Relative Dating (Geology)
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In plain terms
Relative dating tells you what happened first—even if you don’t know the exact year.
Core principles
- Superposition: in undisturbed layers, older is below younger.
- Cross-cutting: a feature that cuts another is younger (faults, dikes).
- Inclusions: fragments inside a rock are older than the host.
- Unconformities: missing time surfaces (erosion/non-deposition).
Key takeaways
- Relationships are evidence—record them carefully.
- Unconformities represent missing time.
- Cross-cutting features are powerful age constraints.
- Correlation links layers across distance.
- Relative dating often guides where to use absolute dating.