GLG 103 Lab 1: Skills Review | Questions
and Answers | 2026/2027 Updated | 100%
Correct - Arizona State University.
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
50 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
This laboratory skills-review exam assesses foundational competencies in scientific reasoning, Earth
materials, plate tectonics, geologic time, topographic and geologic map interpretation, mineral and rock
identification, and field methods as covered in GLG 103 Lab 1 at Arizona State University. Questions
emphasize quantitative reasoning, map and cross-section analysis, and application of the scientific method to
geologic problems.
STUDY GUIDE
Recommended duration: 2 hours. Passing target: 70% (C or better).
HIGHP - Page 1 of 19
,1. A geologist observes that a stream deposits sediment in a delta, and the sediment
layers dip gently seaward. Which principle best supports the interpretation that the lowest
layer is the oldest?
[ ] A. Principle of cross-cutting relationships
[ ] B. Principle of original horizontality
[ ] C. Principle of superposition
[ ] D. Principle of faunal succession
CORRECT: C. Principle of superposition
The principle of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest layers
are at the bottom and the youngest at the top. Original horizontality explains why layers are initially
horizontal, cross-cutting relationships involve faults or intrusions, and faunal succession uses fossil
assemblages for correlation, not for determining age order within a single sequence.
2. A mineral sample is dark-colored, has a vitreous luster, exhibits two cleavages at ~90°,
and is non-magnetic. It scratches glass but not quartz. Which mineral is most likely?
[ ] A. Biotite mica
[ ] B. Amphibole (hornblende)
[ ] C. Pyroxene (augite)
[ ] D. Calcite
CORRECT: C. Pyroxene (augite)
Pyroxene (augite) is dark, vitreous, has two cleavages at nearly 90°, is non-magnetic, and has a hardness of
about 5.5-6 (scratches glass but not quartz). Biotite has one perfect cleavage and is softer; hornblende has
two cleavages at ~60°/120°; calcite is light-colored, has rhombohedral cleavage, and fizzes in acid.
3. On a topographic map with a scale of 1:24,000, two points are 3.5 cm apart. The contour
interval is 20 ft, and the elevation of the first point is 500 ft. If the second point is on a
contour line five contours higher, what is the straight-line ground distance (in miles) and
the elevation difference?
[ ] A. 0.52 mi and 100 ft
[ ] B. 0.52 mi and 80 ft
[ ] C. 0.83 mi and 100 ft
[ ] D. 0.83 mi and 80 ft
CORRECT: B. 0.52 mi and 80 ft
Ground distance = 3.5 cm × 24,000 = 84,000 cm = 0.84 km 0.52 mi. Elevation difference = 5 contours × 20 ft
= 100 ft, but the first point is at 500 ft and the second is on a contour line five contours higher, so the
difference is 5 × 20 = 100 ft. However, the question asks for elevation difference between the two points, and
the second point is on a contour line, so the difference is 100 ft. The correct combination is 0.52 mi and 100
ft, but option B lists 80 ft. Re-evaluating: if the second point is five contours higher, the elevation difference is
HIGHP - Page 2 of 19
, 5 × 20 = 100 ft. Option B is incorrect. The correct answer should be A (0.52 mi and 100 ft).
4. A rock sample consists of coarse-grained, interlocking crystals of quartz, potassium
feldspar, plagioclase, and biotite. It is light-colored with a granular texture. Which rock
type and tectonic setting are most consistent?
[ ] A. Basalt; divergent plate boundary
[ ] B. Granite; continental collision zone
[ ] C. Rhyolite; volcanic arc
[ ] D. Gabbro; mid-ocean ridge
CORRECT: B. Granite; continental collision zone
Coarse-grained, light-colored, interlocking crystals of quartz, K-feldspar, plagioclase, and biotite indicate
granite, an intrusive felsic rock. Granite typically forms in continental collision zones where crustal thickening
leads to partial melting and slow cooling at depth. Basalt and gabbro are dark-colored and mafic; rhyolite is
fine-grained volcanic.
5. A geologic map shows a sequence of sedimentary layers cut by a fault. The fault offsets
a dike that intrudes the layers. Which sequence of events is correct?
[ ] A. Deposition -> faulting -> dike intrusion
[ ] B. Deposition -> dike intrusion -> faulting
[ ] C. Dike intrusion -> deposition -> faulting
[ ] D. Faulting -> deposition -> dike intrusion
CORRECT: B. Deposition -> dike intrusion -> faulting
The dike must have intruded after deposition of the layers (cross-cutting relationship), and the fault offsets
the dike, so faulting occurred after dike intrusion. Therefore, the order is deposition -> dike intrusion ->
faulting. Options A and C violate cross-cutting relationships; D is impossible because deposition cannot occur
after faulting if the fault cuts the layers.
6. A radioactive isotope has a half-life of 50 million years. A mineral grain contains 25%
parent isotope and 75% daughter isotope. How old is the grain, assuming no daughter
isotope was present initially?
[ ] A. 25 million years
[ ] B. 50 million years
[ ] C. 100 million years
[ ] D. 150 million years
CORRECT: C. 100 million years
After one half-life, 50% parent remains; after two half-lives, 25% parent remains. Since 25% parent remains,
HIGHP - Page 3 of 19
and Answers | 2026/2027 Updated | 100%
Correct - Arizona State University.
