1. The youngest rock layer is C. According to the law of superposition, in undisturbed sedimentary rock layers, the oldest layer is at the bottom and each layer above it is progressively younger. Layer C is on top of layers A and B.
2. The extrusion is younger than rock layer B. An extrusion is lava that has cooled and hardened on the Earth’s surface. It must have formed after layer B was already in place, as it covers the top of layer B.
3. The fault is younger than rock layer A. A fault is a break in the rock where movement has occurred. The fault cuts through layer A, meaning layer A had to exist first before the fault could form and displace it.
4. A geologist could use the fossil in rock layer B as an index fossil. If the same type of fossil is found in a rock layer at another location, it indicates that both rock layers are approximately the same age, allowing the geologist to correlate the ages of the two locations.
b 5. fault
h 6. extrusion
g 7. unconformity
e 8. relative age
c 9. law of superposition
d 10. intrusion
a 11. absolute age
f 12. index fossil
Parent Tip: Review the logic above to help your child master the concept of relative age of rocks worksheet.
