Which observation would best support that a fossil sequence shows gradual change over time?

• A. Fossils in progressively younger layers show incremental changes.
• B. Fossils are found only in one small area.
• C. Fossils in older layers show simpler structures that become more complex in younger layers.
• D. Fossils are all identical in form across all layers.

Answer: (C)

Fossil sequences show gradual change over time when older rocks contain simpler organisms and younger rocks contain more complex forms. This pattern reveals a step-by-step transformation within a lineage as you move forward in time, which is what gradual change would look like in the fossil record.

This is the strongest sign because it directly shows a directional trend: traits become more elaborate or new features appear in a successive sequence from past to present. If fossils were identical across layers, there would be no evidence of change. If fossils were found only in a small area, geography isn’t about time. If younger layers show changes, that suggests evolution too, but the clearest evidence of gradual change across time is the progression from simple to more complex forms as you go up through the layers.