All flashcards
Flashcard 1: What does a fault in rock layers show about the sequence of events?
Answer: Rocks broke and moved after the layers formed. Faults form when rocks fracture and shift along the break.
Flashcard 2: What is an unconformity in rock layers?
Answer: A gap in the rock record caused by erosion or nondeposition. Represents missing time in the geological record.
Flashcard 3: Which pattern best indicates erosion occurred between two rock layers?
Answer: An uneven surface separating older rock from younger rock. Erosion creates irregular surfaces before new deposition.
Flashcard 4: What does a layer containing rounded pebbles (conglomerate) usually indicate?
Answer: Sediment was carried and rounded by moving water. Pebbles become rounded through tumbling in streams or waves.
Flashcard 5: What does a fossil-rich layer most directly suggest about the past environment?
Answer: The area once supported many living organisms. Fossils form where life was abundant.
Flashcard 6: What does a layer of ash or lava between sedimentary layers indicate?
Answer: A volcanic event occurred during the rock sequence. Volcanic eruptions deposit ash between sedimentary layers.
Flashcard 7: What does the principle of cross-cutting relationships state?
Answer: A feature that cuts rock is younger than the rock it cuts. Used to determine relative ages of geological features.
Flashcard 8: Identify which is older: a rock layer or an igneous dike that cuts through it.
Answer: The rock layer is older than the dike. The dike must be younger since it cuts through existing rock.
Flashcard 9: What does a tilted set of rock layers most strongly indicate about past events?
Answer: The layers were moved by forces after they formed. Tectonic activity can tilt originally horizontal sedimentary layers.
Flashcard 10: What does a repeating pattern of sandstone, shale, then limestone most likely show?
Answer: The environment changed back and forth over time. Different rock types indicate shifting depositional environments.
Flashcard 11: Identify the best evidence that rock layers were once horizontal before being tilted.
Answer: Sedimentary layers usually form in flat, horizontal sheets. Sediments settle horizontally due to gravity.
Flashcard 12: Which event happened last if a fault cuts across Layers 1–4 and also cuts a dike?
Answer: The faulting happened last. The fault is youngest because it cuts all other features.
Flashcard 13: Identify the relative age: Layer A is below Layer B in undisturbed strata; which is older?
Answer: Layer A is older. Applies the law of superposition to determine relative age.
Flashcard 14: Which feature is the best evidence of a long time gap: a thick layer or an unconformity surface?
Answer: An unconformity surface. Unconformities represent significant time gaps, not just thickness.
Flashcard 15: Identify the correct order of events: deposition, tilting, erosion, new deposition at an angle.
Answer: Angular unconformity formed between old tilted layers and new layers. Shows tilting and erosion occurred before new horizontal layers formed.
Flashcard 16: Which rock-layer pattern most strongly suggests a shoreline moved over time?
Answer: A gradual change from sand layers to mud layers (or the reverse). Fining upward or coarsening sequences indicate shoreline migration.
Flashcard 17: What does a river canyon cutting through many layers show about changes over time?
Answer: Erosion removed rock after the layers formed. Rivers cut downward through existing rock layers over time.
Flashcard 18: Which rock type most often forms visible layers that record changes over time?
Answer: Sedimentary rock. Forms in horizontal layers that preserve time sequences.
Flashcard 19: What is the law of superposition in undisturbed sedimentary rock layers?
Answer: Older layers are at the bottom; younger layers are at the top. This principle helps determine relative ages of rock layers.
Flashcard 20: What does a layer made of very fine particles (like shale) usually suggest about past water movement?
Answer: Slow or calm water conditions. Fine particles only settle when water is still or slow.
Flashcard 21: What does a sudden change from light-colored to dark-colored rock layers most likely show?
Answer: A change in environment or materials being deposited. Color changes often reflect different sediment sources.
Flashcard 22: What does a layer of rounded pebbles (conglomerate) most strongly suggest about past conditions?
Answer: Fast-moving water once carried and rounded the rocks. Strong currents tumble rocks, wearing away sharp edges.
Flashcard 23: What does a fossil found in a rock layer usually indicate about that layer’s past environment?
Answer: The layer formed where that organism once lived. Fossils match the environment where sediments were deposited.
Flashcard 24: What does a sequence that changes from coarse sediment at the bottom to fine sediment at the top suggest?
Answer: Energy of the environment decreased over time. Coarser grains need more energy to transport than fine ones.
Flashcard 25: What does a sequence that changes from fine sediment at the bottom to coarse sediment at the top suggest?
Answer: Energy of the environment increased over time. Higher energy carries away fine particles, deposits coarse ones.
Flashcard 26: Identify what a missing layer between two rock layers most likely indicates.
Answer: Erosion removed rock or deposition stopped for a time. Unconformities represent gaps in the rock record.
Flashcard 27: Which option best indicates a rapid event in the rock record: thick soil layer or thin ash layer?
Answer: Thin ash layer. Volcanic eruptions deposit ash quickly over wide areas.
Flashcard 28: Identify the older layer in an undisturbed stack labeled top A, middle B, bottom C.
Answer: Layer C. Bottom layers form first in undisturbed sequences.
Flashcard 29: Identify the best interpretation if marine shells are found above a layer with land-plant fossils.
Answer: The area changed from land to ocean over time. Sea level rise can flood land areas, changing environments.
Flashcard 30: Which layer is younger if an igneous intrusion cuts across several sedimentary layers?
Answer: The igneous intrusion is younger than the layers it cuts. Intrusions must be younger than what they cut through.