## ES 10 -- The Earth Midterm Exam -- Version A Answer Sheet 10 February 1997

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The correct answers are shown in bold face.

Choose a question number to go straight to that question: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30.

1. If the Earth's radius is 6 x 106 meters and the circumference of a circle is 2 , where r is the radius, about how fast are we going around the center of the Earth (as a result of Earth's rotation on its axis), in miles per hour? (There are 1.6 km per mile and is about 3.14.)

Here's how to do this problem. What you are being asked is how fast does a point on Earth's equator go around the center of the Earth, just due to the daily rotation of the planet?

First, you need to know how big around the Earth is at the equator (the Earth's equatorial circumference). You were given the Earth's radius ( meters), and the formula for figuring out the circumference of a circle, given the circle's radius. So, plugging in the things you know, you can get that the Earth's circumference is

Now, you know the Earth's circumference in meters, but you are asked for a speed in miles per hour, so you should convert the circumference in meters to circumference in miles, like:

and so you now know that the Earth's circumference is about 23,420 miles.

Here, you just have a distance -- but you have been asked for a speed. You therefore need to divide the distance by a time (remember that speed is distance/time). Since you are asked how fast you are going due to the rotation of the earth, and that rotation happens once per day, you should divide your distance in miles by the length of a day in hours. That way you get miles per hour. Since a day is 24 hours long, you just divide 23,420 miles by 24 hours, and get 975.8 miles per hour. The choice below which is closest to that speed is , or 1,000 miles per hour. So the answer to this question is (a).

2. The age of the universe 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

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

4. The primary source of energy in the Sun is:
1. the conversion of lead to uranium
2. the fusion of hydrogen to form helium
3. radioactive decay of potassium to argon
4. burning of fossil fuels

5. The lithosphere can be described as:
1. being composed of partially molten rock and supporting the asthenosphere
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

6. Ionic 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

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

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

9. Igneous 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

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

11. The two elements in greatest abundance in most igneous rocks are:
1. oxygen and silicon
2. hydrogen and helium
3. silicon and iron
4. iron and magnesium

12. Physical 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

13. In an anticline, 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

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

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

16. The oldest rocks in the ocean floors are about how many years old?
1. 6,000
2. 20,000
3. 200 million
4. 4.6 billion

17. The Appalachian mountains 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

18. We know the Earth has a liquid outer core because:
1. seismometers record the ``sloshing'' sounds
2. the outer core does not transmit shear waves
3. images from ground penetrating radar
4. satellite gravity measurements

19. The type of fault which displays both up-and-down motion and lateral offset is:
1. a strike-slip fault
2. a reverse, dip-slip fault
3. an oblique fault
4. not possible

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

21. The imaginary surface that divides a fold as symmetrically as possible is the:
1. overturned limb
2. axial plane
3. plunging syncline
4. vergence

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

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

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

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

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

27. Which mineral is most resistant to weathering:
1. amphibole
2. pyroxene
3. mica
4. quartz

28. The progressive metamorphism of a shale will produce which of the following sequences of rocks:
1. schist-phyllite-slate
2. migmatite-gneiss-granite
3. slate-phyllite-schist
4. claystone-sandstone-mudstone

29. Blueschist metamorphism is characteristic of:
1. low-temperature, low-pressure metamorphism
2. low-temperature, high-pressure metamorphism
3. high-temperature, low-pressure metamorphism
4. high-temperature, high-pressure metamorphism

30. The grain size of 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