Question

1. how is radiometric dating used in the relative dating of different sedimentary layers.

it confirms the age of index fossils.
it provides the dates for specific rock layers which can then be used to correlate and calibrate relative dating principles like the law of superposition.
it is a form of relative dating and determines which rock layers were deposited first.
it does not aid in relative dating methods

Explanation:

Radiometric dating gives absolute ages to specific rock layers. Relative dating (like Law of Superposition) gives age - order (older - younger). By having absolute ages from radiometric dating for some layers, we can calibrate and correlate relative dating principles. Index fossils are used in relative dating (by their known age - range), but radiometric dating's main role is not just confirming index fossil age. Radiometric dating is an absolute dating method (not relative). And it does aid in relative dating by providing age - reference points.

Answer:

It provides the dates for specific rock layers which can then be used to correlate and calibrate relative dating principles like the Law of Superposition.