First Hourly Exam

EXAMPLE!!!!!!!!

EARTH AND PLANETARY SCIENCES 101

SECTION 001 FIRST HOURLY EXAMINATION

Friday, September 19, 1997

Name:____________________________ SSN:_________________________

THIS EXAM IS PRINTED DOUBLE-SIDED. I HOPE THIS IS NOT AN 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 8:55 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 life on this planet and all geologic processes started when the Grateful Dead formed.

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 lithosphere 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. Plateau basalts form as a result of

a) repeated eruptions of cinder cones

b) accumulations of thick layers of siliceous pyroclastic materials

c) widespread ash falls

d) repeated eruption of low viscosity magma from long fissures

e) none 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. Volcanic rocks can usually be distinguished from plutonic rocks by

a) color

b) density

c) composition

d) size of individual mineral grains

e) age

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

a) implies that any rock melts at a single 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. Feldspars

a) are tectosilicates characterized by the essential elements iron, magnesium, and cadmium

b) are, relative to olivine and pyroxene, dense and of higher melting temperature.

c) can be though of as forming through a partial coupled substitution of aluminum for silicon in tetrahedral sites, with the result that additional elements, as cations, like calcium, potassium, and sodium, are needed to create the mineral.

d) are essential minerals in ultramafic rocks.

e) none of the above.

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. To produce magmas, geologic materials must be subjected to elevated temperatures, generally at increased pressures. Rocks originally formed at/near the surface of Earth (i.e. sedimentary rocks and extrusive igneous rocks) can be subjected to increased pressures and temperatures

a) by burial through the accumulation of thick sequences of younger materials

b) by collisional tectonics, where fragments of crust are juxtaposed on top of other fragments of crust, resulting in overthickening of parts of the crust.

c) by meteorite impact

d) by the injection of magmas into the crust, with the immediately surrounding material of lower melting temperature than the injected magma

e) none of the above

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 two most important silicate mineral types in the mantle are

(a) sheet silicates and tectosilicates (feldspars and quartz)

(b) olivine and pyroxenes

(d) tectosilicates and olivines

(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 many aspects of 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 systematic 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. The viscosity of a magma is controlled by several factors. Name two and describe their effect. _______________________________________________________

_________________________________________________________________

_________________________________________________________________.

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

_____________________________________________________________________.

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

10. How does a composite volcano differ from a shield volcano? ________________ _____________________________________________________________________

_____________________________________________________________________.

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

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

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

______________________________________________________________

13. What are some essential characteristics of minerals of the sulfide group? ______ __________________________________________________________________ __________________________________________________________________.

14. What is a subduction zone? _____________________________________ ___________________________________________________________________ ____________________________________________________________________.

III. Longer Answer Questions. Please read this and the following questions carefully. ANSWER ANY ONE OF THE FOLLOWING EIGHT! 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.

8. What are the three kinds of geologic materials (rocks)? How does each kind originate and what kind of general features serve to characterize each of the three types of rocks?

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. approximate radius of Earth

2. Wegener _______ b. mafic composition extrusive rock

3. basalt ______________ c. framework silicate

4. 6400 km ________ d. proponent of continental drift

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

6. vesicle ___________ f. small, surrounded by four packed atoms

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

8. tetrahedral site _______ h. about 5/8 of a mile

9. ash__________ i. holes in rock, as evidence of trapped gases

10. anion __________ j. fine pyroclastic particles