Radiometric dating evidence evolution
Hutton, a Scottish geologist, first proposed formally the fundamental principle used to classify rocks according to their relative ages.
He concluded, after studying rocks at many outcrops, that each layer represented a specific interval of geologic time.
Keyed to the relative time scale are examples of index fossils, the forms of life which existed during limited periods of geologic time and thus are used as guides to the age of the rocks in which they are preserved.
William "Strata" Smith, a civil engineer and surveyor, was well acquainted with areas in southern England where "limestone and shales are layered like slices of bread and butter." His hobby of collecting and cataloging fossil shells from these rocks led to the discovery that certain layers contained fossils unlike those in other layers.
There, you will find a brief description of the method, plus links to take you to other webpages with more extensive information.
The most compelling argument for an age of the earth of 4.5 billion years are the large number of independent tests that have been used to confirm this date.
These tests have been performed on what are thought to be the earth's oldest surviving rocks, meteorites, and moon rocks.
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.