ESS 101 Lab 7 Quiz: Geologic Time | UW
ESS 101 Questions And Well Graded
Solutions With Rationales Updated
2026-2027
Get the ultimate study guide for the ESS 101 Laboratory 7 Quiz on Geologic Time. This comprehensive
resource covers all critical exam topics, including relative dating principles (superposition, cross-
cutting relationships), types of unconformities, radioactive isotope decay half-life calculations, and
Washington State regional geology (Columbia Plateau and Mount Rainier). Perfect for mastering
the University of Washington curriculum and acing your lab quiz with verified answers.
1. If a layer of sediment is deposited on top of an older, flat layer of sedimentary rock,
which principle is best demonstrated?
a) Principle of Cross-Cutting Relationships
b) Principle of Superposition
c) Principle of Inclusions
d) Principle of Lateral Continuity
Answer: c) Principle of Superposition
Rationale: The principle of superposition states that within a sequence of
undisturbed sedimentary rocks, each layer is younger than the one beneath it and
older than the one above it.
2. What geological principle dictates that sedimentary layers are initially deposited flat
under the influence of gravity?
a) Principle of Original Horizontality
b) Principle of Cross-Cutting Relationships
c) Principle of Inclusions
d) Principle of Faunal Succession
Answer: a) Principle of Original Horizontality
Rationale: This principle states that layers of sediment are originally deposited in a
horizontal position due to gravitational settling.
3. If an igneous dike cuts across a layer of limestone, what can be inferred about the
age of the limestone?
a) The limestone is younger than the dike.
b) The limestone is the same age as the dike.
c) The limestone is older than the dike.
d) The limestone's age cannot be determined.
Answer: c) Principle of Cross-Cutting Relationships
Rationale: The principle of cross-cutting relationships dictates that a geologic feature
that cuts through another body of rock must be the younger of the two.
4. Which type of unconformity separates younger, flat sedimentary rocks from older,
tilted or folded sedimentary strata?
a) Disconformity
b) Nonconformity
c) Angular unconformity
d) Paraconformity
, Answer: c) Angular unconformity
Rationale: An angular unconformity is characterized by tilted or folded sedimentary
rocks that are overlain by younger, more flat-lying strata.
5. What type of unconformity is characterized by sedimentary rock layers deposited
directly over eroded metamorphic or plutonic igneous rocks?
a) Disconformity
b) Nonconformity
c) Angular unconformity
d) Paraconformity
Answer: b) Nonconformity
Rationale: A nonconformity exists where upper sedimentary beds rest on an
erosional surface of plutonic igneous or metamorphic rocks.
6. What is a disconformity?
a) An unconformity between two parallel layers of sedimentary rock
b) An unconformity between sedimentary and igneous rock
c) An unconformity between sedimentary and metamorphic rock
d) An unconformity with tilted layers beneath flat layers
Answer: a) Disconformity
Rationale: A disconformity is a type of unconformity where the erosion surface
separates parallel beds of sedimentary rock.
7. If a granite boulder is found inside a sandstone layer, which rock body is older?
a) The sandstone
b) The granite
c) They are the exact same age
d) It is impossible to tell
Answer: b) The granite
Rationale: According to the principle of inclusions, any rock fragments (inclusions)
contained within another rock body must be older than the rock body enclosing them.
8. Which geologic time division represents the largest spans of time?
a) Era
b) Epoch
c) Period
d) Eon
Answer: d) Eon
Rationale: An eon is the largest formal division of geologic time, which is further
subdivided into eras, periods, and epochs.
9. Which of the following correctly lists the geologic time divisions ordered from longest
to shortest duration?
a) Eon, Era, Period, Epoch
b) Epoch, Period, Era, Eon
c) Era, Eon, Epoch, Period
d) Period, Epoch, Eon, Era
Answer: a) Eon, Era, Period, Epoch
Rationale: Geologic time is hierarchical, progressing from the largest unit (Eon) down
to the smallest unit (Epoch).
