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How does the law of superposition help geologists determine the relative age of Cambrian rock layers?

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Cambrian paleogeography — Cambrian Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cambrian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

The law of superposition is a fundamental principle of stratigraphy that allows geologists to determine the relative age of sedimentary rock layers, including those from the Cambrian Period.12

The principle states that in an undisturbed sequence of sedimentary strata, the oldest layers are deposited at the base, while the layers above them are progressively younger. By observing this vertical order, geologists can establish a chronological sequence of geologic events without needing absolute numerical dates.132

However, this method requires careful field observation because the original order can be obscured by geologic activity. In regions where rocks have been subjected to folding, tilting, or thrust faults, strata may be overturned or displaced, potentially placing older rocks on top of younger ones. To ensure accuracy, geologists look for depositional features—such as cross-beds, ripple marks, or fossil orientations—to confirm which side of a layer was the original top. Once the sequence is correctly identified, it provides a reliable relative timeline for the rock units.123