ESS 101 B Lab 7 Quiz: Geologic Time–
UW Course Pack Questions And Well
Graded Solutions With Rationales
Updated 2026-2027
Complete study solution for ESS 101 B Lab 7 Quiz (Geologic Time). Includes verified answers
and rationales covering relative dating laws (Superposition, Cross-Cutting, Inclusions), deep
time math, radiometric isotope decay fractions, and Washington map units (Qgd, Mv). Perfect
for rapid exam prep, mastering stratigraphic sequences, and securing top marks
Question 1: Which of the following represents the largest, longest duration unit of
geologic time?
A) Epoch
B) Period
C) Era
D) Eon
D) Eon
Rationale: Eons are the largest subdivisions of the geologic timescale, spanning
hundreds of millions to billions of years.
Question 2: Which unit of geologic time is smaller than a period but larger than an
age?
A) Eon
B) Epoch
C) Era
D) Century
B) Epoch
Rationale: Epochs are the nested subdivisions that break periods down into finer
intervals based on subtle stratigraphic or biological updates.
Question 3: The Mesozoic Era is widely recognized as which of the following
expressions?
A) Age of Invertebrates
B) Age of Reptiles
C) Age of Mammals
D) Age of Microbes
B) Age of Reptiles
Rationale: The Mesozoic Era is bounded by the rise and dominance of macro-
reptiles, including non-avian dinosaurs, before their extinction.
Question 4: What criteria primarily define the boundaries between different geologic
Eras?
A) Changes in Earth's orbital parameters
B) Major global shifts in dominant fossil lifeforms and mass extinctions
C) Periodic shifts in Earth's magnetic polarity
D) Standard 100-million-year intervals
B) Major global shifts in dominant fossil lifeforms and mass extinctions
Rationale: Eras are defined based on massive transformations in the global fossil
,record, such as the Permian-Triassic or Cretaceous-Paleogene extinction
boundaries.
Question 5: What is the current scientifically accepted numerical age of the Earth?
A) 4.54 million years
B) 454 million years
C) 4.54 billion years
D) 13.8 billion years
C) 4.54 billion years
Rationale: Radiometric dating of meteorites and old terrestrial crystals establishes
the age of Earth and the solar system at 4.54 billion years.
Question 6: In what Eon do we currently live?
A) Phanerozoic
B) Proterozoic
C) Archean
D) Hadean
A) Phanerozoic
Rationale: The Phanerozoic Eon represents the interval of "visible life," which began
roughly 541 million years ago and continues to the present day.
Question 7: Which Era is known as the "Age of Mammals"?
A) Paleozoic
B) Mesozoic
C) Cenozoic
D) Neoproterozoic
C) Cenozoic
Rationale: The Cenozoic Era spans from 66 million years ago to today and is
characterized by the radiation and dominance of mammals.
Question 8: The boundary between the Paleozoic and Mesozoic eras is marked by
which historic event?
A) The extinction of the dinosaurs
B) The Permian mass extinction
C) The Cambrian explosion
D) The filling of the Columbia River Basalts
B) The Permian mass extinction
Rationale: The Permian extinction was the largest mass extinction in Earth's history,
eliminating roughly 90-96% of all species and closing the Paleozoic Era.
Question 9: Macroscopic animals with hard shells or skeletons first appeared
abundantly at the start of which period?
A) Silurian
B) Devonian
C) Cambrian
D) Cretaceous
C) Cambrian
Rationale: The Cambrian Explosion (around 541 million years ago) marks the
widespread appearance of complex organism skeletons and hard body parts in the
fossil record.
Question 10: Approximately what percentage of Earth's total history is represented
by the Precambrian (Hadean, Archean, and Proterozoic Eons combined)?
,A) 12%
B) 50%
C) 88%
D) 99%
C) 88%
Rationale: The Precambrian encompasses everything from Earth's formation (4.54
Ga) to the start of the Cambrian (541 Ma), comprising roughly 88% of Earth's total
existence.
