Earth Sciences 10
Practice Midterm and Answers
Greg Anderson

The midterm exam will cover material from Chapters 1-6 (maybe 1-7?) and Appendices A, B, and F of The Blue Planet as well as the lecture notes from Lectures 1-12.

This practice exam is probably similar to the real exam, but of course not identical. I have indicated the correct answers for the practice exam with bold face. I have also listed where in the lecture notes and textbook you can find more about the questions.

One studying approach which will probably work reasonably well would be to read the book using the relevant lecture notes as a guide to what is most important. However, keep in mind that anything in the lecture notes or book may be on the exam. Also note that I was not involved in writing either the practice or real midterm and that I have not seen the actual exam.

As always, you can contact me after class or via e-mail if you have questions. However, I will be gone after Thursday morning. I will be in the desert doing research work and won't be reading my e-mail or checking my messages. If you want to send me an e-mail and ask questions, my e-mail address is anderson@python.ucsd.edu.

Good luck on the exam!

Multiple-Choice Questions

1. Which of the following statements is false?
   1. Our Sun is in its hydrogen-burning stage of evolution.
   2. The main sequence lifetime of our Sun will last at least 4 billion more years.
   3. After our Sun has exhausted its nuclear "fuel", its outer layers will erupt explosively as a supernova.
   4. The Sun has inherited virtually all elements with masses greater than helium from earlier generations of stars.

   (Chapter 2)

2. Convection is
   1. a mode of heat transfer in which hot, less dense materials rise upwards and are replaced by cold, denser, downward-flowing materials.
   2. the main mechanism of heat transfer in the terrestrial planets.
   3. the end result of the absorption of incoming solar radiation by the Earth.
   4. All of these are true.

   (Introduction and Chapter 6)

3. A rock is
   1. any naturally occurring solid.
   2. a cohesive combination of many mineral grains.
   3. always composed of many different minerals.
   4. always composed of a single type of mineral.
   5. the result of minerals crystallizing from a liquid.

   Note: the answers here are not very good. The best answer is (b), but it's not a very good one. The book's definition of rock, given in Chapter 4, is:

   Any naturally formed, nonliving, firm and coherent aggregate mass of solid matter that consititutes part of a planet. The word mineral does not appear in the definition because rocks can be made of materials that are not minerals, such as natural glass (in the rock called obsidian), or bits of organic matter (in the rock called coal).

   (Chapter 4)

4. 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.

   (Chapter 4 and Lecture 10)

5. The most abundant rock-forming minerals are
   1. the oxides.
   2. the silicates.
   3. iron, nickel and sulfur.
   4. oxygen and silicon.

   (Chapter 4 and Lecture 9)

6. The Earth's crust is composed chiefly of
   1. nitrogen and oxygen.
   2. hydrogen and helium.
   3. nickel and iron.
   4. oxygen and silicon.

   (Chapter 4 (particularly Table 4.1) and Lecture 9)

Fill-in-the-Blank Questions

7. The planets revolve around the sun in elliptical orbits.
   (Chapter 1)

8. The formation of the solar system was completed about 4.6 billion years ago.
   (Chapter 1 and Lecture 3)

9. At the center of each of the terrestrial planets is a core made primarily of iron. (Or metallic iron or iron and nickel.)
   (Chapter 1 and Lecture 3)

10. The outer planets, with the exception of Pluto are shrouded by thick atmospheres rich in hydrogen and helium.
    (Chapter 1)

11. A cluster of a billion or more stars, together with gas and dust, held together by gravity is called a(n) galaxy.
    (Chapter 1)

12. Abrupt movement of faults that releases elastically stored energy is thought to cause earthquakes: this is known as the elastic rebound theory.
    (Chapter 3 and Lecture 11)

13. Vibrations sent out be earthquakes are measured with an instrument called a seismometer or seismograph.
    (Chapter 3 and Lecture 11)

14. The pronounced seismic discontinuity which marks the mantle-crust interface is called the Moho or M-discontinuity or Mohorovicic discontinuity.
    (Chapter 3)

15. The Richter magnitude scale is used to calculate the amount of energy released during an earthquake. (Note: this question is actually incorrect, but it's the answer on the answer sheet.)
    (Chapter 3 and Lecture 11)