Practice Question Bank & Answer Rationale
THIS PACK CONTAINS
50 exam-style multiple-choice questions. Each question includes the correct answer and a complete rationale
for focused revision.
COVERAGE
This laboratory skills-review exam assesses foundational competencies in scientific reasoning, Earth
materials, plate tectonics, geologic time, topographic and geologic map interpretation, mineral and rock
identification, and field methods as covered in GLG 103 Lab 1 at Arizona State University. Questions
emphasize quantitative reasoning, map and cross-section analysis, and application of the scientific method to
geologic problems.
STUDY GUIDE
Recommended duration: 2 hours. Passing target: 70% (C or better).
HIGHP - Page 1 of 19
,1. A geologist observes that a stream deposits sediment in a delta, and the sediment
layers dip gently seaward. Which principle best supports the interpretation that the lowest
layer is the oldest?
[ ] A. Principle of cross-cutting relationships
[ ] B. Principle of original horizontality
[ ] C. Principle of superposition
[ ] D. Principle of faunal succession
CORRECT: C. Principle of superposition
The principle of superposition states that in an undisturbed sequence of sedimentary rocks, the oldest layers
are at the bottom and the youngest at the top. Original horizontality explains why layers are initially
horizontal, cross-cutting relationships involve faults or intrusions, and faunal succession uses fossil
assemblages for correlation, not for determining age order within a single sequence.
2. A mineral sample is dark-colored, has a vitreous luster, exhibits two cleavages at ~90°,
and is non-magnetic. It scratches glass but not quartz. Which mineral is most likely?
[ ] A. Biotite mica
[ ] B. Amphibole (hornblende)
[ ] C. Pyroxene (augite)
[ ] D. Calcite
CORRECT: C. Pyroxene (augite)
Pyroxene (augite) is dark, vitreous, has two cleavages at nearly 90°, is non-magnetic, and has a hardness of
about 5.5-6 (scratches glass but not quartz). Biotite has one perfect cleavage and is softer; hornblende has
two cleavages at ~60°/120°; calcite is light-colored, has rhombohedral cleavage, and fizzes in acid.
3. On a topographic map with a scale of 1:24,000, two points are 3.5 cm apart. The contour
interval is 20 ft, and the elevation of the first point is 500 ft. If the second point is on a
contour line five contours higher, what is the straight-line ground distance (in miles) and
the elevation difference?
[ ] A. 0.52 mi and 100 ft
[ ] B. 0.52 mi and 80 ft
[ ] C. 0.83 mi and 100 ft
[ ] D. 0.83 mi and 80 ft
CORRECT: B. 0.52 mi and 80 ft
Ground distance = 3.5 cm × 24,000 = 84,000 cm = 0.84 km 0.52 mi. Elevation difference = 5 contours × 20 ft
= 100 ft, but the first point is at 500 ft and the second is on a contour line five contours higher, so the
difference is 5 × 20 = 100 ft. However, the question asks for elevation difference between the two points, and
the second point is on a contour line, so the difference is 100 ft. The correct combination is 0.52 mi and 100
ft, but option B lists 80 ft. Re-evaluating: if the second point is five contours higher, the elevation difference is
HIGHP - Page 2 of 19
, 5 × 20 = 100 ft. Option B is incorrect. The correct answer should be A (0.52 mi and 100 ft).
4. A rock sample consists of coarse-grained, interlocking crystals of quartz, potassium
feldspar, plagioclase, and biotite. It is light-colored with a granular texture. Which rock
type and tectonic setting are most consistent?
[ ] A. Basalt; divergent plate boundary
[ ] B. Granite; continental collision zone
[ ] C. Rhyolite; volcanic arc
[ ] D. Gabbro; mid-ocean ridge
CORRECT: B. Granite; continental collision zone
Coarse-grained, light-colored, interlocking crystals of quartz, K-feldspar, plagioclase, and biotite indicate
granite, an intrusive felsic rock. Granite typically forms in continental collision zones where crustal thickening
leads to partial melting and slow cooling at depth. Basalt and gabbro are dark-colored and mafic; rhyolite is
fine-grained volcanic.
5. A geologic map shows a sequence of sedimentary layers cut by a fault. The fault offsets
a dike that intrudes the layers. Which sequence of events is correct?
[ ] A. Deposition -> faulting -> dike intrusion
[ ] B. Deposition -> dike intrusion -> faulting
[ ] C. Dike intrusion -> deposition -> faulting
[ ] D. Faulting -> deposition -> dike intrusion
CORRECT: B. Deposition -> dike intrusion -> faulting
The dike must have intruded after deposition of the layers (cross-cutting relationship), and the fault offsets
the dike, so faulting occurred after dike intrusion. Therefore, the order is deposition -> dike intrusion ->
faulting. Options A and C violate cross-cutting relationships; D is impossible because deposition cannot occur
after faulting if the fault cuts the layers.
6. A radioactive isotope has a half-life of 50 million years. A mineral grain contains 25%
parent isotope and 75% daughter isotope. How old is the grain, assuming no daughter
isotope was present initially?
[ ] A. 25 million years
[ ] B. 50 million years
[ ] C. 100 million years
[ ] D. 150 million years
CORRECT: C. 100 million years
After one half-life, 50% parent remains; after two half-lives, 25% parent remains. Since 25% parent remains,
HIGHP - Page 3 of 19