Part 2: Relative Dating Principles & Chronology
Question 11: Which principle states that in an undisturbed sequence of sedimentary
rocks, the oldest layer is at the bottom?
A) Principle of Cross-Cutting Relationships
B) Principle of Original Horizontality
C) Principle of Lateral Continuity
D) Principle of Superposition
D) Principle of Superposition
Rationale: Superposition dictates that successive layers deposit on top of existing
layers, meaning deeper layers are older.
Question 12: If an igneous dike cuts through a sequence of sedimentary rock layers,
what can be determined about the relative age of the dike?
A) The dike is older than the sedimentary layers.
B) The dike is younger than the sedimentary layers.
C) The dike is exactly the same age as the sedimentary layers.
D) The dike cannot be dated relative to the sedimentary layers.
**B) The dike is younger than the sedimentary layers.
Rationale: The Principle of Cross-Cutting Relationships states that a feature must
exist before it can be cut; thus, the cutting feature is younger.
Question 13: What does the Principle of Original Horizontality imply if you observe a
series of sedimentary beds tilted at a steep angle?
A) They were deposited on a steep underwater mountain slope.
B) A fault or tectonic event tilted the layers after they were deposited.
C) The layers are actually igneous and not sedimentary.
D) The layers must be younger than the fossils they contain.
**B) A fault or tectonic event tilted the layers after they were deposited.
Rationale: Sediments settle flat under gravity. If they are heavily tilted, tectonic
activity deformed them after deposition.
Question 14: You discover a granite boulder trapped entirely inside a layer of
sandstone. According to the Principle of Inclusions, which rock unit is older?
A) The sandstone is older.
B) The granite is older.
C) They are exactly the same age.
D) It is impossible to determine from this configuration.
, **B) The granite is older.
Rationale: Clasts or fragments contained inside another rock mass must already
exist to be incorporated into the host rock, making inclusions older.
Question 15: Which principle allows geologists to correlate rock units across great
distances or separate continents based on matching fossil assemblages?
A) Principle of Superposition
B) Principle of Faunal Succession
C) Principle of Inclusions
D) Principle of Components
B) Principle of Faunal Succession
Rationale: Organisms evolve and go extinct in a globally predictable, non-repeating
chronological order recorded in the stratigraphy.
Question 16: What is an unconformity?
A) A layer of rock that does not match the surrounding regional landscape
B) A break or gap in the geologic rock record representing a period of erosion or
non-deposition
C) A fracture where rock blocks have slipped past one another
D) An unusual concentration of volcanic ash
B) A break or gap in the geologic rock record representing a period of erosion
or non-deposition
Rationale: Unconformities represent missing time intervals where the structural
record was eroded or never deposited before deposition resumed.
Question 17: Which specific type of unconformity separates younger, flat-lying
sedimentary beds from underlying tilted or folded sedimentary rocks?
A) Disconformity
B) Nonconformity
C) Angular unconformity
D) Paraconformity
C) Angular unconformity
Rationale: An angular unconformity features an angular mismatch between
horizontal upper strata and inclined lower strata.
Question 18: A nonconformity is defined as an erosional surface separating which
types of rock packages?
A) Horizontal sedimentary rocks above from vertical sedimentary rocks below
B) Flat sedimentary rocks above from underlying metamorphic or intrusive igneous
rocks
C) Marine sedimentary rocks from terrestrial sedimentary rocks
D) Two identical parallel layers of shale
B) Flat sedimentary rocks above from underlying metamorphic or intrusive
igneous rocks
Rationale: A nonconformity explicitly describes plutonic igneous or metamorphic
basement rocks eroded at the surface and buried by younger sedimentary beds.
Question 19: If a fault cuts across an unconformity surface, what is the relative age
relationship?
A) The fault is older than the unconformity surface.
B) The fault is younger than the unconformity surface.
