Question

which is the first step that geologists must do to compare rock layers at distant locations?
find the absolute age of rocks at both locations
compare a layer at one location to layers at other locations
identify index fossils in one or more layers at one location
collect fossils from different locations to study the organisms lifestyles

Explanation:

Index fossils are key for correlating rock layers. They are widespread, existed for a short time, and are easily recognizable. Identifying them in one location helps start the comparison process. Absolute age determination (first option) is more complex and not the initial step. Comparing layers (second option) and collecting fossils for lifestyle study (fourth option) come after index fossil identification.

Answer:

identify index fossils in one or more layers at one location