GEOL 125: Earth History	Name ____________________________
Dr. Hammond	November 12, 1996
Exam II	Total Points = 62

I. Quickies: Fill in the blank spaces with the word, number, or phrase that is most appropriate. Give units where necessary. (18 pts, one per blank)

a) The interior of the earth is heated by _________________________.

b) Is the ratio of Si to 0 the same in all specimens of granite? ______________

Is the ratio the same in all specimens of quartz? _____________________.

c) Cite one piece of evidence that the atmosphere of the early earth lacked oxygen. ______________________________________

d) Give 2 different mechanisms that could cause a global change in sea level. ___________________________ and ____________________________.

e) Give an example of a sedimentary rock _______________________.

f) If an object has a mass of 4 grams and a volume of 2 cm3, calculate its density (remember to give units)____________. If this object was placed in the earth's mantle, would it rise, sink, or remain in place?____________

g) Marble is formed by metamorphosis of ________________ (give rock name).

h) Recent faulting in Death Valley is primarily _______________________(give type) due to ____________________________ (choose extension or compression).

i) Name one famous geologist ________________________ and a concept that he (or she) formulated. __________________________________.

j) Features useful for recognizing faults are ____________________________________ and _______________________.

k) List 2 phenomena that are explained by the theory of plate tectonics. ________________ and __________________________________________.

II. California Geology: (you may wish to draw a sketch of western North America in the margin to help you answer this one. The sketch is not required, 8 points)

The Sierra Nevada are largely ________________ (give rock type). They crystallized ___________________ (choose slowly or rapidly) about 100-200 million years ago when the western coast of North America was a __________________________ (give type of plate boundary). About 20-25 million years ago, a _________________________ (give name of geologic feature) entered this zone, initiating formation of the _____________________. Subsequently, a second encounter of this type occurred (about 3-5 my ago) and initiated the opening and formation of _________________________(give name of geographic feature). During the last 25 my, compression and folding formed the Sacramento-San Joaquin Valley (Great Valley) which is a structure called a ________________(give structure type). Now, Los Angeles is attached to the _____________ plate which is moving to the _______________( give direction of motion).

III. Matchmaking: Match each item in the left column with the most appropriate description in the right column (choose only one). Letters from the right may be used more than once if you wish. (7 pts)

_______ mineral	a. transform
_______ Appalachian Mts	b. normal
_______ San Andreas	c. could form at 15-30°N
_______ paleomagnetic inclination	d. constructive boundary
_______ Gulf Coast evaporites	e. regular internal structure
_______ limestone	f. aggregate of minerals
_______ East Pacific Rise	g. rapid cooling
	h. paleolatitude indicator
	i. Taconic Orogeny
	j. shell remains

IV. Geologic Time Scale. Fill in the chart below to indicate the geologic time scale (6 pts). Eons are given. Note that the youngest time is at the top. Also answer the following (1 pt each):

a) What criteria have been used to distinguish boundaries in this time scale? ____________________________________

b) What method has been used to establish the absolute age of rocks? __________________________

c) List 2 techniques that can be used to correlate the ages of rocks found in widely separated locations. __________________________________ and ______________________________.

Eon	Era	Period	Epoch
Phanerozoic			xxx
Proterozoic	xxx	xxx	xxx
Archean	xxx	xxx	xxx
Hadean	xxx	xxx	xxx

V. Geoart:

a) Draw a cross-section of a subduction zone (a convergent margin). Label the following: asthenosphere, lithosphere, trench, volcanic activity, accretionary wedge, regions of partial melting and batholith emplacement. Use arrows to show the directions of relative motion and use xxx to indicate zone of seismic activity. (10 pts)

b) Draw a cross-section through the earth that shows the crust, mantle and core. On this diagram, indicate the possible paths that p and s waves could take from an earthquake, illustrating where each type of wave is observed. (5 pts)

VI. Puzzler: (4 points )

The measurements of the earth's magnetic field shown below were made on a transect across the mid-Atlantic Ridge. Given these measurements and the knowledge of the magnetic field orientation through time described below, estimate the rate of plate motion. Show work.