See more information about "Strata" Smith and his original geologic map of England.
Using these key or index fossils as markers, Smith could identify a particular layer of rock wherever it was exposed.
Because fossils actually record the slow but progressive development of life, scientists use them to identify rocks of the same age throughout the world.
Dating is not necessary to demonstrate that evolution is a fact.
Chronological sequence is all that is really required.
It excludes contamination and weathering of travertines and makes possible more precise dating of thin deposits of secondary carbonates.
No web-based resource for this method is available.
Cross-dating is a technique used to take advantage of consistencies in stratigraphy between parts of a site or different sites, and objects or strata with a known relative chronology.
A specialized form of cross-dating, using animal and plant fossils, is known as biostratigraphy.
However, human beings love to see factual precision, and we want to know how old something is.