The geographic time scale of earth is defined by time intervals. The largest unit of time is the supereon which is further divided into shorter interval intervals
Eon: Half a billion years or more and has more than 1 Era.
Era: Several hundred million years and has more than 1 period.
Period: has more than 1 epoch.
Epoch: Tens of million of years and has more than 1 age.
Age: Million of years
Precambrian period is the earliest period in earth's history. The next Eon is the Phanerozoic which is divided into Paleozoic, Mesozoic and Cenozoic Era.
Paleozoic Era has 6 periods Cambrian, Ordovican, Silurian, Devonian, Carboniferous and Permian. It lasted from 541 - 254 million years from Triassic period 230 million years ago.
