GEOLOGY 1001 SOLUTION MANUAL
Course: Introductory Geology
FIRST EXAMINATION — OFFICIAL ANSWER KEY & RATIONALES Total Questions: 53
1. Areas close to all three types of plate boundaries are affected by earthquakes.
Answer: A True
RATIONALE: Seismicity occurs along all plate boundaries (divergent, convergent, and transform) due to differential motion
and fault slip between adjacent tectonic plates.
2. What type of volcanism occurs at/close to convergent (plate) boundaries?
Answer: B intermediate
RATIONALE: Subduction zones involve flux melting of the mantle wedge and crustal assimilation, typically yielding
intermediate (andesitic) magma compositions.
3. Which of the following types of lava shows the highest viscosity?
Answer: C rhyolitic
RATIONALE: Rhyolitic lavas have high silica content ($>68\% \text{ SiO}_2$), forming strong internal tetrahedra linkages
that produce high viscosity and explosive potential.
4. The two most abundant elements in the Earth as a whole, are:
Answer: A iron and oxygen
RATIONALE: By mass, Iron ($\approx 32.1\%$) and Oxygen ($\approx 30.1\%$) dominate the bulk composition of the
Earth, largely due to the dense iron-nickel core.
5. The lithosphere is:
Answer: A cold and brittle
RATIONALE: The lithosphere comprises the rigid, brittle crust and uppermost solid mantle. Note: option e is incorrect as
lithospheric thickness averages $\approx 100\text{ km}$, not $100\text{ m}$.
6. Mid-ocean ridges are associated with what type of plate boundary?
Answer: A divergent
RATIONALE: Mid-ocean ridges are seafloor spreading centers where plates pull apart and new oceanic crust is created via
mantle upwelling.
7. The process of subduction is associated with what type of plate boundary?
Answer: B convergent
RATIONALE: Subduction takes place at convergent boundaries where a denser plate slides beneath an overriding tectonic
plate into the mantle.
8. A plate is typically about ______ thick.
Answer: E 100,000 m
RATIONALE: Tectonic plates are lithospheric plates averaging $100\text{ km}$ in thickness, which equals $100,000\text{
GEOLOGY 1001 — Exam Answer Key Page 1 of 5
, 10. The Principle of Uniformitarianism states that:
Answer: C the present is the key to the past
RATIONALE: Formulated by James Hutton, Uniformitarianism asserts that modern physical and chemical geological
processes operated in the same manner in the geologic past.
11. The depth from the surface of the Earth to the mantle-outer core boundary is about _____ km.
Answer: B 3,000
RATIONALE: The core-mantle boundary (Gutenberg discontinuity) lies at a depth of approximately $2,890\text{ km} \approx
3,000\text{ km}$.
12. For the Earth’s crust, the two most abundant elements are, in order:
Answer: E oxygen and silicon
RATIONALE: In the Earth's crust, Oxygen is most abundant ($\approx 46.6\%$), followed directly by Silicon ($\approx
27.7\%$).
13. The asthenosphere:
Answer: B is hot and ductile
RATIONALE: The asthenosphere is the mechanically weak, ductile layer of the upper mantle beneath the lithosphere that
can deform plastically.
14. The diameter of the Earth is about ______ km.
Answer: D 13000
RATIONALE: The mean radius of Earth is approximately $6,371\text{ km}$, giving a mean diameter of $\approx
12,742\text{ km} \approx 13,000\text{ km}$.
15. Which mineral shows a double chain type of polymerization of SiO₄ tetrahedra?
Answer: B amphibole
RATIONALE: Amphiboles (e.g., hornblende) consist of double-chain inosilicates. Olivine is isolated, pyroxene is single-
chain, and feldspar is a 3D framework.
16. Ionic substitution is possible between which pair of elements?
Answer: D calcium and magnesium
RATIONALE: Ionic substitution requires similar ionic ionic charge and size. $\text{Fe}^{2+}$ and $\text{Mg}^{2+}$ or
$\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ substitute readily in carbonate and silicate lattices.
17. The bonds between sodium and chlorine atoms in the mineral halite are of the ________ variety.
Answer: B ionic
RATIONALE: Halite ($\text{NaCl}$) is held together by electro-static ionic bonding between $\text{Na}^+$ cations and
$\text{Cl}^-$ anions.
