Layer Logic
This type of age tells whether a rock is older or younger than another rock but does not tell us an age in years.
Relative Age
This is a break in rock along which the rocks have moved.
Fault
This is the history of Earth preserved in rock layers and geological features.
The rock record
The collection of fossils preserved in rocks and arranged in chronological order has this name.
The Fossil Record
This kind of age gives the age of a rock as a specific number of years.
Absolute Age
According to this principle, the bottom layer of undisturbed sedimentary rock is the oldest.
Law of Superposition
Magma cools and hardens underground inside existing rock.
Intrusion
This feature shows a gap or missing section in the rock record.
An Unconformity
A fossil from an organism that was widespread but lived for a relatively short time.
An Index Fossil
Geologists combine evidence from rock layers, fossils, faults, and other features to reconstruct this.
Earth's History/ The Past --> Remember the present is the key to the past!
Rock layers usually begin in this position, even if they are later tilted or folded.
Horizontal
Lava cools and hardens at Earth’s surface.
Extrusion
Rock layers that are no longer horizontal provide evidence that the rocks experienced this after they formed.
Movement, tilting, or folding
Two distant rock layers contain the same index fossil. Scientists can infer this about the layers.
They formed during approximately the same time period
A feature must be older or younger than every rock layer it cuts?
Younger
Layers A, B, C, and D are stacked from bottom to top. State their order from youngest to oldest.
D, C, B, A
Imagine layers R, S, and T are stacked from bottom to top. A fault cuts through Layers R and S but does not cut Layer T.
Is layer T older or younger than the fault?
Younger
A rock layer appears on both sides of a canyon. Scientists can infer that the layer was once this.
Connected --> Lateral Continuity
Scientists find an ancient coral fossil. This is evidence that the area once had this type of environment.
Marine, Underwater, Ocean
Layer A is on the bottom, and Layer B is directly above it. A fault cuts through both layers. Place the three events in order from oldest to youngest.
Layer A, Layer B, then the fault
Matching sedimentary layers are found on opposite sides of a canyon. This principle suggests they were once connected.
Lateral Continuity
An intrusion cuts Layers A, B, and C. A fault later cuts the same layers and the intrusion. Name the youngest feature.
A geologist finds horizontal rock layers above an uneven, eroded surface. What does the uneven surface tell the geologist?
Erosion occurred and part of the rock record is missing
Fossil X lived in one location for a very long time. Fossil Y lived in many locations for a short time. Which fossil would be more useful for matching rock layers?
Fossil Y
Layers A, B, and C are stacked from bottom to top. An intrusion cuts through all three layers and then Layer D forms on top.
Place the events in order from oldest to youngest.
Oldest: Layer A, Layer B, Layer C, intrusion, then Layer D youngest