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April 2015
Final Examination – Exercise Template
UNDERSTANDING PLANET EARTH
EPSC 201, SECTION 001
April 22, 2015; 2PM
Examiner:
Alfonso Mucci
Assoc Examiner:
Student Name:
McGill ID:
INSTRUCTIONS: (Examples)

This is a CLOSED BOOK examination.

NO documentation allowed

Calculators are NOT permitted.

This examination consists of thirty questions (30) of equal value. Answer twenty (20)
questions ONLY. If you answer more than twenty (20) questions, only the first twenty (20)
answers will be graded.

Answer in the official language of your choice (English or French).

This examination is PRINTED ON BOTH SIDES of the paper, i.e., five pages counting this one.
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This examination paper MUST BE RETURNED
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Answer in Classroom (Examination) Book.

Turn in the sheets of questions with the exam booklet
Course: EPSC-201
Page 1
1)
Explain, with two lines of evidence, a theory for the formation of the Moon.
Constrained by the age of the oldest Moon rocks recovered by the Apollo missions (~4.47
Ga), it has been proposed that sometime soon after or perhaps during Earth’s
differentiation (because the Moon is mostly felsic and has a very small core), a Mars-sized
protoplanet slammed into the Earth. As a result the colliding body disintegrated, along
with a large part of the Earth’s mantle. While some of the material was melted and/or
vaporized, a ring of debris was formed and retained within the gravitational field of the
Earth formed.
OR
The Moon is made of silica-rich rocks (ejected following the planetesimal collision with the
Earth) of similar chemical and isotopic composition as the Earth’s crust and its age
corresponds with the time of Earth’s differentiation.
2)
Why does the buildup of heavy elements in large burning stars (“Red Giants”) not go beyond the
formation of iron. In other words, why are elements heavier than iron not produced in burning
stars?
In the largest stars the cycle of nuclear fuel depletion, renewed collapse, core temperature rise,
and ignition of a less flammable nuclear fuel is repeated several times, but as the mass number
increases, each merger leads to a smaller loss of mass and to the corresponding production of
heat. Finally, the buildup cannot go beyond the element iron, because beyond iron heat
must be added to the reaction for the nuclei to merge. The binding energy of elements with
an atomic number larger than 26 is smaller than for iron. The reaction is no longer selfsustained.
3)
Most meteorites are believed to originate from the asteroid belt between the orbits of Mars and
Jupiter. As a result of collisions with one another, their orbits can be modified and some pieces can
enter the Earth’s gravitational field. Why are some of the meteorites that collide with the Earth
made of nearly pure iron?
Iron meteorites are believed to be the cores of small planets or large asteroids that have been
broken apart.
4)
Why is the Earth’s climatological equator different than its geographical equator?
Because, at this time, more than 65% of the land surface is concentrated in the northern
hemisphere. As land masses have a lower albedo than water, the northern hemisphere is warmer
and the climatological equator is north of the geographical equator.
Course: EPSC-201
Page 2
5)
What causes seafloor spreading and how do we know that it is occurring?
Seafloor spreading is caused by extension of the oceanic crust and upwelling of magma
from the asthenosphere. The formation of new seafloor is recorded by symmetrical
magnetic anomalies across the inflated mid-ocean ridges where anomalously high heat
flows can be measured. Seafloor spreading rates can also be estimated by measuring (laser
ranging, GPS measurements) the annual increase width of the ocean basins.
6)
What is cleavage and how does cleavage develop in a mineral?
Cleavage is the preferential fracture plane of a mineral. Cleavage forms in directions where
the bonds holding the atoms together in the crystal are the weakest.
7)
a) Where do natural diamonds originate from?
Diamonds form at very high pressures and temperatures, conditions that are only found at
depths around 150 km below the Earth’s surface well within the mantle.
b) Why are they preserved at the Earth’s surface where they should normally be converted to
graphite?
In order to keep the diamonds from converting to graphite at the Earth’s surface, the
magma is brought up and cools very rapidly at the surface. Kimberlite magmas are typically
rich in dissolved gases and froth to the surface rapidly.
8)
What is the seismic evidence that subduction is occurring? Explain your answer.
Extensional faulting of the subducting oceanic slab produces earthquakes to depths of
650km under the overlying crust in the so-called Wadati-Benioff zone. The earthquakes
