concept

Faunal succession

The recognition - reached independently by William Smith in England and by Georges Cuvier with Alexandre Brongniart in France - that fossil assemblages succeed one another through the stratigraphic column in a definite, irreversible order. This turns fossils into a calendar. It works because evolution does not repeat: an extinct species does not return, so the sequence runs one way only. It is the foundation of all biostratigraphy, and it predates any method of absolute dating.