First Hourly Exam

EXAMPLE!!!!!!!!

EARTH AND PLANETARY SCIENCES 101

SECTION 001 FIRST HOURLY EXAMINATION

Wednesday, February 19, 1997

Name:____________________________ SSN:_________________________

THIS EXAM IS PRINTED DOUBLE-SIDED. SORRY FOR ANY INCONVENIENCE. READ THE INSTRUCTIONS FOR EACH OF THE FOUR SECTIONS CAREFULLY. Please DRAW to my ATTENTION of that of another proctor ANY QUESTIONS YOU MAY HAVE. You have until 9:55 to complete this exam.

I. Multiple Choice (there is only one correct answer; 33 points).

1. Concerning the age of geologic materials constituting our planet, which of the following statements is correct?

(a) the Earth is about 4.6 billion years old.

(b) the maximum age of oceanic crust is about three million years.

(c) the extinction of the dinosaurs (and many, many other species) occurred at the Precambrian/Cambrian boundary, at about 65 million years ago.

(d) the oldest rocks found on the surface of Earth are less than 2.0 billion years old.

(e) none of the above

(f) all of the above.

2. To introduce the concept of plate tectonics, I proposed a simple model where a layer of relatively cold, solid material is placed above its equivalent in the liquid or partially liquid state. The liquid or partially liquid state corresponds to

(a) the asthenosphere, which lies beneath the lithosphere

(b) the asthenosphere, which is composed primarily of silicic rocks

(d) the crust

(e) all of the above

3. In the silicate tetrahedron, the silicon atom (with tendency to become a cation) has a coordination number of (or is surrounded by how many oxygen atoms.

(a) 2, (b) 3, (c) 4, (d) 6, (e) 12.

4. What fundamental process is believed to be responsible for plate motion?

(a) subduction

(b) hot spot activity

(d) convection cells in the mantle

(e) density differences

5. Each oxygen atom of the silicate tetrahedron has an effective charge of (a) +5, (b) -4, (c) +4, (d) -2, (f) +1.

6. The magma generated beneath spreading ridges is mostly

a) mafic

b) felsic

c) intermediate

d) all of the above.

7. Which of the following statements about a scientific theory is not true?

(a) it is an explanation for a particular natural phenomenon

(b) it has a large body of supporting evidence

(d) it is testable

(e) it assumes no pre-conceived notion or “faith” in one explanation over another for a particular natural phenomenon

(e) none of the above

8. The earth's outer core

(a) is inferred to be solid

(b) is composed of green cheese

(d) is inferred to be a liquid composed mostly of iron and nickel, the motion of which gives rise to the earth’s magnetic field

(e) is found below the mantle at a depth of 100 km below the earth’s surface.

(f) none of the above

9. Shield volcanoes consist of low relief accumulations of mafic lava. They form as a result of

a) repeated eruptions of cinder cones

b) widespread ash falls

c) accumulation of thick layers of pyroclastic materials

d) eruptions of high viscosity lavas

e) eruptions of low viscosity lava from point sources.

10. The process of partial or fractional melting of geologic materials

a) implies that any rock melts at a unique temperature

b) occurs because most geologic materials are made up of several minerals, with each melting at a different temperature.

c) requires that as the pressure on a solid geologic material is increased, at a constant temperature, melting will occur.

d) explains how an overall high melting temperature magma can be derived from an overall low melting temperature magma

e) none of the above

11. Amphiboles are examples of a) framework silicates, b) sheet silicates, c) ring silicates, d) isolated tetrahedra silicates, e) double-chain silicates.

12. Which of the following pairs of igneous rocks has the same mineral composition?

a. granite-obsidian.

b. andesite-rhyolite

c. pumice-diorite

d. basalt-gabbro

e. peridotite-andesite

13. The chemical formula for olivine is (Fe,Mg)₂SiO₄, which implies that

a) magnesium and iron can freely substitute for one another

b) silicon occupies octahedral sites, requiring the addition of positively charged atoms.

c) the silicate tetrahedra are linked in single chain arrays.

d) the melting temperature remains constant regardless of the relative amount of iron and magnesium in the octahedral sites.

e) none of the above

14. A lithosphere “plate” is composed of the

(a) core and lower mantle;

(b) lower mantle and asthenosphere;

;(d) upper mantle and crust;

(e) continental and oceanic crust.

15. To which of the following groups do most minerals in the earth's crust belong?

(a) carbonates

(b) oxides

(d) halides

(e) native elements

16. Our planet is releasing energy in the form of heat on a constant basis, particularly at mid-ocean ridges. Where does this heat come from?

a) meteorite impacts

b) the sun

c) a combination of the initial cooling of a body which was initially in a nearly totally molten state and the radioactive decay of unstable isotopes of several elements.

d) the lithification of sediment to form sedimentary rocks.

e) combustion of organic matter in sedimentary rocks.

17. The ability of a mineral to break along regularly oriented planes is called:

(a) specific gravity; (b) luster; (c) hardness; (d) atomic mass number; (e) cleavage.

18. An unconformity

a) is a contact separating volcanic rocks from overlying sedimentary rocks

b) represents a “break” in the geologic record, where considerable geologic time is missing, and may be represented by many different kinds of field relations.

c) was first used by Scottish geoscientists in the late 1700’s and early 1800’s to argue that our planet must be very young, possibly less than 10,000 years.

d) minerals used in the manufacture of aluminum cans

e) important energy resources

19. The sharing of electrons by adjacent atoms is a type of bonding referred to as

a) Van der Waals

b) covalent

c) silicate

d) tetrahedral

e) ionic

20. The three most important settings for magmatism are

(a) subduction zones, hot spots, and meteorite impacts

(b) subduction zones, trailing margins of continents (where oceanic and continental lithosphere are fixed), and mid ocean ridges

(d) continental rifts, trailing continental margins, and meteorite impacts

(e) none of the above

21. Although we did not discuss this directly in class, the “principle of uniformitarianism” was implied in several discussions. This principle involves, basically, an assumption that present geologic processes can be used to infer the history of our planet well into the past. This principle is realistic, only if

(a) catastrophic events, the likes of which we have not seen in recorded history, never occurred in the geologic past

(b) plate tectonics started 100 million years ago

(c) the age of our planet is considerably less than the age inferred from numerous estimates using accurate and high precision dating techniques (the details of which we will discuss in a few weeks).

