ES 10 -- The Earth
Practice Midterm Answers


  1. If the escape velocity from the Earth's orbit is 11 km/sec, how many miles per hour is it?

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    For more information, see Section 3.2 of Handout 1


  2. The age of the Earth is determined by:
    1. measuring of radioactive decay products
    2. counting of sedimentary cycles
    3. plotting distance against velocity of galaxies
    4. analyzing solar spectra

    Notes:
    (a) Yes.
    (b) No, because can't tell how long cycles are or how many may be missing.
    (c) No, this tells you about universe age.
    (d) No, this tells you (vaguely) about universe age.

    For more information, see Chapters 1 and 9, Lecture 2 and Lecture 13


  3. The crust of the Earth is made up predominantly of
    1. olivine
    2. silicates
    3. iron
    4. hydrogen and helium

    Notes:
    (a) No. Olivine is the main component of the mantle.
    (b) Yes.
    (c) No. Iron is mostly found in the core.
    (d) No, hydrogen and helium are mostly in the sun.

    For more information, see Chapters 1 and 2, Lecture 2, Lecture 3, and Lecture 5


  4. The primary source of energy in the Earth is:
    1. the conversion of uranium to lead
    2. the fusion of hydrogen to form helium
    3. formation of glacial ice sheets
    4. burning of fossil fuels

    Notes:
    (a) Yes.
    (b) No. H to He is the primary energy source in Sun.
    (c) No. Glaciers are not an energy source.
    (d) No. Burning gas drives cars, makes electricity.

    For more information, see Chapters 1 (Figure 1.6) and 19, Lecture 4


  5. 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

    Notes:
    (a) Yes.
    (b) No. The Earth has a solid inner core.
    (c) No. The lithosphere is strong and riding atop the asthenosphere.
    (d) No.

    For more information, see Chapters 1 (Figure 1.7), 5 (Figure 5.1), and 19


  6. Covalent bonds are made by:
    1. electrostatic attraction between ions produced by the transfer of electrons between atoms from cations to anions
    2. sharing of some electrons in such a way that they orbit around both nuclei
    3. electrostatic attraction between ions that are electrically symmetrical
    4. electrostatic attraction between ions with the same electrical charge, but very different sizes

    Notes:
    (a) No. This is an ionic bond.
    (b) Yes -- sharing electrons is covalent bonding.
    (c) No. I don't know of such a bond. van der Waals bonds are electrically asymmetric.
    (d) No. Like charges repel each other.

    For more information, see Chapter 2, Lecture 5


  7. An isotope of an element is an atom that contains:
    1. additional electrons that are placed in shells closest to the nucleus
    2. one more proton than the original atom of the element
    3. fewer electrons than the original atom of the element
    4. different numbers of neutrons, which change the atomic weight of the element, but retains the same number of protons, which control the chemical properties

    Notes:
    (a) No. This can't happen because of physical laws.
    (b) No. This would, in fact, make a different element.
    (c) No. This would turn the atom into a positively charged ion, a cation.
    (d) Yes.

    For more information, see Chapter 2, Lecture 2


  8. Polymorphs are different minerals that:
    1. contain very different chemical compositions from one another
    2. have the same chemical composition but have different crystal structure
    3. have different isotopes of the same elements
    4. have different chemical compositions but identical physical properties

    Notes:
    (a) No. This would just be a different mineral.
    (b) Yes. The word polymorph means ``many form''
    (c) No. This is in fact very common.
    (d) No.

    For more information, see Chapter 2


  9. Metamorphic rocks are:
    1. sometimes called ``black smokers''
    2. formed by ``cooking'' of other kinds of rocks
    3. formed when rivers flood over their banks
    4. formed from magma

    Notes:
    (a) No. ``Black smokers'' are a form of seafloor hydrothermal vent. Metamorphism occurs, but (b) is better answer.
    (b) Yes. The word metamorphism means ``change form''
    (c) No. This forms flood deposits, which are sedimentary rocks.
    (d) No. This forms igneous rocks.

    For more information, see Chapter 8, Lecture 8


  10. The process that transforms a pile of sedimentary rock into loose fragments is:
    1. crystallization
    2. metamorphism
    3. lithification
    4. weathering

    Notes:
    (a) No. This is the process which makes crystals.
    (b) No. This is the process by which rocks change to a different form of rock.
    (c) No. This is exactly the opposite process! This makes rocks from rubble.
    (d) Yes.

    For more information, see Chapters 6 and 7, Lecture 7


  11. The two elements in greatest abundance in the solar system are:
    1. oxygen and silicon
    2. hydrogen and helium
    3. silicon and iron
    4. iron and magnesium

    Notes:
    (a) Oxygen and silicon are most abundant in earth crust.
    (b) Yes. They make up 99% of our solar system, primarily in the Sun.
    (c) No. Silicon is common in the mantle and crust. Iron is common in the core.
    (d) No. Iron is common in the core, magnesium in the mantle and crust.

