Steno made careful geologic observations and illustrations.
This web page provides an overview of selected geochronology methods used by USGS scientists.
New dating methods are invented all the time, however, most have practical limitations.
Geologic research and mapping requires the determinations of the ages and composition of rocks.
Prior to the late 17th century, geologic time was thought to be the same as historical time.
Archbishop James Ussher of Armagh, Ireland, 1654, added up generations from the Old Testament and determined that Earth formed on October 23, 4004 BCE.