occur because the subducting slab is cold and retains brittle properties to great depths in
the mantle.
Course: EPSC-201
Page 3
9)
Compare and contrast stratovolcanoes and shield volcanoes. Why do they differ?
Stratovolcanoes are large cone-shaped (composite) volcanoes constructed of layers of lava
flows and pyroclastic debris (tephra). In contrast, shield volcanoes are broad (low aspect
ratio) and gentle domes. The difference reflects the differential viscosity (silica content) of
their lava; silica-poor basaltic lavas are fluid and form thin sheets yielding shield volcanoes,
whereas andesitic (more silica-rich) lavas are more viscous, they tend to break up as they flow,
and often lead to explosive volcanism.
10)
Discuss three criteria to distinguish between immature and mature clastic sediments.
Immature clastic sediments have undergone little mechanical weathering (clasts with sharp
edges and poorly sorted) and often rest near the area of origin. In contrast, mature clastic
sediments contain well-rounded and often well-sorted clasts, reflecting long-range
transport from their origin.
11)
How and why do rocks change texturally and chemically during metamorphism?
Metamorphic rocks originate from changes in the mineralogy and/or texture of a rock in
response to modifications of its physical or chemical environment. These changes occur
when the protolith is subjected to heat, pressure, differential stress (push, pull, or shear),
and/or bathe in hydrothermal fluids. First, mineral grains in metamorphic rocks are
typically large and interlock with each other rather than being cemented together like in a
sedimentary rock (they undergo recrystallization with or without a phase change). Second,
metamorphic rocks often display foliation, a parallel alignment of platy minerals and/or the
presence of alternating light-colored and dark-colored layers. Finally, they contain
metamorphic minerals, minerals that grow only under metamorphic temperatures and
pressures.
12)
Explain the facies concept of metamorphism.
A metamorphic facies is a set of metamorphic mineral assemblages indicative of a certain
range of pressure and temperature. Each specific assemblage in a facies reflects a specific
protolith composition. A given metamorphic facies includes several different kinds of rocks
that differ from each other in terms of composition (i.e., mineral content) but all rocks of a
given facies formed under roughly the same temperature and pressure conditions.
Course: EPSC-201
Page 4
13)
Name the five rock types that develop upon prograde metamorphism of a shale?
Slate, phyllite, schist, gneiss and migmatite.
14)
Under what conditions do high grade metamorphic rocks undergo retrograde metamorphism?
Retrograde metamorphism occurs upon the exhumation (uplift) of metamorphic rocks in
the presence of water/fluids. Under cold and dry conditions, retrograde metamorphism cannot
occur since the reactions are too slow and the metamorphic grade of the rock is preserved even
upon exhumation.
15)
How do primary seismic waves (P-waves) travel through the Earth?
P-waves are compressional waves which deform the material by changes in volume as they go
through by pulses of compression and expansion, much like a sound wave or the movement of a
loudspeaker. Compression waves can travel through solids, liquids or gases.
16)
What does an unconformity represent in terms of amount of deposition and time of deposition?
Unconformities represent periods of non-deposition or erosion. Whereas an unconformity is
a physical feature we can identify in a rock sequence, we normally refer to the lapse of time
recorded by an unconformity as a hiatus. In other words, during this period, no new sediment
will accumulate and some of the pre-existing sediment may be eroded away. It is impossible to
tell the duration of the hiatus unless we can correlate the individual beds with others where
a complete sequence of deposition is preserved or by dating the individual beds.
Course: EPSC-201
Page 5
17)
Using the basic principles of stratigraphy (superposition, horizontality, continuity) and crosscutting relationships, describe the chronological sequence of events in the following crosssection (It also suffices to list them in chronological order starting with the oldest).
ABCDEF-
Deformed sediments
Deformed sediments
Sediments
Deformed sediments
Igneous intrusion
Sediments
G- Deformed sediments
H- Sediments
I- Deformed sediments
J- Unconformity
K- Deformed sediments
L- Deformed sediments
M- Deformed sediments
N- Dike
O- Dike
1- Fault
2- Fault
3- Fault
Answer: G-E-2-K-D-L-A-M-(unconformity)-B-I-O-1-J-H-C-F-3-N
18)
Explain the four factors that determine whether folds or faults form during deformation.
Four factors determine whether a rock will deform plastically or break: the confining
