Geologic record

The preserved evidence of Earth’s history in rocks, sediments, fossils, and other geological materials. Its layers and physical traces reveal changes in environments, life, and the planet over time.

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Stratigraphy: The study of rock layers and their relationships in time and space. Its principles establish how layers in the geologic record are ordered and correlated.
Sedimentation: The settling and accumulation of particles or precipitates to form sediment. Accumulating sediment creates many of the layers that preserve geological evidence.
Paleoclimatology: The study of climates before direct instrumental measurements. Geological materials preserve physical and chemical clues to ancient climate.
Geological time scale: A system dividing Earth’s history into ranked intervals defined by geological and biological evidence. Its divisions organize the succession documented in rocks and fossils.
Law of superposition: A principle stating that, in undisturbed strata, older layers lie beneath younger layers. It provides a basic relative-age rule for reading layered records.
Lithification: The processes that turn loose sediment into sedimentary rock, chiefly compaction and cementation. It converts deposited material into durable strata.
Paleoenvironmental reconstruction: The inference of past environments from geological, chemical, and fossil evidence. It uses preserved traces to reconstruct conditions at the time of deposition.
Deep time: The immense span of geological history, extending billions of years before human history. The record provides evidence for Earth’s vast timescale.
Geochronology: The science of determining the ages of rocks, fossils, and geological events. It assigns numerical ages to evidence whose order stratigraphy establishes.
Unconformity: A surface separating rock units across a gap in the geological record. It marks missing time caused by erosion or nondeposition.