10. What is the currently accepted age of the Earth?
a) 4.54 million years
, b) 454 million years
c) 4.54 billion years
d) 45.4 billion years
Answer: c) 4.54 billion years
Rationale: Modern radiometric dating of meteorite material and old Earth rocks
establishes the planet's age at approximately 4.54 billion years.
11. If animals with hard parts first appeared 541 million years ago, approximately what
percentage of Earth's total history contains a rich fossil record?
a) 1.2%
b) 12%
c) 54%
d) 88%
Answer: b) 12%
Rationale: Dividing 541 million years by 4.54 billion years and multiplying by 100
yields approximately 11.9%, which rounds to 12%.
12. Modern humans have existed for about 300,000 years. Approximately what
percentage of Earth's total history does this represent?
a) 0.0066%
b) 0.066%
c) 0.66%
d) 6.6%
Answer: a) 0.0066%
Rationale: (300,,540,000,000) * 100 equals approximately 0.0066%,
illustrating that human existence spans a tiny fraction of geologic time.
13. What criteria do geologists primarily use to separate different geological eras?
a) Changes in the Earth's orbit
b) Major changes in global lifeforms and mass extinctions
c) The rate of tectonic plate movement
d) Accumulation rates of sedimentary layers
Answer: b) Major changes in global lifeforms and mass extinctions
Rationale: Eras are bounded by profound shifts in the fossil record, often marked by
major mass extinction events and the rise of new dominant lifeforms.
14. Which principle states that fossil organisms succeed one another in a definite,
determinable order, allowing rock layers to be correlated globally?
a) Principle of Superposition
b) Principle of Faunal Succession
c) Principle of Inclusions
d) Principle of Lateral Continuity
Answer: b) Principle of Faunal Succession
Rationale: The principle of faunal (or fossil) succession states that fossils occur in a
predictable sequence through time, meaning specific windows of time can be
identified by their fossil content.
15. What is an index fossil?
a) A fossil that is very rare and hard to find
b) A fossil of an organism that existed for a long time over a small area
c) A fossil of an organism that was widespread but existed for a short geological
, duration
d) A fossilized footprint or trail
Answer: c) A fossil of an organism that was widespread but existed for a short
geological duration
Rationale: Index fossils must be easily recognizable, geographically widespread, and
confined to a narrow geologic time interval to be useful for precise correlation.
16. What kind of feature is created when an existing rock unit is exposed to erosion and
a new layer of sediment is deposited on top later?
a) A fault
b) An inclusion
c) An unconformity
d) An intrusion
Answer: c) An unconformity
Rationale: An unconformity represents a break or gap in the geologic rock record,
resulting from an extended period of erosion or non-deposition.
17. If a fault cuts through a sequence of four sedimentary rock layers, what is the relative
age of the fault?
a) It is older than all four layers.
b) It is younger than all four layers.
c) It is the same age as the bottom layer.
d) Its age cannot be related to the layers.
Answer: b) It is younger than all four layers.
Rationale: According to the cross-cutting principle, a fault must be younger than any
rock layers it breaks or disrupts.
18. What large geologic province covers much of eastern Washington with extensive
dark brown volcanic rocks?
a) The Cascade Range
b) The Olympic Peninsula
c) The Columbia Plateau
d) The Puget Lowland
Answer: c) The Columbia Plateau
Rationale: The Columbia Plateau province in eastern Washington is dominated by
extensive sequences of the Columbia River Basalt Group.
19. What specific rock type makes up the vast majority of the Columbia Plateau lava
flows in Washington?
a) Granite
b) Andesite
c) Basalt
d) Rhyolite
Answer: c) Basalt
Rationale: The Columbia Plateau was formed by massive fluid eruptions of basaltic
lava during the Miocene epoch.
