Question

A scientist observes fossil evidence that leads her to believe that certain organisms have a common ancestor.

Which observation most likely led to this conclusion?

She observed older fossils that contained many of the same minerals as the newer ones.
She found skeletons of modern organisms in the same area as fossilized organisms.
She observed a fossil with skeletal structures similar to certain modern organisms.
She found several fossils in rock layers directly below other fossils of similar size.

Answer 1

She observed a fossil with skeletal structures similar to certain modern organisms.

Explanation: Similar anatomical (homologous) structures in fossils and living species are evidence of descent with modification from a common ancestor. The other choices describe mineral content, co-location, or layering/size, which do not directly indicate shared ancestry.