Sedimentary rocks form in horizontal layers called beds. A change in beds indicates which of the following?

• A. A changing environment
• B. A constant environment
• C. A volcanic eruption
• D. Deep burial

Answer: (A)

Sedimentary beds record the conditions under which particles settled, so a sequence of beds reflects changes in the deposition environment over time. When you see a transition from one bed to the next—differences in color, grain size, sorting, or fossil content—that signals the environment where deposition was taking place shifted. In other words, a change in beds indicates a changing environment, such as a shift in energy, sediment source, or water chemistry. If the environment had stayed constant, the beds would remain more uniform without such a clear succession of different layers. A volcanic eruption could create a distinct layer, but that’s a specific event rather than the ongoing pattern described by changing beds. Deep burial changes how rocks are compacted and lithified but doesn’t by itself indicate a change in the surface deposition conditions that formed the beds.