1. The youngest rock layer is C. According to the law of superposition, in an undisturbed sequence of sedimentary rocks, the layers on top are younger than the layers below them. Layer C is at the top of the sequence.
2. The extrusion is younger than rock layer B. An extrusion is a hardened layer of lava on Earth’s surface. It must have formed after layer B was already in place, as it covers the top of layer B and cuts across its upper boundary.
3. The fault is younger than rock layer A. A fault is a break in Earth’s crust that moves rock layers. Since the fault cuts through layer A, the layer must have existed before the fault occurred. Therefore, the fault is younger.
4. A geologist could use the fossil in rock layer B as an index fossil to date a rock layer in another location. Index fossils are remains of organisms that lived for a short period but were widespread geographically. If the same fossil is found in a different location, it indicates that the rock layer there is approximately the same age as layer B.
5. b
6. h
7. g
8. e
9. c
10. d
11. a
12. f
Parent Tip: Review the logic above to help your child master the concept of relative age of rocks worksheet.
