4. How should the fossils in the sediment layers of Earth appear if species have evolved over time? A. All of the layers should contain fossils of simple organisms.
B. All of the layers should contain fossils of complex organisms.
C. The lower layers should contain fossils of more complex organisms.
D. The upper layers should contain fossils of more complex organisms.

The images show two species of tree frogs in a particular region. the gray tree frogs are adapted to the trees of the woodlands, while the green tree frogs can survive in woodlands or grasslands. the gray frog was abundant in the woodlands. because of climatic changes, most of the trees in the region died, and the woodlands changed to grasslands. in such a case, the . the gray tree frog is closely related to the green tree frog genetically, but they have different mating calls. this suggests that speciation occurred because of .