Use fossils found in rock layers as evidence that organisms and environments on Earth have changed over time.
Fossils are the preserved remains or traces of once-living things, and they are usually found inside sedimentary rock layers. Because rock layers can be ordered from oldest to youngest, the fossils found within them can be ordered too, giving scientists real evidence about which kinds of living things existed at different times in Earth's past.
Fossils found in different layers often look quite different from each other, and different from living organisms today. Finding ocean fossils, like shells, in rock layers on top of a mountain is strong evidence that the area was once covered by an ocean and has changed dramatically since those layers formed.
Mastery looks like: They can explain how fossils found within ordered rock layers provide evidence that organisms and environments have changed over time.
Common stumbles: Treating fossils as isolated curiosities rather than evidence tied to their position in ordered rock layers; missing that a changed environment is itself part of the evidence.