What do sedimentary layers indicate regarding historical sea levels?

Sedimentary layers serve as important indicators of historical sea levels because they capture the deposition of materials over time and reflect changes in the coastal environments where they formed. When sea levels rise, sediments are deposited in different patterns compared to when sea levels fall. For instance, during periods of higher sea levels, finer sediments may accumulate in shallow marine environments, while lower sea levels may lead to erosion and the deposition of coarser materials on land or in river deltas.

By analyzing the composition, thickness, and arrangement of sedimentary layers, scientists can infer past environmental conditions, including how far inland the ocean may have extended during various periods. This understanding provides insights into the historical dynamics of climate change and sea-level fluctuations, which can influence coastal ecosystems and human activity over time.

In contrast, while changes in ocean currents, volcanic activity, and tectonic plate shifts can impact sedimentation patterns, they do not directly indicate historical sea level changes in the same way that sedimentary layers do. Hence, focusing on changes in coastal environments through sedimentary evidence offers a clearer understanding of historical sea level variations.