definition
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Definition
cooled and
crystallized from the bottom-up
over millions of years to form a
solid mantle capped by a
primitive crust of basalt and
komatiite |
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Term
Short-lived
radioactive
isotopes only
had |
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Definition
half lives
of a few
million years
and have
long since
decayed |
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Term
Long-lived
radioactive
isotopes keep |
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Definition
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Term
Iron sank during
differentiation of Earth to
form the |
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Definition
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Term
Magma ocean cooled and
crystallized to form |
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Definition
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Term
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Definition
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Term
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Definition
Detrital zircons found in Western Australia
yield ages between 4.2 billion and 4.4
billion years old
Zircon grains found in highly-deformed
ancient rocks of Greenland and western
Canada date back to 4.2 billion years
These minerals provide clues as to when
Earth’s earliest continental crust formed |
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Term
| Oldest zircons recovered from the |
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Definition
| ~3.5 b.y. old Jack Hills metasandstone, Australia. |
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Term
| The zircons are much older than the |
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Definition
| metasandstone, possibly eroded from ancient granites that no longer exist |
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Term
| Acasta Gneiss in NW Canada, dated at |
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Definition
| 3.96 b.y., is the oldest known crustal rock on earth: |
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Term
| Acasta Gneiss in NW Canada, dated at 3.96 b.y., is the oldest known crustal rock on earth: |
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Definition
| Suggests continental crust did not become permanent until about 3.96 b.y. ago |
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Term
| Zircons within Acasta Gneiss date back to |
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Definition
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Term
| Zircons within Acasta Gneiss date back to 4.2 billion years: |
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Definition
–Time of scattered small land masses
–Barren rocky plains and sand
–No life back then, only organic molecules |
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Term
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Definition
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Definition
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Term
| Zircons suggest that the oldest continental crust appeared by |
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Definition
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Term
| The study of Earth’s interior is difficult: |
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Definition
We can drill down a few kilometers into Earth’s crust
–In some cases, rocks formed several kilometers beneath the surface can be sampled
–Geophysical surveys can measure certain properties of deeply-buried rocks |
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Term
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Definition
Earth’s interior based on seismic refraction data
Replicate deep conditions in a laboratory |
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Term
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Definition
| travel through the Earth in all directions as vibrations that we recognize as earthquakes |
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Term
| Slippage along faults releases energy as |
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Definition
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Term
| Tectonic forces can cause the rigid crust of the |
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Definition
| Earth to deform and break along faults |
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Term
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Definition
| instruments that measure the vibrations in the ground |
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Term
| A typical seismic observatory measures three components of ground motion |
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Definition
–Vertical up-down motion
–Horizontal east-west motion
–Horizontal north-south motion |
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Term
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Definition
| the fastest, arrives at station first |
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Term
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Definition
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Definition
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Term
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Definition
| Primary waves that travel through solid rock at an average velocity of ~5 km/sec |
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Term
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Definition
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Term
| Push or pull particles of matter |
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Definition
| in the direction of their path of travel |
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Term
| Movement of P-waves Through Earth Material |
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Definition
| Particles compress and expand in direction of wave travel |
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Term
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Definition
Secondary waves that travel through solid rock at about half the speed of P-waves
Also called shear waves because they push material at right angles (90o) to their path of travel
Unlike P-waves, shear waves cannot travel through liquids or gasses |
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Term
| Movement of S-waves Through Earth Material |
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Definition
| Particles pushed at right angles to direction of wave motion |
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Term
| Rays Originating At The Source And Constructed Perpendicular To Wave Fronts Can Be Used To |
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Definition
| Trace Seismic Waves Through Earth’s Interior |
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Term
| When seismic waves (rays) encounter a boundary between materials with different properties, |
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Definition
| properties, the energy splits into reflected and refracted (bent) waves. |
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Term
| When the velocity of seismic waves increases when passing from one layer into another |
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Definition
| the waves refract (bend) upward towards the boundary separating the layers |
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Term
| When the velocity of seismic waves decreases when passing from one layer into another |
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Definition
| the waves refract (bend) downward away from the boundary separating the layers |
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Term
| Seismic Studies Indicate That The Continental Crust Is Thicker Than |
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Definition
|
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Term
|
Definition
–Ranges from 3 to 15 km thick
–Consists primarily of basalt and gabbro |
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Term
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Definition
–~40 to 65 km thick
–Average composition of granite
–Lighter (more buoyant) than oceanic crust |
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Term
| The Crust and Solid Upper Portion of the Mantle Comprise the |
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Definition
|
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Term
| Lithosphere (sphere of rock |
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Definition
–Relatively cool, rigid layer
–Averages about 100 km in thickness, but may be 250 km or more thick beneath the older portions of the continents
–Lithosphere broken into a series of plates |
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Term
| The Asthenosphere Lies Just Below The |
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Definition
|
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Term
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Definition
| weak zone of partially- melted peridotite that slows down seismic waves |
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Term
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Definition
| outward when traveling through the mantle due to increasing velocity with depth |
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Term
| Increasing velocity due to increasing |
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Definition
| mantle density with depth |
