A scientist studying fossils in undisturbed layers of rock identified a species that appeared to not have changed a lot over the years. Which observation would have most likely led him to this conclusion?

After studying the fossil, the person can figure out which animal it might be of the records of animals we know of, by taking bone tests, etc. they can see the DNA of the animal. The bone structure can show the animal looked different, or even could figure that out through the DNA. During the years, it could've mated with other animals creating an updated breed, or simply just changing to fit into new environments aka evolving  

Explanation:

Hope that helps

emerging idea only occurs as a raw idea that could appear out of nowhere. meanwhile, to reach scientific consensus , that idea must be structured and tested over and over again through various experiments. the scientific consensus transforms the raw idea into idea that is more reliable through the process of scientific elimination.