What do scientists know about fossils found in deeper layers of rock compared to
those found in higher layers?

They know that layering, or bedding, is the most obvious feature of sedimentary rocks.  This Law of Superposition is fundamental to the interpretation of Earth history, because at any one location it indicates the relative ages of rock layers and the fossils in them. Layered rocks form when particles settle from water or air. That is kinda easy :D

Explanation:

wheres the answers ?

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.