C) The unconformity surface cut across the fault plane.
UW Course Pack Questions And Well
Graded Solutions With Rationales
Updated 2026-2027
Complete study solution for ESS 101 B Lab 7 Quiz (Geologic Time). Includes verified answers
and rationales covering relative dating laws (Superposition, Cross-Cutting, Inclusions), deep
time math, radiometric isotope decay fractions, and Washington map units (Qgd, Mv). Perfect
for rapid exam prep, mastering stratigraphic sequences, and securing top marks
Question 1: Which of the following represents the largest, longest duration unit of
geologic time?
A) Epoch
B) Period
C) Era
D) Eon
D) Eon
Rationale: Eons are the largest subdivisions of the geologic timescale, spanning
hundreds of millions to billions of years.
Question 2: Which unit of geologic time is smaller than a period but larger than an
age?
A) Eon
B) Epoch
C) Era
D) Century
B) Epoch
Rationale: Epochs are the nested subdivisions that break periods down into finer
intervals based on subtle stratigraphic or biological updates.
Question 3: The Mesozoic Era is widely recognized as which of the following
expressions?
A) Age of Invertebrates
B) Age of Reptiles
C) Age of Mammals
D) Age of Microbes
B) Age of Reptiles
Rationale: The Mesozoic Era is bounded by the rise and dominance of macro-
reptiles, including non-avian dinosaurs, before their extinction.
Question 4: What criteria primarily define the boundaries between different geologic
Eras?
A) Changes in Earth's orbital parameters
B) Major global shifts in dominant fossil lifeforms and mass extinctions
C) Periodic shifts in Earth's magnetic polarity
D) Standard 100-million-year intervals
B) Major global shifts in dominant fossil lifeforms and mass extinctions
Rationale: Eras are defined based on massive transformations in the global fossil
,record, such as the Permian-Triassic or Cretaceous-Paleogene extinction
boundaries.
Question 5: What is the current scientifically accepted numerical age of the Earth?
A) 4.54 million years
B) 454 million years
C) 4.54 billion years
D) 13.8 billion years
C) 4.54 billion years
Rationale: Radiometric dating of meteorites and old terrestrial crystals establishes
the age of Earth and the solar system at 4.54 billion years.
Question 6: In what Eon do we currently live?
A) Phanerozoic
B) Proterozoic
C) Archean
D) Hadean
A) Phanerozoic
Rationale: The Phanerozoic Eon represents the interval of "visible life," which began
roughly 541 million years ago and continues to the present day.
Question 7: Which Era is known as the "Age of Mammals"?
A) Paleozoic
B) Mesozoic
C) Cenozoic
D) Neoproterozoic
C) Cenozoic
Rationale: The Cenozoic Era spans from 66 million years ago to today and is
characterized by the radiation and dominance of mammals.
Question 8: The boundary between the Paleozoic and Mesozoic eras is marked by
which historic event?
A) The extinction of the dinosaurs
B) The Permian mass extinction
C) The Cambrian explosion
D) The filling of the Columbia River Basalts
B) The Permian mass extinction
Rationale: The Permian extinction was the largest mass extinction in Earth's history,
eliminating roughly 90-96% of all species and closing the Paleozoic Era.
Question 9: Macroscopic animals with hard shells or skeletons first appeared
abundantly at the start of which period?
A) Silurian
B) Devonian
C) Cambrian
D) Cretaceous
C) Cambrian
Rationale: The Cambrian Explosion (around 541 million years ago) marks the
widespread appearance of complex organism skeletons and hard body parts in the
fossil record.
Question 10: Approximately what percentage of Earth's total history is represented
by the Precambrian (Hadean, Archean, and Proterozoic Eons combined)?
,A) 12%
B) 50%
C) 88%
D) 99%
C) 88%
Rationale: The Precambrian encompasses everything from Earth's formation (4.54
Ga) to the start of the Cambrian (541 Ma), comprising roughly 88% of Earth's total
existence.
