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A geologist is studying rock samples from a newly discovered cave system. They find several layers of sedimentary rock, with each layer containing different fossilized organisms. The deepest layer contains trilobites, the middle layer contains ammonites, and the topmost layer contains early mammalian fossils. Assuming no geological disturbance has occurred, what principle allows the geologist to determine the relative ages of these fossils?
- APrinciple of Uniformitarianism
- BPrinciple of Superposition
- CPrinciple of Faunal Succession
- DPrinciple of Original Horizontality
Show answer & explanationAnswer & explanation
Correct answer: B. Principle of Superposition
The Principle of Superposition states that in an undisturbed sequence of sedimentary strata, the oldest layer is at the bottom and the youngest layer is at the top. This allows the geologist to infer that trilobites are older than ammonites, which are older than mammalian fossils.
Why the other options are wrong
- A. Uniformitarianism states that geological processes observed today also occurred in the past, which is a broader concept.
- C. Faunal Succession states that fossil organisms succeed one another in a definite and determinable order, which helps correlate ages across different locations, but Superposition is about vertical layering in one spot.
- D. Original Horizontality states that sedimentary layers are originally deposited horizontally, which helps interpret tilting but not relative age directly in this context.
Principle of Superposition
In an undisturbed sequence of sedimentary rock layers, the oldest layers are at the bottom and the youngest layers are at the top.
- Fundamental concept in stratigraphy and relative dating.
- Assumes no overturning or major deformation of layers.
- Allows for determining the relative age of fossils and geological events.
Memory trick: Superposition: 'Stacking' rocks, oldest on the bottom.