ES 10: The Earth
Practice Final Exam 1998 Answers

David Sandwell
Greg Anderson

This practice final exam is drawn from a large set of final exam questions which are mostly based on the book and lectures, with only a few from other sources (such as the beach walk). Since it's drawn from the large set, it is likely to be very similar to the final exam. You can use it as a study guide to see what the exam might be like, but to do well on the final (which is 50% of your grade in ES 10) you will need to read through your lecture notes and the pages of the book noted on the Final Exam section of the exams page.

As on the real exam, when you read this practice exam, make sure to read each question completely and carefully. We've had people do poorly in the past because they merely skimmed the questions.

The correct answers are in bold face.

Multiple Choice

Choose the BEST and most CORRECT answer from the choices given after each question

1. Why don't continents subduct?
   1. they do not encounter subduction zones
   2. they are too old and cold to subduct
   3. they are too young and hot to subduct
   4. their crust is too thick and buoyant to subduct

2. Suppose you mapped a major fault and wanted to know its history of earthquakes for the past 10,000 years. You would:
   1. examine the earthquake catalogues
   2. date the ages of trees that had fallen in past earthquakes
   3. dig a trench across the fault and look for breaks in the sedimentary layers
   4. none of the above

3. Where did the rounded cobbles on the beach (on the Beach Walk) come from?
   1. longshore current
   2. dump trucks loads to stabilize beach
   3. fell from nearby cliff
   4. breakup of larger boulders by El Nino surf

4. The chemical composition of the Earth's crust is
   1. about the same as that of the Sun.
   2. about the same as that of the mantle.
   3. typical of the overall composition of the Earth.
   4. None of these is true.

5. Nuclear fusion
   1. converts some of the mass of an atom into energy.
   2. has only been achieved in an uncontrolled manner (in hydrogen bombs) on Earth.
   3. represents a potentially limitless energy source for society, if it can be achieved under controlled conditions.
   4. All of these are true.

6. The asthenosphere
   1. is a zone of anomalously low seismic velocity.
   2. underlies the lithosphere.
   3. is a zone of plastic deformation within the upper part of the mantle.
   4. All of these are true.

7. The rock cycle
   1. is more important now than ever before in Earth history.
   2. does not involve the biosphere or the atmosphere, only the solid Earth and the hydrosphere.
   3. describes the processes whereby the internal activities of the solid Earth interact with external activities involving the hydrosphere, biosphere, and atmosphere.
   4. operates independently of the process of plate tectonics.

8. The hardest mineral is
   1. quartz
   2. feldspar
   3. granite
   4. diamond

9. Crater Lake, Oregon, occupies the ____________ left by the prehistoric eruption of Mount Mazama.
   1. volcanic neck
   2. volcanic vent
   3. caldera
   4. tephra cone

10. Which one of the following does not belong with the others?
    1. subduction
    2. convergent margin
    3. island arc
    4. spreading center
    5. stratovolcano

11. Midocean ridges define
    1. convergent plate boundaries.
    2. shear plate boundaries.
    3. divergent plate boundaries.
    4. All of these are true.

12. The number of large lithospheric plates is
    1. twelve.
    2. eight.
    3. about twenty.
    4. too many to count.

13. Which one of the following statements is false?
    1. The midocean spreading ridge environment, although characterized by volcanism, is mainly aseismic (non-seismic).
    2. Most deep-focus earthquakes are located along convergent plate margins.
    3. The majority of circum-Pacific area earthquakes are associated with the process of subduction.
    4. The Pacific Plate, on the west side of the San Andreas Fault, is moving roughly northwards relative to the North American Plate, on the east side of the fault.

14. The principle of stratigraphic superposition states that:
    1. in any sequence of undisturbed sedimentary strata, the order in which the strata were deposited is from the bottom to the top.
    2. older strata are deformed and truncated by erosion before younger strata are deposited across them.
    3. tectonics, erosion, and sedimentation are all closely related.
    4. sediments are deposited in strata that are horizontal, or nearly so, and parallel to the Earth's surface.

15. A modern example of a plate triple junction is found in the area of
    1. the Red Sea and the Gulf of Aden.
    2. the Aleutian Islands.
    3. the Canadian Shield.
    4. the Andean coast of South America.

16. The periodic climatic variation in which tradewinds slacken and surface waters of the central and eastern Pacific become anomalously warm is called
    1. El Niño/Southern Oscillation.
    2. thermohaline circulation.
    3. geostrophic flow.
    4. Ekman transport.

17. Sea levels fluctuate as a result of
    1. changes in water volume due to the waxing and waning of continental glaciers.
    2. changes in ocean-basin volume as lithospheric plates shift their positions.
    3. tidal forces.
    4. All of these are true.

18. A good aquifer is typically
    1. porous but not permeable.
    2. permeable but not porous.
    3. porous and permeable.
    4. dependent on grain size.

19. The rate at which natural processes are removing carbon dioxide from the atmosphere is _____________ the rate at which human activities are adding it.
    1. slower than
    2. faster than
    3. approximately the same as
    4. not comparable to

20. Which one of the following is not one of the changes that scientists predict will be associated with global climatic warming?
    1. shifting of forest boundaries in response to altered temperature and precipitation patterns
    2. global decrease in sea levels due to excess evaporation
    3. increased droughts in some midcontinental agricultural regions
    4. All of these are changes that scientists predict will be associated with global climatic warming.

