Download Ch. 9 Review - 8th Grade Science

Ch. 9 Review
Pgs. 356-357
#1-31
Write Questions and Answers
356-357 #1-5 Answers
• 1. The layer of the upper mantle that can flow
is the: A - Asthenosphere
• 2. Most scientists rejected Wegener’s theory
of continental drift because the theory failed
to explain: D – How the continents move
• 3. Subduction of the ocean floor takes place
at: D - Trenches
• 4. Two plates collide with each other at: B – A
convergent boundary
• 5. A fault in which the hanging wall slides up
and over the footwall is a: A – Reverse Fault
# 6-10 Answers
• 6. The earth’s outer core is made of basalt and
granite: False – Crust
• 7. The spinning of the asthenosphere, made of iron
and nickel, explains why Earth has a magnetic field:
False – Inner Core
• 8. Magnetic strips on the ocean floor are where
oceanic crust sinks back to the mantle: False – Deep
Ocean Trenches
• 9. When two continental plates converge, a rift valley
appears: False – Diverge
• 10. Land subsidence occurs when Earth’s surface
sinks as a result of geologic processes: True
11-12
• 11. How is the inner core different from the outer
core?
– The inner core is a dense ball of solid iron and nickel
that spins. The outer core, by contrast, is a layer of
molten iron and nickel that behaves like a thick liquid.
• 12. Explain why there are convection currents in
the mantle.
– Heat from the Earth’s core heats the mantle. Some
mantle material is soft and can bend like plastic. Over
time, this material can flow slowly, forming convection
currents.
13-14
• 13. How does a hot spot form a volcanic
island?
– At a hot spot on the ocean floor, magma from the
mantle melts through the crust, forming a volcanic
island.
• 14. What evidence of Earth’s climate in the
past supports the hypothesis of continental
drift?
– Evidence includes fossils of tropical plants found in
polar regions and scratches made by continental
glaciers found in places with mild climates.
15-16
• 15. What was the importance of the discovery
that molten rock was coming out of cracks along
the mid-ocean ridge?
– The importance of that discovery is that it supported
the theory that of sea-floor spreading. It also led
scientists to look again at Wegener’s theory of
continental drift.
• 16. Describe the processes that create a faultblock mountain.
– When tension caused by plate movements is great
enough to break the crust, normal faults form. Along
these faults, blocks of crust can slide, creating a faultblock mountain.
17-18
• 17. What happens when a plate of oceanic
crust collides with a plate of continental crust?
Why?
– Oceanic crust is more dense than continental
crust. As a result, when a plate carrying oceanic
crust collides with a plate carrying continental
crust, the oceanic plate sinks beneath the
continental plate (subduction)
• 18. Interview with Alfred Wegener
– Should include mentions of evidence he used,
such as fossils, landforms, and climate evidence.
19-20
• 19. Classify the layers of the earth.
– Solid – Crust, Lithosphere, Inner Core
– Solid but able to flow slowly – Asthenosphere
– Liquid – Outer Core
• 20. Comparing and contrasting oceanic and
continental crust.
– Both are parts of Earth’s outer layer.
– Continental crust consists of less dense rocks such as
granite.
– Oceanic crust consists mainly of denser rocks such as
basalt.
21-22
• 21. What do geologists think is the driving force
of plate tectonics? Explain.
– Convection currents in the mantle. The currents rise
through the asthenosphere, then spread out beneath
the lithosphere, dragging the overlying plate along.
• 22. What events can cause land subsidence and
what is formed as a result?
– Geologic processes such as diverging plates or tension
in the crust can cause land subsidence. With diverging
plates the result may be rift valleys or ocean basins.
23-24
• 23. State in one sentence the most significant
discovery geologists found through their study of
plate tectonics.
– Answers vary. Example: Pieces of Earth’s lithosphere
are in constant, slow motion, driven by convection
currents in the mantle.
• 24. A community has just built a street across a
strike-slip fault that has frequent earthquakes.
How will movement along the fault affect the
street?
– Where the street intersects the fault, the street will
eventually be broken and the segment will be moved
sideways.
25-27
• 25. The part carrying Australia is moving to the
northeast; the part carrying India is moving to the
North
• 26. Because the parts are moving in different
directions, a divergent boundary will form
• 27. This is a convergent plate boundary between two
continental plates. Mountains should form.
28-31
• 28. The arrow at A represents: D – Molten magma
rising from the mantle
• 29. What is occuring at the feature labeled B? F –
New rock is being added to the oceanic plate
• 30. As sea-floor spreading occurs, the oceanic plate:
C – Moves from B to C
• 31. What is occuring at D? G – The oceanic plate is
melting as it sinks into the mantle.