Absolute Dating vs. Relative Dating

Source Institution: Smithsonian National Museum of Natural History

Source Exhibit: David H. Koch Hall of Fossils - Deep Time

Source Url: https://naturalhistory.si.edu/visit/virtual-tour/current-exhibits/deep-time-virtual-tour-fossil-list

Source Kind: interpretive_topic_or_panel

Use: research inspiration only; SAGE will write original interpretation

Dossier Status: scientifically_enriched_concept_room_01

Plain Language Explanation: Relative dating tells scientists whether one geological event happened before or after another. In an undisturbed sequence of sedimentary rock, lower layers are generally older than layers above them. Numerical dating uses physical processes such as radioactive decay to estimate ages in years. Together, relative relationships and radiometric dates build the geologic time scale.

Evidence: Superposition provides relative age relationships in undisturbed sedimentary sequences.; Radioactive isotopes decay at measurable rates that allow suitable minerals and rocks to be numerically dated.; Multiple isotopic systems and stratigraphic relationships can independently test chronological interpretations.

Examples From Collection: A fossil's position in a dated sequence may constrain its age even when the fossil itself cannot be radiometrically dated.; Pecopteris strongii; Chelichnus bucklandi; Miniochoerus sp.

Common Misconception: Paleontologists usually do not radiometrically date the fossil bone itself. They often date suitable volcanic minerals or rock units above, below or associated with the fossil.

What Scientists Still Debate: Individual dates have uncertainties, and geological systems can be disturbed. Scientists test ages using stratigraphy, multiple samples and independent dating methods.

Sources: https://pubs.usgs.gov/gip/geotime/relative.html; https://pubs.usgs.gov/gip/geotime/age.html

Enrichment Method: SAGE original interpretive concept; source title retained; evidence separated from reconstruction and open questions