fossilization

Fossilization is the process by which organic remains are preserved in the geological record. It usually requires rapid burial after death, protection from scavengers and decay, and chemical conditions that promote mineralization or preservation. The study of fossilization is part of taphonomy, which examines how death, decay, transport, burial, and diagenesis influence what becomes fossil and what is lost.

There are several common pathways. Permineralization occurs when mineral-rich groundwater fills pores and replaces organic tissue with minerals, often preserving fine structures in bones and wood. Replacement and recrystallization involve the gradual replacement of original material by minerals or the growth of new minerals that mimic the original structure. Molds and casts form when the original material dissolves, leaving an impression or a three-dimensional replica. Carbonization preserves carbon-rich films as thin sheets, especially in plants. In some cases, original material is preserved intact, as in unaltered bones, or in amber, tar, or ice.

Preservation is uneven; the fossil record is biased toward hard parts, those in anoxic sediments, and environments conducive to rapid burial. Many organisms leave no fossils at all. The timeframe and geochemical conditions during diagenesis control what remains and what is lost. Exceptional deposits, known as Lagerstätten, preserve soft tissues or behaviors and provide detailed views of ancient ecosystems. Fossilization yields evidence about evolution, paleoecology, and past environments, but it is a probabilistic process that reflects taphonomic filters as much as biology.