21. The glassy texture observed in obsidian is due to:
    1. the presence of only one crystal in the rock
    2. cooling over a long period of time during which the atoms actually break down and lose any order they had when the rock first formed
    3. alternating cooling and heating of the rock in the subsurface
    4. super rapid cooling such as that experienced when magma is ejected from a volcano

22. The portion of the conterminous United States that is most likely to have a volcanic eruption in the near future is:
    1. New England
    2. the Pacific Northwest
    3. central Kansas
    4. the coastline along Florida and Georgia

23. The Hawaiian Islands formed because:
    1. the Pacific Plate moved over a hot spot
    2. mid-oceanic basalts erupted and reached the surface of the water
    3. pyroclastic debris built up to reach sea level
    4. a series of composite cones were produced by subduction

24. Sediments composed of broken fragments of preexisting rocks and minerals are termed:
    1. chemoclastic
    2. chemical
    3. clastic or fragmental
    4. carbonates

25. The longshore drift of sand is due to:
    1. rip currents
    2. the backwash of the waves
    3. the incoming rush of the waves
    4. the angle of incidence waves have with the beach

26. The rate of seafloor spreading
    1. is uniform along the entire length of the spreading center.
    2. cannot be measured.
    3. is such that the ocean floors contain no rocks older than about 200 million years.
    4. is greater in deeper water.

27. The movement of the Pacific Plate past the North American Plate along the San Andreas fault is an example of what type of plate boundary?
    1. convergent continent/continent collision
    2. divergent
    3. convergent, ocean/continent collision
    4. transform

28. Continent/continent plate collisions are:
    1. a major producer of folded mountain ranges worldwide
    2. characterized by many deep-focus earthquakes that occur each year
    3. responsible for the formation of massive deposits of basalt on the Earth's surface
    4. best associated with divergent plate boundaries

29. An area that experiences only shallow earthquakes is:
    1. the west coast of South America
    2. southern Alaska
    3. the mid-Atlantic ridge
    4. none of these as they all have deep focus earthquakes

30. Lithosphere is created at spreading ridges. Where is it destroyed?
    1. transform faults
    2. the earth grows in radius
    3. deep ocean trenches
    4. hot spots

31. What is the speed of a seismic shear wave in the ocean?
    1. 1500 m/s
    2. 0 m/s
    3. it is related to ocean depth
    4. 835 km/hour

32. What is the best way to scientifically explain the thousands of feet of coral limestone beneath most atolls?
    1. sea level has fallen thousands of feet since the reef began to grow
    2. the eroded volcano below the limestone rose thousands of feet after the limestone accumulated
    3. the eroded volcano slowly sank as sea level remained steady or rose gradually
    4. the volcano never reached the surface, allowing a very thick cap of coral limestones to accumulate

33. Which two statements concerning the earth's magnetic field are true?
    1. during geologic time, the magnetic and geographic rotational poles have always been close together
    2. the magnetic field has become stronger over geologic time as more iron solidifies inside the inner core
    3. the magnetic field changes rapidly, geologically speaking, and the field has changed polarity many times
    4. the field originates in the lithosphere because the deeper rocks are too hot to be magnetic

34. The asthenosphere can be described as:
    1. being composed of partially molten rock and supporting the lithosphere
    2. having a solid inner core
    3. being strong and riding atop the asthenosphere
    4. being composed of crust some 4.6 billion years old

35. We know the Earth's core is made of iron because:
    1. the outer core does not transmit shear waves
    2. of analysis of solar spectra and meteorites
    3. there is a seismic shadow zone
    4. of satellite gravity measurements

36. Deep-focus earthquakes (more than 200 km deep) are associated with only one type of plate boundary. Which is it?
    1. convergent, subduction
    2. divergent, seafloor spreading
    3. transform, plates sliding past one another

37. What is the radius of the Earth?
    1. 29 km
    2. 290 km
    3. 2900 km
    4. 6400 km

38. Deep ocean trenches are most abundant around the rim of which ocean basin?
    1. Pacific
    2. Atlantic
    3. Indian
    4. Arctic

39. Which features show where oceanic lithosphere sinks downward into the mantle?
    1. deep-ocean trenches
    2. submarine canyons
    3. abyssal seamounts
    4. mid-ocean ridges

40. Which are not associated with mid-ocean ridge systems?
    1. submarine hot springs
    2. submarine basaltic flows
    3. areas of cool old lithosphere
    4. axial rift valleys

41. Which one most completely outlines the edges of the lithospheric plates?
    1. the locations of earthquake epicenters
    2. the edges of the continental shelves
    3. the locations of deep mantle hot spots
    4. the locations of active stratovolcanoes

42. Which source of energy drives mantle convection and plate motions?
    1. the Earth's thermal energy derived from radiogenic heating and residual heat from the Earth's formation
    2. solar heating of the Earth's crust
    3. gravitational energy of the Sun-Earth and Moon-Earth systems
    4. the intergalatic, nebular force-field

43. The age of the Earth accepted by scientists today is what ?
    1. 6.4 billion years
    2. 4.6 billion years
    3. 4.6 million years
    4. 6.4 million years

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