(d) the rates of different geologic processes (e.g. the build-up of detritus at the mouth of the Mississippi River in the Gulf of Mexico) vary considerably over time.

(e) the theory of evolution is inadequate to describe the fossil record.

(f) none of the above.

(g) all of the above

22. The velocity of lithosphere plate motion (i.e. the rate of formation of oceanic lithosphere at mid-ocean ridges) is

(a) typically is on the order of kilometers per year

(b) cannot be measured

( c) is comparable to the rate at which your fingernails grow

(d) typically on the order of centimeters per million years.

II. Very Short Answer Questions. FILL IN THE BLANKS!! (35 pts).

1. What is the crust (continental) and how does its chemical properties differ from those of the mantle?__________________________________________________ __________________________________________________________________.

2. What is a mineral?___________________________________________

___________________________________________________________ _______________________________________________________________.

3.What is a rock? ___________________________________________.
What are the three major groups of rocks? _________________________

___________________________________________________________.

4. Why did our discussion of important rock forming minerals (i.e. silicates) center around the packing of oxygen atoms?________________________________

___________________________________________________________________.

5. What is an explosive or pyroclastic volcanic rock? _____________________ _______________________________________________________________ Explain why the presence of volatiles in magmas may have tremendous effects the formation of explosive volcanic eruptions ___________________________ ______________________________________________________________ ________________________________________________________________.

6. How does a liquid rock (magma) [relative to a solid rock] differ from water [relative to ice] ? ________________________________________________________________

_____________________________________________________________ .

7. Magmas on the surface of the earth are called lava flows. What are some characteristics of lava flows? _____________________________________ ____________________________________________________

______________________________________________________________.

8. Heat is transferred within the Earth by conduction and convection. How do the two processes differ? What is the most dominant beneath mid-ocean ridges? _____________________________________________________________

_____________________________________________________________.

9. What does the term solid solution refer to? _______________________________

_____________________________________________________________________.

Give an example of a silicate mineral that displays solid solution. _________________.

10. In our short discussion of the “evolution” of thought on the nature and age of our planet, we briefly discussed Lord Kelvin’s attempts to estimate the age of the earth. What were these estimates based on? ____________________________________ ___________________________________________________. Why were these estimates in obvious error? ______________________________________________

__________________________________________.

11. Some igneous rocks display a texture where one or a few minerals are much larger (coarser) than the “groundmass” containing them. What is this texture called? ____ ______________________ What are the coarser crystals called? ______________ How does the texture originate? ______________________________________ _________________________________________________________________

12. What are the three most abundant elements in the earth’s crust? _______________________________________________________________________________________________________________________________.

13. Why do intrusive igneous rocks tend to have larger crystals of rock-forming minerals? ____________________________________________________ ________________________________________________________________.

What textural term do we use to describe a coarse-grained, equigranular igneous rock?

_______________________________________

III. Longer Answer Questions. ANSWER ANY ONE OF THE FOLLOWING SEVEN! The question is worth 17 points, so please do not hesitate to provide as much detail as appropriate. Time permitting, you may answer a second question for a maximum of 10 extra points. Provide your answers on the following sheets. Use sketches if you wish.

1. Using melting temperature and density as important considerations, describe the earth's compositional and physical property (mechanical) layers.

2. What are mid-ocean ridges? How do they form? What role do they play in plate tectonics? What is the nature of the ocean crust produced at a mid-ocean ridge?

3. Describe the structure, composition, and ionic charge of the silicate tetrahedron (electron acceptor). Give three examples of how silicate tetrahedra join together to form silicate minerals.

4. Explain how calderas form. Use the following questions as a guide for your discussion: What is an ash-flow tuff (your text uses the term ignimbrite)? What do these rocks consist of? Why are they different from lava flows? Why are they of considerable societal concern?

5. One way of classifying igneous rocks is by their mineralogy and texture (i.e. grain size). Explain in general how this is done. Outline in chart like form the important igneous rocks in relation to abundance of silicate minerals they contain.

6. Discuss the general history of formation of planet Earth, emphasizing how the compositional and mechanical layers of the planet are interpreted to have originated.

7. What are the three most abundant elements in the earth's crust. In the earth in total? With respect to the crust, what, consequently, is the most important (volumetrically) mineral type? What is the single (volumetrically) most important mineral group? Discuss how coordination of anions to cations is important in dictating the structures of these minerals.

Provide your answer to one-half of part III here.

Provide your answer to the second half of part III here.

IV. Matching (10 points, no duplication, write letter in blank)

1. kilometer ______________ a. rapidly quenched magma

2.geothermal gradient_______ b. mafic composition extrusive rock

3. basalt ______________ c. framework silicate

4. volcanic glass________ d. change in temperature with depth

5. meteorites ____________ e. key to the evolution of the solar system

6. vesicle ___________ f. single chain silicate

7. potassium feldspar __________ g. negatively charged atom, like Cl in NaCl

8. pyroxene _______ h. about 5/8 of a mile

9. ash__________ i. evidence of trapped gases

10. anion __________ j. fine pyroclastic particles