16. The asthenosphere is a zone of anomalously slow or low seismic wave speed.
    (Chapter 6)

17. The Earth's core has a high density and is inferred to consist primarily of iron and nickel.
    (Chapter 3, Lecture 3, and Lecture 11)

18. The floatational balance maintained by large segments of the lithosphere which "float" on the underlying asthenosphere is referred to as isostasy or isostatic equilibrium or isostatic balance.
    (Chapter 3 and Lecture 6)

19. Silicates are the most common type of minerals (95% of the crust.
    (Chapter 4 and Lecture 9)

20. The three main kinds of magma are basaltic, andesitic, and rhyolitic or basalt, andesite, and rhyolite.
    (Chapters 4 and 5)

21. Igneous rock may be intrusive/plutonic, meaning it formed within the crust, or extrusive/volcanic, meaning it formed on the surface.
    (Chapters 4 and 5)

22. Basalt and gabbro contain the same minerals but differ in grain size.
    (Chapters 4 and 5)

23. Bubble holes trapped in lava when it solidifies are called vesicles.
    (Chapters 4 and 5)

Short-Answer Questions

24. Define body wave.
    Seismic waves (P- and S-waves) which travel outward from an earthquake focus and pass through the earth.

    (Chapter 3 and Lecture 11)

25. Define earthquake focus.
    The point of the first release of energy during an earthquake.

    (Chapter 3 and Lecture 11)

26. Define andesite.
    A fine-grained igneous rock with the composition of a diorite.

    (Chapters 4 and 5)

27. Define abyssal plain.
    A large, flat area of the deep seafloor having slopes less than about 1 meter/km, and ranging in depth below sea level from 3 to 6 km.

    (Chapter 6)

28. Define collision margin.
    A convergent margin.

    (Chapter 6)

29. Define continental rise.
    A region of gently changing slope where the floor of the ocean basin meets the margin of a continent.

    (Chapter 6)

30. Define convergent margin.
    The zone where plates meet as they move toward each other; subduction zone or continental collision zone.

    (Chapter 6)

31. Define seafloor spreading.
    A theory proposed during the early 1960s in which lateral movements of the oceanic crust away from midocean ridges was postulated.

    (Chapter 6)

32. Define transform fault margin.
    A fracture in the lithosphere along which two plates slide past each other.

    (Chapter 6)

33. Define subduction zone (convergent margin).
    The linear zone along which a plate of lithosphere sinks down into the asthenosphere.

    (Chapter 6)

34. Why does the Sun appear to revolve around the Earth, when we know the opposite to be true?
    The Sun appears to revolve around the Earth because of Earth's daily rotation about its axis, which makes the Sun seem to arc across the sky from east to west every day. This is called apparent motion.

    (Common sense, I should think.)

35. Both the planet Jupiter and the Sun consist primarily of hydrogen and helium gas. What is the main difference between these two bodies?
    The Sun is considerably more massive than Jupiter, so temperatures and pressures in the core of the Sun are high enough for fusion to occur. Nuclear fusion doesn't occur in the core of Jupiter.

    (Lecture 2)

36. How did S-waves reveal that the Earth's outer core is liquid?
    S-waves cannot be transmitted through fluids. S-waves are transmitted through the crust and mantle (which are solid), but not through the liquid outer core.

    (Chapter 3 and Lecture 11)

37. Why does gas bubble our of magma when it moves towards the surface?
    Pressure controls the amount of gas a magma can dissolve; more gas is dissolved at high pressure and less at low. Gas dissolved in a rising magma acts the same way as gas dissolved in soda water. When a bottle of soda is opened bubbles form because the pressure inside the bottle has dropped, allowing gas to come out of solution. Gas dissolved in an upward-moving magma also comes out of solution and forms bubbles as the pressure on the magma drops.

    (Chapter 5)

38. What is the difference between magma and lava?
    Magma is molten rock (along with gases and suspended crystals) that forms at high temperature underground. Lava is magma that reaches the Earth's surface through a volcanic vent.

    (Chapter 5)

39. What is the source of the Earth's magnetism?
    The fluid motions of the liquid iron outer core.

    (Chapter 6)

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