Fossils

Fossils are the preserved remnants or traces of organisms from the past. They are typically found in sedimentary rocks and can include hard parts such as bones, teeth, shells, or imprints of soft tissues. Fossils provide direct evidence of ancient life and help scientists reconstruct past environments, climates, and biological relationships.

Fossils are broadly classified as body fossils, which preserve parts of the organism's body, and trace fossils, which record activities such as footprints, burrows, nests, or fossilized dung (coprolites). Some fossils also preserve chemical signals, such as preserved organic molecules or isotopic ratios, sometimes called chemical fossils or biomarkers.

Preservation occurs through various processes. In permineralization and mineral replacement, minerals fill or replace organic material. Molds and casts form when the original material decays, leaving an impression or a replica. Carbonization preserves a thin carbon film of soft-bodied organisms. Amber entombs organisms in resin, while freezing or desiccation can preserve specimens in near-original condition.

Dating fossils relies on relative methods, such as stratigraphic position, and absolute methods, including radiometric dating (for example, carbon-14 for young fossils; uranium-lead and potassium-argon for older ones). Fossil evidence supports reconstructions of evolutionary lineages, ancient ecosystems, and the timing of major events such as extinctions and radiations.

Limitations include incomplete and biased records due to preservation conditions, rock availability, and geographic exposure. Fossil data are integrated with other evidence from geology, genetics, and comparative anatomy to build robust evolutionary and historical narratives.