formulated over time based on: observations of relative time and measurements of absolute time
arranged into: eons, eras, periods, epochs
-Period nemonic: China Owls Seldom Deceive Clay Pigeons They Just Cant Practice Non-chalence Quietly (Cambrian, Ordovician, Silurian, Devonian, Carboniferous: Mississippian and Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quartenary--> current period
-Eons: Hadean, Archean, Proterozoic, Phanerozoic
-Eras: Precambrian (4.54 billion - 541 million), Paleozoic (541 million - 252 million), Mesozoic (252 - 66 million), Cenozoic (66 - 0 million)
-only had a complex biosphere for a relatively short period of time
-Understanding of the ordering of strata (stratigraphy) & Understanding of
correlation or rocks using fossils (biostratigraphy) By late 1700's / early 1800's ...........
Allows for strata to be place into "geological time periods"