Part 2: Relative Dating Principles & Chronology
Question 11: Which principle states that in an undisturbed sequence of sedimentary
rocks, the oldest layer is at the bottom?
A) Principle of Cross-Cutting Relationships
B) Principle of Original Horizontality
C) Principle of Lateral Continuity
D) Principle of Superposition
D) Principle of Superposition
Rationale: Superposition dictates that successive layers deposit on top of existing
layers, meaning deeper layers are older.
Question 12: If an igneous dike cuts through a sequence of sedimentary rock layers,
what can be determined about the relative age of the dike?
A) The dike is older than the sedimentary layers.
B) The dike is younger than the sedimentary layers.
C) The dike is exactly the same age as the sedimentary layers.
D) The dike cannot be dated relative to the sedimentary layers.
**B) The dike is younger than the sedimentary layers.
Rationale: The Principle of Cross-Cutting Relationships states that a feature must
exist before it can be cut; thus, the cutting feature is younger.
Question 13: What does the Principle of Original Horizontality imply if you observe a
series of sedimentary beds tilted at a steep angle?
A) They were deposited on a steep underwater mountain slope.
B) A fault or tectonic event tilted the layers after they were deposited.
C) The layers are actually igneous and not sedimentary.
D) The layers must be younger than the fossils they contain.
**B) A fault or tectonic event tilted the layers after they were deposited.
Rationale: Sediments settle flat under gravity. If they are heavily tilted, tectonic
activity deformed them after deposition.
Question 14: You discover a granite boulder trapped entirely inside a layer of
sandstone. According to the Principle of Inclusions, which rock unit is older?
A) The sandstone is older.
B) The granite is older.
C) They are exactly the same age.
D) It is impossible to determine from this configuration.
, **B) The granite is older.
Rationale: Clasts or fragments contained inside another rock mass must already
exist to be incorporated into the host rock, making inclusions older.
Question 15: Which principle allows geologists to correlate rock units across great
distances or separate continents based on matching fossil assemblages?
A) Principle of Superposition
B) Principle of Faunal Succession
C) Principle of Inclusions
D) Principle of Components
B) Principle of Faunal Succession
Rationale: Organisms evolve and go extinct in a globally predictable, non-repeating
chronological order recorded in the stratigraphy.
Question 16: What is an unconformity?
A) A layer of rock that does not match the surrounding regional landscape
B) A break or gap in the geologic rock record representing a period of erosion or
non-deposition
C) A fracture where rock blocks have slipped past one another
D) An unusual concentration of volcanic ash
B) A break or gap in the geologic rock record representing a period of erosion
or non-deposition
Rationale: Unconformities represent missing time intervals where the structural
record was eroded or never deposited before deposition resumed.
Question 17: Which specific type of unconformity separates younger, flat-lying
sedimentary beds from underlying tilted or folded sedimentary rocks?
A) Disconformity
B) Nonconformity
C) Angular unconformity
D) Paraconformity
C) Angular unconformity
Rationale: An angular unconformity features an angular mismatch between
horizontal upper strata and inclined lower strata.
Question 18: A nonconformity is defined as an erosional surface separating which
types of rock packages?
A) Horizontal sedimentary rocks above from vertical sedimentary rocks below
B) Flat sedimentary rocks above from underlying metamorphic or intrusive igneous
rocks
C) Marine sedimentary rocks from terrestrial sedimentary rocks
D) Two identical parallel layers of shale
B) Flat sedimentary rocks above from underlying metamorphic or intrusive
igneous rocks
Rationale: A nonconformity explicitly describes plutonic igneous or metamorphic
basement rocks eroded at the surface and buried by younger sedimentary beds.
Question 19: If a fault cuts across an unconformity surface, what is the relative age
relationship?
A) The fault is older than the unconformity surface.
B) The fault is younger than the unconformity surface.
C) The unconformity surface cut across the fault plane.
