Radioactive dating geology
By matching similar fossils in different regions throughout the world, correlations were built up over many years.
Only when radioactive isotopes were developed in the early 1900s did stratigraphic correlations become less important as igneous and metamorphic rocks could be dated for the first time.
He noted that different formations contained different fossils and he could map one formation from another by the differences in the fossils.
These sequences apply from the beginning of the Cambrian period, which contains the first evidence of macro-fossils.Over hundreds to thousands of millions of years, continents, oceans and mountain ranges have moved vast distances both vertically and horizontally.For example, areas that were once deep oceans hundreds of millions of years ago are now mountainous desert regions.Fossil assemblages 'fingerprint' formations, even though some species may range through several different formations.This feature allowed William Smith (an engineer and surveyor who worked in the coal mines of England in the late 1700s) to order the fossils he started to collect in south-eastern England in 1793.