Question

if a geologist finds the same type of index fossil in a rock layer in africa and in a rock layer in south america, what is the most logical conclusion?
the rock layers are the same age because they contain the same index fossil.
the top rock layer is older than the bottom rock layer.
the fossils in the rock layer must be from the same species.
the rock layer in north america is likely a different type of rock.

Explanation:

Index fossils are defined as fossils of organisms that lived for a short, well-defined geologic time period, so their presence in rock layers indicates those layers formed during that same time period. The other options are incorrect: rock layers are oldest at the bottom, the question already states they are the same index fossil type, and North America is irrelevant to the given data.

Answer:

The rock layers are the same age because they contain the same index fossil.