18. Isotopes of carbon all contain the same number of ______.
Answer: B protons
GEOLOGY 1001 — Exam Answer Key Page 2 of 5
Course: Introductory Geology
FIRST EXAMINATION — OFFICIAL ANSWER KEY & RATIONALES Total Questions: 53
1. Areas close to all three types of plate boundaries are affected by earthquakes.
Answer: A True
RATIONALE: Seismicity occurs along all plate boundaries (divergent, convergent, and transform) due to differential motion
and fault slip between adjacent tectonic plates.
2. What type of volcanism occurs at/close to convergent (plate) boundaries?
Answer: B intermediate
RATIONALE: Subduction zones involve flux melting of the mantle wedge and crustal assimilation, typically yielding
intermediate (andesitic) magma compositions.
3. Which of the following types of lava shows the highest viscosity?
Answer: C rhyolitic
RATIONALE: Rhyolitic lavas have high silica content ($>68\% \text{ SiO}_2$), forming strong internal tetrahedra linkages
that produce high viscosity and explosive potential.
4. The two most abundant elements in the Earth as a whole, are:
Answer: A iron and oxygen
RATIONALE: By mass, Iron ($\approx 32.1\%$) and Oxygen ($\approx 30.1\%$) dominate the bulk composition of the
Earth, largely due to the dense iron-nickel core.
5. The lithosphere is:
Answer: A cold and brittle
RATIONALE: The lithosphere comprises the rigid, brittle crust and uppermost solid mantle. Note: option e is incorrect as
lithospheric thickness averages $\approx 100\text{ km}$, not $100\text{ m}$.
6. Mid-ocean ridges are associated with what type of plate boundary?
Answer: A divergent
RATIONALE: Mid-ocean ridges are seafloor spreading centers where plates pull apart and new oceanic crust is created via
mantle upwelling.
7. The process of subduction is associated with what type of plate boundary?
Answer: B convergent
RATIONALE: Subduction takes place at convergent boundaries where a denser plate slides beneath an overriding tectonic
plate into the mantle.
8. A plate is typically about ______ thick.
Answer: E 100,000 m
RATIONALE: Tectonic plates are lithospheric plates averaging $100\text{ km}$ in thickness, which equals $100,000\text{
GEOLOGY 1001 — Exam Answer Key Page 1 of 5
, 10. The Principle of Uniformitarianism states that:
Answer: C the present is the key to the past
RATIONALE: Formulated by James Hutton, Uniformitarianism asserts that modern physical and chemical geological
processes operated in the same manner in the geologic past.
11. The depth from the surface of the Earth to the mantle-outer core boundary is about _____ km.
Answer: B 3,000
RATIONALE: The core-mantle boundary (Gutenberg discontinuity) lies at a depth of approximately $2,890\text{ km} \approx
3,000\text{ km}$.
12. For the Earth’s crust, the two most abundant elements are, in order:
Answer: E oxygen and silicon
RATIONALE: In the Earth's crust, Oxygen is most abundant ($\approx 46.6\%$), followed directly by Silicon ($\approx
27.7\%$).
13. The asthenosphere:
Answer: B is hot and ductile
RATIONALE: The asthenosphere is the mechanically weak, ductile layer of the upper mantle beneath the lithosphere that
can deform plastically.
14. The diameter of the Earth is about ______ km.
Answer: D 13000
RATIONALE: The mean radius of Earth is approximately $6,371\text{ km}$, giving a mean diameter of $\approx
12,742\text{ km} \approx 13,000\text{ km}$.
15. Which mineral shows a double chain type of polymerization of SiO₄ tetrahedra?
Answer: B amphibole
RATIONALE: Amphiboles (e.g., hornblende) consist of double-chain inosilicates. Olivine is isolated, pyroxene is single-
chain, and feldspar is a 3D framework.
16. Ionic substitution is possible between which pair of elements?
Answer: D calcium and magnesium
RATIONALE: Ionic substitution requires similar ionic ionic charge and size. $\text{Fe}^{2+}$ and $\text{Mg}^{2+}$ or
$\text{Ca}^{2+}$ and $\text{Mg}^{2+}$ substitute readily in carbonate and silicate lattices.
17. The bonds between sodium and chlorine atoms in the mineral halite are of the ________ variety.
Answer: B ionic
RATIONALE: Halite ($\text{NaCl}$) is held together by electro-static ionic bonding between $\text{Na}^+$ cations and
$\text{Cl}^-$ anions.
18. Isotopes of carbon all contain the same number of ______.
Answer: B protons
GEOLOGY 1001 — Exam Answer Key Page 2 of 5
