In geology, what does it mean if a rock layer is described as 'nonconformity'?

Describing a rock layer as 'nonconformity' means that it separates sedimentary rock from igneous or metamorphic rock. This geological term indicates a significant break in the geologic record, where the stratification of rocks has been disrupted, often due to erosion or other geological processes. In a nonconformity, the underlying igneous or metamorphic rock was exposed at the surface and then eroded before the deposition of the overlying sedimentary layers. This scenario provides valuable insights into the history of the Earth's crust and the processes that have shaped it over time.

The presence of sedimentary rock above igneous or metamorphic rock suggests a change in conditions that allowed for sedimentation to occur after the formation of the older rock types. Understanding nonconformities is crucial for geologists because they highlight important events in Earth's history and are key in interpreting the geological timeline.