20. In what geographic region of Washington State are the oldest known rocks located?
a) Southwest
b) Northeast
c) Northwest
d) Southeast
ESS 101 Questions And Well Graded
Solutions With Rationales Updated
2026-2027
Get the ultimate study guide for the ESS 101 Laboratory 7 Quiz on Geologic Time. This comprehensive
resource covers all critical exam topics, including relative dating principles (superposition, cross-
cutting relationships), types of unconformities, radioactive isotope decay half-life calculations, and
Washington State regional geology (Columbia Plateau and Mount Rainier). Perfect for mastering
the University of Washington curriculum and acing your lab quiz with verified answers.
1. If a layer of sediment is deposited on top of an older, flat layer of sedimentary rock,
which principle is best demonstrated?
a) Principle of Cross-Cutting Relationships
b) Principle of Superposition
c) Principle of Inclusions
d) Principle of Lateral Continuity
Answer: c) Principle of Superposition
Rationale: The principle of superposition states that within a sequence of
undisturbed sedimentary rocks, each layer is younger than the one beneath it and
older than the one above it.
2. What geological principle dictates that sedimentary layers are initially deposited flat
under the influence of gravity?
a) Principle of Original Horizontality
b) Principle of Cross-Cutting Relationships
c) Principle of Inclusions
d) Principle of Faunal Succession
Answer: a) Principle of Original Horizontality
Rationale: This principle states that layers of sediment are originally deposited in a
horizontal position due to gravitational settling.
3. If an igneous dike cuts across a layer of limestone, what can be inferred about the
age of the limestone?
a) The limestone is younger than the dike.
b) The limestone is the same age as the dike.
c) The limestone is older than the dike.
d) The limestone's age cannot be determined.
Answer: c) Principle of Cross-Cutting Relationships
Rationale: The principle of cross-cutting relationships dictates that a geologic feature
that cuts through another body of rock must be the younger of the two.
4. Which type of unconformity separates younger, flat sedimentary rocks from older,
tilted or folded sedimentary strata?
a) Disconformity
b) Nonconformity
c) Angular unconformity
d) Paraconformity
, Answer: c) Angular unconformity
Rationale: An angular unconformity is characterized by tilted or folded sedimentary
rocks that are overlain by younger, more flat-lying strata.
5. What type of unconformity is characterized by sedimentary rock layers deposited
directly over eroded metamorphic or plutonic igneous rocks?
a) Disconformity
b) Nonconformity
c) Angular unconformity
d) Paraconformity
Answer: b) Nonconformity
Rationale: A nonconformity exists where upper sedimentary beds rest on an
erosional surface of plutonic igneous or metamorphic rocks.
6. What is a disconformity?
a) An unconformity between two parallel layers of sedimentary rock
b) An unconformity between sedimentary and igneous rock
c) An unconformity between sedimentary and metamorphic rock
d) An unconformity with tilted layers beneath flat layers
Answer: a) Disconformity
Rationale: A disconformity is a type of unconformity where the erosion surface
separates parallel beds of sedimentary rock.
7. If a granite boulder is found inside a sandstone layer, which rock body is older?
a) The sandstone
b) The granite
c) They are the exact same age
d) It is impossible to tell
Answer: b) The granite
Rationale: According to the principle of inclusions, any rock fragments (inclusions)
contained within another rock body must be older than the rock body enclosing them.
8. Which geologic time division represents the largest spans of time?
a) Era
b) Epoch
c) Period
d) Eon
Answer: d) Eon
Rationale: An eon is the largest formal division of geologic time, which is further
subdivided into eras, periods, and epochs.
9. Which of the following correctly lists the geologic time divisions ordered from longest
to shortest duration?
a) Eon, Era, Period, Epoch
b) Epoch, Period, Era, Eon
c) Era, Eon, Epoch, Period
d) Period, Epoch, Eon, Era
Answer: a) Eon, Era, Period, Epoch
Rationale: Geologic time is hierarchical, progressing from the largest unit (Eon) down
to the smallest unit (Epoch).
