Review Geologic Time-1

These layers have not been overturned or folded. Based on that, which layer is the oldest?

  1. A

    No. A is on top, which means the other layers had to be there before it could be deposited. A is younger than B and C.
  2. B

    No. By the law of Superposition, layer C had to be in place before B could form on top of it. Layer B is older than A, but younger than C.
  3. C

    Yes! As the bottom layer, the Law of Superposition tells us that it is older than layers A and B. This layer had to be in place before A and B could form on top of it..
  4. D

    No. Layer D is actually a pile of rock fragments, mostly from layer A. These fragments are the result of weathering and erosion of layers A, B, and C. D is the youngest deposit at this location.

Click to see which state standards this question tests, and which of my videos, experiments, and other resources support that topic.


SC.7.E.6.3 Identify current methods for measuring the age of Earth and its parts, including the law of superposition and radioactive dating.


UT.8.III.3.c Explain why some sedimentary rock layers may not always appear with youngest rock on top and older rocks below (i.e., folding, faulting).


4-ESS1-1 Identify evidence from patterns in rock formations and fossils in rock layers to support an explanation for changes in a landscape over time.