EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
Name _______key_______________
Part I. Fill in the blank with a word or a phrase. 1 point per answer.
1. In the Big Bang, the only chemical elements that were synthesized were __H____,
___He____ and a small amount of Li.
2. Primitive meteorites, that is those that are thought to preserve material from the solar
nebula and therefore tell us about the early stages of solar system formation, are all of
the class called __chondrites____, in reference to the small spherical droplets they
contain.
3. Give an example of a carbonate mineral _calcite (or aragonite, dolomite, etc.)__ .
4. How do we know that the Earth’s outer core is liquid? __________________________
___shear waves do not pass through it________ .
5. In micas, the silica tetrahedra are organized into __sheets____.
6. Olivine, plag, etc._ is an example of a mineral that is actually a solid solution, in which
_Mg, Na and Si, etc__ may substitute for __Fe, Ca and Al, etc.__ and vice versa.
7. Name two properties of water that make it a highly unusual substance:
___best solvent, highest heat capacity and heat of fusion except NH4, highest heat
of evaporation, solid is more dense that the liquid, negative coefficient of thermal
expansion less than 4˚C______
8. The four terrestrial planets are __Mercury_, _Venus_, ___Mars_ and Earth.
9. The two sources of heat and energy in the Earth’s interior are __radioactive decay__,
and ____initial heat_____.
1
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
10. The velocity of seismic waves varies as the square root of the ratio of the elastic
modulus to ___density__ .
11. In the spaces provided below, write the name of the appropriate metamorphic facies.
(This question is worth 5 points – you get full credit if you correctly list just 5 facies).
12. The Earth’s moment of inertia has been determined from the rate of precession of its
rotation axis. The moment of inertia turns out to be less than it would be if the Earth
were a sphere of uniform density. What does that tell us about the Earth?
_________increases with depth_______________ .
13. The age of the Earth is approximately ___4.5 billion years___ years.
2
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
14. The outermost part of the Earth that forms a thermal boundary layer and behaves
rigidly is known as the ____lithosphere______ .
15. A depression in the Earth that forms when the roof of a magma chamber collapses
following a volcanic eruption is known as a ____caldera___ .
16. Compressive forces typically result in ___thrust, reverse_____ faults, which are most
common at __convergent_ plate boundaries.
17. What can you determine about an earthquake from the difference in arrival times of pand s-waves at recording station (i.e., a seismograph)? ________________
______distance to the epicenter (also travel time)________________.
18. The Rayleigh Number of the Earth’s mantle has been estimated to be 108. What can
we conclude from this? _____mantle convects_______
_______________________________________________.
19. When strain is elastic, it is linearly proportional to ___stress____ . Furthermore, the
strain is _____reversible______ .
20. A metamorphic ___facies____ is a set of metamorphic mineral assemblages, each for
a specific rock composition, that form over a specific range of pressure and
temperature.
3
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
21. On the folds below, label the anticlines (antiforms) and synclines (synforms).
22. Newton predicted that form of the Earth would be an oblate spheroid rather than a
sphere. Why? ______centrifugal force acts against gravity near the equator__
__________________________________________________________________
23. The gravitational equipotential surface of the Earth; i.e., the radial distance at which the
force of gravity is the same, differs slightly from an oblate spheroid. The name of this
surface is the ___geoid_____.
24. What other planetary bodies in our solar system have an oxygen-rich atmosphere?
___________none____________________
25. What is the key difference between amorphous solids and liquids on the one hand and
a crystalline solid on the other?
________only crystals have long range order of atoms__________________
___________________________________________________________________
26. The mineral with the chemical formula Fe3O4 is called ______magnetite_____.
4
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
27. The compass direction that the trace of a fault makes on a map is known as the
____strike____ ; the angle that the plane of the fault makes to horizontal is known as
the ___dip____.
28. A light-colored, fine-grained, relatively silica-rich igneous rock containing the minerals
alkali feldspar, biotite, and quartz is known as a ___rhyolite___ .
29. An igneous rock having the same composition and mineralogy and the one in the
question above, but with a coarse grain size would be known as a _____granite____.
30. A foliated, but not banded, metamorphic rock rich in sheet silicates such as mica,
whose individual crystals are large enough to make out with the naked eye would be
called a ___schist____ .
31. The temperature at which a multiphase substance begins to melt is known as the
_____solidus___ .
32. The energy required to melt a specific mass (e.g., 1g) of a substance is known as its
________(latent) heat of fusion/melting____________ .
Part II Answer with a sketch, drawing or a few sentences.
33. What causes the melting the produces the volcanoes in subduction zones? (2 points)
Water (released from the subduction lithosphere which lowers the melting
temperature in the mantle wedge).
5
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
34. Sketch the silicon tetrahedron, showing the relative positions of the silicon and oxygen
atoms. (8 points)
35. Explain why volcanoes that form over mantle plumes are analogous to cumulus clouds
(10 points)
Volcanoes are like cumulus clouds because both form when a phase change
occurs in a rising convection current. In clouds, clouds form when rising
warm air cools enough that water vapor condenses. Condensation begins at a
fixed height in the atmosphere – as air moves above this point condensation
continues, so the higher the air rises the more condensation. Melting in
rising hot mantle plumes works the same way: melting begins at a specific
depth, and the more the mantle rises above that depth, the more melt is
created. In both cases, the phase conversion is only partial – only some of
the vapor condenses and only some of the rock melts.
6
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
36. The Ocean Drilling Program (ODP) was initiated as a test of plate tectonic theory.
What predictions of the theory about the ocean floor was ODP designed to test? What
was the outcome? (8 points)
Plate tectonics predicted the ocean floor should get older away from midocean ridges and that the sediment layer should get thicker. Drilling showed
that both predictions were correct.
37. The solid Earth consists of 3 distinct layers: the crust, mantle and core. Why does this
layered structure exist? When did these layers form? Did the crust and core form
immediately when the Earth formed, or did they form later? Did the crust and core
form at the same time? (6 pts)
The layering reflects density stratification of the Earth: each layer is
denser than the one above it. The core formed more or less simultaneously
with the formation of the Earth (although the inner core has grown with
time), the crust formed later (continental crust grew through geologic time;
oceanic crust continually created and destroyed).
7
EAS 2200
Spring 2011
Introduction to the Earth System
Prelim Exam 1
38. Describe the difference between seismic p- and s-waves. In particular, describe the
difference in motion these waves induce in the material through which they travel.
Which wave travels more rapidly? (8 points)
In P-waves, particle motion is parallel (back and forth) to direction of wave
propagation, in s-waves, motion is perpendicular to wave propagation (e.g., up
and down). P-waves travel faster.
39. Describe how the pattern of magnetic anomalies parallel to mid-ocean ridges can be
accounted for by sea-floor spreading. Use sketches if you wish. (10 points)
New seafloor is continually created at mid-ocean ridges as magma rises to
surface. As this is happening, the Earth’s magnetic field reverses
occasionally (about every 500,000 years or so). Lavas of the new seafloor
are magnetized parallel to the Earth’s field at the time they form. The field
of seafloor forming during normal magnetic epochs adds to the Earth’s field,
creating positive anomalies, seafloor forming during reversed epochs
subtracts from the Earth’s field, forming negative anomalies. Thus we see
bands of magnetic anomalies parallel to the ridge.
8