10. What is the currently accepted age of the Earth?
a) 4.54 million years
, b) 454 million years
c) 4.54 billion years
d) 45.4 billion years
Answer: c) 4.54 billion years
Rationale: Modern radiometric dating of meteorite material and old Earth rocks
establishes the planet's age at approximately 4.54 billion years.
11. If animals with hard parts first appeared 541 million years ago, approximately what
percentage of Earth's total history contains a rich fossil record?
a) 1.2%
b) 12%
c) 54%
d) 88%
Answer: b) 12%
Rationale: Dividing 541 million years by 4.54 billion years and multiplying by 100
yields approximately 11.9%, which rounds to 12%.
12. Modern humans have existed for about 300,000 years. Approximately what
percentage of Earth's total history does this represent?
a) 0.0066%
b) 0.066%
c) 0.66%
d) 6.6%
Answer: a) 0.0066%
Rationale: (300,,540,000,000) * 100 equals approximately 0.0066%,
illustrating that human existence spans a tiny fraction of geologic time.
13. What criteria do geologists primarily use to separate different geological eras?
a) Changes in the Earth's orbit
b) Major changes in global lifeforms and mass extinctions
c) The rate of tectonic plate movement
d) Accumulation rates of sedimentary layers
Answer: b) Major changes in global lifeforms and mass extinctions
Rationale: Eras are bounded by profound shifts in the fossil record, often marked by
major mass extinction events and the rise of new dominant lifeforms.
14. Which principle states that fossil organisms succeed one another in a definite,
determinable order, allowing rock layers to be correlated globally?
a) Principle of Superposition
b) Principle of Faunal Succession
c) Principle of Inclusions
d) Principle of Lateral Continuity
Answer: b) Principle of Faunal Succession
Rationale: The principle of faunal (or fossil) succession states that fossils occur in a
predictable sequence through time, meaning specific windows of time can be
identified by their fossil content.
15. What is an index fossil?
a) A fossil that is very rare and hard to find
b) A fossil of an organism that existed for a long time over a small area
c) A fossil of an organism that was widespread but existed for a short geological
, duration
d) A fossilized footprint or trail
Answer: c) A fossil of an organism that was widespread but existed for a short
geological duration
Rationale: Index fossils must be easily recognizable, geographically widespread, and
confined to a narrow geologic time interval to be useful for precise correlation.
16. What kind of feature is created when an existing rock unit is exposed to erosion and
a new layer of sediment is deposited on top later?
a) A fault
b) An inclusion
c) An unconformity
d) An intrusion
Answer: c) An unconformity
Rationale: An unconformity represents a break or gap in the geologic rock record,
resulting from an extended period of erosion or non-deposition.
17. If a fault cuts through a sequence of four sedimentary rock layers, what is the relative
age of the fault?
a) It is older than all four layers.
b) It is younger than all four layers.
c) It is the same age as the bottom layer.
d) Its age cannot be related to the layers.
Answer: b) It is younger than all four layers.
Rationale: According to the cross-cutting principle, a fault must be younger than any
rock layers it breaks or disrupts.
18. What large geologic province covers much of eastern Washington with extensive
dark brown volcanic rocks?
a) The Cascade Range
b) The Olympic Peninsula
c) The Columbia Plateau
d) The Puget Lowland
Answer: c) The Columbia Plateau
Rationale: The Columbia Plateau province in eastern Washington is dominated by
extensive sequences of the Columbia River Basalt Group.
19. What specific rock type makes up the vast majority of the Columbia Plateau lava
flows in Washington?
a) Granite
b) Andesite
c) Basalt
d) Rhyolite
Answer: c) Basalt
Rationale: The Columbia Plateau was formed by massive fluid eruptions of basaltic
lava during the Miocene epoch.
20. In what geographic region of Washington State are the oldest known rocks located?
a) Southwest
b) Northeast
c) Northwest
d) Southeast