pressure, temperature, time (strain-rate) and the rock composition. The higher the
temperature, the weaker and less brittle a solid becomes. An increase in confining pressure
tends to keep a solid mass together in a single unit and hinders the formation of fractures.
The lower the strain rate, the greater the tendency for ductile behaviour. There are two
aspects to the composition, the water content and the mineral composition. The presence of
water in interstitial voids of a rock (i.e., tiny spaces between mineral grains) enhances the
ductile properties of a rock as it lubricates movement between mineral grains. The strength
of individual minerals making up a rock also influences the overall strength of a rock.
Course: EPSC-201
Page 6
19)
Draw a cross-section through a zone of continent-continent collision showing detachment and
thrust faults. Explain your cross-section.
Compression upon continental collision leads to deformation, reverse and thrust faulting.
Thrust faulting (e.g., shallow angle reverse faulting) can transport sheets of rocks hundred of
kilometers on top of older rocks along a detachment fault. Movement on reverse faults
pushes older rocks over younger ones, thereby shortening and thickening the crust.
20)
If a ship weighs 52,000 tons and is in isostatic equilibrium when 6,000 tons of cargo is added, what
is the total mass of water that will be displaced by the ship after the cargo is added?
Answer: 58,000 tons
21)
22)
James Hutton, the “father of modern geology” put forth the principle of uniformitarianism.
Explain this principle.
Processes we observe today also operated in the past and were responsible for the
formation of the geological features we see in outcrops today. In other words that “The
present is the key to the past”.
23)
Is there any evidence for extraterrestrial life on Earth? Explain.
Microscopic structures that look like modern bacteria filaments have been observed in
meteorites. Likewise, the presence of strings of magnetite nanocrystals, observed in a
meteorite believed to originate from Mars, are thought to have been formed by
magnetotectic bacteria such as those that live on Earth today.
Course: EPSC-201
Page 7
24)
25)
Describe and explain the evidence that bacteria oxygenated Earth’s atmosphere ~2.5 billion years
ago.
Before 2.2 Ga, pyrite (iron sulphide) occurs as clasts in sediment, this would not be possible
if the atmosphere contained a little oxygen since pyrite weathers rapidly in the presence of
oxygen. The presence of red beds, clastic sedimentary rocks colored by the presence of
bright red hematite (iron oxide) and the occurrence of banded-iron formations (BIF)
deposits, the main source of iron ore today, attest to the presence of oxygen in the
atmosphere after 2.2 Ga.
26)
Why is the absence of oxygen so critical in the accumulation and preservation of organic matter
destined to be converted to oil, gas and coal? In other words, what is the usual fate of organic
matter that accumulates in oxygenated environments?
To be preserved, organic matter must be deposited in an oxygen-poor environment,
otherwise the organic matter would react with oxygen to produce CO2 or could simply be
eaten by bottom-dwelling organisms such as worms and disappear. In the absence of
oxygen, the degradation of organic matter is much slower and higher organisms cannot
survive and are therefore absent.
27)
a) How is electricity generated from hydroelectric dams?
b) What two sources of energy are being exploited?
c) What are the drawbacks of hydroelectric power?
a) As water flows downslope, its potential energy converts to kinetic energy. The water
flow drives turbines, which in turn drive generators that produce electricity.
b) Gravity (potential energy as water flows down a gradient) and sunlight (as heat
evaporates water and rain redeposits it on the continents).
c) The construction of large dams floods large areas, disrupts the local hydrology, and
destroy ecosystems. Furthermore, the degradation of organic matter in the inundated
soils produces carbon dioxide and methane that contribute to the inventory of
greenhouse gases.
28)
Course: EPSC-201
Page 8
29)
Discuss black smokers in the context of metallic mineral deposits.
Seawater percolating through fractures in the mid-ocean ridge crests is heated and leaches
metals from the fresh basalt. When the hydrothermal fluids come in contact with the cold
seawater, the dissolved metals instantly precipitate as tiny crystals of metal sulphide minerals
(e.g., Pb, Ni), creating black clouds called black smokers. The minerals in the cloud
eventually sink and form a pile of nearly pure ore minerals around the vent. Black smokers
are found at mid-ocean ridges where hydrothermal fluids at temperatures as high as 350ºC
and carrying high concentrations of dissolved metal and sulphur debouch from chimneys.
30)
Course: EPSC-201
Page 9