A rock layer, also known as a geological layer, is a distinct stratum of rock that forms over time through various geological processes. These layers can be composed of different types of rock, such as sedimentary, igneous, or metamorphic, and they often contain fossils and minerals that provide insights into Earth's history. Rock layers are typically found in sedimentary environments, where materials accumulate and compact over time. The study of these layers, known as stratigraphy, helps scientists understand the age of the Earth, past climates, and the evolution of life. Each layer represents a specific period in geological time, revealing valuable information about the planet's development.