    For more information, see Chapter 1, Lecture 2


  12. Chemical weathering will be most intense in which climate?
    1. warm and moist, where daily temperature variations are small
    2. cold and moist, where daily temperature variations are large and span the freezing point of water
    3. warm and dry, where daily temperature variations are small
    4. cold and dry, where daily temperature variations are large and span the freezing point of water

    Notes:
    (a) Yes. Chemical weathering fastest in hot, moist climates.
    (b) No. Physical weathering fastest here.
    (c) No. Medium rates of chemical weathering.
    (d) No. Slowest of all.

    For more information, see Chapter 6, Table 6.1, Lecture 7


  13. In an syncline, the limbs dip:
    1. away from the axial trace and the youngest rocks are at the center
    2. away from the axial trace and the oldest rocks are at the center
    3. toward the axial trace and the oldest rocks are at the center
    4. toward the axial trace and the youngest rocks are at the center

    Notes:
    (a) No. This would imply that the rock layers had been flipped over at some point.
    (b) No. This is an anticline.
    (c) No, for the same reason as in (a).
    (d) Yes.

    For more information, see Chapter 10, Lecture 12


  14. Rocks that are brittle tend to be associated with:
    1. lakes and streams
    2. folds
    3. synclines
    4. normal faults

    Notes:
    (a) No. These are sediments, which can be loose or ductile.
    (b) No. Folds are associated with ductile rocks.
    (c) No. A syncline is a kind of fold.
    (d) Yes.

    For more information, see Chapter 10, Lecture 12


  15. When the magnetic field of the Earth is reversed, the:
    1. Earth flips over in its orbit so that North is always up
    2. sense of rotation of the Earth is reversed
    3. magnetization of all existing rocks in the ocean is reversed to match the orientation of the new magnetic field
    4. magnetic polarity of the Earth is such that the north-seeking end of a magnetic compass needle would point toward the south magnetic pole

    Notes:
    (a) No! This is essentially impossible!
    (b) No! This is essentially impossible!
    (c) No. This would be really tough to do.
    (d) Yes.

    For more information, see Chapters 19 and 20, Lecture 10


  16. The oldest rocks in the crust are about how many years old?
    1. 6,000
    2. 20,000
    3. 200 million
    4. 3.8 billion

    Notes:
    (a) No. This is Bishop Ussher's age for the Earth, which he said was formed on October 25, 4004 B.C. at 9 in the morning!
    (b) No.
    (c) No. The oldest seafloor is 200 million years old.
    (d) Yes. The oldest crustal rocks are about 3.8 billion years old. Some zircon crystals have been found which are 4.28 billion years old -- these are the oldest crystals found on Earth.

    For more information, see Lecture 2


  17. The Hawaiian Islands are the result of:
    1. a hot-spot
    2. a major transform fault like the San Andreas
    3. an ancient continent-continent collision
    4. a meteorite impact some 65 million years ago

    Notes:
    (a) Yes! They are, in fact, a classic hot-spot example.
    (b) No. This makes cracks in the ground, not islands in the middle of plates.
    (c) No. This forms mountains like the Appalachians.
    (d) No. This is the asteroid which finished off the dinosaurs.

    For more information, see Chapter 5


  18. 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

    Notes:
    (a) No. This says something about liquid or solid core.
    (b) Best answer. Looking at spectra and meteorites tells us that there is probably iron in the Earth, but since we don't see it on the surface, it has to be at depth. Since iron is dense, it's probably in the core.
    (c) No. This says something about liquid or solid core.
    (d) No, this sort of information is just confirmation for (b).

    For more information, see Chapters 1, 19, and 20, Lecture 2 and Lecture 3,


  19. The type of fault which has steeply dipping fault surfaces, with the hanging wall overhanging the footwall is:
    1. a strike-slip fault
    2. a normal dip-slip fault
    3. an oblique fault
    4. not possible

    Notes:
    This was a poorly-written question. It should read as ``The type of fault which has steeply dipping fault surfaces, with the hanging wall downdropped relative to the footwall is:

    (a) No. This is only horizontal motion, no vertical.
    (b) Yes, but this would have been hard to figure out given the original wording.
    (c) No. This has both vertical and horizontal motion.
    (d) No. It is possible.

    For more information, see Chapter 10, Lecture 12


  20. The principle that allows us to say that a rock layer in the middle of an undisturbed pile is older than those overlying it and younger than those under it is:
    1. the principle of uniformitarianism
    2. the principle of superposition
    3. the principle of original horizontality
    4. based on the number of radioactive isotopes in each of the layers

    Notes:
    (a) No. This says that the same geologic processes which operate today operated in the past.
    (b) Yes.
    (c) No. This says that layers were originally horizontal, so that an undisturbed set of layers should still be basically horizontal.
    (d) No.

