Question

a student examines a road cut where the strata reveal many different colored bands of sedimentary rock. an igneous intrusion cuts across the sedimentary layers.
how can these features help determine the relative ages of the rock layers? choose two correct answers.
a. according to the law of superposition, the rock layer that formed first is the layer at the top.
b. the igneous intrusion was formed at the same time each of the layers of sediment were deposited.
c. the igneous intrusion is the oldest feature, and the sedimentary rock formed in layers around it.

Explanation:

1. The law of superposition states that in undisturbed sedimentary rock layers, the oldest layer is at the bottom, and each layer above is younger. Option A incorrectly states the oldest is at the top, so it is wrong.
2. An igneous intrusion cuts through existing rock layers, meaning the sedimentary layers must have formed before the intrusion. So the intrusion is younger than the layers it cuts, making options B and C incorrect.

*(Note: Assuming there are missing correct options not fully visible in the image, but based on the provided choices, none of A, B, C are correct. However, if we correct the superposition statement, the valid reasoning for relative age is:

• Undisturbed sedimentary layers: oldest at bottom (correct superposition rule).
• Igneous intrusion is younger than all sedimentary layers it cuts through.)*

Answer:

(Note: None of the provided options A, B, C are correct. The valid principles for determining relative ages here are:

1. Using the law of superposition: In undisturbed sedimentary sequences, the bottom layer is the oldest, with each overlying layer being younger.
2. Using the principle of cross-cutting relationships: The igneous intrusion is younger than all the sedimentary layers it cuts across.)