Layers of sediment can build one above another. In an upright, undisturbed stack, lower layers formed before those on top. A fault or intrusion that cuts a layer formed later than that layer. A later layer can cover an older fault without being cut. Look for what was present before each event.
Earth and geology · Discover & try
What happened first in these rock layers?
Reading level 1 of 5 · EarlyChange
Word help
Superposition
In an upright undisturbed stack, lower sedimentary layers are older.
Intrusion
Rock formed when magma enters and solidifies within existing material.
Cross-cutting relationship
A feature is younger than the material it cuts.
Watch · Try · Explain
See how it works
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Original upright-layer reconstruction; no real outcrop dates, overturned beds or missing-time estimates are implied.
What to look for
- Build the bottom layer first.
- Check which layers a feature actually cuts.
- Keep event order separate from elapsed years.
Explain what you noticed
In another outcrop, a fault cuts beds M and N, but an undisturbed bed P covers the fault. Which sequence fits?
Keep this idea: Relative dating puts events in order without assigning ages in years.
Follow the sources
Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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