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Unit 7 Test Review
1. The Richter scale measures earthquakes by the amount of energy released. How much stronger
is a 7.0 magnitude earthquake than a 5.0 magnitude earthquake? The Richter scale is a
logarithmic scale. An increase of a whole number on the scale equals an earthquake 10x’s more
powerful. So the correct answer is 100 times more powerful.
2. Ocean crust is thinner and more dense than continental crust. (thicker, thinner) and (more/less
dense)
3. Continental crust is thickest under what geologic formation?_mountains
4. What material is the ocean crust mostly composed of?_basalt What material is the continental
crust composed of? _granite
5. Of basalt and granite, which is more dense and therefore more likely to subduct under the
other? basalt
6. Who came up with the initial idea of continental drift? Alfred Wegner
7. What pieces of evidence were used in favor of continental drift? Africa and South America fitting
together, the fossil record, and polar wandering
8. What process formed the Hawaiian islands? What kind of plate boundary is associated with this?
The Hawaiian Islands formed as a result of a magma plume burning through the middle of the
Pacific plate. Hawaii is also known as a hot spot volcano. Trick question: there is no plate
boundary associated with the formation of Hawaii.
9. Describe the asthenosphere. Plastic in consistency, molten rock that allows plates to move
around by convection currents
10. Describe the process of sea floor spreading. Divergent plate boundary where new material is
added by plumes of magma. This plate boundary is described as being constructive.
11. What type of plate boundary is responsible for the Himalaya Mountains? Convergent boundary.
This is also referred to as a destructive boundary.
12. The Mid-Atlantic ridge and the Eastern African Rift valley are a result of what type of boundary?
Divergent plate boundaries
13. What did the Deep Sea Drilling Project teach us about the age of the oceans? The plate is oldest
at the edges of the continents and youngest near the mid ocean ridges.
14. What is causing the volcanic eruption on the island of Hawaii? A plume of magma referred to as
a hot spot.
15. What causes hot spots? Convective currents and plumes of magma rising from the core.
16. The Mariana Trench has been created by what type of plate boundary? Convergent
17. What are isostatic sea level changes a result of? Plate movement (sea floor spreading) and
thermal expansion
18. The magnetic pattern from magnetic field reversal around a sea floor spreading site could be
described as a zebra pattern
19. Subduction zones are associated with which type of plate boundary? Is it constructive or
destructive? Convergent and destructive.
20. The deepest point in any ocean is in which ocean, and what is the name of the deepest point?
Pacific Ocean, Mariana Trench. The deepest point is called Challenger Deep.
21. Kauai has moved 519 km from its original spot over the last 5,000,000 years. How fast did the
Pacific plate move in order for this to happen? (in cm/yr) 10.38 cm/yr
22. A map of major seismic activity (earthquakes) could show us what? Plate boundaries
23. Describe the difference between an isostatic sea level change and an eustatic sea level change.
Eustatic involves a change in volume (melting or freezing of glaciers). Isostatic involves a change
in the ocean floor or thermal expansion of the water.
24. How can plate tectonics lead to mass extinction events? Brand new competition between
species, reduction in continental shelf in the ocean, changing the local climate (either hot or
cold)
25. How can plate tectonics affect global carbon dioxide levels? Volcanic eruptions caused by
shifting plates release more carbon dioxide
FREE RESPONSE PRACTICE
26. Divergent boundaries occur both under continental crust and oceanic crust. Discuss the
different outcomes of each type and the mechanism that cause these differences. (Hint SeaFloor spreading and Rift valleys)
Keep in mind for this question you need to differentiate between what is happening in Iceland
or Eastern Africa and what is happening in the middle of the Atlantic Ocean. The driving force
for the whole thing is heat distribution from the core, in terms of convection currents.
27. Describe how the density and isostasy of the continental crust and oceanic crust differ. Include
definitions of density and isostasy, what affect this difference has on the crustal landscape and
oceanic landscape when a continental crust approaches an oceanic crust, and when two
continental crusts approach each other.
Density is mass per unit volume. Isostasy is how a plate rides on the asthenosphere in terms of
density and thickness. Remember continental crust is less dense than oceanic crust and tends to
“ride on top” of the more dense ocean crust. When we get ocean and continental crust colliding,
typically a subduction zone forms, much like that off the shore of Japan (Mariana Trench). Also,
on the continental crust, a volcanic mountain chain forms (Sierra Nevada). When two
continental crusts collide, a mountain range develops (the Himalayas).