Fossil record

The preserved remains and traces of past organisms found in geological strata. Its distribution through rock layers documents the history of life, though preservation is incomplete and uneven.

Fossil: A preserved remain, impression, or trace of an organism from the past. The fossil record is the accumulated set of fossils preserved across geological strata.
Permineralization: Fossil preservation in which mineral-rich water deposits minerals within the pores of buried remains. This common process preserves internal structure in many fossil bones and wood.
Biostratigraphy: The dating and correlation of rock layers using their fossil content. Fossil successions let geologists compare strata across distant regions.
Molecular clock: A method estimating evolutionary divergence times from the accumulation of genetic differences. It estimates lineage ages independently of fossil appearances, with different uncertainties.
Fossilization: The processes by which remains or traces become preserved as fossils. It explains how only some organisms and traces enter the record.
Mold and cast: A fossil pair formed when an organism leaves a cavity and sediment or minerals later fill it. Molds and casts preserve shapes when the original material decays.
Index fossil: A widespread, short-lived fossil species used to identify and correlate geological strata. Its restricted time range helps assign ages to fossil-bearing rocks.
Living fossil: A living organism that closely resembles ancient forms known from the fossil record. It illustrates that some lineages retain recognizable traits across vast spans of time.
Sedimentary rock: Rock formed from deposited sediment or precipitated minerals, often in layers. Its layers contain most fossils and provide their geological context.
Trace fossil: A fossil recording an organism's activity, such as a footprint, burrow, or feeding mark. Traces preserve behavior even when an organism's body is absent.

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