Final answer:
The presence of the same index fossil in rock layers at different locations indicates that they are the same age, in this case, 250 million years old.
Step-by-step explanation:
The question relates to the age of rock layers based on the presence of index fossils for assigning relative ages. When an index fossil that is 250 million years old is found in different locations, the rock layers containing that fossil are regarded as being of the same age due to the principle of fossil correlation. This principle, along with the understanding of stratigraphy, allows scientists to determine that the other rock layer with the same index fossil found 1,000 miles away is also 250 million years old (Option A).