Question

Which geologic principle explains why the bottom stratum in a section of rock is the oldest? . . Cross-cutting relationships . . Superposition . . Unconformities . . Uniformitarianism .

Answer 1

The law of superposition explains why the bottom stratum in a section of rock is the oldest, indicating that in undisturbed sedimentary rock layers, each layer is younger than the one below it.

Step-by-step explanation:

The geological principle that explains why the bottom stratum in a section of rock is the oldest is called the law of superposition. According to this principle, in undisturbed layers of sedimentary rocks, each layer is younger than the one below it, which means the oldest rocks are found at the bottom. This principle is foundational in the study of stratigraphy and is crucial for understanding the relative dating of geological formations.

While the principle of cross-cutting relationships is also significant, it is used to determine the relative ages of geological features that cut through existing formations, such as faults or igneous intrusions. Any feature that cuts across a stratum must be younger than the stratum itself. In contrast, unconformities represent gaps in the geological record where layers have been removed by erosion or never deposited, and uniformitarianism is a broader concept asserting that the same geological processes operating today have always operated in the past.

Answer 2

Superposition is the geologic principle which explains why the bottom stratum in a section of rock is the oldest. The word literally means placing one thing on top of another where the lower strata are the older.