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Term
| Seismic Velocities Increase With Depth But... |
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Definition
| Slow Down In Upper Asthenosphere |
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Term
| The Lower Asthenosphere Include |
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Definition
| IncludesTwo Transition Zones Characterized By Increases In Seismic Wave Velocities |
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Term
| Two Transition Zones Characterized By |
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Definition
Increases In Seismic Wave Velocities
400 km Olivine to spinel crystal structure |
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Term
| Two Transition Zones Characterized By Increases In Seismic Wave Velocities |
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Definition
| 670 km Spinel to perovskite crystal structure |
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Term
| Below The 670 Km Transition Zone Lies The |
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Definition
Mesosphere (Lower Mantle)
Velocities of P- and S-waves increase with depth in the Mesosphere |
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Term
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Definition
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Term
| Velocities of P- and S-waves increase with |
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Definition
| depth in the Lower Mantle |
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Term
| Rocks in the Mesosphere are solid but |
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Definition
| very hot and capable of flow |
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Term
| Seismic Studies Suggest That The |
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Definition
Outer Core is Composed of Liquid Iron
S-waves cannot pass through it
P-WAVES SLOW DOWN |
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Term
| P-waves bend downward when |
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Definition
entering the outer core due to a decrease in velocity…
Bending of P-waves in the outer core creates P-wave shadow zone
…and bend again when they leave |
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Term
| S-waves cannot travel through |
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Definition
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Term
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Definition
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Term
| Liquid iron in the outer core is stirred into convective motion by |
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Definition
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Term
| Circulation of the liquid iron produces |
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Definition
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Term
| These electric currents, in turn |
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Definition
| generate the Earth’s magnetic field |
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Term
| Cylinders of spiraling liquid iron in outer core behave like |
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Definition
| coil of current passing through wires of electromagnet |
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Term
| Earth’s magnetic field envisioned as |
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Definition
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Term
| Earth’s temperature gradually increases with depth |
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Definition
| at a rate known as the geothermal gradient: |
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Term
| Earth’s temperature gradually increases with depth at a rate known as the geothermal gradient: |
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Definition
Varies considerably from place to place
–Averages between about 20C and 30C per km in the crust
–Rate of increase of heat with depth significantly less in the mantle and core |
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Term
| The Geothermal Gradient is |
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Definition
| a curve showing the increase of temperature with depth |
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Term
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Definition
Process called conduction
–Not very efficient at transferring heat |
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Term
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Definition
There is only a modest increase in temperature with depth in the mantle
–Mantle must have an effective method of transmitting heat from the core upward to base of the crust
–Convection would be an effective process |
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Term
| Two layer mantle convection |
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Definition
–Separate convection cells for the upper and lower mantle
–Boundary between the upper and lower mantle is the 670 km transition zone |
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Term
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Definition
Upper and lower mantle part of one large convection system
–Hot, rising mantle plumes originate at the core- mantle boundary |
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Term
| Two-Layer Convection Model: Upper And Lower Mantle Have |
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Definition
Separate Convective Systems
Boundary is the 670 km transition zone
Shallow convection cells carry lithosphere like a conveyor belt |
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Term
| Whole-Mantle Convection Model: Upper And Lower Mantle Part Of One |
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Definition
|
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Term
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Definition
Three dimensional model of Earth’s interior based on seismic imaging
Requires seismic records from many different earthquakes
Identifies regions where P- and S-waves are faster or slower than average |
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Term
| Velocity variations of seismic waves attributed to variable temperatures and other material properties |
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Definition
Higher temperatures, slower velocities
–Lower temperatures, greater velocities |
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Term
| Western U.S. tectonically active |
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Definition
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Term
| Earth's overall density is calculated to be 5.52 grams per cubic centimeter. However, crustal rocks only give densities around 2.9 grams per cubic centimenter. Where is the excess density? |
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Definition
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Term
| hich of the following statements regarding heat flow on Earth is TRUE? |
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Definition
| Heat flow, as measured on Earth's surface, is higher along mid-ocean ridges and other volcanically active regions but lower within the interiors of stable continents. |
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Term
| The bending of seismic waves when passing through Earth's interior is due to changes in wave ____________ when encountering different Earth materials. |
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Definition
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Term
| The bending of seismic waves when passing through Earth's interior is called ________ |
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Definition
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Term
| the Moho is the boundary between the ________ and _________ |
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Definition
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Term
| What happens to S-waves as they pass through the asthenosphere? |
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Definition
.
S-waves slow down because of the presence of a few percent partial melt |
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Term
| What happens to P- and S-waves when encountering transition zones at 400 km and 700 km depths? |
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Definition
| They speed up due to density increases in mantle rock resulting from phase changes in minerals. |
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Term
| What changes in P- and S-waves occur when encountering the outer core that lead scientists to conclude that this layer is composed of liquid iron? |
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Definition
| S-waves cannot pass through the outer core while P-waves slow down significantly when passing through this layer. |
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Term
| The upper mantle is composed largely of a rock called ___________ |
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Definition
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Term
| P-wave shadow zones are regions on Earth's surface where |
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Definition
| No P-waves are detected by seismometers. |
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Term
| Circulation of liquid iron in the outer core is thought to be responsible for Earth's _____________ |
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