    For more information, see Chapter 9, Lecture 13


  21. If a continental area undergoes extension, such as what has occurred in eastern Africa, the resulting feature is termed a(n):
    1. overthrust
    2. transform fault
    3. rift valley
    4. plunging anticline

    Notes:
    (a) No. An overthrust is when one block is shoved up on top of another. See figure 10.24.
    (b) No. A transform fault has blocks of rock sliding past each other. An example is the San Andreas Fault. See figure 20.7, 10.21.
    (c) Yes. See figure 20.4
    (d) No. See figure 10.14

    For more information, see Chapters 10, 20, Lecture 12


  22. The periods of the Tertiary Era, in chronological order begining with the earliest, were:
    1. Paleogene, Neogene, Quaternary
    2. Archean, Proterozoic, Phanerozoic
    3. Triassic, Jurassic, Cretaceous
    4. Paleocene, Eocene, Oligocene

    Notes:
    (a) Yes
    (b) No. These are the eons.
    (c) No. These are the periods in the Mesozoic Era.
    (d) No. These are the epochs of the Paleogene period.

    For more information, see Chapter 9, Figure 9.11, Lecture 13


  23. Which of the following is not a metamorphic rock?
    1. schist
    2. hornfels
    3. gneiss
    4. tholeite

    Notes:
    (a)-(c) Are all metamorphic rocks.
    (d) Tholeite (or tholeiite) is a basaltic igneous rock.

    For more information, see Chapter 8


  24. If we find a rock in the field that has a crack along which relative motion has occurred, we are looking at a:
    1. fault
    2. fold
    3. syncline
    4. joint

    Notes:
    (a) Yes. This is the definition of a fault.
    (b) No. This is just crumpled rocks.
    (c) No. This is a fold which looks like a trough or valley.
    (d) No. This is a crack with no relative motion.

    For more information, see Chapter 10, Lecture 12


  25. An overturned fold is one in which:
    1. both limbs dip in different directions
    2. the axial plane is vertical
    3. the axial plane is inclined
    4. the strata in one limb are horizontal

    Notes:
    (a) No. These are asymmetric folds.
    (b) No. These are symmetric folds.
    (c) Yes.
    (d) No.

    For more information, see Chapter 10, Lecture 12


  26. The sedimentary environment that would display the most sorted group of clasts would be:
    1. alluvial fans
    2. a deep-water marine area
    3. an organic reef complex
    4. wind-deposited areas

    Notes:
    (a) No. This is actually the most poorly sorted.
    (b) Yes.
    (c) No. This is, in fact, not a clastic environment.
    (d) No. The degree of sorting in wind deposits depends on the wind strength and how constant the strength is...

    For more information, see Chapter 7, Lecture 7


  27. Which mineral is least resistant to weathering?
    1. amphibole
    2. pyroxene
    3. mica
    4. quartz
    Notes:
    A way to remember how resistant the minerals are is to remember ``PAMQ''. This gives the minerals above in order of increasing resistance to weathering: pyroxene, amphibole, mica, quartz.

    For more information, see Chapter 6, Table 6.2


  28. The metamorphism of a limestone will produce which of the following rocks?
    1. schist
    2. gneiss
    3. slate
    4. marble
    Notes:
    (a)-(c) All these rocks come from shales, mudstones, or sandstones.
    (d) Yes. Limestone becomes marble.

    For more information, see Chapter 8, Table 8.1


  29. Contact metamorphism is characterised by:
    1. low-temperature, low-pressure metamorphism
    2. low-temperature, high-pressure metamorphism
    3. high-temperature, low-pressure metamorphism
    4. high-temperature, high-pressure metamorphism

    Notes:
    (a) No.
    (b) No. This is regional metamorphism found in subduction zones.
    (c) Yes. Contact metamorphism is mainly due to heat from igneous intrusions into or on top of cold rocks.
    (d) No. Volcanic/plutonic regional metamorphism or burial metamorphism.

    For more information, see Chapter 8, Figures 8.11 and 8.16


  30. The degree of roundness of clasts in a sandstone at a single outcrop can be used to infer the:
    1. velocity of the current by which it was deposited
    2. distance over which the sand had been transported
    3. number of times the sand had been reworked by successive currents
    4. grain size of the rocks from which the sand weathered

    Notes:
    (a) No. The sizes of the grains in the outcrop would indicate the velocity of the current which deposited it. A larger grain size means a faster current was carrying the rock before it was dropped.
    (b) Yes.
    (c) No. Bedding characteristics indicate reworking.
    (d) No.

    For more information, see Chapter 7, figure 7.3


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Greg Anderson
ganderson@ucsd.edu
Sat Feb 8 11:59:50 PST 1997